Gastrointestinal tract structure

Because of die wide distribution of parasympadietic nerves, tiiese drugs affect many organs and structures of die body, including the eyes, die respiratory and gastrointestinal tracts, the heart, and the bladder (see Display 25-1). 

These studies represent the first report of the metabolism of brevetoxins by mammalian systems. PbTx-3 was rapidly cleared from the bloodstream and distributed to the liver, muscle, and gastrointestinal tract. Studies with isolated perfused livers and isolated hepatocytes conflrmed the liver as a site of metabolism and biliary excretion as an important route of toxin elimination. [ H]PbTx-3 was metabolized to several compounds exhibiting increased polarity, one of which appeared to be an epoxide derivative. Whether this compound corresponds to PbTx-6 (the 27,28 epoxide of PbTx-2), to the corresponding epoxide of PbTx-3, or to another structure is unknown. The structures of these metabolites are currently under investigation. 

Milieu conditions in gastrointestinal tract can influence the pectin structure and properties. Under the acid conditions of the stomach (pH 2-4) extraction of pectin from plant cell walls and hydrolysis of side chains can occur. In small intestine (pH 5-6) -elimination of main chains or de-esterification seems to be possible. In caecum and colon (pH 6-8) a strong fermentation of pectin takes place causing depolymerization to oligomers and leading to formation of short chain fatty acids and gases. The presence of OligoGalA is not yet clarified. 

Irritable bowel syndrome (IBS) is a disorder of the gastrointestinal tract that interferes with the normal functions of the colon. At various points in the past, IBS has been referred to as mucous colitis, spastic colon, irritable colon, or nervous stomach. IBS is generally described as afunctional disorder rather than a disease per se. A functional disorder involves symptoms that cannot be attributed to a specific injury, infection, or other physical problem. A functional disorder occurs because of altered physiologic processes rather than structural or biochemical defects and may be subject to nervous system influence. IBS is associated with frequent fluctuation in symptoms, loss of productivity, and decreased quality of life. Although IBS has been referred to as functional bowel disease, true functional bowel disease may be more indicative of widespread gastrointestinal involvement including (but not limited to) the colon. 

Basophils are the least abundant of the leukocytes and account for less than 1% of the total number of white blood cells. They are similar structurally and functionally to the mast cells found in connective tissues, especially in the lungs, skin, and gastrointestinal tract. Basophils and mast cells play an important role in allergic reactions. The granules of these cells contain many substances, including ... 

Smooth muscle is distributed throughout the body, largely around hollow structures such as blood vessels, the gastrointestinal tract and the genitourinary system. Normal function requires that the smooth muscles contract and relax at appropriate times, and abnormalities of contraction underlie such important pathologies as hypertension, incontinence and abnormal childbirth. Since contraction is initiated by an increase of cytoplasmic Ca2+ concentration then normal function requires appropriate Ca2+ handling. 

In this section several recently published studies on the interaction of nonionic surfactants with a variety of biological systems, including enzymes, bacteria, erythrocytes, leukocytes, membrane proteins, low density lipoproteins and membranes controlling absorption from the gastrointestinal tract, nasal and rectal cavities, will be assessed. This is a selective account, work having been reviewed that throws light on structure-activity relationships and on mechanisms of surfactant action. 

After oral administration, paracetamol is completely absorbed from the gastrointestinal tract with peak plasma concentrations being reached in less than an hour. The drug is eliminated by conjugation with glucoronic acid in the liver. The chemical structure is liable to oxidation. 

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