3. Vitamin A 👁️Functions, Deficiency & Toxicity, Fat-Soluble Vitamins | MBBS Biochemistry USMLE

Описание: 𝐒𝐮𝐛𝐬𝐜𝐫𝐢𝐛𝐞 𝗙𝐨𝐫 𝗠𝐨𝐫𝐞 𝗜𝐧𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧 𝐨𝐧 𝗛𝐞𝐚𝐥𝐭𝐡 👩‍⚕‍ 𝐚𝐧𝐝 𝗠𝐞𝐝𝐢𝐜𝐢𝐧𝐞💉🩺💊
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👁️ Vitamin A | Chemistry, Functions, Deficiency & Toxicity | Fat-Soluble Vitamins | MBBS Biochemistry | USMLE Step 1

📜 Detailed YouTube Description:

👋 Hello future doctors and biochem learners! Vitamin A is the vision vitamin, but its role goes far beyond eyesight — it is essential for epithelial integrity, reproduction, immunity, and growth. Both its deficiency and toxicity have serious clinical consequences, making it a must-know vitamin for MBBS, NEET PG, FMGE, and USMLE Step 1.

This lecture explains the chemistry, absorption, transport, functions, deficiency, toxicity, and clinical aspects of Vitamin A in a simplified, exam-oriented way. 🧬📚

🌟 Chemistry & Sources

Forms (Retinoids):
• Retinol (alcohol form, storage/transport).
• Retinal (aldehyde form, vision).
• Retinoic acid (acid form, gene regulation).

Provitamin A: β-carotene (plant source).

Sources:
• Animal: liver, fish oils, egg yolk, milk.
• Plant: green leafy vegetables, yellow/orange fruits (carrots, mango).

🌟 Absorption, Transport & Storage

Absorbed in small intestine with dietary fat (needs bile salts).

Transported in blood bound to retinol-binding protein (RBP).

Stored mainly in liver (stellate/ITO cells).

🌟 Functions of Vitamin A

1️⃣ Vision (Retinal):

Component of rhodopsin in rods → night vision.

Visual cycle: 11-cis retinal ↔ all-trans retinal.

2️⃣ Growth & Epithelial Integrity (Retinoic Acid):

Maintains mucous-secreting epithelium.

Promotes growth and bone remodeling.

3️⃣ Reproduction:

Spermatogenesis in males, placental development in females.

4️⃣ Immunity:

Enhances resistance to infections.

5️⃣ Antioxidant (β-carotene):

Protects against oxidative stress.

🌟 Vitamin A Deficiency

Early: Night blindness (nyctalopia).

Ocular changes (Xerophthalmia spectrum):
• Conjunctival xerosis.
• Bitot’s spots.
• Corneal xerosis → keratomalacia → blindness.

Other: Follicular hyperkeratosis, impaired immunity, growth retardation.

High-yield: Common in malnutrition, fat malabsorption, measles infection.

🌟 Vitamin A Toxicity (Hypervitaminosis A)

Acute: Headache, nausea, vomiting, blurred vision.

Chronic: Alopecia, dry skin, hepatosplenomegaly, bone pain, pseudotumor cerebri.

Teratogenic: Causes congenital malformations (avoid excess intake in pregnancy).

🩺 Clinical Uses

Vitamin A supplementation in children to prevent blindness.

Used in acne & psoriasis (retinoic acid derivatives like isotretinoin).

Measles management (WHO recommends Vitamin A therapy).

🎯 Exam Integration

Retinal = vision. Retinoic acid = growth & gene expression.

Deficiency = Night blindness → Xerophthalmia → Keratomalacia.

Toxicity = Pseudotumor cerebri + teratogenic.

RBP = transport protein.
👉 Classic exam vignette: “Child with night blindness and Bitot’s spots = Vitamin A deficiency.”

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❓Should we cover Vitamin D (calcitriol, rickets, osteomalacia, toxicity) next as part of the Fat-Soluble Vitamin series? Drop your request in the comments below! 😊

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