Thursday, May 22, 2014

Pancreas - Information



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. 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 found? 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 blood-stream. 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) 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 produced 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 – helps to control the release of other hormones. • Gastrin – which aids digestion in the stomach. How does the pancreas work? The digestive enzymes produced 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 via nerves to the pancreas. 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 blood stream, 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 There are various types. The common type is called ductal adenocarcinoma of the pancreas and arises from cells of the pancreatic duct. This mainly occurs in people over 60. There are some rare types of cancer which arise from other types of cells within the pancreas. For example, cells in the pancreas that make insulin or glucagon can become cancerous ('insulinomas' and 'glucagonomas'). Acute pancreatitis This is when the pancreas becomes inflamed over a short time - within a few days or so. It causes abdominal pain. It usually settles in a few days but sometimes it becomes severe and very serious. The usual causes are gallstones or drinking a lot of alcohol. Chronic pancreatitis This is when the inflammation in the pancreas is persistent. The inflammation tends to be less intense than acute pancreatitis but, as it is ongoing, it can cause scarring and damage. This can cause abdominal pain, poor digestion, diabetes and other complications. Drinking a lot of alcohol over a number of years is the common cause. Type 1 diabetes With type 1 diabetes the pancreas stops making insulin. It is treated with insulin injections and a healthy diet. ==--==



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.

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 found?

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 blood-stream. 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) 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 produced 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 – helps to control the release of other hormones.
  • Gastrin – which aids digestion in the stomach.

 

How does the pancreas work?

The digestive enzymes produced 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 via nerves to the pancreas. 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 blood stream, 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

There are various types. The common type is called ductal adenocarcinoma of the pancreas and arises from cells of the pancreatic duct. This mainly occurs in people over 60. There are some rare types of cancer which arise from other types of cells within the pancreas. For example, cells in the pancreas that make insulin or glucagon can become cancerous ('insulinomas' and 'glucagonomas').

Acute pancreatitis

This is when the pancreas becomes inflamed over a short time - within a few days or so. It causes abdominal pain. It usually settles in a few days but sometimes it becomes severe and very serious. The usual causes are gallstones or drinking a lot of alcohol.

Chronic pancreatitis

This is when the inflammation in the pancreas is persistent. The inflammation tends to be less intense than acute pancreatitis but, as it is ongoing, it can cause scarring and damage. This can cause abdominal pain, poor digestion, diabetes and other complications. Drinking a lot of alcohol over a number of years is the common cause.

Type 1 diabetes

With type 1 diabetes the pancreas stops making insulin. It is treated with insulin injections and a healthy diet.





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Male Reproductive System - Information




Male Reproductive System

This article gives a brief overview of the male reproductive system.

What is the male reproductive system?

