Intestine synthesis

Correct answer = A. Pancreatic lipase hydrolyzes dietary triacylglycerol primarily to 2-monoacylglycerol plus two fatty acids. These products of hydrolysis can be absorbed by the intestinal mucosal cells. Bile salts do not inhibit release of fatty acids from triacylglycerol, but rather are necessary for the proper solubilization and hydrolysis of dietary triacylglycerol in the small intestine. Short- and medium-chain length fatty acids enter the portal circulation after absorption from the small intestine. Synthesis of apolipoproteins, especially apo B-48, is essential for the assembly and secretion of chylomicrons. 

Factors which cause a decrease in bioavailability include 111 high urinary excretion (2) destruction by certain mlesiinal bacteria (2) increased urinary excretion caused by vitamin C (4) presence of sulfonamides which block intestinal synthesis and (5) a decrease in absorption mechanisms. Increase in bioavailability can be provided by stimulating intestinal bacterial synthesis in certain species. No toxicity due to folic acid has been reported in humans. 

Bioavailability of Niacin. Factors which cause a decrease in macm availability include (1) Cooking losses (2) bound form in corn (maize), greens, and seeds is only partially available (3) presence of oral antibiotics (4) diseases which may cause decreased absorption (5) decrease in tiyptophan conveision as in a vitamin B deficiency. Fac.tois that increase availability include (1) alkali treatment of cereals (2) storage in bver and possibly in muscle and kidney tissue and (3) increased intestinal synthesis. 

Svennerholm A-M, Lange S, Holmgren J (1978) Correlation between intestinal synthesis of specific immunoglobulin A and protection against experimental cholera in mice. In Infect. Immun. 21 1—6. 

C. L. Bisgaier and R. M. Ghckman, Intestinal synthesis, secretion and transport of lipoproteins, Annu. Rev. Physiol. 45 625-636 (1983). 

Increased absorption is almost certainly the cause of the raising of the blood and tissue levels of vitamin B12 by sorbitol and some other substances. Intestinal synthesis is responsible for the far more dramatic sparing of other B vitamins by sorbitol, ascorbic acid, and several other substances, so that animals become completely independent of dietary sources of these vitamins. Finally, the ability of ascorbic acid to prolong the life of animals deficient in folic acid is very probably due to the promotion of the synthesis of this vitamin in the tissues. 

Impaired hepatic synthesis could be a cause for the low HDL levels. In severe cholestasis fat absorption usually is strongly impaired. This diminishes the contribution of the intestinal synthesis of A-I. 

Lipids of Bile and Intestinal Synthesis of Glycerides Federation Proc. 21(Suppl. No. 11) 25-27 (1962) CA 57 14322b... 

These studies show that germ-free existence is possible. In addition they throw fresh light on the question of intestinal synthesis of B vitamins, for the concentration of B vitamins in the gut does not necessarily imply bacterial synthesis. 

Since naturally occurring forms of vitamin K are fat-soluble, absorption is related to that of fat and is impaired when bile is absent from the intestinal tract and in the steatorrheas. It is conceivable that prolonged administration of antibiotics may depress intestinal synthesis of vitamin K and lead to deficiency. The deficiency which occurs in newborn infants may be due largely to limited food intake or, perhaps, to sterility of the intestinal tract. 

Another of the water-soluble B vitamins known to have a function for some bacteria and animals is biotin. A role in carbohydrate metabolism has been suggested. A protein substance called avidin, when fed in the form of large amounts of raw egg yolk, combines with biotin, and may thus cause a biotin deficiency in some species. Somewhat similar symptoms have been reported in human subjects (Sydenstricker et al., 1942). Intestinal synthesis and the antivitamin may explain the failure to confirm this observation. No definite requirement for the diet can be stated. 

In general, the combined urinary and fecal excretion of biotin exceeds the dietary intake. It seems likely that the fecal excretion of biotin is an indication of intestinal synthesis, whereas urinary excretion is a reflection of the dietary intake. Published reports of normal values of biotin in blood vary too widely for diagnostic use without carefully controlled observations. 

In addition to having activity as a growth factor for certain bacteria, PABA has considerable folacin activity when fed to deficient animals in which intestinal synthesis of folacin takes place. For example, for rats and mice, it can completely replace the need for a dietary source of folacin. This explains why para-aminobenzoic acid was once considered to be a vitamin in its own right. 

