Vitamin-A | Absorption Transport Function Deficiency Manifestations & Therapeutic Use

Summary

This video provides a comprehensive overview of vitamin A, focusing on its absorption, transport, and key physiological roles. It explains the difference between retinoids and beta-carotenes, the process by which vitamin A is absorbed and transported through the lymphatic system, and its critical functions in vision, reproduction, growth, and epithelial tissue maintenance. The video highlights the role of vitamin A in the visual cycle, including how it helps maintain dark and light adaptation in the eyes. It also discusses the consequences of vitamin A deficiency, such as night blindness and skin issues, as well as its therapeutic uses, including treating acne and aging skin.

Takeaways

• 😀 Vitamin A is a fat-soluble vitamin found in both animal and plant sources, with animal sources providing active forms like retinol and plant sources providing inactive beta-carotene.
• 😀 Beta-carotene from plants is converted into retinol in the intestines, contributing to vitamin A intake in the body.
• 😀 The absorption of vitamin A involves its hydrolysis into retinol by intestinal enzymes, while beta-carotene is directly absorbed and converted inside the intestinal cells.
• 😀 Vitamin A is transported via the lymphatic system in chylomicrons, which are lipid droplets surrounded by proteins, for further use by the liver and other tissues.
• 😀 Retinol is stored in the liver as retinyl palmitate and is released when needed, carried by plasma retinol-binding protein to target tissues.
• 😀 The most crucial physiological function of vitamin A is its role in vision, particularly through its involvement in the regeneration of rhodopsin in the retina.
• 😀 The visual cycle includes the conversion of 11-cis retinal to all-trans retinal in response to light, triggering a nerve impulse that enables vision in low light.
• 😀 Vitamin A deficiency can lead to night blindness, which is one of the earliest signs, as well as severe dry eye conditions such as xerophthalmia and irreversible blindness.
• 😀 Deficiency of vitamin A also impacts growth in children, causing decreased growth rates, and can lead to infertility in males due to degeneration of the germinal epithelium.
• 😀 Vitamin A derivatives like isotretinoin are used therapeutically to treat dermatological conditions like acne, but isotretinoin is teratogenic, requiring precautions during pregnancy.

Q & A

What is vitamin A and what are its sources?

Vitamin A is a fat-soluble vitamin that exists in two forms: retinoids, which are obtained from animal sources, and beta-carotene, which is derived from plant sources.

How is beta-carotene converted into active vitamin A in the body?

Beta-carotene is absorbed as it is and then converted into retinal in the intestinal cells. This retinal is then reduced to retinol, the active form of vitamin A.

How does the body absorb and transport vitamin A?

Vitamin A compounds are hydrolyzed into retinol in the intestines. Retinol is re-esterified with fatty acids and transported via chylomicrons in the lymphatic system to the liver. The liver stores vitamin A as retinyl palmitate and releases free retinol as needed.

What role do chylomicrons play in vitamin A transport?

Chylomicrons are lipid droplets that package the retinol esters, stabilizing them in the aqueous environment and enabling their transport through the lymphatic system to the liver.

How is retinol transported to target tissues in the body?

Retinol is transported to extra-hepatic tissues by plasma retinol-binding protein. This complex binds to specific receptors on the surface of target cells, allowing retinol to enter and exert its effects.

What are the major physiological functions of vitamin A?

Vitamin A is essential for vision, reproduction, growth and bone development in children, and the maintenance and differentiation of epithelial tissues.

How does vitamin A contribute to vision?

Vitamin A, in the form of 11-cis-retinal, is a key component of rhodopsin in the rod cells of the retina. When light hits rhodopsin, 11-cis-retinal is converted to all-trans-retinal, triggering a nerve impulse that is sent to the brain.

What is the visual cycle, and why is it important?

The visual cycle involves the conversion of all-trans-retinal to 11-cis-retinal, which regenerates rhodopsin for vision. This cycle is critical for both dark adaptation and visual function. A deficiency in vitamin A disrupts this cycle, leading to night blindness.

What are the symptoms of vitamin A deficiency?

Vitamin A deficiency can lead to symptoms such as night blindness, rough and dry skin, xerophthalmia (dryness of the conjunctiva and cornea), and, in severe cases, corneal ulceration and blindness.

What therapeutic uses does vitamin A have?

Vitamin A derivatives, such as isotretinoin, are used to treat dermatological conditions like acne and skin aging. However, isotretinoin is teratogenic, so its use is contraindicated during pregnancy.