Digestive tract, cells

Historically, dietary fiber referred to iasoluble plant cell wall material, primarily polysaccharides, not digested by the endogenous enzymes of the human digestive tract. This definition has been extended to iaclude other nondigestible polysaccharides, from plants and other sources, that are iacorporated iato processed foods. Cellulose [9004-34-6] (qv) is fibrous however, lignin [9005-53-2] (qv) and many other polysaccharides ia food do not have fiberlike stmctures (see also Carbohydrates). 

Animals, including humans, cannot synthesise all the different amino adds they need and thus require them in their diet. These amino adds are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animal s cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitrogen from the soil (as nitrate) with organic molecules derived from carbon from the atmosphere (as CO2). 

These are four monoamines synthesized and seereted within many mammalian tissues, ineluding various regions in the brain, sympathetic nervous system, enlero-chromafhn cells of the digestive tract, and adrenal mednlla. These biogenic amines (indoleamine and catecholamines — dopamine, norepinephrine, and epinephrine) are synthesized within the cell from their precursor amino acids and have been associated with many physiological and behavioral functions in animals and humans. 

The function of the digestive system is to make ingested food available to the cells of the body. Most ingested food is in the form of very large molecules that must be broken down by mechanical and biochemical processes into their smaller components (see Table 18.1). These smaller units are then absorbed across the wall of the digestive tract and distributed throughout the body. Not all ingested materials may be completely... 

Mucosa. The innermost layer of the wall is the mucosa, which consists of a mucous membrane, the lamina propria, and the muscularis mucosa. The mucous membrane provides important protective and absorptive functions for the digestive tract. The nature of the epithelial cells lining the tract varies from one region to the next. Rapidly dividing stem cells continually produce new cells to replace worn out epithelial cells. The average life span of these epithelial cells is only a few days. The lamina propria is a thin middle layer of connective tissue. This region contains the capillaries and small lymphatic vessels that take up the digested nutrient molecules. The muscularis mucosa is a thin layer of smooth muscle. Contraction of this muscle may alter the effective surface area for absorption in the lumen. 

Glucagon is a single-chain polypeptide of 29 amino acid residues and a molecular mass of 3500 Da. It is synthesized by the A-cells of the islets of Langerhans, and also by related cells found in the digestive tract. Like insulin, it is synthesized as a high molecular mass from which the mature hormone is releases by selective proteolysis. 

Takei, M. et al., Dendritic cells maturation promoted by Ml and M4, end products of steroidal ginseng saponins metabolized in digestive tracts, drive a potent Th 1 polarization, Biochem Pharmacol, 68,441, 2004. 

Serum lipase is synthesized and stored in the granules of pancreatic acinar cells and is excreted from the apical poles of the acinar cells into the duct system of the gland. Lipases are produced not only in the pancreas but also at various sites in the human digestive tract [126][127]. Lipases are also found in leucocytes, adipose tissue, lung, and milk. 

The main precursors of gluconeogenesis in the liver are lactate from anaerobically working muscle cells and from erythrocytes, glucogenic amino acids from the digestive tract and muscles (mainly alanine), and glycerol from adipose tissue. The kidney mainly uses amino acids for gluconeogenesis (Glu, Gin see p.328). 

It is interesting that the digestive tracts of sea hares and fish that feed upon L. ma.iuscula are not affected by the aplysia-toxins and lyngbyatoxin A. Preliminary studies by Fujiki suggest that the cells of sea hares may lack the tumor promoter-binding receptors that are so common in mammalian cells (34). 

Decubitus ulcer (e.g. bed sores, pressure sores) Diabetic ulcers Varicose ulcers Rodent ulcers Peptic ulcers Ulcer due to continuous pressure exerted on a particular area of skin often associated with bed-ridden patients Ulcers (e.g. diabetic leg ) caused by complications of diabetes Due to defective circulation, sometimes associated with varicose veins An ulcerous cancer (basal cell carcinoma), usually affecting the face Ulcer of the digestive tract, caused by digestion of the mucosa by acid and pepsin may occur in e.g. the duodenum (duodenal ulcer), or the stomach (gastric ulcer)... 

Pollen consists of reproductive cells released by plants (and sometimes carried by insects) at certain times of the year. Individual species of plant are identifiable by the grains of pollen they generate. Klaus Oeggl of Innsbruck University, James H. Dickson at the University of Glasgow in Scotland, and their colleagues have studied pollen samples obtained from Otzi s digestive tract. Some of this pollen may have been eaten intentionally, but Otzi probably swallowed most of it accidentally, either in the course of eating a meal or by inhalation. 

For example, chemicals that enter the digestive tract must be absorbed by the cells lining the small intestine and then be transferred through the cells, where the chemical can then be absorbed by the capillary cells into the bloodstream. Chemicals that are inhaled must pass through the alveoli, the cells of the lungs, to get to the capillaries and enter the bloodstream. 

---