TAILIEUCHUNG - Chapter 100. Megaloblastic Anemias (Part 3)

Most foods contain some folate. The highest concentrations are found in liver, yeast, spinach, other greens, and nuts (100 µg/100 g). The total folate content of an average Western diet is ~250 µg daily, but the amount varies widely according to the type of food eaten and the method of cooking. Folate is easily destroyed by heating, particularly in large volumes of water. Total-body folate in the adult is ~10 mg, the liver containing the largest store. Daily adult requirements are ~100 µg, so stores are only sufficient for 3–4 months in normal adults and severe folate deficiency may. | Chapter 100. Megaloblastic Anemias Part 3 Most foods contain some folate. The highest concentrations are found in liver yeast spinach other greens and nuts 100 pg 100 g . The total folate content of an average Western diet is 250 pg daily but the amount varies widely according to the type of food eaten and the method of cooking. Folate is easily destroyed by heating particularly in large volumes of water. Total-body folate in the adult is 10 mg the liver containing the largest store. Daily adult requirements are 100 pg so stores are only sufficient for 3-4 months in normal adults and severe folate deficiency may develop rapidly. Absorption Folates are absorbed rapidly from the upper small intestine. The absorption of folate polyglutamates is less efficient than for monoglutamates on average 50 of food folate is absorbed. Polyglutamate forms are hydrolysed to the monoglutamate derivatives either in the lumen of the intestine or within the mucosa. All dietary folates are converted to 5-methylTHF 5-MTHF within the small-intestinal mucosa before entering portal plasma. The monoglutamates are actively transported across the enterocyte by a carrier-mediated mechanism. Pteroylglutamic acid at doses 400 iig is absorbed largely unchanged and converted to natural folates in the liver. Lower doses are converted to 5-MTHF during absorption through the intestine. About 60-90 iig of folate enters the bile each day and is excreted into the small intestine. Loss of this folate together with the folate of sloughed intestinal cells accelerates the speed with which folate deficiency develops in malabsorption conditions. Transport Folate is transported in plasma about one-third is loosely bound to albumin and two-thirds unbound. In all body fluids plasma cerebrospinal fluid milk bile folate is largely if not entirely 5-MTHF in the monoglutamate form. Two types of folate-binding protein are involved in entry of MTHF into cells. A high-affinity folate receptor takes folate into cells by

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