Tampilkan postingan dengan label Anatomy. Tampilkan semua postingan
Jumat, 31 Agustus 2018
Brain Cancer and Brain tumor
Brain Cancer and Brain tumor
The treatment and outlook vary greatly depending on factors such as type of tumor and the location in the brainThe main parts of the brain include:
1. The cerebrum : this is divided into the right side (right hemisphere) which controls the left side of the body, and the left hemisphere which controls the righr side of the body. Each hemisphere is divided into various sub-selecetion, the main divisions being the frontal lobe, tempolar lobe, parietal lobe and occipital lobe. the cerebrum is also where you think and store your memory
2. The cerebllum : This lies behind and below the cerebrum. one of its main functions is to help control balance and co-ordination.
3. The Brainstem : This helps to control basic bodily function such as the heartbeat, breading and blood pressure. nerves from the cerebrum also pass through the brainstem to spinal cord
4. The meninges : These are thin layers of tissue which separete the skull from the brain. The outer layer to the skull is called the dura. the next layer is called the arachnoid. under the arachnoid tissue is the cerebrospinal fluid (CSF) which bathes the brain and spinal cord
5. The pituitary gland. this releases various hormones into the bloodstream
The main type of cell in the brain is called a neuron, there are millions of neurons in the brain. neurons have long thin nerve fibres which enable them to send massages to other parts of the brain and down the spinal cord to all parts of the body, the brain also contains glial cells. there are various type of glial cell, including astrocytes, oligodendrocytes and ependymal cell.
What is cancer ?
Cancer is disease of the cell in the body.the body is made up from milions of tiny cell. there are many deferent type of cell in the body and there are many deferent type of cancer have in common is that the cancer cell are abnomal multiply out of control.
Non- cancerous (benign) tumours may form in various parts of the body. benign tumors grow slowly and do not spread or invade into other tissues.there are not usually life-threatening. they often do no harm if they are left alone. however, some beningn tumours can caouse probloms. for example, some grow quite large and may cause local pressure symptoms (especially in the brain). also, some benign tumours which arise from cells in hormone glands (see piutary tumours, below) can make too much hormone which can cause anwanted effects.
A cancerous (malingnant) tumour is a lump or growth or tissue made up from cancer cells which continue to multiply. malignant tumours invade into nearby tissues and organs, which can cause damage. malignant tumours may also spread to other part of the body. this happens if some cells break off from the first (primary) tumours and are carried in the bloodstream or lymp channels to other parts of the body. these small groups of cell may then multiply to from secondary tumours (metastases) in one or more parts of the body. these secondary tumours may then grow, invade and damage nearby tissues and spread again.
Some cancers are more serious than other; some are more easily treated than other (particularly if diagnosed at an early stage); some have a better outlook (prognosis) than other . so cancer is not just one condition. in each case it is important to know exctly what type of cancer has developed, how large it has become, and whether it has spread. this will enable you to obtain reliable information on treatment options and outlook.
Primary of secondary tumours
The original site where a tumour first develops is called a primary tumor. cancerous (malignant) tumours may also spread to other parts of the body to from secondary tumours (metastases). these secondary tumours may the grow, invade and damage nearby tissues and spread again
Primary malignat brain tumours
A primary malignant brain tumour is a cancer which arieses from a cell within the brain. the cells of the tumour grow into and damage normal brain tissue, also, like non-cancerous (benign) brain tumours, they can increase the preasure inside the skull. However, unlike most other type of malignant tumours. primary brain tumours rarely spread (metastasise) to other parts of the body
There are various types of primary malignant brain tumour. the deferent types develop from diferent type of cell in the brain. As a general guide, each type is graded on a scale of 1-4 grade 1 and 2 tumours are said to be low grade and the grade 3 and 4 high -grade. the higher the grade, the more aggressive the tumour tends to be and faster it tends to grow. the treatment options and outlook (prognosis) very depending on the type and grade of the tumour
Secondary malignant brain tumours
A secondary malignant brain tumour means that a cancer which started in another part of the body has spand to the brain. many types of cancer can spread to the brain. the most common type that do this are cancers of the breast, lung, bowel, kidney, and skin (melanoma)
Defferent type of brain tumours
there are many type of non cancerous (benign) brain tumours and primary cancerous (malignant) brain tumours. many are very rare. the following is brief description of the most common type
Meningioma
meningiomas are usually benign. they grow from cell in the tissues that surround the brain (the maninges)
Medulloblastoma
these are high-grade malignant tumours that grow in the cerebellum. they are uncommon in adults but are one of two most common brain tumours in children, there often astrocytoma in cerebellum
Gliomas
these are malignant primary brain tumours that arise of glial cells, there are various types, depending on the cell of origin- for example:
⦁ Astrocytomas (originating from astrocyte cells) there are various type of astrocytoma thery include : Astrocytomas is low grade, anaplastic astrocytoma this is a high- grade tumours and glioblastoma multiforme this is a high-grade tumour which tends to grow quickly. it is most common type of primary malignant brain tumours in adults.
⦁ Oligodenrogliomas : (originating from oligodendrocytes). these can vary in there grade
⦁ Ependymoma : (originating from ependymal cells). these are rare, but are usually low-grade
Primitive neuroectodermal tumours ( PNETs)
These are very similiar or medulloblastomas and mainly occur in children
Pituitary tumours
There are various type of tumours which arise from the diffrent cells in the pituitary gland. they tend to be benign whoever, the cell of the tumours may produce large quantities of hormones which can cause various symptoms, as they grow, they may also cause pressure symptoms, the nerves of sight (optic nerves) are near to pituitary and so a growing pituitary gland tumour may press on optic nerve and effect vision
Acoustic neuroma (schwannoma)
this is a benign tumour which aries from schwann cells which cover the nerve that goes to the ear. symptoms can include deafness on the affected side and dizziness with a spinning sensation (Vertigo)
What causes brain tumours
the cause of most non cancerous (benign) brain tumours and primary cancerous (malignant) brain tumours is not know
Genetic factor may a be a risk from some people-perhaps in about 1 in 20 cases. for example, people with the hereditary diseseases called neurofribromatosis type 1, turcot's syndrome, Li- fraumeni cancer syndrome, and tuberous slerosis have a higher-than-average risk of developing a glioma. then people with these diseases develop a glioma it trends occur in chidhood or early adult life. however, these cases are only small proportion of all glioma tumours.
How common are brain tumours
non-cancerous (benign) brain tumours and cancerous (malignant) primary brain tumours are uncommon. Overall they occur in about 12 in 100,00, people each year
the most common type in adults are benign meningioma and a glioma called glioblastoma multiforme. some type are very rare
Brain tumours can occur at any age. some type (such as medullablastoma) are more common in children and some are more common in adults. generally, the tummour that tend to occur in adults become more common with increasing age
secondary (metastatic) brain tumours are more common than benign brain tumours and malignant primary brain tumours
What are the symptoms of brain tumour
General symptoms
Early symptoms may include headaches and feeling sick. these are due to increased pressure within the skull (raised intracranial preassure). these symptoms may come and go first and tend to be worse in the morning. coughing. sneezing and stooping may make the headaches worse. epileptic seizures (convulsions) sometimes occour. increasing drowsiness may occur as tumour enlarges
Symptoms due to location in the brain
As a tumour grows it can damage the nearby brain tissue. The fungtions of the defferent parts of the body are controlled by defferent parts of the brain. therefore, symptoms vary from case to case, depending on which part of the brain is affacted and on the size of affacted area. for example one or more of the following may develop:
⦁ Weakness of muscles in arm, leg , part of face or eyes
⦁ problems with balance, co-ordination, vision, hearing, speech, communication or swallowong
⦁ loss of smell
⦁ Dizziness or unsteadiness
⦁ Numbness or weakness in a part of the body
⦁ confution
⦁ personality changes
⦁ symptoms related to hormonal changes if you have pituitary tumour
How are brain tumours diagnosed and assessed
A doctor will examine you if a brain tumour is suspected from the symptoms. this will include checking on the functions of the brain and nerves (movemonts, reflexes, vision, etc)
An MRI scan or CT scan of the head is the common test done to confirm or rude out the presense of a brain tumour. see separate leaflets called MRI Scan and CT scan for more details. if a tumour is identifed, further more detailed scan and tests may be done. for example, a PET scan or a cerebral angiogram are sometimes done to obtain more information about tumour
A small tissue sample (a biopsi) may be needed to be sure of the type of tumour. the sample is than examined under the microscope to look for abnormal cells. to obtain a biopsy from a brain tumor you need to have a small operation, usually done under anasthetic. small hole is bored in the skull to allow a fine needle though to obtain a small type of tumour can be identified. if it cancerous (malignant), the tumour grade can be determined (see above)
Blood test and other tests on other parts of the body may be done if the tumour is thought to be a secondary (metastatic) tumour. for example, it is quite common for a lung cancer to spread to the brain. therefore a chest X- ray may be done if this is dupected. various hormone tests may be done if a pituitary tumour is suspencted
What are the treatmants for the brain tumours
The main treatment used for brain tumours are surgery, chemotherapy, radiotherapy and medication to control symptoms such as seizues. the treatment or combination of treatments advised in each case depends on various factor, for example:
⦁ The type of brain tumour
⦁ The grede of the tumour if it is cancerous (malignant)
⦁ The exact site of the tumour
⦁ Your general health
Surgery
Surgery is often the main treatment for non- cancerous (benign) brain tumours is primary and primary cancerous (malignant) tumours. the aim of surgery is to remove (or even of the tumours) whilst doing as little damage as possible to the normal brain tissue. Your specialist will advase on whether surgery is possible option
Radiotherapy
Radiotherapy is a treatment which uses high- enery beams of radiation which are focused on cancerous tissue. this kills cancers cells or stops cancer cells from multiplying.
