威廉姆斯-甲状旁腺亢进.doc

– PTH + + 1,25 D Ca Ca Ca ECF Ca Figure 28-2 Parathyroid hormone (PTH)-calcium feedback loop that con-trols calcium homeostasis. Four organs—the parathyroid glands, intestine, kidney, and bone—together determine the parameters of calcium homeo-stasis. +, positive effect; ?, negative effect; 1,25?D, 1,25-dihydroxyvitamin D3; ECF, extracellular fluid. (1,25-dihydroxyvitamin D or calcitriol), and fibroblast growth factor 23 (FGF23)—the major hormones involved in mineral ion homeostasis. Subsequent sections cover the wide variety of clinical disorders that accompany abnor-malities in this hormonal network. PARATHYROID HORMONE PTH is the peptide hormone that controls the minute-to-minute level of ionized calcium in the blood and ECF. PTH binds to cell surface receptors in bone and kidney, trigger-ing responses that increase blood calcium (Fig. 28-2). PTH also increases renal synthesis of calcitriol, the hormonally active form of vitamin D, which then acts on the intestine to augment absorption of dietary calcium, in addition to promoting calcium fluxes into blood from bone and kidney. The resulting increase in blood calcium (and in Figure 28-3 Sequences of pre-proparathyroid hormone from six species. Completely conserved residues are in boldface. Arrows indicate the sites of signal sequence (“pre”) and “pro” sequence cleavage. Numbers start at residue +1 of mature parathyroid hormone (PTH); because of gaps, the numbers correspond only to the mammalian and not to the chicken sequence. Amino acids are indicated by single-letter codes: A, Ala; R, Arg; N, Asn; D, Asp; C, Cys; Q, Gln; E, Glu; G, Gly; H, His; I, Ile; L, Leu; K, Lys; M, Met; F, Phe; P, Pro; S, Ser; T, Thr; W, Trp; Y, Tyr; V, Val. Hormones and Disorders of Mineral Metabolism 1239 calcitriol) feeds back on the parathyroid glands to decrease the secretion of PTH. The parathyroid glands, bones, kidney, and gut are thus the crucial organs that participate in PTH-mediated calcium homeostasis. Parathyroid Gland