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Blood In Human Body
- The blood transports nutrients, gases, waste, hormones and heat
- There are about 5-7 litres of blood in an adult body
- The distribution is as follows:
- 55% plasma which contains 90% water and 10% soluble materials
- 45% are blood cells
- The blood is also the main defense against diseases as it has platelets that form clots and they have white blood cells which have phagocytes which engulfs bacteria and lymphocytes which produce antibodies.
White blood cells and immunity
- When we cut ourselves we not only lose blood but we also make it easier for bacteria to get inside our bodies.
- Therefore the body must stop the flow of blood and block the breach in the skin to prevent blood loss and infection. For this to be effective it needs to be quick.
- Platelets in the blood carry an enzyme, which is released into the plasma when the platelets come into contact with air or damaged cells.
- The enzyme changes the soluble plasma protein fibrinogen into the insoluble fibrin.
- Fibrin is sticky and forms long threads creating a net, which traps some red blood cells. This makes a plug called a blood clot.
- Phagocytes, attracted to the damaged site, engulf the pathogens.
- The clot hardens and becomes a scab. This protects the wound as the skin heals beneath.
- There are two types of white blood cell, phagocytes and lymphocytes. Their role in defence against disease is different.
- Phagocytes wander around the blood looking for foreign bodies. When these are encountered a phagocyte will surround the foreign body and engulf it. The phagocyte then digests the foreign body, killing it.
- There are two types of lymphocytes, B-lymphocytes and T-lymphocytes. They work in different ways.
- B-cells make special proteins called antibodies. These proteins will stick onto the surface of foreign bodies.
- T-cells hunt foreign cells, cells infected by viruses, and cancer cells. When they find them they inject them with toxins, which destroy them.
- When you become ill due to a disease-causing organism you eventually recover as your body's defense system defeats the invading pathogen.
- When you encounter the pathogen again, your body remembers the past infection and is ready to fight it.
- The invader is usually defeated before you even get any symptoms of being ill. This is known as immunity.
- The cells responsible for immunity are the lymphocytes.
- All cells have surface proteins called antigens.
- The lymphocytes recognise the antigens which belong in the body, and detect all others as foreign.
Blood travels via arteries until it reaches smaller vessels called capillaries. It is here that materials are exchanged between blood and the tissue cells.
- Sometimes people get transplants from other people with organs that have different antigens so the body might attack the new organ.
- That is why donors tissues are checked to see if the antigens are close to the one of the transplant recipient. The closer the antigens, the lower the chance of a failure transplant.
- The blood enters a capillary bed. These vessels are very leaky and are only wide enough for one cell at a time to pass through. The capillary walls are only 1 cell thick!
- The blood pressure forces some of the blood plasma to leak out of the capillary. This fluid is high in nutrients and oxygen (from the red blood cells). Large objects like red blood cells and protein molecules cannot pass through the walls of the capillary. The fluid that is surrounding the tissue cells is called tissue fluid. It is from this fluid that materials will diffuse into the cells.
- White blood cells are the only cells, which can leave the blood, so they can hunt down pathogens.
- Waste materials like carbon dioxide and urea diffuse from the cells into the tissue fluid. This fluid is drawn back into the blood capillary by an osmotic pressure supplied by the large proteins in the blood.
- Not all the tissue fluid flows back into the blood. If it did not return the tissues would swell with fluid. Sets of vessels, called lymph vessels, drain this tissue fluid and carry it away from the tissues. Eventually the fluid (called lymph) drains back into the blood.
- The blood leaves the capillary beds and travels back to the heart via veins.
|11-19-2014 08:26 AM
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RE: Blood In Human Body
Immunity palys a vital role in human body especially when the flu come. People with strong immunity can produce antibody immediately to defeat the virus.
|09-08-2015 10:14 AM