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What is the primary active form of vitamin D in the body?
What is the primary active form of vitamin D in the body?
Vitamin D can be synthesized in the body when the skin is exposed to sunlight.
Vitamin D can be synthesized in the body when the skin is exposed to sunlight.
True
What effect does vitamin D have on the intestinal absorption of calcium?
What effect does vitamin D have on the intestinal absorption of calcium?
It stimulates the absorption of calcium.
The two main sources of vitamin D activity are _____ and _____, derived respectively from plants and animal tissues.
The two main sources of vitamin D activity are _____ and _____, derived respectively from plants and animal tissues.
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Match the following effects of vitamin D with its corresponding body processes:
Match the following effects of vitamin D with its corresponding body processes:
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What is a common dietary source of vitamin D?
What is a common dietary source of vitamin D?
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Vitamin D can only be obtained through dietary sources and cannot be synthesized by the body.
Vitamin D can only be obtained through dietary sources and cannot be synthesized by the body.
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What condition is characterized by soft, pliable bones due to vitamin D deficiency in children?
What condition is characterized by soft, pliable bones due to vitamin D deficiency in children?
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Exposure to proper sunlight is essential to prevent _______ of vitamin D.
Exposure to proper sunlight is essential to prevent _______ of vitamin D.
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Match the following conditions with their descriptions:
Match the following conditions with their descriptions:
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Study Notes
Lecture 41: Importance of Vitamin D
- Vitamin D is a group of sterols with hormone-like functions.
- Vitamin D is also called the "sunshine vitamin" due to its synthesis in the skin in response to sunlight.
- Vitamin D deficiency is more common during winter months due to decreased sunlight exposure.
- The active form of vitamin D, 1,25-dihydroxycholecalciferol (Calcitriol), binds to intracellular receptor proteins.
Specific Objectives
- Students will understand the synthetic pathway of vitamin D in the body.
- Students will be able to explain the activation process of vitamin D.
- Students will be able to explain the main functions of vitamin D.
- Students will discuss the clinical effects of vitamin D deficiency.
Distribution of Vitamin D
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Diet:
- Ergocalciferol (vitamin D2) is found in plants.
- Cholecalciferol (vitamin D3) is found in animal tissues.
- Both are preformed vitamin D sources.
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Endogenous precursor:
- 7-Dehydrocholesterol, an intermediate in cholesterol synthesis, is converted to cholecalciferol in the dermis and epidermis when exposed to sunlight.
Synthesis and Regulation of Calcitriol
- Diagram demonstrating the synthesis and regulation of calcitriol.
- Vitamin D3 (cholecalciferol) formation from 7-dehydrocholesterol in the skin,
- 25-hydroxylation in the liver,
- conversion to the active form, calcitriol (1,25-dihydroxycholecalciferol) in the kidneys.
- PTH (parathyroid hormone) and serum phosphate levels affect the pathway.
Function of Vitamin D
- The primary function of calcitriol is to maintain adequate plasma calcium levels.
- Aids in calcium and phosphorus absorption and retention for bone building.
Effect of Vitamin D on the Intestine
- 1,25-dihydroxyvitamin D3 (calcitriol) stimulates intestinal absorption of calcium and phosphate.
- Increased calcium binding protein (calbindin) synthesis enhances calcium uptake.
- Mechanism of action is typical of steroid hormones.
Effect of Vitamin D on Renal Tubules
- Calcitriol increases calcium and phosphorus reabsorption in renal tubules, conserving both minerals.
Effect of Vitamin D on Bone
- Calcitriol stimulates osteoblasts which in turn secrete alkaline phosphatase.
- Increased local phosphate concentration is a result.
- Increased ionic product of calcium and phosphorus results in bone mineralization.
Other Functions of Vitamin D
- Enhances immune function.
- Possible cancer prevention effects.
- Aids in infection control.
- Reduces inflammation.
- Boosts mood.
- Potential aid in weight loss.
- Promotes rheumatoid arthritis reduction.
- Lowers risk of type II diabetes.
- Might reduce heart disease risk.
Deficiency of Vitamin D
- Nutritional Deficiency: Insufficient sunlight exposure or inadequate vitamin D intake.
- Malabsorption: Conditions like obstructive jaundice or steatorrhea.
- Activation Abnormalities: Liver or kidney disease hindering hydroxylation reactions.
Clinical Indications
- Vitamin D deficiency causes bone demineralization leading to rickets (children) and osteomalacia (adults).
- Rickets characterized by collagen matrix formation without complete mineralization, resulting in pliable bones.
- Osteomalacia involves pre-existing bone demineralization, increasing fracture risk.
Toxicity of Vitamin D
- Vitamin D is a fat-soluble vitamin and is stored in the body, metabolized slowly.
- High doses (e.g., 100,000 IU for weeks/months) cause loss of appetite, nausea, thirst, and stupor.
Reference
- Vasudevan, DM, Sreekumari, S, and Kannan, V. (2011). Textbook of biochemistry for medical students, 6th Edition.
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Description
This quiz delves into the vital role of vitamin D in the body, focusing on its active forms, sources, and impacts on calcium absorption. Test your knowledge on vitamin D synthesis, dietary sources, and deficiency-related conditions.
