Photomicrograph dark staining network of reticular

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Photomicrograph: Dark-staining network of reticular connective tissue (350x). Photomicrograph: Smear of human blood (1500x); two white blood cells are seen among the red blood cells. White blood cell (lymphocyte) Neutrophil (white blood cell) Red blood cells Monocyte (white blood cell) Reticular fibers (h) Diagram: Blood (g) Diagram: Reticular Reticular cell Reticular fibers Spleen Blood cell White blood cell Red blood cells Blood cells in capillary
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sue type ( areola small open space). Because of its loose and fluid nature, areolar connective tissue provides a reservoir of water and salts for the sur- rounding tissues, and essentially all body cells obtain their nutrients from and release their wastes into this “tissue fluid.” When a body region is in- flamed, the areolar tissue in the area soaks up the excess fluid like a sponge, and the area swells and becomes puffy, a condition called edema. Many types of phagocytes wander through this tissue, scavenging for bacteria, dead cells, and other de- bris, which they destroy. Adipose Tissue Adipose (ad ı˘-po ¯s) tissue is com- monly called fat . Basically, it is an areolar tissue in which fat cells predominate (Figure 3.19f). A glis- tening droplet of stored oil occupies most of a fat cell’s volume and compresses the nucleus, dis- placing it to one side. Since the oil-containing re- gion looks empty and the thin rim of cytoplasm containing the bulging nucleus looks like a ring with a seal, fat cells are sometimes called signet ring cells . Adipose tissue forms the subcutaneous tissue beneath the skin, where it insulates the body and protects it from extremes of both heat and cold. Adipose tissue also protects some organs individu- ally. For example, the kidneys are surrounded by a capsule of fat, and adipose tissue cushions the eye- balls in their sockets. There are also fat “depots” in the body, such as the hips and breasts, where fat is stored and available for fuel if needed. Reticular Connective Tissue Reticular connective tissue consists of a delicate network of inter- woven reticular fibers associated with reticular cells, which resemble fibroblasts (Figure 3.19g). Reticular tissue is limited to certain sites: it forms the stroma (literally, “bed” or “mattress”), or in- ternal framework, which can support many free blood cells (largely lymphocytes) in lymphoid organs such as lymph nodes, the spleen, and bone marrow. Blood Blood, or vascular tissue, is considered a connec- tive tissue because it consists of blood cells, sur- rounded by a nonliving, fluid matrix called blood plasma (Figure 3.19h). The “fibers” of blood are soluble protein molecules that become visible only during blood clotting. Still, we must recog- nize that blood is quite atypical as connective tissues go. Blood is the transport vehicle for the cardiovascular system, carrying nutrients, wastes, respiratory gases, and many other substances throughout the body. Blood is considered in detail in Chapter 10.
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