Radiotherapy is sometimes used insted of surgery when an operation is not possible for a malignant brain tumour. sometimes it is used in addition to surgery it is possible to remove all the tumour with surgery or to kill cancerous cell which may be left behind following surgery
Chemotherapy
chemotherapy is a treatment which uses anti- cancer medicines to kill cancer cell, or to stop them from multiplying. it may be used in addition or other treatments such as surgery or radiotherapy; again, depending on various factor such as the type of tumours
Medication to control symptoms
if you have sizeures by the tumour then anticonvulsant mediation will usually control be sizeures. painkillers may be need to ease any beadaches steroid medication is also commonly used to reduce inflamation around a brain tumour. this reduces the pressure inside the skull, which helps to ease headaches and other pressure symptoms
you should have a full discussion with specialist who you know case the will ba able to give the pros an cons, likely success rate, possible side-effects and other details about possible treatment option for your type of brain tumour
What is the outlook
it is difficult to give an overall outlook. every case is different, for example if you have a non- cancerous (benign) maningoma which is in a suitable place for surgery, the outlook is excellent
for primary cancerous (malignant) brain tumours, the outlook above is very general. the specialist who know your case can give more accurate information about your particular outlook and how well your type and stage of cancer is likely to respond to treatment.
Selasa, 07 Juli 2015
The Heart and Blood Vessels
The Heart and Blood Vessels
What are the heart and blood vessels?
The heart is a muscular pump that pushes blood through blood vessels around the body. Essential to life, the heart beats continuously, pumping the equivalent of more than 14,000 litres of blood every day.
Blood vessels form the living system of tubes that carry blood both to and from the heart. All cells in the body need oxygen and the vital nutrients found in blood. Without oxygen and these nutrients, the cells will die. The heart helps to provide oxygen and nutrients to the body’s tissues and organs by ensuring a rich supply of blood. Not only do blood vessels carry oxygen and nutrients, but they also transport carbon dioxide and waste products away from our cells. Carbon dioxide is passed out of the body by the lungs, and most of the other waste products are disposed of by the kidneys.
Where are the heart and blood vessels found?
The heart is a fist-sized organ which lies within the chest behind the sternum (breastbone). The heart sits on the diaphragm, the main muscle of breathing, which is found beneath the lungs. The heart is considered to have two ‘sides’ - the right side and the left side.
The heart has four chambers – an atrium and ventricle on each side. The atria are both supplied by large blood vessels that bring blood to the heart (see below for more details). Atria have special valves that open into the ventricles. The ventricles also have valves but, in this case, they open into blood vessels. The walls of the heart chambers are made mainly of special heart muscle. The different sections of the heart have to contract (squeeze) in the correct order for the heart to pump blood efficiently with each heartbeat.
What do the heart and blood vessels do?
The heart's main function is to pump blood around the body. Blood carries both nutrients and waste products, and is vital to life. One of the essential nutrients found in blood is oxygen.
The right side of the heart receives deoxygenated blood (lacking oxygen) from the body. After passing through the right atrium and right ventricle this blood is pumped to the lungs. Here blood picks up oxygen and loses another gas called carbon dioxide. Once through the lungs, the blood flows back to the left atrium. It then passes into the left ventricle and gets pumped into the aorta, the main artery supplying the body. Oxygenated blood is then carried though blood vessels to all the body’s tissues. Here oxygen and other nutrients pass into the cells where they are used to perform the body’s essential functions.
A blood vessel's main function is to transport blood around the body. Blood vessels also play a role in controlling your blood pressure.
Blood vessels are found throughout the body. There are five main types of blood vessels: arteries, arterioles, capillaries, venules and veins.
Arteries carry blood away from the heart to other organs. They can vary in size. The largest arteries have special elastic fibres in their walls. This helps to complement the work of the heart, by squeezing blood along when heart muscle relaxes. Arteries also respond to signals from our nervous system, either constricting (tightening) or dilating (relaxing).
Arterioles are the smallest arteries in the body. They deliver blood to capillaries. Arterioles are also capable of constricting or dilating and, by doing this, they control how much blood enters the capillaries.
Capillaries are tiny vessels that connect arterioles to venules. They have very thin walls which allow nutrients from the blood to pass into the body tissues. Waste products from body tissues can also pass into the capillaries. For this reason, capillaries are known as exchange vessels.
Groups of capillaries within a tissue reunite to form small veins called venules. Venules collect blood from capillaries and drain into veins.
Veins are the blood vessels that carry blood back to the heart. They may contain valves which stop blood flowing away from the heart.
How do the heart and blood vessels work?
The heart works by following a sequence of electrical signals that cause the muscles in each chamber to contract in a certain order. If these electrical signals change, the heart may not pump as well as it should.
The sequence of each heartbeat is as follows:
The sinoatrial node (SA node) in the right atrium is like a tiny in-built 'timer'. It fires off an electrical impulse at regular intervals. (About 60-80 per minute when you are resting and faster when you exercise. This controls your heart rate.) Each impulse spreads across both atria, which causes them to contract. This pumps blood through one-way valves into the ventricles.
The electrical impulse gets to the atrioventricular node (AV node) at the lower right atrium. This acts like a 'junction box' and the impulse is delayed slightly. Most of the tissue between the atria and ventricles does not conduct the impulse. However, a thin band of conducting fibres called the atrioventricular bundle (AV bundle) acts like 'wires' and carries the impulse from the AV node to the ventricles.
The AV bundle splits into two - a right and left branch. These then split into many tiny fibres (the Purkinje system) which carry the electrical impulse throughout the ventricles. The ventricles contract and pump blood through one-way valves into large arteries.
a. The arteries going from the right ventricle take blood to the lungs.
b. The arteries going from the left ventricle take blood to the rest of the body.
The heart then rests for a short time (diastole). Blood coming back to the heart from the large veins fills the atria during diastole.
a. The veins coming into the left atrium are from the lungs (full of oxygen).
b. The veins coming into the right atrium are from the rest of the body (depleted of oxygen).
The sequence then starts again for the next heartbeat. The closing of the valves in the heart make the 'lub-dub' sounds that a doctor can hear with a stethoscope.
If you exercise, your body tissues need more oxygen and will produce more carbon dioxide. This means your heart must speed up to meet those needs. Your heart rate (how fast your heart beats) is controlled in a number of different ways. The brain controls the heart rate through the nervous system. A special part of the brain, called the medulla oblongata, receives information from many different systems of the body. The brain then co-ordinates the information and either sends signals to increase or decrease the heart rate depending on what is necessary.
Even before physical activity begins, your heart may speed up in anticipation of what is to come. This is because a special part of the nervous system sends signals to the medulla. As physical activity starts, receptors (cells of the nervous system which monitor changes in the body) send signals about the position of your muscles to the brain. This can increase your heart rate.
The body also has other receptors which measure levels of chemicals, such as carbon dioxide, in your blood. If levels of carbon dioxide rise, signals are sent via the nervous system to the brain. The brain then sends electrical signals to the heart via nerves to speed it up. The signals cause the release of hormones which make the SA node fire more often. This means the heart beats more frequently. The brain can also send signals to the heart to slow it down.
Other hormones, such as those from the thyroid gland, can also influence your heart rate, as can certain substances found in your blood.
The most important function of the cardiovascular system (the heart and blood vessels together) is to keep blood flowing through capillaries. This allows capillary exchange to take place. Capillary exchange is the process of nutrients passing into the body’s cells and waste products passing out. Blood vessels are uniquely designed to allow this to happen.
Blood leaves the heart in the larger arteries. These vessels help to propel blood, even when the heart is not beating, because they have elastic walls which squeeze the blood in them. Arterioles are smaller than arteries and provide the link between the arteries and the capillaries. Capillaries allow nutrients and waste products to move in and out of the bloodstream. Venules take blood from the capillaries to the veins. Veins take blood back to the heart. This constant circulation of blood keeps us alive.
Your blood vessels also play a part in the regulation of your blood pressure. Certain chemicals in the body can cause our blood vessels either to contract or dilate. Signals from our nervous system can also make our blood vessels relax or contract. These changes cause a change in the size of the lumen of the vessel. This is the space through which blood flows. In simple terms, constriction of blood vessels causes an increase in blood pressure. Dilation of blood vessels causes a decrease in blood pressure. However, blood vessels don’t just control blood pressure by themselves. Your body controls blood pressure using a complicated system. This involves hormones, signals from your brain and nervous system and the natural responses of your blood vessels.
The blood supply to the heart
Like any other muscle, the heart muscle needs a good blood supply. The coronary arteries take blood to the heart muscle. These are the first arteries to branch off the aorta - the large artery that takes blood to the body from the left ventricle.
1. The right coronary artery mainly supplies the muscle of the right ventricle.
2. The left coronary artery quickly splits into two and supplies the rest of the heart muscle.
3. The main coronary arteries divide into many smaller branches to supply all the heart muscle.
Some disorders of the heart and blood vessels
Angina
Abdominal aortic aneurysm
Arrhythmias (abnormal heart rhythms)
Atheroma
Atrial fibrillation
Cardiomyopathy - dilated
Cardiomyopathy - hypertrophic
Deep vein thrombosis
Endocarditis
Heart failure
Heart valves and valve disease
High blood pressure
Myocardial infarction (heart attack)
Myocarditis
Pericarditis
Peripheral arterial disease in legs
Superficial thrombophlebitis
Supraventricular tachycardia
Varicose veins
Angina
Abdominal aortic aneurysm
Arrhythmias (abnormal heart rhythms)
Atheroma
Atrial fibrillation
Cardiomyopathy - dilated
Cardiomyopathy - hypertrophic
Deep vein thrombosis
Endocarditis
Heart failure
Heart valves and valve disease
High blood pressure
Myocardial infarction (heart attack)
Myocarditis
Pericarditis
Peripheral arterial disease in legs
Superficial thrombophlebitis
Supraventricular tachycardia
Varicose veins
The Eyes and Vision
The Eyes and Vision
This leaflet gives a brief overview of the eyes, eye function, and how we see.
Structure of the eye
The coloured part of your eye is called the iris. The iris is made up of muscle fibres which help to control the size of the pupil. The pupil is not an actual structure but the circular opening in the middle of the iris. The pupil appears as the dark central part of the eye. The pupil can change size depending on the amount of light going through it. In darkness your pupils will get bigger to allow more light in.
