The small intestine is one of the important organs for digestion, absorption and metabolism. It not only synthesizes 9%-12% of the body's protein, but also is an important defense barrier against the entry of exogenous antigens into the body. The protein turnover ability of intestinal tissues is much higher than that of parenteral tissues, such as intestinal mucosa. The protein turnover of intestinal mucosa in growing animals is 10 times that of parenteral tissues, and that of adult animals is 30 times. With such high protein and energy use, the intestine naturally has special nutritional needs while maintaining its growth and function. Lindberg et al. confirmed that piglet intestinal tissue does have special nutritional needs: 1 using nearly 50% of the daily intake of amino acids; 2 metabolism of non-essential amino acids (glutamic acid, aspartic acid and Gln) is much higher than essential amino acids ; 3 intestinal tissue utilization of essential amino acids accounted for 50% of its intake of amino acids; 4 intestinal tissue consumption of glucose 85% from arterial ingestion. Thus, nutrients, especially amino acids, play an important role in maintaining gut health and function.
1 small intestinal mucosal barrier
The intestinal mucosal barrier includes the intestinal mucus barrier (mainly mucin secreted by goblet cells) and the intestinal cell barrier (tight junction between intestinal epithelial cells). The mucus layer is composed of gelatinous glycoprotein secreted by mucosal epithelial cells and mucous cells. Its functions are: 1 to maintain the pH gradient in the intestine; 2 to prevent acid and protease from corroding the intestinal mucosa; 3 to lubricate the intestinal tract The mucosa is protected from mechanical damage; 4 prevents direct microbial erosion of intestinal mucosa; 5 provides a suitable living environment for normal flora. The mucus layer may be degraded by mechanical force, endogenous microbial flora, trypsin, bile, pepsin, etc. This degradation may increase the absorption of macromolecular antigens and adhesion of microbial organisms. The mucin forms a protective layer covering the villi, and its secretion may be regulated by both nerves and hormones. The tight junction between intestinal epithelial cells can effectively prevent macromolecular substances (such as pathogens, antigens, etc.) from entering the body. Therefore, the intestinal mucosa is not only a place for the body to digest and absorb nutrients, but also has an important defense function. Therefore, maintaining the integrity and health of the intestinal mucosa is important for the growth and development of animals.
2 intestinal arginine and Gln metabolism and its effects
After the amino acid enters the intestinal tissue, it is metabolized by three pathways: 1 synthetic protein; 2 by transamination to generate other amino acids, metabolic substrates or intermediates; 3 completely oxidized to CO2 and H2O. In the first two metabolic pathways, amino acids can be used by the body for growth or other biological functions. Once completely oxidized to CO2, it is a waste of amino acids, especially essential amino acids.
2.1 arginine metabolism and biological function
L-arginine plays a major physiological role in the body. L-arginine is synthesized in the liver or kidney, and the synthetic precursor is glutamic acid or Gln. After a plurality of steps, L-ornithine is formed, and L-arginine is formed from L-ornithine. In addition to the components of proteins, arginine is mainly involved in the ornithine cycle to form urea. It is also a precursor of nitric oxide (NO) formation, which plays an important role in regulating the immune system and nervous system and promotes wound healing. It plays an important role in promoting hormone secretion and maintaining positive nitrogen balance in the body.
2.2 Gln metabolism and its effects
Gln is mainly synthesized and released in skeletal muscle. The synthetic carbon scaffold is derived not only from muscle glycogen and blood glucose, but also from the decomposition products of branched chain amino acids such as proline and isoleucine. The part of branched chain amino acid amino group is synthetic Gln. Required. Under the action of Gln synthase, glutamic acid reacts with ammonia to form Gln. Gln is a special nutrient for intestinal mucosal cells. It has a certain effect on improving nitrogen balance and saving protein, enhancing immune function, maintaining acid-base balance, increasing cell volume, and enhancing protein synthesis of skeletal muscle cells. It can be provided like glucose. Carbon chain oxidation releases energy. Gln has different metabolic functions in different tissues. In the kidney, it is the main nitrogen source of renal tubular secretion; in the liver, it is the raw material of gluconeogenesis and urea synthesis; in nerve tissue, it is the precursor substance of neurotransmitter; in the blood, it is temporarily released. The role of ammonia poisoning.
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