Regulation, hormone transport

Transport of thyroid hormones Transport of vitamin A Osmotic regulation of plasma Non-specific carrier... 

Kudo, N., Katakura, M., Sato, Y., Kawashima, Y. Sex hormone-regulated renal transport of perfluorooctanoic acid. Chem. Biol Interac., 139 301-316 (2002). 

Aldastenme is a steroid hormone secreted by the zona glomerulosa of the adrenal gland (Figure 10.5). The steroid hormones are biosynthesized from cholesterol. Aldosterone is called a mineralocorlicoid because it regulates the transport of minerals, Na and K- Aldosterone received its name because it contains an aldehyde group —CH=0. 

Gut motility influences absorption and secretion. The amount of time in which luminal content is in contact with the epithelium is under neural and hormonal control. Neurohormonal substances, such as angiotensin, vasopressin, glucocorticoid, and aldosterone, and neurotransmitters also regulate ion transport. 

Calcium Regulating Hormones. II. Calcium Transport, Bone Metabolism, and New Drugs. Contrib Nephrol. Morii H, Ed. Karger Basel, 1991, Vol. 91, pp. 116-122. 

Many hormones influence membrane permeability, thereby regulating ion transport and water metabolism across the membrane. The antidiuretic hormone increases reabsorption of water in the kidney. 

In addition to its effects on bone and kidney cells, PTH affects the transport of calcium in the cells of the intestine and the lactating mammary gland. The hormone increases the absorption of calcium from the gut and its secretion in milk. Thus parathormone resembles vitamin D in regulating calcium transport in various kinds of cell. It too may act by regulating the biosynthesis of a specific protein, since actinomycin D prevents the action of PTH on osteoclasts which results in mobilization of bone mineral. Actinomycin D, however, does not affect the increased phosphate excretion by the kidney caused by PTH, so presumably a different mechanism is involved. 

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

The influx of Ca(Il) across the presynaptic membrane is essential for nerve signal transmission involving excitation by acetylcholine (26). Calcium is important in transducing regulatory signals across many membranes and is an important secondary messenger hormone. The increase in intracellular Ca(Il) levels can result from either active transport of Ca(Il) across the membrane via an import channel or by release of Ca(Il) from reticulum stores within the cell. More than 30 different proteins have been linked to regulation by the calcium complex with calmoduhn (27,28). 

We turn now to the biosynthesis of lipid structures. We begin with a discussion of the biosynthesis of fatty acids, stressing the basic pathways, additional means of elongation, mechanisms for the introduction of double bonds, and regulation of fatty acid synthesis. Sections then follow on the biosynthesis of glyc-erophospholipids, sphingolipids, eicosanoids, and cholesterol. The transport of lipids through the body in lipoprotein complexes is described, and the chapter closes with discussions of the biosynthesis of bile salts and steroid hormones. 

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