The retina is a layer of the eyeball, found on its back wall. It contains highly specialised nerve cells which convert the light received into electrical signals to be passed to the brain. Near the centre of the retina is the macula. The macula is a small highly sensitive part of the retina. It is responsible for detailed central vision. It contains the fovea, the area of your eye which produces the sharpest
The white of your eye is called the sclera. This is a protective layer which covers all the eyeball except the cornea. The cornea is a transparent layer which allows light to enter the eye. Beneath the sclera is the choroid. The choroid is another layer of the eye, which lies between the retina and the sclera. Its function is to provide oxygen and nutrients to the retina below. In order to do this the choroid has many blood vessels within it. At the front of the eyeball the choroid connects with the ciliary body.
In order for an object to be seen, the light coming from the object must hit the retina. Structures in the eye are needed to make sure that light entering the eye reaches the retina and is focused. The cornea and lens help to do this by bending light entering the eye. The cornea gives an initial bend to the light. But the lens is the fine tuner. The lens can change shape with the help of the ciliary body which contains fine muscle fibres. Depending on the angle of the light coming into the eye, the lens becomes more or less convex (curved) to focus the light correctly on to the macula on the back of the eye. This is very similar to a lens in a camera which focuses the light on to the film. The optic nerve carries the electrical impulses created in the retina to the brain.
The eye needs to keep its shape so that light rays are focused accurately on to the retina. So, most of the eye is filled with a substance like jelly called the vitreous humour (humour meaning fluid). The front of the eye is filled with a clear fluid called aqueous humour, which is more watery.
The aqueous humour is made continuously by cells that line the ciliary body. The fluid circulates through the front part of the eye, and then drains away through an area called the trabecular meshwork, which is located near the base of the iris. So, there is constant production and drainage of fluid.
Eye movements
The movement of each eye is controlled by six muscles that pull the eye in various directions. For example, to look left, the lateral rectus muscle of the left eye pulls the left eye outward and the medial rectus of the right eye pulls the right eye inward towards the nose. Levator palpebrae superioris opens the upper eyelid.
The eyelids
The upper and lower eyelids help to protect the eye, and keep its surface moist. The upper eyelid is more movable and is attached to a special muscle, called the levator palpebrae superioris. This muscle allows you to control the movements of the upper eyelid. Eyelids help to spread the tear film across the eye. They also contain a special oil which slows down the evaporation of the tear film.
The eyelids are made up of several different layers including the conjunctiva.
In order for an object to be seen, the light coming from the object must hit the retina. Structures in the eye are needed to make sure that light entering the eye reaches the retina and is focused. The cornea and lens help to do this by bending light entering the eye. The cornea gives an initial bend to the light. But the lens is the fine tuner. The lens can change shape with the help of the ciliary body which contains fine muscle fibres. Depending on the angle of the light coming into the eye, the lens becomes more or less convex (curved) to focus the light correctly on to the macula on the back of the eye. This is very similar to a lens in a camera which focuses the light on to the film. The optic nerve carries the electrical impulses created in the retina to the brain.
The eye needs to keep its shape so that light rays are focused accurately on to the retina. So, most of the eye is filled with a substance like jelly called the vitreous humour (humour meaning fluid). The front of the eye is filled with a clear fluid called aqueous humour, which is more watery.
The aqueous humour is made continuously by cells that line the ciliary body. The fluid circulates through the front part of the eye, and then drains away through an area called the trabecular meshwork, which is located near the base of the iris. So, there is constant production and drainage of fluid.
Eye movements
The movement of each eye is controlled by six muscles that pull the eye in various directions. For example, to look left, the lateral rectus muscle of the left eye pulls the left eye outward and the medial rectus of the right eye pulls the right eye inward towards the nose. Levator palpebrae superioris opens the upper eyelid.
The eyelids
The upper and lower eyelids help to protect the eye, and keep its surface moist. The upper eyelid is more movable and is attached to a special muscle, called the levator palpebrae superioris. This muscle allows you to control the movements of the upper eyelid. Eyelids help to spread the tear film across the eye. They also contain a special oil which slows down the evaporation of the tear film.
The eyelids are made up of several different layers including the conjunctiva.
The conjunctiva is the thin layer you see on the inside of your eyelid, which makes contact with the eyeball itself. The surface of the eyeball also has its own conjunctiva. When the blood vessels in this conjunctiva become enlarged they can be seen, giving a bloodshot appearance. Eyelashes help to stop debris and direct sunlight from entering the eyes.
Tear formation
To avoid damage to the sensitive surface of the eye it needs to be kept moist. The eyes are in constant contact with your eyelids. Without some form of lubrication, the friction created between the two layers of conjunctiva would cause rubbing. To prevent this, and to help remove debris, the eye produces a tear film. The tear film is made up from three layers - the main middle watery layer, the thin outer lipid (oily) layer, and the thin inner mucus layer.
The main middle watery layer is what we may think of as tears. The watery fluid comes from the lacrimal glands. There is a lacrimal gland just above, and to the outer side, of each eye. The lacrimal glands constantly make a small amount of watery fluid which drains on to the upper part of the eyes. When you blink, the eyelid spreads the tears over the front of the eye.
Tiny glands in the eyelids (meibomian glands) make a small amount of lipid (oily) liquid which covers the outer layer of the tear film. This layer helps to keep the tear surface smooth and to reduce evaporation of the watery tears.
Cells of the conjunctiva at the front of the eye and inner part of the eyelids also make a small amount of mucus-like fluid. This allows the watery tears to spread evenly over the surface of the eye.
The tears then drain down small channels (canaliculi) on the inner side of the eye into a tear sac. From here they flow down a channel called the tear duct (also called the nasolacrimal duct) into the nose.
Tear formation in people can also occur in response to emotion. When this happens the lacrimal glands simply produce more lacrimal fluid which spills over the eyelids.
How does the visual system work?
When you look at an object you see it because light reflects off the object and converges (to focus or come together) on the layer of the eye called the retina. The eyes receive light from many different directions and distances. To be seen, all light must focus on the comparatively tiny area of the retina. This means the eyes have to bend light from different angles and directions so that it comes together on that very small part of the eye.
Firstly, light passes through the transparent cornea. Most bending of light occurs here. Light then travels through the pupil and hits the lens. The lens also bends light, increasing the amount focused on the highly specialised cells of the retina. In myopia (short-sightedness), rays of light focus on a point before the retina. This means that distant objects can’t be seen clearly. In hypermetropia (long-sightedness), light converges on a point behind the retina. This means nearby objects can’t be seen well.
The retina is made up of millions of light-sensitive nerve cells called photoreceptors. These cells help to turn the light into electrical signals which are sent to the brain to be interpreted. Photoreceptors contain special chemicals which are changed when light hits them. This change causes an electrical signal which is sent to the brain via the optic nerve. Different types of photoreceptor allow us to see in a huge range of different conditions, from dark to light, and all the colours of the rainbow. Photoreceptors called rods help us to see in dim light, whereas cones help with colour vision and in bright light.
The electrical signals travel to a part of the brain called the thalamus via the optic nerve. The thalamus acts as a relay station, sending on the information received from the optic nerve to an area of brain called the visual cortex. The visual cortex is a specialised part of the brain which processes visual information. Located at the back of the head, it interprets the electrical signals to get information about the object's colour, shape and depth. Other parts of the brain put this information together to create the whole picture.
Tear formation
To avoid damage to the sensitive surface of the eye it needs to be kept moist. The eyes are in constant contact with your eyelids. Without some form of lubrication, the friction created between the two layers of conjunctiva would cause rubbing. To prevent this, and to help remove debris, the eye produces a tear film. The tear film is made up from three layers - the main middle watery layer, the thin outer lipid (oily) layer, and the thin inner mucus layer.
The main middle watery layer is what we may think of as tears. The watery fluid comes from the lacrimal glands. There is a lacrimal gland just above, and to the outer side, of each eye. The lacrimal glands constantly make a small amount of watery fluid which drains on to the upper part of the eyes. When you blink, the eyelid spreads the tears over the front of the eye.
Tiny glands in the eyelids (meibomian glands) make a small amount of lipid (oily) liquid which covers the outer layer of the tear film. This layer helps to keep the tear surface smooth and to reduce evaporation of the watery tears.
Cells of the conjunctiva at the front of the eye and inner part of the eyelids also make a small amount of mucus-like fluid. This allows the watery tears to spread evenly over the surface of the eye.
The tears then drain down small channels (canaliculi) on the inner side of the eye into a tear sac. From here they flow down a channel called the tear duct (also called the nasolacrimal duct) into the nose.
Tear formation in people can also occur in response to emotion. When this happens the lacrimal glands simply produce more lacrimal fluid which spills over the eyelids.
How does the visual system work?
When you look at an object you see it because light reflects off the object and converges (to focus or come together) on the layer of the eye called the retina. The eyes receive light from many different directions and distances. To be seen, all light must focus on the comparatively tiny area of the retina. This means the eyes have to bend light from different angles and directions so that it comes together on that very small part of the eye.
Firstly, light passes through the transparent cornea. Most bending of light occurs here. Light then travels through the pupil and hits the lens. The lens also bends light, increasing the amount focused on the highly specialised cells of the retina. In myopia (short-sightedness), rays of light focus on a point before the retina. This means that distant objects can’t be seen clearly. In hypermetropia (long-sightedness), light converges on a point behind the retina. This means nearby objects can’t be seen well.
The retina is made up of millions of light-sensitive nerve cells called photoreceptors. These cells help to turn the light into electrical signals which are sent to the brain to be interpreted. Photoreceptors contain special chemicals which are changed when light hits them. This change causes an electrical signal which is sent to the brain via the optic nerve. Different types of photoreceptor allow us to see in a huge range of different conditions, from dark to light, and all the colours of the rainbow. Photoreceptors called rods help us to see in dim light, whereas cones help with colour vision and in bright light.
