vitamin A metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving any of the vitamin A compounds, retinol, retinal (retinaldehyde) and retinoic acid, all of which are derivatives of beta-carotene. [GOC:jl, http://www.dentistry.leeds.ac.uk/biochem/thcme/vitamins.html#k]

Vitamin A, also known as retinol, is a fat-soluble vitamin that plays a critical role in various physiological processes, including vision, cell growth and differentiation, immune function, and reproduction. The metabolic process of vitamin A involves a series of interconnected reactions that convert dietary precursors into active forms and regulate their availability in the body.

**Dietary Intake and Conversion:**
- Vitamin A is obtained from the diet in two forms: preformed vitamin A (retinol) found in animal products like liver, eggs, and dairy, and provitamin A carotenoids (beta-carotene, alpha-carotene, and beta-cryptoxanthin) found in plants like carrots, sweet potatoes, and spinach.
- Carotenoids are converted to retinol in the intestinal mucosa through a series of enzymatic reactions.

**Absorption and Transport:**
- Retinol and carotenoids are absorbed in the small intestine with the help of bile salts and dietary fat.
- Once absorbed, retinol is incorporated into chylomicrons, lipoproteins that transport lipids from the gut to the liver.
- In the liver, retinol is esterified to retinyl esters, the storage form of vitamin A, and stored in hepatic stellate cells.

**Retinol Metabolism:**
- Retinol is released from the liver as needed and transported bound to retinol-binding protein (RBP) in the bloodstream.
- RBP delivers retinol to target tissues, including the retina, skin, and reproductive organs.

**Retinol to Retinoid Conversion:**
- Retinol can be converted to retinaldehyde, an aldehyde form of vitamin A, by retinal dehydrogenase enzymes.
- Retinaldehyde is crucial for vision as it is the precursor to rhodopsin, the light-sensitive pigment in the retina.
- Retinaldehyde can also be converted to retinoic acid, the active form of vitamin A involved in cell growth and differentiation.

**Retinoic Acid Signaling:**
- Retinoic acid binds to nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which regulate gene expression.
- Retinoic acid signaling plays a vital role in embryonic development, cell proliferation, and differentiation, immune function, and epithelial cell maintenance.

**Regulation of Vitamin A Metabolism:**
- Vitamin A metabolism is tightly regulated to maintain adequate levels in the body while preventing toxicity.
- Retinol storage and release are controlled by liver-specific mechanisms.
- Retinoid synthesis and degradation are regulated by feedback mechanisms involving retinoic acid receptors and other signaling pathways.

**Vitamin A Deficiency and Toxicity:**
- Deficiency in vitamin A can lead to various health problems, including night blindness, impaired immune function, skin disorders, and growth retardation.
- Excess vitamin A intake can cause toxicity, characterized by liver damage, bone pain, and birth defects.

The metabolic process of vitamin A is essential for maintaining overall health and well-being. It involves a complex series of reactions that ensure the availability of active forms of vitamin A to meet the diverse physiological needs of the body.'
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Proteins (3)

Compounds (7)