Small intestine carbohydrates

Postprandial hyperglycemia strongly depends on the amount of absorbed monosaccharides and the velocity of absorption in the small intestine. Carbohydrates are recommended to account for -50% of the daily supply of calories in type 2 diabetes. Monosaccharides play only a minor role as dietary carbohydrates. They consist mainly of complex carbohydrates, such as starch (-60%), and disaccharides, such as sucrose (-30%). Complex carbohydrates and disaccharides must be hydrolyzed by intestinal and pancreatic enzymes before they can be tfansported through the mucosa of the bowel. Thus, any medication that delays breakdown of complex carbohydrates should decrease postprandial hyperglycemia and improve insulin sensitivity, as well as protecting the beta cells of the pancreas. 

Absorption of nutrients occurs mainly in the small intestine. Carbohydrates are absorbed as monosaccharides by active transport, a process involving carrier proteins. Amino acids and fatty acids are also absorbed by active transport, but emulsified triglycerides are absorbed by passive diffusion. Large molecules, especially the immunoglobulins present in colostrum, are absorbed by a process known as pinocytosis. Many minerals and vitamins require special processes of absorption. 

Acarbose is a nonabsorbable a-glucosidase inhibitor which blocks the digestion of starch, sucrose, and maltose. The digestion of complex carbohydrates is delayed and occurs throughout the small intestine rather than in the upper part of the jejunum. Absorption of glucose and other monosaccharides is not affected. Acarbose is adrninistered orally three times a day and chewed with the first mouthful of food. 

A wide diversity of herbal remedies have purported abilities to stimulate defense functions. Complexes of carbohydrate and lignin, which are present in some herbs, modulate enteric immune functions (Kiyohara et al, 2000), and the changes in cytokine secretion (Matsumoto and Yamada, 2000) can trigger systemic responses. The polysaccharides present in other herbal medicines augment production of immunoglobulin (Ig) A by the Peyer s patches in the small intestine (Sakushima et al, 1997 Yu et al, 1998). The responses of the enteric immune system to lectins are variable (Pusztai 1993), and can elicit systemic responses (Lavelle et al, 2000). Other phytochemicals provide protection by inducing detoxification pathways in mucosal cells (Williamson et al, 1998). 

Saponins and phenolics also have anti-microbial properties (Chung et ah, 1998) and have been associated with reduced rumen functions (Klita et al., 1996 Reed, 1995), thereby limiting the nutrient quality of forages. Also, carbohydrate complexes with hgnins and other compounds reduce carbohydrate utilization by rumen bacteria (Cornu et al., 1994). The influence of such anti-microbials on rumen functions can affect small intestine characteristics by altering nutrient concentrations (Barry and McNabb, 1999). 

The food, now in a liquid form known as chyme, passes through the pyloric sphincter into the duodenum, where stomach acid is neutralized. There is wide variation in lengths of the components of the small intestine (i.e., duodenum, jejunum, and ileum) between individuals (Table 98-1). Most absorption of digested carbohydrate and protein occurs within the jejunum. Most fat absorption occurs within the jejunum and ileum. In the small bowel, breakdown of macronutrients (i.e., carbohydrate, protein, and fat) occurs both within the lumen of the gut and at the intestinal mucosal membrane surface. The absorptive units on the intestinal mucosal membrane are infoldings known as... 

Digestion and absorption in the small intestine. Most digestion and absorption of carbohydrates, proteins, and lipids occurs in the small intestine. A summary of the digestive enzymes involved in these processes is found in Table 18.3. 

The absorption efficiency of the different carotenoids is variable. For example, (3-cryptoxanthin has been reported to have higher absorption efficiency than a-cryptoxanthin in rats (Breithaupt and others 2007). Carotenoids must be liberated from the food before they can be absorbed by intestinal cells (Faulks and Southon 2005). Mechanical disruption of the food by mastication, ingestion, and mixing leads to carotenoid liberation (Guyton and Hall 2001). The enzymatic and acid-mediated hydrolysis of carbohydrates, lipids, and proteins (chemical breaking of the food) also contributes to carotenoids liberation from the food matrix (Faulks and Southon 2005). Once released, carotenoids must be dissolved in oil droplets, which are emulsified with the aqueous components of the chyme. When these oil droplets are mixed with bile in the small intestine, their size is reduced, facilitating the hydrolytic processing of lipids by the pancreatic enzymes (Pasquier and others 1996 Furr and Clark 1997 ... 