The electrical signals travel to a part of the brain called the thalamus via the optic nerve. The thalamus acts as a relay station, sending on the information received from the optic nerve to an area of brain called the visual cortex. The visual cortex is a specialised part of the brain which processes visual information. Located at the back of the head, it interprets the electrical signals to get information about the object's colour, shape and depth. Other parts of the brain put this information together to create the whole picture.
Some disorders of the eyes and vision
Amblyopia
Blepharitis
Cataracts
Chalazion
Conjunctivitis - allergic
Conjunctivitis - infective
Corneal Injury
Dry eyes
Ectropion
Entropion
Glaucoma - acute
Glaucoma - chronic
Herpes simplex eye infection
Long sight - hypermetropia
Macular degeneration
Presbyopia
Retinal detachment
Short sight - myopia
Sjögren's syndrome
Squint (childhood)
Stye
Subconjunctival haemorrhage
Tear duct blockage of babies
Uveitis and iritis
Watering eyes
The Spleen
The Spleen
This leaflet gives a brief overview of the spleen and its functions.
What is the spleen?
The spleen is an organ about the size of a clenched fist found on the left-hand side of your upper abdomen. Its main functions are to filter your blood, create new blood cells and store platelets. It is also a key part of your body's immune system.
Where is the spleen found?
The spleen is found on the left side of your body, behind the stomach on a level with the 9th to 11th ribs. It is similar in structure to a lymph node, and is the largest lymphatic organ in the body. The spleen contains two main types of tissue - white pulp and red pulp. White pulp is lymphatic tissue (material which is part of the immune system) mainly made up of white blood cells. Red pulp is made up of venous sinuses (blood-filled cavities) and splenic cords. Splenic cords are special tissues which contain different types of red and white blood cells.
What does the spleen do?
Blood flows into the spleen where it enters the white pulp. Here, white blood cells called B and T cells screen the blood flowing through. T cells help to recognise invading pathogens (germs - for example, bacteria and viruses) that might cause illness and then attack them. B cells make antibodies that help to stop infections from taking hold.
Blood also enters red pulp. Red pulp has three main functions:
1.It removes old and damaged red blood cells. Red blood cells have a lifespan of about 120 days. After this time they stop carrying oxygen effectively. Special cells called macrophages break down these old red blood cells. Haemoglobin (a chemical which carries oxygen) found within the cells is also broken down and then recycled.
2.Red pulp also stores up to one third of the body's supply of platelets. Platelets are fragments of cells circulating in the bloodstream that help to stop bleeding when we cut ourselves. These extra stored platelets can be released from the spleen if severe bleeding occurs.
3.In fetuses (unborn babies) red pulp can also act like bone marrow, producing new red blood cells. Usually this stops after birth, but may start again in some people with certain diseases.
While the spleen performs a number of important functions, it is not essential to life. Other organs such as the liver and bone marrow are able to take over many of its jobs. Your spleen may be removed (splenectomy) for various reasons - for example, because of an illness that affects the spleen, or if it is damaged by an injury. Also, the spleen may not work well in some diseases - for example, sickle cell disease, thalassaemia, and lymphomas.
However, people who have had their spleen removed are more likely to get infections and may be put on long-term antibiotics to prevent this. See separate leaflet called Preventing Infection after Splenectomy or if you do not have a Working Spleen for further detail.
Kamis, 25 Juni 2015
The Pancreas
The Pancreas
The pancreas is an organ the upper abdomen. Enzymes (chemicals) made by cells in the pancreas pass into the gut to help digest food. The hormones insulin and glucagon are also made in the pancreas and help to regulate the blood sugar level.
The pancreas is an organ the upper abdomen. Enzymes (chemicals) made by cells in the pancreas pass into the gut to help digest food. The hormones insulin and glucagon are also made in the pancreas and help to regulate the blood sugar level.
What is the pancreas?
The pancreas is an organ in the upper abdomen. It is about the size of a hand.
Where is the pancreas?
The pancreas is in the upper abdomen and lies behind the stomach and intestines (guts). The pancreas has a connection to the duodenum (the first part of the gut, which is connected to the stomach) via a duct (tube). This connecting duct allows the enzymes produced by the pancreas to pass into the intestines.
What does the pancreas do?
The pancreas has two main functions:
- To make digestive enzymes which help us to digest food. Enzymes are special chemicals which help to speed up your body’s processes.
- To make hormones which regulate our metabolism. Hormones are chemicals which can be released into the bloodstream. They act as messengers, affecting cells and tissues in distant parts of your body.
About 90% of the pancreas is dedicated to making digestive enzymes. Cells called acinar cells within the pancreas produce these enzymes. The enzymes help to make proteins, fats and carbohydrates smaller. This helps the intestines to absorb these nutrients. The acinar cells also make a liquid which creates the right conditions for pancreatic enzymes to work. This is also known as pancreatic juice. The enzymes made by the pancreas include:
- Pancreatic proteases (such as trypsin and chymotrypsin) - which help to digest proteins.
- Pancreatic amylase - which helps to digest carbohydrates (sugars).
- Pancreatic lipase - which helps to digest fat.
Approximately 5% of the pancreas makes hormones which help to regulate your body’s metabolism. These hormones are made by several different cells which clump together like little islands (islets) within the pancreas. The islets are called islets of Langerhans and there are about one million islets dotted about in an adult pancreas. The hormones made by the cells in the islets of Langerhans within the pancreas include:
- Insulin - which helps to regulate sugar levels in the blood.
- Glucagon – which works with insulin to keep blood sugar levels balanced.
- Somatostatin – which helps to control the release of other hormones.
- Gastrin – which aids digestion in the stomach.
How does the pancreas work?
The digestive enzymes made by the pancreas are controlled by the body’s nervous system and its hormones. When the body senses food in the stomach, electrical signals are sent to the pancreas via nerves. These signals stimulate the pancreas to put more enzymes into the pancreatic juice. Acinar cells respond by increasing the amount of enzymes they produce. The enzymes leave the cells and pass into tiny ducts (tubes). These ducts join together like branches of a tree to form the main pancreatic duct. The pancreatic duct drains the enzymes produced into the duodenum (the part of the gut just after the stomach).
The enzymes are made in an inactive form so that they don't digest the pancreas itself. Once they enter the intestines the enzymes are activated and can begin breaking food down.
The main hormones released by the pancreas are insulin and glucagon. These hormones help to regulate the amount of sugar found in the blood and the body’s cells. The body’s cells need energy to function. The most readily available form of energy is glucose, a type of sugar. Insulin helps to take glucose from the blood into the cells themselves. This allows the cells to function properly. Glucagon stimulates cells in the liver to release glucose into the blood when levels are low.
The pancreas carefully monitors the level of glucose in the blood. When levels of glucose are high in the blood, cells within the pancreas make insulin. Insulin gets released into the bloodstream where it causes glucose to move into cells. This decreases the amount of glucose in the bloodstream, lowering blood sugar levels. Low blood sugar levels stimulate the pancreas to make glucagon. Glucagon works on cells in the liver, causing the release of glucose. If sugar levels in the blood rise above normal, the pancreas stops releasing glucagon. Insulin may then be released to balance the system again.
This system helps to keep the level of glucose in your blood at a steady level. When you eat, levels of sugar in your blood rise and insulin helps to bring them down. Between meals, when your sugar levels fall, glucagon helps to keep them up.
The digestive enzymes made by the pancreas are controlled by the body’s nervous system and its hormones. When the body senses food in the stomach, electrical signals are sent to the pancreas via nerves. These signals stimulate the pancreas to put more enzymes into the pancreatic juice. Acinar cells respond by increasing the amount of enzymes they produce. The enzymes leave the cells and pass into tiny ducts (tubes). These ducts join together like branches of a tree to form the main pancreatic duct. The pancreatic duct drains the enzymes produced into the duodenum (the part of the gut just after the stomach).
The enzymes are made in an inactive form so that they don't digest the pancreas itself. Once they enter the intestines the enzymes are activated and can begin breaking food down.
The main hormones released by the pancreas are insulin and glucagon. These hormones help to regulate the amount of sugar found in the blood and the body’s cells. The body’s cells need energy to function. The most readily available form of energy is glucose, a type of sugar. Insulin helps to take glucose from the blood into the cells themselves. This allows the cells to function properly. Glucagon stimulates cells in the liver to release glucose into the blood when levels are low.
The pancreas carefully monitors the level of glucose in the blood. When levels of glucose are high in the blood, cells within the pancreas make insulin. Insulin gets released into the bloodstream where it causes glucose to move into cells. This decreases the amount of glucose in the bloodstream, lowering blood sugar levels. Low blood sugar levels stimulate the pancreas to make glucagon. Glucagon works on cells in the liver, causing the release of glucose. If sugar levels in the blood rise above normal, the pancreas stops releasing glucagon. Insulin may then be released to balance the system again.
This system helps to keep the level of glucose in your blood at a steady level. When you eat, levels of sugar in your blood rise and insulin helps to bring them down. Between meals, when your sugar levels fall, glucagon helps to keep them up.
Some disorders of the pancreas
- Cancer of the pancreas
- Cancer of the pancreas
- Diabetes - type 1
- Pancreatitis - acute
- Pancreatitis - chronic
Senin, 22 Juni 2015
The Thyroid and Parathyroid Glands
The Thyroid and Parathyroid Glands
This leaflet gives a brief overview of the thyroid and parathyroid glands and the hormones that they make.
What are the thyroid and parathyroid glands?
Both the thyroid and parathyroid glands are endocrine glands. This means they make and secrete (release) hormones. Hormones are chemicals which can be released into the bloodstream. They act as messengers, affecting cells and tissues in distant parts of your body. Thyroid hormones affect the body's metabolic rate and the levels of certain minerals in the blood. The hormone produced by the parathyroid also helps to control the amount of these essential minerals.
Where is the thyroid found?
The thyroid gland is found in the front part of your neck, just below the large cartilage tissue in your neck (your Adam's apple). It is made up of two lobes - the right and the left lobes. These two lobes are joined by a small bridge of thyroid tissue called the isthmus. The two lobes lie on either side of your trachea (windpipe).
What does the thyroid do?
