Question

Digestion absorption and metabolism of vitamin a

Answer 1

 Schematic representation of vitamin A (VA) digestion, absorption, transport, and metabolism in the body. Dietary VA from plant and animal sources is digested in the intestinal lumen and absorbed by enterocytes via different mechanisms. Within the enterocytes, the dietary VA is converted into retinyl esters, which are packaged into chylomicrons for the secretion into the lymph and eventually enter the circulation. The lipoprotein lipase hydrolyzes triglycerides (TGs) on the chylomicrons to produce chylomicron remnants. The retinyl ester-containing chylomicron remnants are eventually taken up by hepatocytes, where the retinyl esters are again hydrolyzed into retinol. The released retinol can be transported to target cells and catabolized into retinal, retinoic acid (RA), or other metabolites. Excessive retinol is re-esterified into retinyl esters, which are stored in stellate cells. BB-REH, brush-border retinyl ester hydrolase; LRAT, lecithin:retinol acyltransferase; ARAT, acyl-CoA:retinol acyltransferase; RBP, retinol binding protein; RDH, retinol dehydrogenase; RALDH, retinal dehydrogenase; REH, retinol ester hydrolase; STRA6, stimulated by retinoic acid 6; RA, retinoic acid; RARE, retinoic acid responsive element; RAR, retinoic acid receptor; RXR, retinoid X receptor; TTR, transthyretin; PPAR, peroxisome proliferator-activated receptor; HNF4 α , hepatocyte nuclear factor 4 α ; COUP-TFII, chicken ovalbumin up-stream transcription factor II. 

Go to publication