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Urinary excretion of vitamin C depends on body stores, intake and renal function.Ascorbic acid has been found to be involved in a number of biochemical processes.
Bioavailability of vitamin C in feeds is limited, but apparently 80% to 90% appears to be absorbed (Kallner et al., 1977).
Site of absorption in the guinea pig is in the duodenal and proximal small intestine, whereas the rat showed highest absorption in the ileum (Hornig et al., 1984).
Under normal conditions, dogs and cats can synthesize vitamin C within their body.
Because of de novo synthesis, vitamin C is not technically a dietary required vitamin for healthy dogs and cats.
Function of vitamin C is related to its reversible oxidation and reduction characteristics; however, the exact role of this vitamin in the living system is not completely understood, since a coenzyme form has not yet been reported.
In addition to the relationship of ascorbic acid to hydroxylase enzymes, Franceschi (1992) suggests that vitamin C is required for differentiation of connective tissue such as muscle, cartilage and bone derived from mesenchyme (embryonic cells capable of developing into connective tissue).It is assumed that those species that are not scurvy prone do have an absorption mechanism by diffusion (Spencer et al., 1963).Ascorbic acid is readily absorbed when quantities ingested are small, but limited intestinal absorption occurs when excess amounts of ascorbic acid are ingested.In guinea pigs, rats, and rabbits, CO2is the major excretory mechanism for vitamin C.Primates do not normally utilize the CO2 catabolic pathway, with the main loss occurring in the urine.Tissue levels are decreased by virtually all forms of stress, which also stimulates the biosynthesis of the vitamin in those animals capable of synthesis.Ascorbic acid is excreted mainly in urine, with small amounts in sweat and feces.Vitamin C is a white to yellow-tinged crystalline powder.It crystallizes out of water as square or oblong crystals (Illus.In its metabolism, ascorbic acid is first converted to dehydroascorbate by several enzymes or nonenzymatic processes and can then be reduced back to ascorbic acid in cells (Johnston et al., 2007).Absorbed vitamin C readily equilibrates with the body pool of the vitamin.