THE LYMPHATIC SYSTEM

Lymph Capillaries: The lymph vascular system originates as lymph capillaries. These are small vessels occur in the tissues of almost all organs. They are blind- end’ tubes, in that they have no entrance at the end residing in interstitial regions; the only opening is one that merges with the larger lymph vessels. The lymph capillary walls consist of only a single layer of endothelial cells. They seem to be permeable to all substances dissolved in the interstitial fluid.

Lymph: The composition of lymph is similar to that of blood. Lymph contains water, some plasma, proteins, electrolytes and lymphocytes, but it lacks RBCs, platelets and most of the blood proteins. Lymph is derived from the fluid portion of the blood that passes from the arterial ends of capillaries out into the spaces around the cells. The fluid lymph surrounds and bathes the cells of the body.

Lymph Nodes: Are located at intervals along lymph vessels. All lymph trickles through at least one of these nodes before being delivered to the blood stream. Lymph nodes are especially present in the neck, near the arm pits and in the groin area.

Structure: Each node has an outer capsule of fibrous connective tissue. Partitions from this capsule extend into the node itself, the spaces between are packed with lymphocytes and plasma. The node produces lymphocytes, and antibodies for the defense of the body.

Cause of Flow: The flow of lymph in the lymph vessel is brought about by the contraction and relaxation of the skeletal muscles and the breathing movement. The- direction of movement towards the main trunk and the back flow is prevented by valves present in the major vessels.

The two main lymphatic ducts are (i) Thoracic duct (ii) Right lymphatic duct

i. Thoracic duct: The lymphatic vessels of the legs join to those from the alimentary canal to form the thoracic duct. This empties lymph into the left subclavian vein.

ii. Right lymphatic duct: The right lymphatic duct drains lymph back into the blood stream via the right subclavian vein.

iii. Lymphoid Organs: It includes lump nodes, spleen, thymus (an endocrine gland), tonsils and patches of lymphoid tissue in the small intestine.

Functions:

(a) In an average person about three liters more fluid leaves the blood capillaries than is reabsorbed by them each day. It returns this excess fluid and its dissolved proteins and other substances to the blood.

(b) The lacteals of villi absorb large fat globules, which are released by interstitial cells after the products of digestion of fats are absorbed. After a fatty meal these fat globules may make up 1% of the lymph.

(c) The lymphatic system helps defend the body against foreign invaders. Lymph nodes have lymphocytes and macrophages that destroy the bacteria and viruses. The painful swelling of lymph nodes in corsair diseases (mumps is an extreme example) is largely a result of the accumulation of dead lymphocytes and macrophages.


(d) Just as the lymph nodes filler lymph, the spleen filters blood, exposing it to macrophages and lymphocytes that destroy foreign particles and aged red blood cells.