Gastrointestinal mucosa

Hookworm infection is caused by Ancylostoma duodenale or Necator americanus. N. americanus is found in the southeastern United States. Infective larvae enter the host in contaminated food or water or penetrate the skin and migrate to the small intestine. The adult worm attaches to gastrointestinal mucosa and causes injury by lytic destruction of the tissue. Over a period of time, the adult worm can cause anemia and hypopro-teinemia in the host. 

Aphthous ulcer A small superficial area of ulceration within the gastrointestinal mucosa, typically found in the oral cavity. 

Pseudopolyp An area of hypertrophied gastrointestinal mucosa that resembles a polyp and contains nonmalignant cells. 

The anti-ulcer agents omeprazole, lanzoprazole, and pantoprazole have been introduced during the past decade for the treatment of peptic ulcers. Gastric acid secretion is efficiently reduced by prazole inhibition of H+K+-ATPase in the parietal cells of the gastrointestinal mucosa [75]. The prazoles themselves are not active inhibitors of the enzyme, but are transformed to cyclic sulfenamides in the intracellular acidic compartment of parietal cells [76]. The active inhibitors are permanent cations at pH < 4, with limited possibilities of leaving the parietal cells, and thus are retained and activated at the site of action. In the neutral body compartments the prazoles are stable, and only trace amounts are converted to the active drugs. (For a review on omeprazole, see Ref. [77].)... 

Absorption. Absorption of cyanide across the gastrointestinal mucosa depends on the pH of the gut and the pKa and lipid solubility of the particular cyanide compound. Hydrogen cyanide is a weak acid with a pKa of 9.2 at 25 °C. The acidic environment in the stomach favors the non-ionized form of hydrogen cyanide and facilitates absorption. Information regarding the rapid lethal effects following oral intake of cyanide in humans (Gosselin et al. 1976) indicates that cyanide is rapidly absorbed from the gastrointestinal tract. 

Back DJ, Rogers SM (1987) First-pass metabolism by gastrointestinal mucosa. Aliment Pharmacol Ther 1 339-357. 

Mason KA, Milas L, Peters LJ. Effect of paclitaxel (taxol) alone and in combination with radiation on the gastrointestinal mucosa. Int J Radiat Oncol Biol Phys 1995 32(5) 1381-1389. 

In most organs and tissues the injury and the underlying mechanism for that injury are complex and may involve a combination of events. The extent and severity of this tissue injury are dependent upon the radiosensitivity of the various cell types in that organ system. Rubin and Casarett (1968) describe and schematically display the events following radiation in several organ system types. These include a rapid renewal system, such as the gastrointestinal mucosa a slow renewal system, such as the pulmonary epithelium and a nonrenewal system, such as neural or muscle tissue. In the... 

Fig. 1. Folate-cobalamin interaction in the synthesis of purines and pyrimidines and, therefore, of DNA. (1) In gastrointestinal mucosa cells (2) in the liver (3) in peripheral tissues. C, cobalamine DAC, desoxyadenosylcobalamine HC, hydroxy cobalamine MC, methylcobalamine F, folic acid MTHF, methyltetrahydrofolic acid THF, tetrahydrofolic acid DHF, dihydrofolic acid dUMP, deoxyuridinemonophosphate dTMP, deoxythymidine-monophosphate. (Adapted from Far-...

Absorption after oral administration is incomplete and variable. Its bioavailability ranges from 20% to 50%. Cyclosporine can also be given intravenously. Plasma protein binding is about 90% and cyclosporine also accumulates in red blood cells. It is extensively metabolized in the gastrointestinal mucosa and in the liver by the cytochrome P450-enzyme system. Its elimination half-life is about 19 hours in adults with a range of 10-27 hours and about 9 hours in children with a range of 3-19 hours. Over 30 different metabolites have been... 

A combination of neomycin and nonabsorbable erythromycin base given orally prior to colorectal surgery can markedly reduce the incidence of postoperative wound infection. Orally administered neomycin is sometimes used to suppress the facultative flora of the gut in patients with hepatic encephalopathy. It is unclear how this improves coma, but one theory is that it reduces systemic absorption of the bacterial metabo-htes that allegedly cause hepatic encephalopathy. Although more than 95% of an oral dose of neomycin is excreted unchanged in the stool of normal subjects, the bioavaUabUity of neomycin may be much higher in patients with an abnormal gastrointestinal mucosa. 

Guadalupe M, Sankaran S, George MD et al (2006) Viral suppression and immune restoration in the gastrointestinal mucosa of human immunodeficiency virus type 1-infected patients initiating therapy during primary or chronic infection. J Virol 16 8236-8247... 

Aldosterone and other steroids with mineralocorticoid properties promote the reabsorption of sodium from the distal part of the distal convoluted tubule and from the cortical collecting renal tubules, loosely coupled to the excretion of potassium and hydrogen ion. Sodium reabsorption in the sweat and salivary glands, gastrointestinal mucosa, and across cell membranes in general is also increased. Excessive levels of aldosterone produced by tumors or overdosage with synthetic mineralocorticoids lead to hypokalemia, metabolic alkalosis, increased plasma volume, and hypertension. 

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