Vitamin D

What role does Vitamin D play in the body's response to hypocalcemia, or low levels of calcium in the blood?

Hypocalcemia results in an increase in parathyroid hormone which is released. Parathyroid hormone causes an increaseed production of 1,25-OH2-D, which then induces calbindin (CBD) synthesis and bone demineralization which occurs as a result of the decreased calcium levels in the blood.

What is the major function that Vitamin D plays a role in the body?

Main function of Vitamin D is in calcium and phosphorus homeostasis, which acts on the kidneys, intestines, and bones

What Percentage of Available (Pre-Vitamin D3) 7-Dehydrocholesterol is actually converted to active Vitamin D in the skin? What is this affected by?

Only 5-15% of the available (Pre-Vitamin D3) 7-Dehydrocholesterol is converted to active forms of Vitamin D3. This amount of activity is affected mainly by the intrinsic properties of the skin, the environment, the time of day and the current season.

What stimulates the production of 1,25 dihydroxy D3 1-hydroxylase

Parathyroid Hormone, and low calcium status both stimulate the production of 1,25 dihydroxy D3 1-hydroxylase.

What are some symptoms of Vitamin D Toxicity?

Vitamin D Toxicity can result in a rapid increase in serum calcium, as well as the calcification of soft tissues, and demineralization of bones as well.

How does vitamin D affect calcium and phosphorous homeostasis in the intestines?

Vitamin D acts in increasing the absorption of Calcium in the small intestine by increasing the synthesis of albindin (CBP) and subsequently opens calcium channels as a result, allowing more calcium to become absorbed through the small intestine.

How does Vitamin D act in increasing the mineralization and demineralization of bone?

Vitamin D increases the mineralization and demineralization of bone by increasing the activity of osteoclasts and osteoblasts in the bones.

How does vitamin D affect the kidneys in Calcium and phosphorous homeostasis mechanisms?

Vitamin D increases the re-absorption of both phosphate and calcium in the renal tubule.

What is the mechanism of action for Vitamin D?

Vitamin D's mechanism of action follows the typical model of steroid hormones, including specific receptors on specific cells in target organs. Receptor-ligand moves into the nucleus where it binds to DNA and then stimulates or represses transcription of particular genes which then produce mRNA as a result.

What are the main sources of Vitamin D2 (Ergocalciferol)

Vitamin D2 (Ergocalciferol) is obtained through the diet mainly from plants, and in the major synthetic form used in nutrition, it is produced primarily by irradiation of ergosterol.

What are some diseases and phenomenon commonly caused by a chronic ongoing Vitamin D deficiency?

Rickets (softening of bone in children), Osteomalacia (softening of bone in adults), osteoporosis (brittle bones in adults).

What factors can lead to Vitamin D deficiency?

Some factors which can promote a vitamin D deficiency include the lack of sunlight, lack of dietary Vitamin D, malabsorptive syndromes, liver disease, kidney disease, and chronic use of anti-convulsant drugs.

How is 25-Hydroxylase enzyme activity affected during the deficiency of Vitamin D?

25-hydroxylase enzyme activity is increased during a deficiency of Vitamin D.

How is Vitamin D transported in the body after its absorption?

After it is absorbed, Vitamin D is transported in the form Chylomicrons Transcalciferol (DBP).

After it has been hydroxylated to 25-OH-D3 in the liver, how is Vitamin D further metabolized?

After its hydroxylation, Vitamin D is then transported to the kidneys, where the second hydroxyl group is added at carbon 1, then producing 1,25 dihydroxyl-D3 1-hydroxylase as a result.

How is Cholecalciferol (Vitamin D3) produced in by the body?

Cholecalciferol (Vitamin D3) is primarily produced endogenously by ultraviolet light, which is converted from 7-dehydrocholesterol (Previtamin D3) in the epidermal layer of the skin

What decreases the production of 1,25-dihydroxy D3 1-hydroxylase

High phosphorous status decreases the production of 1,25 dihydroxy D3 1-hydroxylase activity in the body via feedback inhibition mechanisms.

What factors affect the amount of Vitamin D3 (Cholecalciferol) found in an animal source?

The amount of Vitamin D3 (Cholecalciferol) obtained from animal sources depends primarily on the diet of the animal as well as its exposure to sunlight.

What are the two most prominent forms of Vitamin D?

The two most prominent forms of Vitamin D are Vitamin D3 (Cholecalciferol), and Vitamin D2 (ergocalciferol).

How is Vitamin D first digested and absorbed from food sources?

Vitamin D is absorbed from fat soluble compounds, its efficiency absorption is approximately 50%, an it is absorbed the fastes in the duodenum, while most is absorbed in the ileum.

What are the major dietary sources of Vitamin D?

Vitamin D is mainly found in animal foods, most food sources have very low amounts of vitamin D, and other sources include the fortification of baked goods, grain products, milk and infant foods

How is Vitamin D metabolized after it has been transported by chylomicrons and DBP?

Vitamin D is taken up by the liver with chylomicrons and DBP and is then hydroxylated to 25-OH-D3.