Prayercard 3 - True Life In God

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Prayercard 3 - True Life In God

under a variety of sometimes less well appreciated circumstances such as neurologic disease,stress, hypotension, sepsis, and protein-calorie malnutrition. An appreciation of themechanisms of acid secretion as well as barrier disruption and repair, therefore, are importantfor most clinicians, as is an understanding of approaches that enhance the repair process.Gastric Acid SecretionThe mammalian stomach is a specialized organ of the digestive tract that serves to store andprocess food for subsequent intestinal absorption. One of its features, considered to be thehallmark of gastric function, is its ability to secrete acid. In most species this is a continuousprocess that varies in intensity in response to a variety of exogenous and endogenous stimuli.In the dog, however, and possibly in the cat, animals that ancestrally, at least, can go for dayswithout eating, acid secretion is more variable, with the distinct possibility that little or nobasal acid secretion occurs in these species.The gastric mucosa consists of a variety of cell types, predominantly mucus-filled tallcolumnar epithelial cells, which form a single protective layer. The secretory unit of thegastric mucosa is the gastric (or oxyntic) gland, of which the normal human stomach has beenestimated to contain approximately one billion. These contain parietal (acid-producing andsecreting) cells, chief (pepsinogen-producing and secreting) cells, mucous neck cells, and avariety of endocrine cells. Mucous neck cells are relatively few in number and are scatteredamong the parietal cells. Parietal cells are located mainly in the isthmus and neck region ofthe gland, whereas chief cells are located at its base. Adjacent to the parietal cells arehistamine-secreting enterochromaffin-like (ECL) cells and somatostatin-secreting "D cells".The surface epithelial cells have a life span of about three days and are replaced by division ofcells just below the opening of the gastric glands. Immediately below the surface epithelialcell layer is a rich network of blood vessels, nerves, and lymphatics supported by a connectivetissue matrix, which collectively form the submucosa.The stomach secretes hydrogen ions, sodium, chloride, pepsinogen, lipase, and varyingquantities of mucus into its lumen. Hydrogen ions are secreted into the lumen of the gastricgland in exchange for potassium by an energy-dependent exchange enzyme in the mucosalsurface of the parietal cell called the hydrogen potassium-adenosine triphosphatase (H + K + -ATPase). During acid secretion, the H + K + -ATPase secretes H + ions into the lumen of thegland in exchange for K + ions, which have previously moved out of the cell down theirconcentration gradient. Simultaneously, chloride ions move from the cell into the lumen downan electrochemical gradient. Water moves out of the cell in response to the subsequentosmotic gradient, to form hydrochloric acid. This acid then flows from the glands throughpores in the overlying mucus, which acts to prevent back-diffusion of acid from the lumen.Acid secretion can be stimulated by the binding of acetylcholine or histamine to specificreceptors in the serosal membrane of the parietal cell. Gastrin, another important stimulus ofacid secretion, is believed to bind to receptors on the ECL cells and to stimulate them torelease histamine. It can, however, also stimulate the parietal cell directly via CCK-B(2)receptor. When gastrin, acetylcholine, or histamine bind with the cell, a variety of secondmessengers are stimulated that increase intracellular cyclic AMP (gastrin and histamine) orcalcium (acetylcholine) concentration. These in turn stimulate acid secretion.Nervous stimulation from the CNS causes release of acetylcholine from the myenteric plexus.This binds with a muscarinic M3 receptor on the parietal cell, which results in an increase in2

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