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At the capillary end of the arteries, the walls are only one-cell thick. The pressure in the arterial capillaries is also quite high. These leads the plasma to leak into the interstitial space. The interstitial space is the space between the cells of the tissue. The fluid is plasma minus the proteins (as the proteins cannot pass through the walls of the capillaries) and is called the interstitial fluid or the tissue fluid.
However, at the venous end of the capillaries, the pressure is not that high and some of the fluid goes back into the blood vessels. There is still some fluid that has to be returned to the blood vessel along with the dissolved solutes. This fluid if not cleared from the interstitial space will result in oedema or swelling. The fluid then enters the closed vessels called the lymph vessels and is called the lymph.
The lymph vessels also have walls that are single celled in thickness. The lymph vessels join together to form the bigger lymph ducts. The lymph vessels have no muscles but have valves that allow only unidirectional lymph flow. An example of a lymph vessel is the lacteal that are present in the villi of the small intestine. The digested fats enter the lacteals and are transported to the blood stream via the lymph ducts.
The lymph is circulated in the body with the help of the action of the muscles surrounding the lymph vessels. Thus, the movement of lymph is slow and uncertain. Exercise improves the rate of lymph flow. The lymph vessels are provided with valves to prevent backflow of the lymph. Throughout the lymphatic system, the lymphatic ducts enlarge at various places to form sinuses or cavities called the lymph glands or nodes. The lymph nodes are cavities lined with phagocytic cells and have numerous lymphocytes.
The lymphocytes produce antibodies against the bacteria and other germs and attack them. The phagocytes of the lymph node also attack the bacteria and the other foreign bodies. Their activity becomes more during an infection. This causes an increase in their size. For example, the tonsils enlarge and become painful during a bacterial infection. The lymph is returned to the venous blood near the heart.
| Heart Attack
Heart attack is clinically Also called coronary thrombosis. The blood vessel supplying blood to the heart is blocked. This affects/stops the functioning of the heart resulting in heart attacks.
If the blocked artery is one of the arteries supplying to the brain, it causes a condition called stroke. Stroke is the inactivation of a certain region of the brain which controls a particular activity. It may be sight, limb movements, etc.
The heart may have a valve that does not function properly. This results in heart murmur that can be detected by the stethoscope.
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