Question

If blood calcium levels drop, the parathyroid gland releases the hormone called  ____________ . This hormone has multiple effects.

(1) The hormone stimulates bone cells to break down bone tissue and  ____________  calcium ion into the blood.

(2) The hormone stimulates the  ____________  to conserve calcium ions, preventing their excretion, and to activate vitamin  ____________  which increases calcium uptake from the diet.

(3) The hormone increases the  ____________  of calcium from the intestines.

The result of the these hormonal effects is to  ____________  blood calcium levels.

Answer 1

If blood calcium levels drop, the parathyroid gland releases the hormone called Para thyroid hormone(Parathormone/PTH). This hormone has multiple effects.

(1) The hormone stimulates bone cells to break down bone tissue and  Release calcium ion into the blood.

(2) The hormone stimulates the Kidney to conserve calcium ions, preventing their excretion, and to activate vitamin  D  which increases calcium uptake from the diet.

(3) The hormone increases the  Absorption of calcium from the intestines.

The result of the these hormonal effects is to Increase blood calcium levels.

Explanation:

Parathyroid hormone regulates serum calcium through its effects on bone, kidney, and the intestine.

In bone, PTH enhances the release of calcium from the large reservoir contained in the bones. Bone reabsorption is the normal destruction of bone by osteoclasts, which are indirectly stimulated by PTH.

In the kidney, around 250 mmol of calcium ions are filtered into the glomerular filtrate per day. Most of this (245 mmol/d) is reabsorbed from the tubular fluid, leaving about 5 mmol/d to be excreted in the urine. This reabsorption occurs throughout the tubule (most, 60-70%, of it in the proximal tubule), except in the thin segment of the loop of Henle.Circulating parathyroid hormone only influences the reabsorption that occurs in the distal tubules and the renal collecting ducts.

Another Important effect of PTH on the kidney is its stimulation of the conversion of 25-hydroxy vitamin D into 1,25-dihydroxy vitamin D (calcitriol), which is released into the circulation. This latter form of vitamin D is the active hormone which stimulates calcium uptake from the intestine.

Via the kidney, PTH enhances the absorption of calcium in the intestine by increasing the production of activated vitamin D.