Gastrointestinal tract calcium

Soluble Compounds. The mechanism of barium toxicity is related to its ability to substitute for calcium in muscle contraction. Toxicity results from stimulation of smooth muscles of the gastrointestinal tract, the cardiac muscle, and the voluntary muscles, resulting in paralysis (47). Skeletal, arterial, intestinal, and bronchial muscle all seem to be affected by barium. 

Calcium chloride solutions, typically employed at 2—5% concentration, are used as antispasmodics, diuretics (qv), and in the treatment of tetany. Concentrated solutions of calcium chloride cause erythema, exfoUation, ulceration, and scarring of the skin (39). Injections into the tissue may cause necrosis. If given orally calcium chloride can cause irrita tion to the gastrointestinal tract unless accompanied by a demulcent. There is no pubHshed information on mutagenicity or carcinogenicity caused by calcium ions or calcium chloride. Calcium chloride has been given a toxicity or hazard level 3 (40). Materials in this classification typically have LD q below 400 mg/kg or an LC q below 100 ppm. 

Gastrointestinal absorption of lead is influenced by dietary and nutritional calcium and iron status. An inverse relationship has been observed between dietary calcium intake and PbB concentration (Mahaffey et al. 1986 Ziegler et al. 1978). Complexation with calcium (and phosphate) in the gastrointestinal tract and competition for a common transport protein have been proposed as possible mechanisms for this interaction (Barton et al. 1978a Heard and Chamberlain 1982). Absorption of lead from the... 

The final mechanism of action of PTH involves the activation of vitamin D3 through the stimulation of la-hydroxylase in the kidney. In the gastrointestinal tract, vitamin D3 is essential for the absorption of calcium. Enhanced absorption of calcium from dietary sources serves to further increase the concentration of calcium in the blood. Many foods, in particular, dairy products, which are rich in calcium, are fortified with vitamin D. The release of PTH from the parathyroid glands is regulated by plasma calcium levels through negative feedback. A decrease in the level of calcium in the blood stimulates the secretion of PTH and an increase in the calcium level in the blood inhibits it. 

Inorganic compounds such as aluminium hydroxide, sodium bicarbonate, and magnesium and calcium carbonates are commonly used as antacids. There is much scope for the redesign of these agents to achieve fine control of local pH values in the gastrointestinal tract via control of the rate of release of the active bases (e.g., from insoluble compounds). 

Meat and such high protein plant foods as soy are excellent sources of phosphorus as well as protein. The phosphorus in meat is readily absorbed from the gastrointestinal tract however, much of the phosphorus in plant products is in a bound form which may inhibit the absorption of calcium as well as phosphorus. This study was designed to determine the effect of different levels of calcium and phosphorus with plant protein or animal protein on bone breaking strength and calcium and phosphorus utilization of weanling mice. 

Bile acids and salts have been found to enhance the absorption of both calcium and vitamin D hence, to increase calcium absorption both directly and indirectly (3,37). However, the ability of some dietary fibers such as lignin and pectin to absorb conjugated and deconjugated bile salts onto their surfaces to be excreted in the feces (a mechanism credited to the hypocholesterolemic effect of some dietary fibers) may result in an overall decrease in calcium absorption from the gastrointestinal tract (7,33,38-40). 

Interest in the possible connection between intake of fat and absorption of calcium was generated by the concurrent massive losses of calcium in patients with steatorrhea, fatty diarrhea (46, 47). Ordinarily, however, fat is very efficiently absorbed from the gastrointestinal tract. Results of several studies in human adults and children indicate little or no effect of level of dietary fat on absorption of calcium (48-54). However, influence of level of dietary fat on calcium absorption in rat studies has produced conflicting results (55-57). 

Human food, both plant and animal, usually contains satisfactory amounts of zinc to cover the requirement for this metal, which is present within the range of few to several pg per g of product. Zinc deficiencies are usually caused by a reduction of its absorption in the gastrointestinal tract rather than by its lack. Reduction in absorption may be caused by antagonistic activity of cadmium, calcium or phytates. A decrease in assimilation of zinc is also observed among alcoholics. 

Absorption from the gastrointestinal tract can be affected by other drugs and by food. Aluminum, calcium, and magnesium ions in antacids or dairy products form insoluble chelates with all tetracyclines and inhibit their absorption. Food inhibits tetracycline absorption but enhances doxycycline absorption food delays but does not diminish metronidazole absorption fatty food enhances griseofulvin absorption. 

These antibiotics are partially absorbed from the stomach and upper gastrointestinal tract. Food impairs absorption of all tetracyclines except doxycycline and minocycline. Absorption of doxycycline and minocy-cbne is improved with food. Since the tetracyclines form insoluble chelates with calcium (such as are found in many antacids), magnesium, and other metal ions, their simultaneous administration with milk (calcium), magnesium hydroxide, aluminum hydroxide, or iron will interfere with absorption. Because some of the tetracyclines are not completely absorbed, any drug remaining in the intestine may inhibit sensitive intestinal microorganisms and alter the normal intestinal flora. 

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. 

Other portions of the gastrointestinal tract can also be injured. Chronic alcohol ingestion is by far the most common cause of chronic pancreatitis in the Western world. In addition to its direct toxic effect on pancreatic acinar cells, alcohol alters pancreatic epithelial permeability and promotes the formation of protein plugs and calcium carbonate-containing stones. 

In food-producing animals, tetracyclines can be administered orally through feed or drinking water, parenterally, or by intramammary infusion. However, oral administration suppresses initially die ruminal fermentation of plant fiber. The absorption of tetracyclines can be further adversely affected by the presence of metallic ions in the gastrointestinal tract. All tetracyclines have an affinity for metallic ions and should not be administered with milk or high calcium levels in feed unless an upward adjustment in the dosage is made (226-228). 

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