Vitamin D Metabolism and Synthesis

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What is the location where the conversion of 25-OH-D3 to 1,25-(OH)2D3 takes place?

Proximal convoluted tubule (correct)

Distal convoluted tubule

Small intestine

Liver

Who demonstrated the conversion of 25-OH-D3 to 1,25-(OH)2D3?

Fraser and Kodicek (correct)

DeLuca

HF DeLuca and Kodicek

Holick et al.

What is the name of the enzyme responsible for the conversion of vitamin D3 to 25-OH-D3?

CYP2R1 (correct)

CYP27B1

CYP11A1

CYP24A1

What is the function of the vitamin D system suggested by the presence of CYP27B1 in several cells?

Paracrine/autocrine function Signup and view all the answers

What is the reason for the elimination of the liver as the site of conversion of 25-OH-D3 to 1,25-(OH)2D3?

Subtotal hepatectomy Signup and view all the answers

What is the consequence of the discovery of vitamin D?

Establishment of the vitamin D endocrine system Signup and view all the answers

What is the significance of the cloning of CYP27B1?

Understanding of the autocrine function of the vitamin D system Signup and view all the answers

What is the primary function of fibroblast growth factor 23 (FGF23) in calcium regulation?

To decrease serum phosphorus levels Signup and view all the answers

What is the primary site of 1,25(OH)2D3 production?

Kidney Signup and view all the answers

What is the effect of calcitonin on calcium levels?

Decreases calcium reabsorption in the kidney Signup and view all the answers

What is the role of parathyroid hormone (PTH) in calcium regulation?

To increase serum calcium levels Signup and view all the answers

What is the enzyme responsible for converting 25-OH-D3 to 1,25(OH)2D3?

CYP2R1 Signup and view all the answers

Where does the conversion of 25-OH-D3 to 1,25-(OH)2D3 take place?

In the kidney Signup and view all the answers

What is the effect of a high-calcium diet on vitamin D metabolism?

Decreases vitamin D production Signup and view all the answers

What is the result of feeding a low-calcium diet to an animal?

An increase in 1,25-(OH)2D3 levels Signup and view all the answers

What is the role of parathyroid hormone (PTH) in vitamin D regulation?

To stimulate the synthesis of 1,25-(OH)2D3 Signup and view all the answers

What is the role of estrogens in bone mineral homeostasis?

Suppresses bone resorption Signup and view all the answers

What is the outcome when the parathyroid glands are removed from an animal?

A decrease in 1,25-(OH)2D3 levels Signup and view all the answers

What is the effect of a high-calcium diet on 1,25-(OH)2D3 synthesis?

It suppresses the synthesis of 1,25-(OH)2D3 Signup and view all the answers

What is the role of the 1a-hydroxylase enzyme in vitamin D metabolism?

To convert 25-OH-D3 to 1,25-(OH)2D3 Signup and view all the answers

What is the mechanism by which the parathyroid glands sense hypocalcemia?

Through the detection of low calcium levels by the parathyroid glands Signup and view all the answers

What percentage of bisphosphonates is absorbed when taken orally?

Less than 10% Signup and view all the answers

What is the primary mechanism of action of cinacalcet?

Blocks PTH secretion Signup and view all the answers

What is a primary difference between etidronate and other bisphosphonates?

It causes less gastric irritation Signup and view all the answers

What is the primary therapeutic use of plicamycin (mithramycin)?

Paget's disease treatment Signup and view all the answers

What is the effect of raloxifene on breast tissue?

Antiestrogenic Signup and view all the answers

What is the effect of intermittent low-dose PTH on bone?

Increases bone formation without stimulating bone resorption Signup and view all the answers

What is the primary mechanism of action of raloxifene on bones?

Selectively activates estrogen receptors Signup and view all the answers

What is the mechanism of action of Teriparatide in osteoporosis treatment?

Stimulating new bone formation Signup and view all the answers

What is the frequency of Prolia (Denosumab) administration for postmenopausal osteoporosis?

Two shots a year Signup and view all the answers

What is the molecular weight of Denosumab?

147 kDa Signup and view all the answers

What is the primary function of calcitonin in serum calcium homeostasis?

Secondary regulation of serum calcium homeostasis Signup and view all the answers

What is the class of compounds that bisphosphonates are analogues of?

Pyrophosphates Signup and view all the answers