Male Reproductive System This article gives a brief overview of the male reproductive system. What is the male reproductive system? The organs and structures of the male reproductive system give men the ability to fertilise a woman's ovum (egg) to produce a baby. Several different organs and structures make up the male reproductive system. These include the testes, where sperm is made, several ducts (tubes) where sperm is stored, and the penis. The penis has a single duct called the urethra, this releases both sperm and urine. Also included in the male reproductive system are the accessory sex glands, which include the prostate gland and seminal vesicles. These glands make special fluids, which are added to sperm as it travels through the ducts. Together the liquid is known as semen. Hormones are also made by parts of a man's reproductive system. The testes start developing inside the internal body cavity in a growing baby (foetus). About two months before a male baby is born the testes start to descend into the scrotal sacs. Because they are outside the main body cavity the testes are slightly cooler. This difference in temperature helps sperm production. The penis contains the urethra, which passes both urine and semen. There are three main parts of the penis, the root, body and glans. The root is the part attached to the lower abdomen. The body of the penis is made up of a spongy type of tissue, which swells when blood enters during an erection. The glans penis is the slightly larger area towards the end of the penis and contains the opening of the urethra. What does the male reproductive system do? Its main function is to give men the ability to fertilise a woman's ovum by producing and delivering semen. The testes also make hormones which help men develop the characteristics associated with being male. This includes the distribution of pubic hair, enlargement of the penis and deepening of the voice. How does the male reproductive system work? During puberty, levels of certain hormones in the brain begin to increase. These changes cause an increase in the production and release of two hormones from the pituitary gland - luteinising hormone (LH) and follicle-stimulating hormone (FSH). (The pituitary gland is a small gland at the base of the brain. It makes various hormones which are released into the bloodstream including LH and FSH.) LH in the bloodstream causes cells in the testes to make and release testosterone, another hormone. Some of this testosterone gets converted into another form. Together, the two forms of testosterone help to develop and enlarge the penis and other male sex organs. Testosterone also helps to encourage muscle and skeletal growth and deepen the male voice. FSH and testosterone work together to stimulate the testes to produce sperm. Each sperm cell takes between 65-75 days to form, and around 300 million are produced every day. Inside the testes sperm is made in structures called the seminiferous tubules. At the top and to the back of each testis is the epididymis, which stores sperm. Leading from the epididymis is the vas deferens. The vas deferens carries sperm to the penis. To do this the vas deferens passes into the internal cavity of the body. Passing close to the bladder the vas deferens eventually enters the prostate gland where the tube becomes the urethra. The prostate gland lies just beneath the bladder (see diagram). It is normally about the size of a chestnut. The prostate gland makes a specialised fluid which is added to sperm during ejaculation. The seminal vesicles also add fluid to the sperm during ejaculation. The mixture of sperm, fluid from the prostate and fluid from the seminal vesicles is called semen. About 60-70% of the volume of semen comes from the seminal vesicles. The urethra (the tube which transports urine and semen) runs through the middle of the prostate. When sexually aroused a number of changes occur inside the penis. The arteries supplying the penis expand allowing more blood to enter its tissues. The increase in blood flow causes the penis to enlarge. The extra blood flow plus signals from the nervous system and chemical changes cause an erection. Ejaculation (the contractions that release semen) is a reflex action, which means it is not consciously controlled. As part of the reflex action, the opening that drains the bladder is closed. This means that urine is not released at the same time as semen. The volume of semen in a typical ejaculation is between 2.5-5 millilitres (mL) with more than 20 million sperm per mL. Some disorders of the male reproductive system • Balanitis • Cancer of the Penis • Cancer of the Prostate • Cancer of the Testes • Epididymo-orchitis • Erectile Dysfunction (Impotence) • Gonorrhoea in Men • Hydrocele in Adults • Hypospadias • Prostate Gland Enlargement • Prostatitis • Sexually Transmitted Infections • Urethral Stricture • Urethritis - Non Gonococcal • Urethritis and Urethral Discharge in Men • Urine Infection In Men • Varicocele ==--==

The organs and structures of the male reproductive system give men the ability to fertilise a woman's ovum (egg) to produce a baby. 

Several different organs and structures make up the male reproductive system. These include the testes, where sperm is made, several ducts (tubes) where sperm is stored, and the penis. The penis has a single duct called the urethra, this releases both sperm and urine. Also included in the male reproductive system are the accessory sex glands, which include the prostate gland and seminal vesicles. These glands make special fluids, which are added to sperm as it travels through the ducts. Together the liquid is known as semen. 

Hormones are also made by parts of a man's reproductive system.

The testes start developing inside the internal body cavity in a growing baby (foetus). About two months before a male baby is born the testes start to descend into the scrotal sacs. Because they are outside the main body cavity the testes are slightly cooler. This difference in temperature helps sperm production. 

The penis contains the urethra, which passes both urine and semen. There are three main parts of the penis, the root, body and glans. The root is the part attached to the lower abdomen. The body of the penis is made up of a spongy type of tissue, which swells when blood enters during an erection. The glans penis is the slightly larger area towards the end of the penis and contains the opening of the urethra. 

 

What does the male reproductive system do?

Its main function is to give men the ability to fertilise a woman's ovum by producing and delivering semen. The testes also make hormones which help men develop the characteristics associated with being male. This includes the distribution of pubic hair, enlargement of the penis and deepening of the voice.

 

How does the male reproductive system work?