The thyroid makes three hormones that it secretes into the bloodstream. Two of these hormones, called thyroxine (T4) and triiodothyronine (T3), increase your body's metabolic rate. Essentially, the body's metabolic rate is how quickly the cells in your body use the energy stored within them. Thyroid hormones make cells use more energy. By controlling how much energy our cells use, thyroid hormones also help to regulate our body temperature. Heat is released when energy is used, increasing our body temperature. Thyroid hormones also play a role in making proteins, the building blocks of the body's cells. They also increase the use of the body's fat and glucose stores.
In order to make T3 and T4, the thyroid gland needs iodine, a substance found in the food we eat. T4 is called this because it contains four atoms of iodine. T3 contains three atoms of iodine. In the cells and tissues of the body most T4 is converted to T3. T3 is the more active hormone, it influences the activity of all the cells and tissues of your body.
The other hormone that the thyroid makes is called calcitonin. This helps to control the levels of calcium and phosphorus in the blood. These minerals are needed, among other things, to keep bones strong and healthy.
How does the thyroid work?
The main job of the thyroid gland is to produce hormones T4 and T3. To do this the thyroid gland has to take a form of iodine from the bloodstream into the thyroid gland itself. This substance then undergoes a number of different chemical reactions which result in the production of T3 and T4.
The activity of the thyroid is controlled by hormones produced by two parts of the brain, the hypothalamus and the pituitary. The hypothalamus receives input from the body about the state of many different bodily functions. When the hypothalamus senses that levels of T3 and T4 are low, or that the body's metabolic rate is low, it releases a hormone called thyrotropin-releasing hormone (TRH). TRH travels to the pituitary via the connecting blood vessels. TRH stimulates the pituitary to secrete thyroid-stimulating hormone (TSH).
TSH is released from the pituitary into the bloodstream and travels to the thyroid gland. Here, TSH causes cells within the thyroid to make more T3 and T4. T3 and T4 are then released into the bloodstream where they increase metabolic activity in the body's cells. High levels of T3 stop the hypothalamus and pituitary from secreting more of their hormones. In turn this stops the thyroid producing T3 and T4. This system ensures that T3 and T4 should only be made when their levels are too low.
Calcitonin is released by the thyroid gland if the amount of calcium in the bloodstream is high. Calcitonin decreases the amount of calcium and phosphorus in the blood. It does this by slowing the activity of cells found in bone, called osteoclasts. These cells cause calcium to be released as they 'clean' bone. Calcitonin also accelerates the amount of calcium and phosphorus taken up by bone. Calcitonin works with parathyroid hormone to regulate calcium levels (see below for full explanation).
Where are the parathyroid glands found?
The body has four parathyroid glands. They are small, pea-sized glands, located in the neck just behind the butterfly-shaped thyroid gland. Two parathyroid glands lie behind each 'wing' of the thyroid gland.
What do the parathyroid glands do?
The parathyroid glands release a hormone called parathyroid hormone. This hormone helps to control the levels of three minerals in the body: calcium, phosphorus and magnesium. Parathyroid hormone has a number of effects in the body:
- It causes the release of calcium from bones.
- It causes calcium to be absorbed (taken up into the blood) from the intestine.
- It stops the kidneys from excreting (getting rid of) calcium in the urine.
- It causes the kidneys to excrete phosphate in the urine.
- It increases blood levels of magnesium.
How do the parathyroids work?
Normally, parathyroid hormone release is triggered when the level of calcium in the blood is low. When the calcium level rises and is back to normal, the release of parathyroid hormone from the parathyroids is suppressed. However, parathyroid hormone and calcitonin work together to control calcium levels in the blood. The blood calcium level is the main stimulus for the release of these hormones, as the release of these hormones is not controlled by the pituitary.
When the calcium level is high in the bloodstream, the thyroid gland releases calcitonin. Calcitonin slows down the activity of the osteoclasts found in bone. This decreases blood calcium levels. When calcium levels decrease, this stimulates the parathyroid gland to release parathyroid hormone. Parathyroid hormone encourages the normal process of bone breakdown (essential for maintenance and growth of the bone). This process of bone breakdown releases calcium into the bloodstream. These actions raise calcium levels and counteract the effects of calcitonin. By having two hormones with opposing actions, the level of calcium in the blood can be carefully regulated.
Parathyroid hormone also acts on the kidneys. Here it slows down the amount of calcium and magnesium filtered from the blood into the urine. Parathyroid hormone also stimulates the kidneys to make calcitriol, the active form of vitamin D. Calcitriol helps to increase the amount of calcium, magnesium and phosphorus absorbed from your intestines (guts) into the blood.
Normally, parathyroid hormone release is triggered when the level of calcium in the blood is low. When the calcium level rises and is back to normal, the release of parathyroid hormone from the parathyroids is suppressed. However, parathyroid hormone and calcitonin work together to control calcium levels in the blood. The blood calcium level is the main stimulus for the release of these hormones, as the release of these hormones is not controlled by the pituitary.
When the calcium level is high in the bloodstream, the thyroid gland releases calcitonin. Calcitonin slows down the activity of the osteoclasts found in bone. This decreases blood calcium levels. When calcium levels decrease, this stimulates the parathyroid gland to release parathyroid hormone. Parathyroid hormone encourages the normal process of bone breakdown (essential for maintenance and growth of the bone). This process of bone breakdown releases calcium into the bloodstream. These actions raise calcium levels and counteract the effects of calcitonin. By having two hormones with opposing actions, the level of calcium in the blood can be carefully regulated.
Parathyroid hormone also acts on the kidneys. Here it slows down the amount of calcium and magnesium filtered from the blood into the urine. Parathyroid hormone also stimulates the kidneys to make calcitriol, the active form of vitamin D. Calcitriol helps to increase the amount of calcium, magnesium and phosphorus absorbed from your intestines (guts) into the blood.
Some disorders of the thyroid and parathyroid glands
- Cancer of the thyroid
- Goitre (thyroid swelling)
- Hyperparathyroidism - overactive parathyroid
- Hyperthyroidism - overactive thyroid
- Hypoparathyroidism - underactive parathyroid
- Hypothyroidism - underactive thyroid
The Immune System
The Immune System
This leaflet gives a brief overview of the immune system and how it works.
A. What is the immune system?
We are surrounded by millions of bacteria, viruses and other microbes (germs) that have the potential to enter our bodies and cause harm. The immune system is the body's defence against pathogens (disease-causing microbes). The immune system is made up of non-specialised defences such as skin and the acidic juice produced by your stomach. But it also has some highly specialised defences which give you immunity against (resistance to) particular pathogens. These defences are special white blood cells called lymphocytes. Other types of white blood cells play an important part in defending your body against infection.
The lymphatic system is also part of the immune system. The lymphatic system is made up of a network of vessels (tubes) which carry fluid called lymph. It contains specialised lymph tissue and all of the structures dedicated to the production of lymphocytes.
B. Where is the immune system found?
The immune system is generally divided into two parts. The first part is the defences you are born with. These form what are known as the innate system.
The second part of your immune system, known as immunity, develops as you grow. Your immunity gives you protection against specific pathogens. Not only can this system recognise particular pathogens, it also has a memory of this. This means that if you encounter a certain pathogen twice, your immune system recognises it the second time around. This usually means your body responds quicker to fight off the infection.
The innate system is found in many different places around the body. First line of defence is your skin. Skin forms a waterproof barrier that prevents pathogens from entering the body. Your body cavities, such as the nose and mouth, are lined with mucous membranes. Mucous membranes produce sticky mucus which can trap bacteria and other pathogens. Other fluids produced by the body help to protect your internal layers from invasion by pathogens. Gastric juice produced by the stomach has high acidity which helps to kill off many of the bacteria in food. Saliva washes pathogens off your teeth and helps to reduce the amount of bacteria and other pathogens in your mouth.
If bacteria or other pathogens manage to get through these initial defences, they encounter a second line of defence. Most of these defences are present in your blood, either as specialised white blood cells or as chemicals released by your cells and tissues.
The second part of your immune system, the part that gives you immunity, involves the activation of lymphocytes. This will be described later on. Lymphocytes are found in your blood and also in specialised lymph tissue such as lymph nodes, the spleen and the thymus.
C. How does the immune system work?
The first line of defence is your body's skin and mucous membranes, as mentioned above.
If pathogens manage to get through these barriers, they encounter special white blood cells present in your bloodstream. There are different types of white cells, called neutrophils (polymorphs), lymphocytes, eosinophils, monocytes, and basophils.
White blood cells travel in the bloodstream and react to different types of infection caused by bacteria, viruses or other pathogens. Neutrophils engulf bacteria and destroy them with special chemicals. Eosinophils and monocytes also work by swallowing up foreign particles in the body. Basophils help to intensify inflammation (swelling).
Inflammation is part of your body's immune response. Damage to your tissues causes the release of chemicals into the blood. These chemicals make blood vessels leaky, helping specialised white blood cells get to where they are needed. They also attract neutrophils and monocytes to the site of the injury, which helps to protect against a bacterial infection developing.
Lymphocytes have a variety of different functions. They attack viruses and other pathogens. They also make antibodies which help to destroy bacteria. Lymphocytes are divided into T cells and B cells. Bone marrow is the tissue found within the internal cavity of bones. It contains stem cells, which create B and T cells. B cells mature in the bone marrow whereas T cells mature in the thymus.These are the cells responsible for developing immunity to particular types of bacteria and virus.
B cells and T cells work in different ways. B cells produce antibodies. Antibodies are a special type of protein which attacks antigens. Antigens are like flags to our immune system. They usually identify a molecule as being foreign. They can be found on the surface of bacteria, but they can also be found on substances which don't cause disease - for example, in pollen, egg white or transplanted organs. An antigen is a chemical part of a molecule which generates an antibody response in the body. Literally it means antibody generator. One of the most amazing features of the immune system is that B cells can recognise millions of different antigens. B cells can recognise antigens that have never entered the body before, and even man-made molecules that don't exist in nature.