Intestinal synthesis. Vitamin K, is synthesized by the normal bacteria in the small intestine and the colon hence, an adequate supply is generally present. Since the intestine of a newborn infant is sterile at birth, however, the supply of vitamin K is inadequate until normal bacterial flora of the intestine develops on about the third or fourth day of life. 

The intestinal synthesis of vitamin K reduces the food dietary requirements for the vitamin in man and other mammals (but not birds birds have such a short intestinal tract and harbor so few microorganisms that they require a dietary source of vitamin K), although it appears that little of the vitamin K produced in the lower gut is absorbed. It is noteworthy, however, that animals that practice coprophagy, such as the rabbit, can utilize much of the vitamin K that is eliminated in the feces. 

RECOMMENDED DAILY ALLOWANCE OF VITAMIN K. Because of the synthesis of vitamin K by intestinal bacteria in healthy individuals (except newborn babies), no specific recommended allowance is made for this vitamin by the Food and Nutrition Board of the NRC-National Academy of Sciences. However, because the adequacy of the intestinal synthesis over a long period is uncertain, NRC does give an estimated adequate dietary intake of vitamin K. (See section on VITAMIN [S], Tab le V-5, Vitam i n Tab le.)... 

The intake suggested for young infants is based on 2 meg/ kg, assuming no intestinal synthesis. Therefore, the amount provided by current formulas of 4 mcg/100 kcal should be ample for normal infants. The suggested intake of 12 meg/day is also in the range supplied by breast milk (15 mcg/liter). 

Roth et al. (196), using C -carboxyl labeled nicotinic acid or nicotinamide, have shown that the compounds are rapidly excreted. A total of about 3% of the carboxyl group was expired as carbon dioxide within 1 day after the injection. A few more per cent is given off as exhaled carbon dioxide several days later. It has been estimated that approximately 15 % of the radioactivity fixed in the tissue is exhaled as carbon dioxide. In later studies it was shown that carbon dioxide production from labeled nicotinic acid and nicotinamide also occurs in hamsters, rats, and dogs (221). Hamsters and rats excrete somewhat more by this route, and the dog very little. This is illustrated in Fig. 10. It is of importance to note that very little of the radioactivity appears in the feces. This may be significant with regard to intestinal synthesis of the vitamin. 

Wang, X, A.M. Lawler, G. Steel, I. Sipila, A.H. Milam, and D. Valle, 1995. Mice lacking omithine-delta-amino-transferase have paradoxical neonatal hypoomithinaemia and retinal degeneration. Nat. Genet. 11, 185-190. Watford, M, 1994. Glirtartrine-metabolism in rat small-intestine - synthesis of 3-carbon products in isolated enterocyles. Biochim. Biophys. Acta 1200, 73-78. 

Although Osborne and Mendel had shown that feces from healthy rats contained a growth factor, it remained for Portier and Random. (16) to demonstrate that feces from animals on a deficient diet also contained the protective factor, thereby eliminating the possibility that the effect was due to any unabsorbed dietary residue or excreted surplus in the animals yielding the feces, and pointing strongly to intestinal synthesis in the deficient donor animals. 

Numerous workers (72, 74, 75) have reported that the rat can thrive well on a black tongue producing diet. Balance studies (76) showed that rats excreted as much as 40 y of nicotinic acid in excess of the intake. The fecal output alone was three times the intake, a strong evidence for intestinal synthesis which has been shown to occur in the cecum (77). It has also bpen claimed to take place in the tissue of the rat (78). Ruminants (79) also thrive well for a long period on a ration deficient in nicotinic acid with no ill effects. In sheep the excretion of nicotinic acid (80, 81) remains substantial despite a deficient intake and the nicotinic acid level in the blood (81) is comparable in value to that of animals fed a stock ration. A study of the rumen of the calf (51, 52) showed clearly that nicotinic acid is synthesized to a considerable extent. Similar results were obtained in the cow (76). 

The use of the insoluble sulfonamides for the study of intestinal synthesis has been most productive. The demonstration that folic acid and biotin... 

This reduction in the number of coliform organisms is accompanied by a diminution in the intestinal synthesis of various vitamins (as measured by the amounts found in feces)... 

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