Vitamin D3 Metabolism and Actions

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Questions and Answers

What is the active form of vitamin D3 called?

Cholecalciferol
25-hydroxycholecalciferol
1,25-dihydroxycholecalciferol (correct)
Calcitonin

Where does the hydroxylation of 25-OH-D3 to its active form occur?

Kidney (correct)
Skin
Liver
Intestine

Which hormone is secreted in response to increased calcium concentration in the blood?

25-OH-D3
Vitamin D3
Calcitonin (correct)
Parathyroid hormone (PTH)

What effect does 1,25-dihydroxycholecalciferol have on calcium absorption?

<p>Increases calcium absorption (C)</p> Signup and view all the answers

What is the primary action of calcitonin in the regulation of calcium levels?

<p>Inhibits bone resorption (A)</p> Signup and view all the answers

Flashcards

What is 25-hydroxycholecalciferol (25-OH-D3)?

The inactive form of vitamin D found in the liver, formed from vitamin D3 from diet or sunlight.

What is 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3)?

The biologically active form of vitamin D, produced in the kidneys.

What is calcitonin?

This hormone, produced by the thyroid gland, decreases blood calcium levels by inhibiting the effects of PTH and vitamin D.

What does the active form of Vitamin D do?

This hormone increases calcium absorption in the intestines and enhances the effect of PTH on bone resorption.

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What is parathyroid hormone (PTH)?

This hormone, produced by the parathyroid gland, increases blood calcium levels by promoting bone resorption and increasing calcium reabsorption in the kidneys.

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Study Notes

Vitamin D3 Metabolism

Vitamin D3 (cholecalciferol) is obtained from diet or sun exposure.
The liver converts vitamin D3 to 25-hydroxycholecalciferol (25-OH-D3), an inactive form.
The kidney hydroxylates 25-OH-D3 to 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3), the active form.

Vitamin D Actions

The active form of vitamin D increases calcium (Ca2+) absorption in the intestines.
It enhances parathyroid hormone (PTH) effects on bone resorption.

Calcitonin

Calcitonin is produced by cells in the thyroid gland.
Released when blood calcium levels elevate.
Reduces calcium levels by inhibiting PTH and vitamin D actions.
Not crucial for normal calcium regulation, but vital during hypercalcemia (high calcium blood).