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Calcitriol is a hormone and the active form of vitamin D, normally made in the kidney. [8][9][10] It is also known as 1,25-dihydroxycholecalciferol. It binds to and activates the vitamin D receptor in the nucleus of the cell, which then increases the expression of many genes. [11]
PTH is secreted primarily by the chief cells of the parathyroid glands. The gene for PTH is located on chromosome 11. It is a polypeptide containing 84 amino acids, which is a prohormone. It has a molecular mass around 9500 Da. [6] Its action is opposed by the hormone calcitonin. There are two types of PTH receptors.
proteins. 25-Hydroxyvitamin D 1-alpha-hydroxylase (VD 1A hydroxylase) also known as calcidiol 1-monooxygenase[ 5 ] or cytochrome p450 27B1 (CYP27B1) or simply 1-alpha-hydroxylase is a cytochrome P450 enzyme that in humans is encoded by the CYP27B1 gene. [ 6 ][ 7 ][ 8 ] VD 1A hydroxylase is located in the proximal tubule of the kidney and a ...
A diet insufficient in vitamin D, combined with inadequate sunlight exposure, can lead to vitamin D deficiency, which is defined as a blood 25-hydroxyvitamin D or 25(OH)D level below 12 ng/mL (30 nmol/liter). Vitamin D insufficiency, on the other hand, is characterized by a blood 25(OH)D level between 12–20 ng/mL (30–50 nmol/liter).
Hyperparathyroidism is an increase in parathyroid hormone (PTH) levels in the blood. [1][4] This occurs from a disorder either within the parathyroid glands (primary hyperparathyroidism) or as response to external stimuli (secondary hyperparathyroidism). [1] Symptoms of hyperparathyroidism are caused by inappropriately normal or elevated blood ...
The level of serum 1,25(OH)D (calcitriol) is not usually used to determine vitamin D status because it often is regulated by other hormones in the body such as parathyroid hormone. [53] The levels of 1,25(OH)D can remain normal even when a person may be vitamin D deficient. [53] Serum level of 25(OH)D is the laboratory test ordered to indicate ...
Calcifediol, also known as calcidiol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D3 (abbreviated 25 (OH)D3), [1] is a form of vitamin D produced in the liver by hydroxylation of vitamin D 3 (cholecalciferol) by the enzyme vitamin D 25-hydroxylase. [3][4][5] Calcifediol can be further hydroxylated by the enzyme 25 (OH)D-1α-hydroxylase ...
CYP2R1 is cytochrome P450 2R1, an enzyme which is the principal vitamin D 25-hydroxylase. [5] [6] In humans it is encoded by the CYP2R1 gene located on chromosome 11p15.2. [7]It is expressed in the endoplasmic reticulum in liver, where it performs the first step in the activation of vitamin D by catalyzing the formation of 25-hydroxyvitamin D. [8]