During puberty, levels of certain hormones in the brain begin to increase. These changes cause an increase in the production and release of two hormones from the pituitary gland - luteinising hormone (LH) and follicle-stimulating hormone (FSH). (The pituitary gland is a small gland at the base of the brain. It makes various hormones which are released into the bloodstream including LH and FSH.) LH in the bloodstream causes cells in the testes to make and release testosterone, another hormone. Some of this testosterone gets converted into another form. Together, the two forms of testosterone help to develop and enlarge the penis and other male sex organs. Testosterone also helps to encourage muscle and skeletal growth and deepen the male voice. 

FSH and testosterone work together to stimulate the testes to produce sperm. Each sperm cell takes between 65-75 days to form, and around 300 million are produced every day. Inside the testes sperm is made in structures called the seminiferous tubules. At the top and to the back of each testis is the epididymis, which stores sperm. 

Leading from the epididymis is the vas deferens. The vas deferens carries sperm to the penis. To do this the vas deferens passes into the internal cavity of the body. Passing close to the bladder the vas deferens eventually enters the prostate gland where the tube becomes the urethra. 

The prostate gland lies just beneath the bladder (see diagram). It is normally about the size of a chestnut. The prostate gland makes a specialised fluid which is added to sperm during ejaculation. The seminal vesicles also add fluid to the sperm during ejaculation. 

The mixture of sperm, fluid from the prostate and fluid from the seminal vesicles is called semen. About 60-70% of the volume of semen comes from the seminal vesicles. The urethra (the tube which transports urine and semen) runs through the middle of the prostate.

When sexually aroused a number of changes occur inside the penis. The arteries supplying the penis expand allowing more blood to enter its tissues. The increase in blood flow causes the penis to enlarge. The extra blood flow plus signals from the nervous system and chemical changes cause an erection. Ejaculation (the contractions that release semen) is a reflex action, which means it is not consciously controlled. As part of the reflex action, the opening that drains the bladder is closed. This means that urine is not released at the same time as semen. The volume of semen in a typical ejaculation is between 2.5-5 millilitres (mL) with more than 20 million sperm per mL.

 

Some disorders of the male reproductive system

  • Balanitis
  • Cancer of the Penis
  • Cancer of the Prostate
  • Cancer of the Testes
  • Epididymo-orchitis
  • Erectile Dysfunction (Impotence)
  • Gonorrhoea in Men
  • Hydrocele in Adults
  • Hypospadias
  • Prostate Gland Enlargement
  • Prostatitis
  • Sexually Transmitted Infections
  • Urethral Stricture
  • Urethritis - Non Gonococcal
  • Urethritis and Urethral Discharge in Men
  • Urine Infection In Men
  • Varicocele




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Know About Blood - Information