Since in mammalian species metals first need to be assimilated from dietary sources in the intestinal tract and subsequently transported to the cells of the different organs of the body through the bloodstream, we will restrict ourselves in this section to the transport of metal ions across the enterocytes of the upper part of the small intestine (essentially the duodenum), where essentially all of the uptake of dietary constituents, whether they be metal ions, carbohydrates, fats, amino acids, vitamins, etc., takes place. We will then briefly review the mechanisms by which metal ions are transported across the plasma membrane of mammalian cells and enter the cytoplasm, as we did for bacteria, fungi and plants. The specific molecules involved in extracellular metal ion transport in the circulation will be dealt with in Chapter 8. 

Mantle, M., and Husar, S. D. (1994). Binding of Yersinia enterocolitica to purified, native small intestinal mucins from rabbits and humans involves interactions with the mucin carbohydrate moiety. Infect. Immun. 62,1219-1227. 

Teneberg, S., Angstrom, J., and Ljungh, A. (2004). Carbohydrate recognition by enterohemorrhagic Escherichia coli Characterization of a novel glycosphingolipid from cat small intestine. Glycobiology 14, 187-196. 

Suppose we start with a starch-rich meal, say one containing a lot of pasta or bread. The digestion of starches begins in the mouth. Saliva contains an enzyme, salivary amylase (aka ptyalin), which catalyzes the conversion of starch to simple sugars such as glucose. This process is completed in the small intestine under the influence of other enzymes in the amylase class. This completes the first phase of carbohydrate catabolism the conversion of complex, polymeric carbohydrates (e.g., starches) to their simple monomeric units, the sugars. 

The stomach receives food from the buccal cavity, it partially digests protein, fat and carbohydrate and it then delivers the resulting mixture (chyme) into the small intestine. The inner surface of the stomach is folded into ridges, to allow for distension after a meal, they contain gastric pits into which several gastric glands discharge their secretions (Table 4.1). 

Reactions in the stomach and small intestine are primarily the breakdown of carbohydrates and dissaccharide sugars into monosaccharides... 

The wall of the small intestine is permeable to water and to small molecules such as the amino acids produced by protein breakdown and sugars produced by carbohydrate breakdown so this system is a reactor-separator combination, a membrane reactor. Finally the undigested food passes into the large intestine, where more water is removed through the permeable wall before exiting the reactor. 

Acarbose and miglitol are a-glucosidase inhibitors of carbohydrate digestion in small intestine... 

Saline laxatives like MgS04, Mg(OH)2, Mg2 Citrate and Na+ Phosphates act via their osmotic pressure to retain water in the colon. Other osmotic laxatives are carbohydrates such as lactulose, glycerin, sorbitol, and mannitol. They are not absorbed and are resistant to digestion in the small intestine. Most agents are orally administered. It should be noted however that glycerin, sodium phosphates and sorbitol are formulated for rectal use. From lactulose lactic and acetic acids are formed by intestinal bacteria and apart from its osmotic effects it thus acidifies the content of the colon. The reduction of the pH stimulates motility and secretion. 

By competitively inhibiting the alpha-glucosidase enzymes in the mucosa cells of the small intestine these agents suppress the breakdown of di-, oligo-and polysaccharides into monosaccharides and thus decrease carbohydrate absorption. In this way postprandial elevations of blood glucose levels can be prevented or diminished. 

Mecfianism of Action A cinchona alkaloid that relaxes skeletal muscle by increasing the refractory period, decreasing excitability of motor end plates (curare-like), and affecting distribution of calcium with muscle fiber. Antimalaria Depresses oxygen uptake, carbohydrate metabolism, elevates pH in intracellular organelles of parasites. Therapeutic Effect Relaxes skeletal muscle produces parasite death. Pharmacokinetics Rapidly absorbed mainly from upper small intestine. Protein binding 70%-95%. Metabolized in liver. Excreted in feces, saliva, and urine. Half-life 8-14 hr (adults), 6-12 hr (children). 

Most food absorption takes place in the small intestine. The gastrointestinal tract possesses specialized carrier systems for certain nutrients such as carbohydrates, amino acids, calcium, and sodium. Some xenobiotics use these routes of passage through the cells, while others enter through passive diffusion. 

B. Further digestion of carbohydrates by pancreatic enzymes occurs in the small intestine... 

Role of PI in membrane protein anchoring Specific proteins can be covalently attached via a carbohydrate bridge to membrane-bound PI (Figure 17.9). [Note Examples of such proteins include alkaline phosphatase (a digestive enzyme found on the surface of the small intestine that attacks organic phosphates), and acetylcholine esterase (an enzyme of the postsynaptic membrane that... 

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