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维生素D_3通常由它的先躯物7-脱氢胆固醇经日光的作用,在皮肤里形成。它必须经过两个代谢步骤才发挥作用。首先在肝和肠中羟化为25OHD_3,其后经肾脏进一步羟化成1.25(OH)_2D_3。后者是调节钙代谢最有效的体液因素。近来对1.25(OH)_2D_3的生理调节因素有所争论,认为甲状旁腺激素(PTH)调节肾脏维生素D代谢虽然重要,但仅是其中之一,尚有1.25(OH)_2D_3本身、血浆或饮食磷酸盐、血浆钙浓度参加调节均很重要。由于临床仍无法解释在正常健康人(儿童迅速生长期、妊娠期、哺乳期)钙吸收的极大变化,故推测尚
Vitamin D_3 is usually formed by the sun light of its precursor 7-dehydrocholesterol in the skin. It has to go through two metabolic steps to make a difference. Hydroxylated to 25OHD_3 in the liver and intestine, followed by further hydroxylation to 1.25 (OH) _2D_3 by the kidneys. The latter is the most effective humoral factors regulating calcium metabolism. Recently, there is controversy about the physiological regulation of 1.25 (OH) _2D_3. It is considered that although PTH regulates renal vitamin D metabolism, although it is important, there is only 1.25 (OH) _2D_3 itself, and plasma or diet Phosphate, plasma calcium concentration in regulation is very important. As clinical still can not explain the normal changes in calcium absorption in healthy (rapid growth of children, pregnancy, lactation), it is speculated that