· It consists of lymph, lymph capillaries, lymph vessels and lymph nodes.
1. Lymph:
· Blood never leaves the arteries and veins as their thick walls are impervious to the
contained blood.
· Blood never leaves the arteries and veins as their thick walls are impervious to the
contained blood.
· But the walls of capillaries are extremely thin, a little epithelium, and form permeable.
· Therefore, by ultrafiltration, most plasma of the blood sleeps out readily through the capillary wall into the intercellular spaces of the tissues.
· This colourless watery liquid that lies between and bathes the cells of the body is called lymph (Latin for water).
· It is similar in constitution except that it does not contain some proteins (having larger molecules) and lacks red blood cells.
· It does, however, contain more lymphocytes than are present in the blood.
· There is four to five times as much lymph in the body as there is blood.
2. Lymph capillaries:
· There is continuous renewal and absorption of the tissue fluid.
· Towards the arterial end the capillaries ooze out fluid due to hydrostatic pressure.
· But, towards the venous end, some fluid is reabsorbed due to low pressure within.
· Only some lymph is returned to blood capillaries in this way.
· Most of the lymph, however, is drained into a network of special blind endings called lymph capillaries located in the tissues spaces.
· Their walls are composed of simple epithelium which is extremely permeable even to protein molecules.
· Fluid pressure within these lymph capillaries is nearly zero.
· They are not connected with blood capillaries and their diameter is also not uniform throughout.
3. Lymph vessels:
· The lymph capillaries lead into larger lymph vessels rather than thin-walled veins.
· The lymph capillaries lead into larger lymph vessels rather than thin-walled veins.
· There is no pumping station or lymph hearts in mammals such as found in lower vertebrates (e.g. frog).
· Movement of lymph mainly due to squeezing pressure of the surrounding muscles.
· The vessels are also provided with valves that keep the lymph flowing in one direction.
· Eventually all the vessels join to form two main ducts, the thoracic duct and the right lymphatic duct, which open into the place of union of left and right external jugular veins and the corresponding subclavian veins, respectively.
4. Lymph nodes:
· In mammals lymph vessels pass at certain places through lymph glands, or better, lymph nodes.
· In mammals lymph vessels pass at certain places through lymph glands, or better, lymph nodes.
· These consist of a network of connective tissue fibres enclosed in the capsule.
· The nodes produce the lymphocytes of the blood.
Functions:
· It acts as the middle man between blood and tissues.
· It is responsible for the absorption of fat through lymph capillaries or lacteals in the intestinal
· The tissue fluid or the lymph passes on food, oxygen, hormones and other chemicals from the blood to the cells, and the waste products, carbon, etc. from the cells to the blood, thus maintaining the constant chemical environment around the tissues.
· The lymph nodes produce and maintain the lymphocytes of the blood. They also act as filters of poisonous and foreign substances such as dust, bacteria, etc, thus purifying the blood, infection of lymph nodes causes them to swell up to become painful. Tonsils, adenoids and appendix provide such cases.
Functions:
· It acts as the middle man between blood and tissues.
· It is responsible for the absorption of fat through lymph capillaries or lacteals in the intestinal
· The tissue fluid or the lymph passes on food, oxygen, hormones and other chemicals from the blood to the cells, and the waste products, carbon, etc. from the cells to the blood, thus maintaining the constant chemical environment around the tissues.
· The lymph nodes produce and maintain the lymphocytes of the blood. They also act as filters of poisonous and foreign substances such as dust, bacteria, etc, thus purifying the blood, infection of lymph nodes causes them to swell up to become painful. Tonsils, adenoids and appendix provide such cases.
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