Key Features of the Lymphatic System

Parts: Lymphatic ducts, trunks, nodes, afferent vessels, efferent vessels, lymphatic nodules, tonsils, spleen, thymus gland, red bone marrow
Major Tissue Type:Variable
Characteristic Cell Types: Macrophages, monocytes, lymphocytes, neutrophils, plasma cells
Functional Unit: White pulp in spleen, Sinuses in lymph nodes

It is appropriate that our last lecture should rely on an important concept studied in the first series of lectures. The dual concepts of "body wall" and "body cavity" explain the systems of lymphatic nodes throughout the body. Superficial aka parietal nodes drain body wall structures like skin, fascia and skeletal muscle. Deep aka visceral nodes drain the structures of the body cavities. Apply this principle to exhibits 15.1 through 15.5 beginning on page 488 of your textbook.

Because the two systems of nodes are separate, cancerous lymph nodes located in the groin, for example, can be surgically removed before the circulating fluid we call "lymph" can carry them to other parts of the body. In fact, the structure of a lymph node traps invading agents. Afferent vessels begin in the interstitial spaces of the body and end at a sinus in the cortex of a lymph node. Lymph percolates through both cortical and medullary sinuses. Macrophages and lymphocytes destroy invaders, thus removing them from the lymph. The filtered lymph then passes into efferent vessels which unite to form the major lymphatic trunks of the body.

This is our last official lecture. Start studying for the final exam.