Final answer:
Animal sources of vitamin A come from retinyl esters and plant sources from provitamins like β-carotene. Vitamin A is absorbed through the intestines and stored in the liver. The exact absorption rates are not specified, but fat-soluble vitamins like vitamin A are absorbed with dietary fats.
Step-by-step explanation:
Animal and Plant Sources of Vitamin A and Absorption Rates The content loaded question of what are animal and plant sources of vitamin A, and what percentage of each gets absorbed, pertains to the intake and utilization of vitamin A in the human body. Animal sources of vitamin A come mainly through the hydrolysis of retinyl esters to retinol in the intestine, while plant sources provide provitamins like β-carotene that are converted into active vitamin A in the body. For instance, the body synthesizes vitamin A from the β-carotene found in orange vegetables such as carrots and sweet potatoes.
Retinol is absorbed into the bloodstream through the cell membrane of the intestine, and then it is stored in the liver as palmitate esters. The process of conversion for β-carotene into Vitamin A involves an enzyme called β-carotene 15, 15'-oxygenase, predominantly found in the liver of humans and the intestinal wall of other animals. This enzyme catalyzes the cleavage of β-carotene, yielding two molecules of vitamin A aldehyde (retinal), which is then reduced to form vitamin A alcohol (retinol).
It is important to note that the absorption rate of vitamin A can vary and is not provided in the reference information. However, fat-soluble vitamins like vitamin A are absorbed in conjunction with dietary fats and can accumulate in the body's lipid stores, potentially leading to hypervitaminosis if taken in excess.