Untitled Quiz

Vitamins Classification

• Water-soluble vitamins include B vitamins (Thiamin, Niacin, B12, Biotin, Riboflavin, B6, Folate, Pantothenic acid) and Vitamin C.
• Fat-soluble vitamins include Vitamins A, D, E, and K.

Vitamin A Food Sources

• Vitamin A is primarily found in the fat of animal foods.
• Beta-carotene, a precursor of Vitamin A, is abundant in dark green leafy vegetables and deep orange fruits (apricots, cantaloupe) and vegetables (squash, carrots, sweet potatoes, pumpkin).

Vitamin A Absorption, Storage, and Transport

• Retinol is absorbed in the intestines and incorporated into micelles, then packed into chylomicrons for transport via the lymphatic system to the vascular system.
• Approximately 70-80% of Vitamin A is stored in the liver, with the rest in adipocytes, kidneys, ovaries, intestines, and heart.
• Retinol binding protein (RBP) transports retinol in the blood.

Vitamin A and Vision

• Rhodopsin in retinal cells consists of opsin (protein) and cis-retinal (Vitamin A).
• Light absorption by rhodopsin causes retinal to change from cis to trans, triggering nerve impulses for visual perception.

Xerophthalmia

• Progressive blindness caused by Vitamin A deficiency, with symptoms including xerosis (drying of mucous membranes) and keratomalacia (softening of cornea leading to total blindness).
• Vitamin A deficiency is the leading cause of blindness globally.

Vitamin A and Epithelial Tissue Integrity

• Vitamin A supports the structure and function of mucous membranes and epithelial tissue.
• Epithelial tissues cover body surfaces, including skin and linings of the GI tract and respiratory tract.

Keratinization

• Keratin accumulation occurs due to reduced mucous membrane integrity from Vitamin A deficiency.
• Effects on the GI tract include diminished goblet cells, limiting nutrient absorption, while skin integrity declines, increasing infection risk.

Vitamin A Specifics

• Other names include Retinol, retinal, retinoic acid; precursor is beta-carotene.
• Chief functions: vision, maintenance of the retina, cornea, epithelial cells, skin integrity, bone remodeling, reproduction, immunity, and antioxidant action of beta-carotene.
• Food sources for Retinol: fortified milk/dairy, margarine, eggs, liver; for beta-carotene: leafy greens, orange fruits and vegetables.
• Deficiency diseases include night blindness and xerothalmia with symptoms such as corneal drying and weakened immunity.
• Toxicity can result in hypercarotenemia (orange skin) and hypervitaminosis A (acute symptoms like headache and blurred vision), mainly from supplements, not food.

Teratogenic Effects of Vitamin A Toxicity

• Excess Vitamin A can cause birth defects, including cleft palate; therefore, Accutane is contraindicated during pregnancy.
• Beta-carotene is not toxic or teratogenic.

Vitamin D

• Available through dietary sources like fortified dairy, cereals, egg yolks, and fatty fish.
• Can also be synthesized in the body through sunlight exposure, requiring 10-15 minutes of sunlight a few times a week for adequate production. Factors such as pollution and sunscreen can affect synthesis.

Vitamin D Synthesis

• Not classified as an essential nutrient since it can be synthesized from cholesterol with sunlight assistance.