T

I Plasma CT

t Urinary excretion of phosphate

4 Urinary excretion V Calcium of calcium release t Urinary excretion of phosphate

4 Urinary excretion V Calcium of calcium release

I Plasma phosphate

V Plasma calcium

Effects of calcitonin (CT) on calcium and phosphate metabolism.

\|r Plasma calcium | Plasma PTH

^ Renal 1 a-hydroxylase activity

|1,25-(OH)2 D3 formation

Plasma Calcium

moting the retention of both ions in the body. However, this is a weak and probably only minor effect of the hormone. In bones, the hormone promotes actions of PTH on osteoclasts, increasing bone resorption (see Fig. 36.9).

In the gastrointestinal tract, 1,25-dihydroxycholecalcif-erol stimulates calcium and phosphate absorption by the small intestine, increasing plasma concentrations of both ions. This effect is mediated by increased production of calcium transport proteins resulting from gene transcription events and usually requires several hours to appear.

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Essentials of Human Physiology

Essentials of Human Physiology

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