Blood What is blood? Blood is made up of liquid, called plasma, and various different types of cells. An average-size man has about 5-6 litres of blood in his body, a woman has slightly less. Blood has many different functions - detailed below. Where is blood found? Blood is found in blood vessels. Blood vessels supply every part of your body. These include arteries, arterioles, capillaries, venules and veins. Blood is pumped through blood vessels by your heart. What is normal blood made up of? • 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: o 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. o White cells (leucocytes). 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. They also make antibodies which help to destroy bacteria. o Platelets. These are tiny and help the blood to clot if we cut ourselves. • 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. 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. What does blood do? 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 for exhalation. It carries nutrients, hormones and waste products. • 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. • 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. The bone marrow, stem cells and blood cell production Bone marrow Blood cells are made in the bone marrow by 'stem' cells. The bone marrow is the soft 'spongy' material in the centre of bones. The large flat bones such as the pelvis and breast-bone (sternum) contain the most bone marrow. To constantly make blood cells you need a healthy bone marrow. You also need nutrients from your diet including iron and certain vitamins. 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: o B lymphocytes make antibodies which attack infecting bacteria, viruses, etc. o T lymphocytes help the B lymphocytes to make antibodies. o 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. Blood production You make millions of blood cells every day. Each type of cell has an expected life-span. 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 life-span. 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. 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 special chemical called haemoglobin is found 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. • If you have type A antigens on the surface of your red blood cells, you also have anti-B antibodies in your plasma. • If you have type B antigens on the surface of your red blood cells, you also have anti-A antibodies in your plasma. • 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. • If you have neither type A or 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 antigen 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 less 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. • Too many red cells is called polycythaemia and can be due to various causes. • Too few white cells is called leucopenia. Depending on which type of white cell is reduced it can be called neutropenia, lymphopenia, or eosinopenia. There are various causes. • Too many white blood cells is called leucocytosis. Depending on which type of white cell is increased it is called neutrophilia, lymphocytosis, eosinophilia, monocytosis, basophilia. There are various causes. For example: o Various infections can cause an increase of white blood cells. o Certain allergies can cause an eosinophilia. o Leukaemia causes a large increase in the number of white blood cells. The type of leukaemia depends on the type of white cell affected. • Too few platelets which is called thrombocytopenia. This may make you bruise or bleed easily. There are various causes. • Too many platelets which is called thrombocythaemia (or thrombocytosis). This is due to disorders which affect cells in the bone marrow which make platelets. Bleeding disorders There are various conditions where you tend to bleed excessively if you damage or cut a blood vessel. For example: • Too few platelets (thrombocytopenia) - due to various causes. • Genetic conditions where you do not make one or more clotting factors. The most well known is haemophilia A which occurs in people who do not make factor VIII. • Lack of vitamin K can cause bleeding problems as you need this vitamin to make certain clotting factors. • Liver disorders can sometimes cause bleeding problems as your liver makes most of the clotting factors. Clotting disorders (thrombophilia) Sometimes a blood clot forms within a blood vessel which has not been injured or cut. For example: • A blood clot which forms within a coronary (heart) artery or in an artery within the brain is the common cause of heart attack and stroke. The platelets become sticky and clump next to patches of atheroma (fatty material) in blood vessels and activate the clotting mechanism. • Sluggish blood flow can make blood clot more readily than usual. This is a factor in deep vein thrombosis (DVT) which is a blood clot that sometimes forms in a leg vein. • Certain genetic conditions can make the blood clot more easily than usual. • Certain medicines can affect the blood clotting mechanism, or increase the amount of some clotting factors, which may result in the blood clotting more readily. • Liver disorders can sometimes cause clotting problems as your liver makes some of the chemicals involved in preventing and dissolving clots. Problems with blood groups If you have a blood transfusion, it is vital that the blood you receive is compatible with your own. For example, if you receive blood from a person who is A positive and you are B positive, then the anti-A antibodies in your plasma will attack the red blood cells of the donated blood. This causes the red cells of the donated blood to clump together. This can cause a serious or even fatal reaction in your body. So, before a blood transfusion is done, a donor bag of blood is selected with the same ABO and rhesus blood group as yourself. Then, to make sure there is no incompatibility a sample of your blood is mixed with a sample of the donor blood. After a short time the mixed blood is looked at under a microscope to see if there has been any clumping of blood. If there is no clumping, then it is safe to transfuse the blood. Some disorders of blood • Anaemia (various types) • Idiopathic Thrombocytopenic Purpura (ITP) • Leukaemia • Myeloma • Sickle Cell Disease and Sickle Cell Anaemia • Sickle Cell Trait and Sickle Cell Screening Tests • Thalassaemia • Thrombophilia ==--==



Blood


What is blood?

Blood is made up of liquid, called plasma, and various different types of cells. An average-size man has about 5-6 litres of blood in his body, a woman has slightly less. Blood has many different functions - detailed below.

 

Where is blood found?

Blood is found in blood vessels. Blood vessels supply every part of your body. These include arteries, arterioles, capillaries, venules and veins. Blood is pumped through blood vessels by your heart.

 

What is normal blood made up of?

  • 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:
    • 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.
    • White cells (leucocytes). 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. They also make antibodies which help to destroy bacteria.
    • Platelets. These are tiny and help the blood to clot if we cut ourselves.
  • 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.
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.

 

What does blood do?

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 for exhalation. It carries nutrients, hormones and waste products.
  • 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.
  • 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.

