Blood and Coelomic Fluid in Relation to Internal Defense in Polychaete Annelids
In mammals the blood system and the lymphatic system, though inter-related, are clearly defined. Hemoglobin is confined to the erythrocytes which remain in the blood, while the various types of white cells, each of which plays a different role, are distributed in both blood and lymph. Blood is maintained at a relatively high pressure and circulates quickly; lymph is maintained at low pressure and circulates slowly, but both fluids convey defensive cells and pass through special organs concerned with their regulation. Because of the rapid circulation of the blood it provides the means of conveying cells promptly to sites of injury, while the more slowly circulating lymph is better adapted to mediate the transmission of cells and humoral factors in relation to the longer term immune response. The coelom and its contained fluid form the body cavity, with the fluid acting as a visceral lubricant. The volume of coelo-mic fluid is very small compared with that of the lymph and of the blood. It is, perhaps, instructive to bear these familiar facts in mind when considering the blood and body fluid systems in annelids and the part each fluid and their contained cells plays in internal defense.
KeywordsBody Cavity None None Coelomic Fluid Internal Defense Collagenous Basement Membrane
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