When a foreign particle enters the body, B cells recognise it, binding to the antigen on its surface. This activates the B cell which then changes into a plasma cell. The plasma cell makes antibodies specific to that antigen. Antibodies can immobilise bacteria, encourage other cells to 'eat' the pathogen and activate other immune defences. While some B cells become plasma cells, others don't. These cells live on as memory B cells that respond more vigorously should the same antigen invade the body again.
T cells directly attack the invading organism; however, they are not able to recognise antigens without the help of other cells. These cells process the antigen and then present them to T cells. T cells are very different from each other. When an antigen enters the body only a few T cells are able to recognise and bind to the antigen. While T cells also bind to antigens they need a second signal to become activated. Once activated, T cells get bigger and start to divide. These cells then target the invaders and release chemicals that destroy the pathogen. Like B cells, some of the T cells remain to form memory T cells. This allows the body to respond quickly if the same antigen enters the body.
The lymphatic system is a major part of the body's defence against infection. Lymph nodes are one of the components of this system. These are specialised structures which are found in lymph vessels. Lymph nodes are a filter for the lymph flowing through the vessels. They contain B and T cells which recognise bacteria and pathogens which have entered the lymph via the bloodstream. When foreign material is detected, other dedicated immune cells are recruited to the node to deal with the infection. This helps to prevent the infection from spreading throughout the body.
There are around 600 lymph nodes throughout the body, usually in groups. Large groups of lymph nodes are found in the groin (inguinal nodes), in the armpit (axillary nodes) and in the neck area (cervical nodes). In health they are pea-sized but if you develop an infection you may find that they become enlarged. This is due to an accumulation of lymphocytes and other cells of the immune system.
Lymphoid tissue helps to defend mucosal surfaces, such as the mouth and intestines, from infection. The tonsils, which are found in the back of the throat, often become enlarged in response to infection. These tissues help to trap bacteria and other pathogens and activate white blood cells.
The thymus is an important lymphatic organ. Found in front of your trachea (windpipe), its main role is to teach white blood cells to recognise our own cells. In order for the immune system to function properly, white blood cells must be able to discriminate between invading pathogens and the body's own cells. After T cells are produced in the bone marrow they migrate to the thymus. Here they are educated by the thymus to stop them from attacking our own cells. It is thought that some forms of autoimmune disease (where the body attacks itself) may be due to problems with this process. The thymus is at its largest during puberty, and gets smaller as you age.
The spleen is the largest single mass of lymphatic tissue in the body. Located close to the rib cage on the left side of the body, the spleen helps to filter the blood. It contains specialised tissue called white pulp. This contains white blood cells which respond to bacteria and other pathogens in a similar way to those in lymph nodes. Other tissue in the spleen, called red pulp, helps to remove damaged red blood cells and store platelets.
Minggu, 21 Juni 2015
The Ears, Hearing and Balance
The Ears, Hearing and Balance
Your ears do the remarkable job of allowing you to hear a huge range of sounds, from a whisper to a loud band. To do this, the ear transforms sound energy into electrical signals which the brain can interpret. Your ears also help to maintain your balance.
Structure of the ear
The ear is roughly divided into three parts. The external (outer) ear includes the part you can see, called the pinna, and the narrow tube-like structure - the ear canal. At the end of the canal is the eardrum. This separates the external ear from the middle ear. The eardrum is a tightly stretched membrane, a bit like the skin of a drum.
The vestibular system is made up of a network of tubes, called the semicircular canals, plus the vestibule. The vestibular system also contains special sensory cells, but here they detect movement instead of sound. Both the cochlea and the vestibular system are connected to a nerve which carries electrical signals to the brain.
How do you hear?
Sound waves are created when air vibrates. To hear, the ear must change sound into electrical signals which the brain can interpret. The pinna (outer part of the ear) funnels sound waves into the ear canal. When sound waves reach the eardrum they cause it to vibrate. Vibrations of the eardrum cause the tiny bones in the middle ear to move too. The last of these bones, the stapes, passes on the vibrations to the cochlea. When the cochlea receives the vibrations, the fluid inside it moves. As the fluid moves, it causes the special sensory cells to create an electrical signal. This electrical signal is sent to the brain. Special areas in the brain receive these signals and translate them into what we know as sound.
Your ears create electrical signals that represent an extraordinary variety of sounds. For example, the speed at which the eardrum vibrates varies with different types of sound. With low-pitched sounds the eardrum vibrates slowly. With high-pitched sounds it vibrates faster. This means that the special hair cells in the cochlea also vibrate at varying speeds. This causes different signals to be sent to the brain. This is one of the ways we are able to distinguish between a wide range of sounds.
How do you keep your balance?
Balance is maintained not only by the vestibular system found in your ears but also by your visual and sensory systems. If any one of these systems is damaged, you may experience dizziness or loss of balance.
The brain uses the visual system to help orientate us in our surroundings. The vestibular system detects both circular motion and movement in a straight line. This includes everyday actions such as stopping, starting or turning. The sensory system keeps track of the movement and tension of our muscles and joints. It also monitors the position of our body with respect to the ground. The brain receives signals from all these systems and processes the information gathered to produce a sensation of stability.
The tubes and sacs within the vestibular system are filled with fluid. When we move our heads, this fluid also moves. The vestibular system also contains specialised sensory cells. Movement of the fluid causes these sensory cells to bend. This change results in an electrical signal which is carried, via a nerve, to the brain for interpretation.
Once the brain has interpreted the signals as movement, it controls your eyes so that they keep providing information about your position. The brain also sends signals to your muscles so that they help to ensure balance regardless of the position of your body.
Some common disorders of the ear
- Barotrauma of the ear
- Benign paroxysmal positional vertigo
- Ear infection (otitis media)
- Earwax
- Eustachian tube dysfunction
- Glue ear
- Labyrinthitis and vestibular neuritis
- Ménière's disease
- Otitis externa
- Otosclerosis
- Perforated eardrum
- Presbyacusis (hearing loss of older people)
- Tinnitus
Jumat, 19 Juni 2015
The Lungs and Respiratory Tract
The Lungs and Respiratory Tract
This leaflet gives a brief overview of the lungs, lung function, and how we breathe.
Where are the lungs found?
The lungs are found in the chest on the right and left side. At the front they extend from just above the clavicle (collarbone) at the top of the chest to about the sixth rib down. At the back of the chest the lungs finish around the tenth rib. The pleura (the protective membranes which cover the lung) continue down to the twelfth rib. From front to back the lungs fill the rib cage, but are separated by the heart, which lies in between them.
Air that we breathe enters the nose, flows through the pharynx (throat) and larynx (voice box) and enters the trachea (windpipe). The trachea eventually divides into two parts called bronchi. The right main bronchus (bronchus is the word for one of the bronchi) supplies the right lung; the left main bronchus supplies the left lung. These bronchi then go on to divide into smaller bronchi. Eventually, the bronchi become known as bronchioles – the smallest air tubes in the lungs. This system of air tubes can be thought of as an upside down tree, with the trachea being the main trunk and the bronchi and bronchioles being the branches. The medical term for all the air tubes is 'the respiratory tract'.
At the end of the smallest bronchioles are alveoli. Alveoli are tiny sacs that are lined by a very thin layer of cells. They also have an excellent blood supply. The tiny alveoli are the place where oxygen enters the blood and where carbon dioxide (CO2) leaves the blood.
The lungs are divided into different parts by what are known as fissures. Fissures are separations of the tissue of the lung that divide the lung into lobes. The right lung has three lobes called upper, middle and lower lobes. The left lung only has two lobes, the upper and lower.
The lungs are found in the chest on the right and left side. At the front they extend from just above the clavicle (collarbone) at the top of the chest to about the sixth rib down. At the back of the chest the lungs finish around the tenth rib. The pleura (the protective membranes which cover the lung) continue down to the twelfth rib. From front to back the lungs fill the rib cage, but are separated by the heart, which lies in between them.
Air that we breathe enters the nose, flows through the pharynx (throat) and larynx (voice box) and enters the trachea (windpipe). The trachea eventually divides into two parts called bronchi. The right main bronchus (bronchus is the word for one of the bronchi) supplies the right lung; the left main bronchus supplies the left lung. These bronchi then go on to divide into smaller bronchi. Eventually, the bronchi become known as bronchioles – the smallest air tubes in the lungs. This system of air tubes can be thought of as an upside down tree, with the trachea being the main trunk and the bronchi and bronchioles being the branches. The medical term for all the air tubes is 'the respiratory tract'.
At the end of the smallest bronchioles are alveoli. Alveoli are tiny sacs that are lined by a very thin layer of cells. They also have an excellent blood supply. The tiny alveoli are the place where oxygen enters the blood and where carbon dioxide (CO2) leaves the blood.
The lungs are divided into different parts by what are known as fissures. Fissures are separations of the tissue of the lung that divide the lung into lobes. The right lung has three lobes called upper, middle and lower lobes. The left lung only has two lobes, the upper and lower.
What do the lungs do?
The lungs' main function is to help oxygen from the air we breathe enter red blood cells. Red blood cells then carry oxygen around the body to be used in the cells found in our organs and tissues. The lungs also help the body to get rid of CO2 gas when we breathe out. There are a number of other jobs carried out by the lungs that include:
1. Changing the pH of blood (whether the blood is more acid or alkali) by increasing or decreasing the amount of CO2 in the body.
2. Filtering out small blood clots formed in veins.
3. Filtering out small gas bubbles that may occur in the bloodstream.
4. Converting a chemical in the blood called angiotensin I to angiotensin II. These chemicals are important in the control of blood pressure.
How do the lungs and breathing work?
Breathing in is called inhalation. For air to flow into the lungs there must be a difference in the air pressure in the lungs and the pressure outside. Air is made up of tiny particles including oxygen. If these particles are held together, in a bottle for example, they push on the sides of the bottle. This ‘push’ is what is known as pressure. If the size of the bottle and the amount of air in it stay the same, the pressure in the bottle will stay the same. But the pressure in the bottle can change. If the size of the bottle increases without allowing more air in, the pressure in the bottle goes down. This is because there are fewer particles inside than outside. If you then removed the lid, air would flow into the bottle. This would make the pressure on the inside the same as the outside.