 

The bone marrow, stem cells and blood cell production

 

Bone marrow

Blood cells are made in the bone marrow by 'stem' cells. The bone marrow is the soft 'spongy' material in the centre of bones. The large flat bones such as the pelvis and breast-bone (sternum) contain the most bone marrow. To constantly make blood cells you need a healthy bone marrow. You also need nutrients from your diet including iron and certain vitamins.

 

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.

 

Blood production

You make millions of blood cells every day. Each type of cell has an expected life-span. 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 life-span. 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.

 

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 special chemical called haemoglobin is found 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.
  • If you have type A antigens on the surface of your red blood cells, you also have anti-B antibodies in your plasma.
  • If you have type B antigens on the surface of your red blood cells, you also have anti-A antibodies in your plasma.
  • 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.
  • If you have neither type A or 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 antigen 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 less 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.
  • Too many red cells is called polycythaemia and can be due to various causes.
  • Too few white cells is called leucopenia. Depending on which type of white cell is reduced it can be called neutropenia, lymphopenia, or eosinopenia. There are various causes.
  • Too many white blood cells is called leucocytosis. Depending on which type of white cell is increased it is called neutrophilia, lymphocytosis, eosinophilia, monocytosis, basophilia. There are various causes. For example:
    • Various infections can cause an increase of white blood cells.
    • Certain allergies can cause an eosinophilia.
    • Leukaemia causes a large increase in the number of white blood cells. The type of leukaemia depends on the type of white cell affected.
  • Too few platelets which is called thrombocytopenia. This may make you bruise or bleed easily. There are various causes.
  • Too many platelets which is called thrombocythaemia (or thrombocytosis). This is due to disorders which affect cells in the bone marrow which make platelets.

 

Bleeding disorders

There are various conditions where you tend to bleed excessively if you damage or cut a blood vessel. For example:
  • Too few platelets (thrombocytopenia) - due to various causes.
  • Genetic conditions where you do not make one or more clotting factors. The most well known is haemophilia A which occurs in people who do not make factor VIII.
  • Lack of vitamin K can cause bleeding problems as you need this vitamin to make certain clotting factors.
  • Liver disorders can sometimes cause bleeding problems as your liver makes most of the clotting factors.

 

Clotting disorders (thrombophilia)

Sometimes a blood clot forms within a blood vessel which has not been injured or cut. For example:
  • A blood clot which forms within a coronary (heart) artery or in an artery within the brain is the common cause of heart attack and stroke. The platelets become sticky and clump next to patches of atheroma (fatty material) in blood vessels and activate the clotting mechanism.
  • Sluggish blood flow can make blood clot more readily than usual. This is a factor in deep vein thrombosis (DVT) which is a blood clot that sometimes forms in a leg vein.
  • Certain genetic conditions can make the blood clot more easily than usual.
  • Certain medicines can affect the blood clotting mechanism, or increase the amount of some clotting factors, which may result in the blood clotting more readily.
  • Liver disorders can sometimes cause clotting problems as your liver makes some of the chemicals involved in preventing and dissolving clots.

 

Problems with blood groups

If you have a blood transfusion, it is vital that the blood you receive is compatible with your own. For example, if you receive blood from a person who is A positive and you are B positive, then the anti-A antibodies in your plasma will attack the red blood cells of the donated blood. This causes the red cells of the donated blood to clump together. This can cause a serious or even fatal reaction in your body.

So, before a blood transfusion is done, a donor bag of blood is selected with the same ABO and rhesus blood group as yourself. Then, to make sure there is no incompatibility a sample of your blood is mixed with a sample of the donor blood. After a short time the mixed blood is looked at under a microscope to see if there has been any clumping of blood. If there is no clumping, then it is safe to transfuse the blood.

 

Some disorders of blood

  • Anaemia (various types)
  • Idiopathic Thrombocytopenic Purpura (ITP)
  • Leukaemia
  • Myeloma
  • Sickle Cell Disease and Sickle Cell Anaemia
  • Sickle Cell Trait and Sickle Cell Screening Tests
  • Thalassaemia
  • Thrombophilia




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