BIOL 153 Final: Urinary Physiology - Final notes .doc
Document Summary
During metabolism, many unnecessary and even toxic substances accumulate in the body, including: excess sodium, chloride, sulfate, hydrogen, and nitrogenous wastes such as urea. These waste products, as well as some other toxic products which may have been introduced into the body are removed by the kidneys. In addition, a number of hormones are secreted by the kidneys (this, in part, accounts for the decreases seen in some hormone levels over time). Finally, the kidneys are the main organ for regulating water balance in our bodies. In the kidney, tight junctions between cells will block passage of most solutes through the paracellular pathway. Thus, substances must travel through the cells themselves, in order to pass across the tissue layer. Lipid-soluble = diffusion passively into the cell. Water-soluble = pores, protein channels, or carrier proteins are needed. Some of the capillaries in the kidney are very porous (fenestrated), allowing fluid to leak out.