Getting fresh air into the lungs works on a similar principle. For inhalation to happen, the lungs must get bigger. This lowers the pressure inside the lungs in comparison to the outside. Air rushes into the lungs to make the pressure equal – a breath in.
The size of your lungs varies according to what you are doing. The body has a special set of muscles that help to make the lungs increase in size. The most important muscle of inhalation is the diaphragm. Found beneath the lungs, the diaphragm is a dome-shaped muscle. When this muscle contracts (gets tighter), it flattens and the lungs increase in size. During exercise the diaphragm flattens more than when you are resting. This causes the lungs to expand more, causing more air to flow in.
Exhalation is the process of breathing out. Essentially, this is the opposite of inhalation, except that it is usually a passive process. This means that muscle contractions are not generally required. Exhalation also relies on the difference in pressure between the inside and outside of the lungs. However, in this case, the pressure on the inside is greater than on the outside. This causes air to flow out of the lungs.
The lungs receive deoxygenated blood (blood that has lost its oxygen) from the heart through blood vessels called the pulmonary arteries. The deoxygenated blood is then sent to the alveoli. Here, oxygen that has been funnelled through the bronchi and bronchioles can pass across the thin membranes found in the alveoli. A chemical substance within red blood cells, called haemoglobin, has a great attraction to oxygen. Haemoglobin binds oxygen tightly within red blood cells, allowing oxygen to be carried in the bloodstream. At the same time as oxygen is going into the bloodstream, CO2 is coming out. CO2 moves out of the blood and enters the alveoli. This allows the CO2 gas to be exhaled.
Once the blood passing through the lungs picks up oxygen, it is known as oxygenated blood. This blood returns to the heart in the pulmonary veins. Once in the heart, the oxygenated blood is then pumped around the body. The oxygen carried by the red blood cells can then be used in the body’s cells.
The basic rhythm of breathing is controlled by the brain. Part of the brain called the brain stem has a special area dedicated to maintaining your breathing pattern. Nerves originating in this area generate electrical impulses. These impulses control the contractions of your diaphragm and the other muscles of breathing. This is all done without thinking. However, other parts of the brain can temporarily overrule the brain stem. This is how we are able consciously to hold our breath or change our pattern of breathing.
While the brain controls the basic rhythm, it also receives information from sensors in the body. These sensors are nerve cells and provide information that influences the rate and depth of breathing. The main sensors monitor levels of CO2 in the blood. When the level of CO2 rises, the sensors send electrical impulses to the brain. These impulses cause the brain to send more electrical signals to the muscles of breathing. Breathing gets deeper and faster and more CO2 is exhaled. The blood level of CO2 then decreases and the sensors stop sending signals to the brain.
Some disorders of the respiratory tract, lung and chest
Asthma
Bornholm disease
Bronchiectasis
Cancer of the lung
Chronic obstructive pulmonary disease
Cystic fibrosis
Hiccups (hiccoughs)
Idiopathic pulmonary fibrosis
Pleural effusion
Pleurisy
Pneumothorax
Pulmonary embolism
Sarcoidosis
Sleep apnoea
Some infections of the respiratory tract
Bronchiolitis
Bronchitis
Colds
Cough
Epiglottitis
Laryngitis
Legionnaires' disease
Pneumonia
Sinusitis
Sore throat
Tonsillitis
Tuberculosis
Upper respiratory tract infections
Whooping cough
Selasa, 16 Juni 2015
The Gut
Acute
,
Anatomy
,
Askep
,
Bone
,
Cancer
,
child
,
chronic
,
Disease
,
Doctor
,
eyes
,
first aid
,
foot health
,
lung
,
man
,
Midwife
,
Neurologi
,
Nurse
,
Sexual
,
symtoms
,
women
Tidak ada komentar
:
The Gut
This leaflet gives a brief overview of the gut and how the gut works.
What is the gut?
The gut (gastrointestinal tract) is the long tube that starts at the mouth and ends at the anus. Cross-section diagram of the abdomen showing the full gastrointestinal organs
Where is the gut found?
The mouth is the first part of the gastrointestinal tract. When we eat, food passes down the oesophagus (gullet), into the stomach, and then into the small intestine. The small intestine has three sections - the duodenum, jejunum and ileum. The duodenum is the first part of the small intestine and follows on from the stomach. The duodenum curls around the pancreas creating a c-shaped tube. The jejunum and ileum make up the rest of the small intestine and are found coiled in the centre of the abdomen. The small intestine is where food is digested and absorbed into the bloodstream. Following on from the ileum is the first part of the large intestine, called the caecum. Attached to the caecum is the appendix. The large intestine continues upwards from here and is known as the ascending colon. The next part of the gut is called the transverse colon because it crosses the body. It then becomes the descending colon as it heads downwards. The sigmoid colon is the s-shaped final part of the colon which leads on to the rectum. Faeces is stored in the rectum and pushed out through the anus when you go to the toilet. The anus is a muscular opening that is usually closed unless you are passing stool. The large intestine absorbs water, and contains food that has not been digested, such as fibre.
What does the gut do?
The gut processes food - from the time it is first eaten until it is either absorbed by the body or passed out as faeces. The process of digestion begins in the mouth. Here your teeth and enzymes (chemicals made by the body) begin to break down food. Muscular contractions help to move food into the oesophagus and on to the stomach. Chemicals produced by cells in the stomach begin the major work of digestion.
While some foods and liquids are absorbed through the lining of the stomach, the majority are absorbed in the small intestine. Muscles in the wall of the gut mix your food with the enzymes produced by the body. They also move food along towards the end of the gut. Food that can't be digested, waste substances, bacteria and undigested food all get passed out as faeces.
How does it work?
The mouth contains salivary glands which release saliva. When food enters your mouth the amount of saliva increases. Saliva helps to lubricate food and contains enzymes that start chemically digesting your meal. Teeth break down large chunks into smaller bites. This gives a greater surface area for the body's chemicals to work on. Saliva also contains special chemicals that help to stop bacteria from causing infections.
The amount of saliva released is controlled by your nervous system. A certain amount of saliva is normally continuously released. The sight, smell or thought of food can also stimulate your salivary glands.
To pass food from your mouth to the oesophagus you must be able to swallow. Your tongue helps to push food to the back of the mouth. Then the passages to your lungs close and you stop breathing for a short time. The food passes into your oesophagus. The oesophagus releases mucus to lubricate food. Muscles push your meal downwards towards the stomach.
The stomach is a j-shaped organ found between the oesophagus and duodenum. When empty, it is about the same size as a large sausage. Its main function is to help digest the food you eat. The other main function of the stomach is to store food until the gut is ready to receive it. You can eat a meal faster than your intestines can digest it.
Digestion involves breaking food down into its most basic parts. It can then be absorbed through the wall of the gut into the bloodstream and transported around the body. Just chewing food doesn't release the essential nutrients, so enzymes are needed.
The wall of the stomach has several different layers. The inner layers contain special glands. These glands release enzymes, hormones, acid and other substances. These secretions form gastric juice, the liquid found in the stomach.
Muscle and other tissue form the outer layers. A few minutes after food enters the stomach the muscles within the stomach wall start to contract (tighten). This creates gentle waves in the stomach contents. This helps to mix the food with gastric juice.
Using its muscles, the stomach then pushes small amounts of food (now known as chyme) into the duodenum. The stomach has two sphincters, one at the bottom and one at the top. Sphincters are bands of muscles that form a ring. When they contract the opening, the control closes. This stops chyme going into the duodenum before it is ready.
Digestion of food is controlled by your brain, nervous system and various hormones released in the gut. Even before you begin eating, signals from your brain travel via nerves to your stomach. This causes gastric juice to be released in preparation for food arriving. Once food reaches the stomach, receptors (special cells which detect changes in the body) send their own signals. These signals cause the release of more gastric juice and more muscular contractions.
When food starts to enter the duodenum this sets off different receptors. These receptors send signals that slow down the muscular movements and reduce the amount of gastric juice made by the stomach. This helps to stop the duodenum being overloaded with chyme.
Diagram showing detail around the pancreas
The duodenum, jejunum and ileum make up the small intestine. The first part of the duodenum receives food from the stomach. It also receives bile from the gallbladder via the bile duct, and pancreatic enzymes made by cells in the pancreas via the pancreatic duct. Pancreatic enzymes are needed to break down and digest food. Bile, although not essential, helps in the digestion of fatty foods. Cells and glands in the lining of the the small intestines also produce intestinal juice that helps digestion. Contractions in the wall of the small intestine help to mix food and to move it along.
The small intestine also has special features which help to increase the amount of nutrients absorbed by the body. The inner layer of the small intestine has millions of what are known as villi. These are tiny finger-like structures with small blood vessels inside. They are covered by a thin layer of cells. Because this layer is thin, it allows the nutrients released by digestion to enter the blood. Most of the important nutrients needed by the body are absorbed at different points of the small intestine.
Following on from the ileum is the large intestine. The inside of the large intestine is wider than the small intestine. It does not contain villi, and mainly absorbs water. Bacteria in the large intestine also help with the final stages of digestion. Once chyme has been in the large intestine for 3-10 hours it becomes semi-solid. This is because most of the water has been removed. These remnants are now known as faeces.
Movements of the muscles found in the large intestine help to digest the chyme and move faeces towards the rectum. When faeces are present in the rectum, the walls of the rectum stretch. This stretch activates special receptors. These receptors send signals via nerves to the spinal cord. The spinal cord signals back to the muscles in the rectum, increasing pressure on the first sphincter of the anus. The second, or external sphincter of the anus is under voluntary control. This means you can decide whether you will open your bowels or not. Young children have to learn to control this during toilet training.
