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Biology_Passage_Notes - calcium absorption by the...

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The conjugate base of a strong acid (such as chloride, the conjugate base of the strong acid HCl) is pH neutral in solution . The conjugate acid of a weak base (such as Pb2+, the conjugate acid of the weak base lead hydroxide) is slightly acidic lead chloride would be an acidic salt. Recall that Δ H = H products - H reactants . In order for the reaction to be exothermic (negative Δ H ), H reactants must be greater than H products . The H of a molecule is the sum of the bond energies. Watch out, though, because you have to remember that bond strength is inversely related to bond energy ! So the bond strength of the reactants has to be less than that of the products in order for the reaction to be exothermic. Both PTH and calcitriol increase bone resorption , which helps to increase serum calcium. Additionally, they help to increase serum calcium at different points in the body; PTH by increasing calcium reabsorption at the kidney and calcitriol by increasing
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Unformatted text preview: calcium absorption by the intestines. PTH does not inhibit intestinal absorption of calcium. In fact, PTH has an indirect role in increasing intestinal absorption of Ca 2+ by increasing the conversion of calcidiol to calcitriol In the absence of vitamin D, intestinal absorption of calcium will be reduced because calcitriol cannot be produced, so plasma calcium levels will be lower than normal. This would trigger the release of PTH to increase plasma calcium through other means, primarily via bone resorption. Sulfur is less electronegative than O, sulfur has a lower electron affinity than O, and sulfur is a larger atom than O. Sulfur—just like other elements in the third and lower rows in the periodic table—can exceed its valence octet because of the availability of a valence d orbital; O cannot because there is no 2 d orbital....
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