关于血钙浓度的调节，叙述正确的是（）
A.糖皮质激素与雌激素协同作用调节血钙浓度
B.降钙素由甲状旁腺激素分泌
C.甲状腺C细胞作用可使血钙降低
D.甲状旁腺功能减退使血钙升高
E.雌激素对血钙无调节作用
参考答案：C
解析：雌激素对肠道钙的吸收，肾脏钙的重吸收以及钙、磷在骨质中的沉积均有促进作用。甲状旁腺激素有升高血钙的作用。甲状腺C细胞分泌降钙素，可使血钙浓度下降。
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