Calcium homeostasis on the USMLE Step 1 exam

Tyler York

Calcium homeostasis is controlled by Parathyroid hormone, Vitamin D and Calcitonin. Both PTH and Vitamin D increase the serum calcium level while Calcitonin decreases the serum calcium. Disorders of any of these hormones or nutritional deficiencies present as various diseases.

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Full Calcium homeostasis on the USMLE Step 1 exam video transcript:

Hello Ruben. I'm such a te in today's video. I would like to talk about calcium homeostasis.

Calcium balance is influenced by intestinal absorption dietary intake, renal excretion and bone remodeling parathyroid hormone, calcitonin and vitamin D, are the major hormones involved in calcium metabolism.

Serum calcium, which is in the iron ice form is a metabolically, active form of calcium in the body and its levels are tightly regulated in the bloodstream.

Parathyroid hormone is produced by the parathyroid gland, the cell, membrane of the parathyroid gland has a calcium sensing receptor, which is a g. Protein-coupled receptor. When the plasma calcium increases, it binds to the calcium sensing receptor which then increases the intracellular calcium level in the parathyroid gland, which in turn inhibits, the release of parathyroid hormone or pth.

When the plasma calcium decreases, there is decreased calcium-binding. To the calcium sensing receptor which in turn increases or stimulates the release of pdh from the parathyroid gland hypermagnesemia inhibits. The secretion of pth while hypomagnesemia stimulates the secretion of pdh only in severe cases of hypomagnesemia. Real b. B t h release the inhabited,

Pth receptors are present, in the proximal and distal convoluted tubules of the kidney as well as a osteoblast. In the abuse of the kidney pth to meet increases, the reabsorption of calcium. Where is in the proximal convoluted tubule, pth stimulates the activity of the enzyme one alpha hydroxylase, which is important and vital in the synthesis of the active form of vitamin D.

Pth inhibits, the reabsorption of phosphate in the proximal convoluted tubule by inhibiting. The sodium phosphate co-transporter. It also increases the levels of CMP in the urine.

BTS increases the serum calcium by acting directly on the osteoblast and indirectly on the osteoclast agent, is a member of the tumor necrosis Factor cytokine, super family, and it isn't important transcription factor, that is involved in calcium. Metabolism pth, increases the production of rank of Sergeant or rank L by the osteoblast.

The receptor for rent, Legend is known as a blank rank is present. On the surface of osteoclast, The Binding of rank Legend to rank stimulates the osteoclast, which then increases the resumption of bone,

the activity of rank Legend is blocked by osteoprotegerin or OPG.

Calcitonin is produced by Parra for cuva or C cells of the thyroid gland. The effects of calcitonin on calcium metabolism are opposite to that of pdh in that, it decreases the serum, calcium levels by inhibiting. The osteoclast and inhibiting resorption of bone,

It does so by interfering with cytoskeletal structures that are involved with osteoclasts addition, like acting and integrating. And also by inhibiting ranked Legend

Vitamin D is not only involved in calcium metabolism but it is also an important metabolic hormone. It's directly and indirectly affects growth and differentiation of cells. It promotes mineralization of bone formation of new bone or osteoid

Vitamin D3 is also called is cholecalciferol and it is synthesized in the skin. After exposure, to sunlight from 7-dehydrocholesterol, the plant version of vitamin D is called as vitamin D2 or or go cholecalciferol.

The active form of vitamin D is 125 dihydroxycholecalciferol, also known as 125, dihydroxyvitamin, D, or Kelsey trial. It is produced by two hydroxylation steps at carbon-12 and carbon 25, the first step occurs in the liver, where carbon 25 is hydroxylated. This is followed by hydroxylation at Carbon one that happens in the kidney.

hydroxylation of vitamin D in the kidney is done by the enzyme one alpha hydroxylase, which is stimulated by pdh

the active form of vitamin D, binds to the vitamin D receptor which then mediate the transcription of genes involved in vitamin D metabolism, in the nucleus

vitamin D, induces, the expression of a calcium channel in the epochal membrane of the internal site which is involved in absorption of calcium from food sources. It all the expression of a calcium binding, protein called Cal binding and calcium atpase

Cal binding facilitates a translocation of calcium to the enterocytes and prevents calcium toxicity. Why is calcium atp's helps in translating the couch across the basolateral membrane of the interstate into the bloodstream.

Vitamin D. Also increases the absorption of phosphate and magnesium in the insane and the absorption of calcium and phosphate in the renal tubules.

Let's summarize the effects of hormones on the levels of calcium and phosphate vitamin D increases the serum levels of both calcium and phosphate pth increases the level of calcium while in decreases. The level of phosphate. On the other hand, calcitonin decreases, the levels of both calcium and phosphate,

Hope this video help you understand some Concepts on calcium homeostasis, always doing coming up with the video on disorders of calcium metabolism. Next, thanks for watching
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