Some disorders of the gut
•Acid reflux and oesophagitis
•Anal fissure
•Appendicitis
•Barrett's oesophagus
•Cancer of the bowel
•Cancer of the liver
•Cancer of the oesophagus
•Cancer of the pancreas
•Cancer of the stomach
•Cholecystitis
•Coeliac disease
•Constipation
•Crohn's disease
•Cystic fibrosis
•Diarrhoea
•Diverticula
•Duodenal ulcer
•Dyspepsia
•Gallstones
•Gastroenteritis
•Haemorrhoids (piles)
•Helicobacter pylori and stomach pain
•Hernia
•Hiatus hernia
•Irritable bowel syndrome
• ect..
Blood
A. BloodThis article gives a brief overview of
B. What is blood?
Blood is made up of liquid, called plasma, and various different types of cells. An average-sized man has about 5-6 litres of blood in his body; a woman has slightly less. Blood has many different functions - detailed below.
c. Where is blood found?
Blood is found in blood vessels. Blood vessels (arteries, arterioles, capillaries, venules and veins) take blood to and from every part of your body. Blood is pumped through blood vessels by your heart.
D. What is normal blood made up of?
1. Blood cells, which can be seen under a microscope, make up about 40% of the blood's volume. Blood cells are divided into three main types:
2. Red cells (erythrocytes). These make blood a red colour. One drop of blood contains about five million red cells. A constant new supply of red blood cells is needed to replace old cells that break down. Millions of red blood cells are made each day. Red cells contain a chemical called haemoglobin. This binds to oxygen, and takes oxygen from the lungs to all parts of the body.
3. White cells (leukocytes). There are different types of white cells which are called neutrophils (polymorphs), lymphocytes, eosinophils, monocytes, and basophils. They are part of the immune system. Their main role is to defend the body against infection. Neutrophils engulf bacteria and destroy them with special chemicals. Eosinophils and monocytes also work by swallowing up foreign particles in the body. Basophils help to intensify inflammation. Inflammation makes blood vessels leaky. This helps specialised white blood cells get to where they are needed. Lymphocytes have a variety of different functions. They attack viruses and other pathogens (germs). They also make antibodies which help to destroy pathogens Platelets. These are tiny and help the blood to clot if we cut ourselves.
4. Plasma is the liquid part of blood and makes up about 60% of the blood's volume. Plasma is mainly made from water, but also contains many different proteins and other chemicals such as hormones, antibodies, enzymes, glucose, fat particles, salts, etc.
5. When blood spills from your body (or a blood sample is taken into a plain glass tube) the cells and certain plasma proteins clump together to form a clot. The remaining clear fluid is called serum.
E. What does blood do?
1. Blood has a variety of different functions. These include: Transport. Blood takes oxygen from the lungs to the cells of the body. It takes carbon dioxide from the body's cells to the lungs where it is breathed out. Blood carries nutrients, hormones and waste products around the body.
2. Regulation. Blood helps to keep the acid-alkali balance of the body in check. It also plays a part in regulating body temperature. Increasing the amount of blood flowing close to the skin helps the body to lose heat.
3. Protection. White blood cells attack and destroy invading bacteria and other pathogens. Blood clots, which protects the body from losing too much blood after injury.
F. The bone marrow, stem cells and blood cell production
1. Bone marrow
Blood cells are made in the bone marrow by stem cells. The bone marrow is the soft spongy-like material in the centre of bones. The large flat bones such as the pelvis and breastbone (sternum) contain the most bone marrow. To make blood cells constantly you need a healthy bone marrow. You also need nutrients from your diet, including iron and certain vitamins.
2. Stem cells
Stem cells are primitive (immature) cells. There are two main types in the bone marrow - myeloid and lymphoid stem cells. These derive from even more primitive common pluripotent stem cells. Stem cells constantly divide and produce new cells. Some new cells remain as stem cells and others go through a series of maturing stages (precursor or blast cells) before forming into mature blood cells. Mature blood cells are released from the bone marrow into the bloodstream.
Lymphocyte white blood cells develop from lymphoid stem cells. There are three types of mature lymphocytes:
B lymphocytes make antibodies which attack infecting bacteria, viruses, etc.
T lymphocytes help the B lymphocytes to make antibodies.
Natural killer cells which also help to protect against infection.
All the other different blood cells (red blood cells, platelets, neutrophils, basophils, eosinophils and monocytes) develop from myeloid stem cells.
G. Blood production
You make millions of blood cells every day. Each type of cell has an expected lifespan. For example, red blood cells normally last about 120 days. Some white blood cells last just hours or days - some last longer. Every day millions of blood cells die and are broken down at the end of their lifespan. There is normally a fine balance between the number of blood cells that you make, and the number that die and are broken down. Various factors help to maintain this balance. For example, certain hormones in the bloodstream, and chemicals in the bone marrow, called growth factors, help to regulate the number of blood cells that are made.
H. Blood, oxygen and other chemicals
The cells that make up the organs and tissues of your body need oxygen to live. They also produce carbon dioxide which needs to be removed from the body. One of the main functions of blood is to transport oxygen and carbon dioxide around the body. A chemical called haemoglobin is present inside red blood cells. Haemoglobin has a strong attraction to oxygen. Red blood cells pass through the lungs within the bloodstream. Here in the lungs the oxygen you breathe in passes into red blood cells, and binds to haemoglobin. Blood then flows from the lungs to the heart. The heart pumps blood around the body. When red blood cells come into contact with tissues that need oxygen, haemoglobin releases the oxygen it is carrying. Carbon dioxide produced by your body's tissues is also carried by blood. When it reaches the lungs it passes out of the blood vessels and into your airways. This allows carbon dioxide to leave your body when you breathe out. As well as transporting oxygen and carbon dioxide, blood carries many of the chemicals and nutrients essential to life. This includes the nutrients produced by the digestion of food, enzymes (chemicals produced by the body), hormones and waste products. Blood also helps to buffer all the different chemicals in the body. By doing this it stops your body fluids from becoming too acidic or too alkali.
Blood and blood vessels
The main function of blood vessels is to transport blood around the body. Blood vessels are found throughout the body. There are five main types of blood vessels: arteries, arterioles, capillaries, venules and veins. Arteries carry blood away from the heart to other organs. They can vary in size. Arterioles are the smallest arteries in the body. They deliver blood to capillaries. Arterioles are also capable of constricting or dilating and by doing this they control how much blood enters the capillaries. Capillaries are tiny vessels that connect arterioles to venules. They have very thin walls which allow nutrients from the blood to pass into the body tissues. Waste products from body tissues can also pass into the capillaries. For this reason capillaries are known as exchange vessels. Groups of capillaries within a tissue reunite to form small veins called venules. Venules collect blood from capillaries and drain into veins. Veins are the blood vessels that carry blood back to the heart. They may contain valves which stop blood flowing away from the heart.
What is a blood group?
Red blood cells have certain proteins on their surface, called antigens. Also, your plasma contains antibodies which will attack certain antigens if they are present. There are various types of red blood cell antigens - the ABO and rhesus types are the most important.
ABO types
These were the first type discovered.
a. If you have type A antigens on the surface of your red blood cells, you also have anti-B antibodies in your plasma.
b. If you have type B antigens on the surface of your red blood cells, you also have anti-A antibodies in your plasma.
c. If you have type A and type B antigens on the surface of your red blood cells, you do not have antibodies to A or B antigens in your plasma.
d. If you have neither type A nor type B antigens on the surface of your red blood cells, you have anti-A and anti-B antibodies in your plasma.
Rhesus types
Most people are rhesus positive, as they have rhesus antigens on their red blood cells. But, about 3 in 20 people do not have rhesus antibodies and are said to be rhesus negative.
Blood group names
Your blood group depends on which antigens occur on the surface of your red blood cells. Your blood group is said to be:
A+ (A positive) if you have A and rhesus antigens.
A– (A negative) if you have A antigens, but not rhesus antigens.
B+ (B positive) if you have B and rhesus antigens.
B– (B negative) if you have B antigens, but not rhesus antigens.
AB+ (AB positive) if you have A, B and rhesus antigens.
AB– (AB negative) if you have A and B antigens, but not rhesus antigens.
O+ (O positive) if you have neither A nor B antigens, but you have rhesus antigens.
O– (O negative) if you have do not have A, B or rhesus antigens.
Other blood types
There are many other types of antigens which may occur on the surface of red blood cells. However, most are classed as minor and are not as important as ABO and rhesus.
How does blood clot?
Within seconds of cutting a blood vessel, the damaged tissue causes platelets to become sticky and clump together around the cut. These activated platelets, and the damaged tissue, release chemicals which react with other chemicals and proteins in the plasma, called clotting factors. There are 13 known clotting factors which are called by their Roman numbers - factor I to factor XIII. A complex cascade of chemical reactions involving these clotting factors quickly occurs next to a cut. The final step of this cascade of chemical reactions is to convert factor I (also called fibrinogen - a soluble protein) into thin strands of a solid protein called fibrin. The strands of fibrin form a meshwork, and trap blood cells and platelets so that a solid clot is formed. If a blood clot forms within a healthy blood vessel it can cause serious problems. So, there are also chemicals in the blood which prevent clots from forming, and chemicals which dissolve clots. So, there is a balance between forming clots and preventing clots. Normally, unless a blood vessel is damaged or cut, the balance tips in favour of preventing clots forming within blood vessels.
Some types of blood disorders
Problems with blood cells
Anaemia means that you have fewer red blood cells than normal, or have less haemoglobin than normal in each red blood cell. There are many causes of anaemia. For example, the most common cause of anaemia in the UK is a lack of iron. (Iron is needed to make haemoglobin.) Other causes include lack of vitamins B12 or folate which are needed to make red blood cells. Abnormalities of red blood cell production can cause anaemia. For example, various hereditary conditions such as sickle cell disease and thalassaemia.
Details of the following disorders can be found at
1. Anaemia (various types).
2. Idiopathic Thrombocytopenic Purpura (ITP).
3. Leukaemia.
4. Myeloma.
5. Sickle Cell Disease and Sickle Cell Anaemia.
6. Sickle Cell Trait and Sickle Cell Screening Tests.
7. Thalassaemia.
Thrombophilia.
Human Physiology/Blood physiology
From Wikibooks, the open-content textbooks collection.
blood, blood cells and how they work.
Langganan:
Postingan
(
Atom
)
