Vitamin D3 and Calcitonin Metabolism

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Questions and Answers

What is the primary function of 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3)?

To inhibit calcitonin secretion
To increase calcium absorption in the intestine (correct)
To decrease calcium absorption in the intestine
To convert vitamin D3 into an inactive form

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

Calcitriol
Insulin
Calcitonin (correct)
Parathyroid hormone (PTH)

How is vitamin D3 activated in the body?

It is directly absorbed from the diet
It is secreted from the thyroid gland
It is converted into calcitonin
It undergoes hydroxylation in the kidney (correct)

What effect does calcitonin have on parathyroid hormone (PTH) activity?

<p>It inhibits the actions of PTH. (C)</p> Signup and view all the answers

What triggers the secretion of calcitonin?

<p>Hypercalcemic stimulus (D)</p> Signup and view all the answers

Flashcards

Vitamin D3

A form of vitamin D that is produced in the skin by exposure to sunlight or obtained through the diet.

25-hydroxycholecalciferol (25-OH-D3)

The inactive form of vitamin D that is produced in the liver from Vitamin D3.

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

The active form of vitamin D that is produced in the kidneys from 25-OH-D3. Its main function is to increase calcium absorption in the intestines.

Calcitonin

A hormone produced by the thyroid gland in response to high blood calcium levels. Its function is to lower blood calcium levels by inhibiting the actions of PTH and vitamin D.

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Parathyroid hormone (PTH)

This hormone, produced by the parathyroid glands, increases blood calcium levels by promoting calcium absorption in the intestines, bone resorption, and 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).
25-OH-D3 is an inactive form of vitamin D.
The kidney hydroxylates 25-OH-D3 to 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3), the active form.
Active vitamin D increases calcium (Ca2+) absorption in the intestines.
Active vitamin D enhances parathyroid hormone (PTH)'s effect on bone resorption.

Calcitonin

Calcitonin is produced by the medullary cells of the thyroid gland.
Calcitonin secretion occurs when blood calcium (Ca2+) levels rise.
Calcitonin lowers blood calcium levels by inhibiting PTH and vitamin D.
Calcitonin is not normally secreted for routine calcium regulation.
It responds to high calcium (hypercalcemic) stimuli.

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Description

Explore the metabolism of Vitamin D3 and the role of Calcitonin in calcium regulation in this quiz. Learn how Vitamin D3 is converted into its active form and the physiological effects of both hormones on calcium levels in the body. Test your understanding of these essential biochemical processes.