Ho

Pyrocalciferol

7-Dehydrocholesterol provitamin D3

FIGURE 9-6 Photochemical pathway of production of vitamin D3 (calciferol) from 7-dehydrocholesterol. The starting point is the irradiation of a provitamin D, which contains the mandatory A5'7-conjugated double bonds; in the skin this is 7-dehydrocholesterol. After absorption of a quantum of light from sunlight (UV-B), the activated molecule can return to the ground state and generate at least six distinct products. The four steroids that do not have a broken 9, 10-carbon bond (provitamin D, lumisterol, pyrocalciferol, and isopyrocalciferol) represent the four diastereomers with either an a- or a /3-orientation of the methyl group on carbon-10 and the hydrogen on carbon-9. The three secosteroid products, vitamin D3, previtamin D and tachysterol, have differing positions of the three conjugated double bonds. In the skin the principal product is previtamin D, which then undergoes a 1,7-sigmatropic hydrogen transfer from C-19 to C-9, yielding the final vitamin D. Vitamin D can be drawn as either a 6-s-trans representation (this figure) or a 6-s-cis representation (see Figure 9-7), depending upon the state of rotation about the 6,7-single bond. The resulting vitamin D3, which is formed in the skin, is removed by binding to the plasma transport protein, the vitamin D-binding protein (DBP), present in the capillary bed of the dermis. The DBP-D3 then enters the general circulatory system.

FIGURE 9-6 Photochemical pathway of production of vitamin D3 (calciferol) from 7-dehydrocholesterol. The starting point is the irradiation of a provitamin D, which contains the mandatory A5'7-conjugated double bonds; in the skin this is 7-dehydrocholesterol. After absorption of a quantum of light from sunlight (UV-B), the activated molecule can return to the ground state and generate at least six distinct products. The four steroids that do not have a broken 9, 10-carbon bond (provitamin D, lumisterol, pyrocalciferol, and isopyrocalciferol) represent the four diastereomers with either an a- or a /3-orientation of the methyl group on carbon-10 and the hydrogen on carbon-9. The three secosteroid products, vitamin D3, previtamin D and tachysterol, have differing positions of the three conjugated double bonds. In the skin the principal product is previtamin D, which then undergoes a 1,7-sigmatropic hydrogen transfer from C-19 to C-9, yielding the final vitamin D. Vitamin D can be drawn as either a 6-s-trans representation (this figure) or a 6-s-cis representation (see Figure 9-7), depending upon the state of rotation about the 6,7-single bond. The resulting vitamin D3, which is formed in the skin, is removed by binding to the plasma transport protein, the vitamin D-binding protein (DBP), present in the capillary bed of the dermis. The DBP-D3 then enters the general circulatory system.

logical range of this divalent cation. Serum concentrations of calcium that fall above or below this range are likely to be due to the presence of disease states that perturb the integrated calcium-phosphorus homeo-static mechanisms.

A key signal transduction question relates to the identification of the mechanism(s) by which the surface of a parathyroid cell can sense a fall in the ambient extracellular ionized calcium concentrations and signal the secretion of PTH. A Ca2+-sensing receptor from bovine parathyroid tissue has been cloned and sequenced. This 120-kDa protein (1085 amino acids) features a large extracellular domain (600 amino acid) with clusters of acidic amino acid residues possibly

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Cure Tennis Elbow Without Surgery

Cure Tennis Elbow Without Surgery

Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.

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