Lymphatic system cell components

The common mucosal immune system (CMIS) is now well established as a separate component of the host s immune apparatus, quite distinct from and independent of the systemic immune system described above. Moreover, if an immune response is induced at one site in the mucosal system this generally leads to responses at distal mucosal sites of the CMIS, presenting a potentially large advantage. It should be noted that there are approximately 6 x 1010 antibody producing cells in mucosal tissues and 2.5 x 1010 lymphocytes in the entire lymphatic system. 

A major component of the immune system is the class of cells called leukocytes, otherwise known as white blood cells. Like all blood cells, they arise from common precursor cells (stem cells) in the bone marrow. Unlike other blood cells, however, they can leave the blood vessels and circulate in the lymphatic system. Lymphoid tissues (such as lymph nodes, the spleen, and, above all, the thymus gland) play important roles in the workings of the immune system. 

Distribution describes the movement of a compound from its site of absorption to other areas of the body. When a compound is absorbed it passes through absorptive cells into the interstitial fluid of the organ these body fluids (interstitial fluid, intracellular fluid, and blood plasma) are not isolated and separate, but represent one continuous pool. In contrast to fast-moving blood that allows mechanical transport to occur, interstitial- and intracellular fluids remain in place with a slow movement of components such as water and electrolytes into and out of cells. Any compound can leave the interstitial fluid by entering local tissue cells, the circulating blood, or the lymphatic system. After entry into... 

The delayed phase occurs when the injured tissue is infiltrated by white blood cells. White blood cells (also called leukocytes or immune cells) are components found in the blood. They are also found in the spleen, the lymphatic system, and other tissues. They help defend the body against infectious disease and foreign material as part of the immune system. The three main types of leukocytes... 

Absorption of fatty adds in the small intestine follows a complex process that varies in efficiency depending on certain qualitative characteristics of dietary fat. Unsaturated fatty acids tend to be absorbed at a higha- effidraicy than saturated fatty adds. Fatty acids with slO carbons are directly absorbed into the portal drculation, while fatty acids with al2 carbons are absorbed into the lymphatic system packaged as chylomicrons. Fat digestion products incorporated into micelles occur largely through passive diffusion. Absorption of micellar components into intestinal mucosal cells depends on the penetration of the micelles across the unstirred water layer that separates the intestinal content from the brush border of the small intestine. ... 

Figure 7. Mixed micelles carry the solubilized hydrophobic lipids through the aqueous digest medium into close proximity with the intestinal mucosal cells (enterocytes). Micelles are not absorbed intact, but the various components are taken up by the enterocytes at independent rates. Intracellular esterification of cholesterol by acyl-coenzyme A prevents its transport back to the intestinal lumen. After esterification, cholesterol esters are assembled into chylomicrons and secreted into the lymphatic system and, finally, to the blood circulation.

After its absorption into the intestinal mucosal cell, cholesterol, together with triglycerides, phospholipids, and a number of specific apoproteins, is assembled into a large lipoprotein called the chylomicron (see later section on lipoprotein metabolism, exogenous pathway). One apoprotein component known as apolipoprotein (apo) B-48 is vital to the formation of chylomicrons, and in people with a rare deficiency of apo B-48 synthesis, chylomicron formation, and consequently cholesterol and fat absorption, is severely impaired. Chylomicrons enter the lymphatics, which empty into the thoracic duct and eventually enter the systemic venous circulation at the junction of the left subclavian vein and left internal jugular vein. 

The spleen is the largest of all lymphatic tissues and rests against the lower ribs (nine through eleven), the diaphragm, the stomach, and the left kidney in the left hypochondral region. A parenchyma of red and white pulp is surrounded by a capsule of fibrous connective tissue that contains efferent lymphatics, blood vessels, nerves, and some smooth muscle. The red pulp is a cordal and sinusoidal system concerned primarily with the production of blood products. The while pulp, which is lymphoid tissue, produces ihymus-dependent T lymphocytes and B lymphocytes and plasma cells. The latter components produce the humeral antibody component of the immune system, and the T-lymphocytes are involved in the cell-mediated arm of the system. The vasculature consists of the splenic artery, the largest branch from the celiac trunk, and the splenic vein, which unites with the mesenteric vein to form the portal vein. 

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