Calcium secretion

The RUA for calcium in adults over the age of 24 is 0.8 g. The RIM for w omcn during pregnancy and lactation is 1.2 g. The increased level of 1.2 g is required to supply the fetus with the 30 g of calcium present in the newborn and to provide the 0.24 g ol calcium secreted in the milk each day. The RDA for persons from 11 to 24 years of age is 1,2 g the Rl3As for children (0.8 g) and infanta (0.6 g) are lower. Eggs supply about 30% of dietary calcium and 30% of dietary phosphate for the overall population in the United States. Meat, poultry, and ifish supply 20-257n of our phosphate, but only 107q of our calcium. Milk and dairy products supply 20-25"n of our phosphate, and 50% of our calcium (Calvo and Park, 1996), A dietary deficiency in calcium is quite rare, though calcium nutririon receives much attention because of mainstream health concerns related to calcium, such as osteoporosis, hypercalcemia, and hypocalcemia. 

Hedley, R.H., 1956b. Studies on serpulid tube formation. II. The calcium secreting glands in the peristomium of Spirorbis, Hydroides and Serpula. Q. J. Microsc. Sci., 97 421— 427. 

The observation of fecal excretion of radioactive strontium of weeks to decades after an oral exposure or over shorter time periods after an intravenous exposure suggests the existence of a mechanism for transfer of absorbed strontium into gastrointestinal tract, either from the bile or directly from the plasma. Evidence for direct secretion of strontium from the plasma into the intestine is provided by studies conducted with the in situ lumen-perfused rat intestine. When the lumen of either the small or large intestine was perfused (below the entrance of the bile duct), in situ and radioactive strontium was injected intravenously, radioactive strontium was detected in the lumen, indicating that strontium was secreted from blood into the intestine (Palmer and Thompson 1961). The amount of strontium secreted into the small intestine was approximately 4-8 times that in the large intestine however, the strontium calcium secretion ratio was approximately 1 in the small intestine and 1.3 in the large intestine. The mechanism by which strontium is secreted into the intestine has not been determined. Transfer of strontium from the serosal (blood) side of the intestinal epithelium to the mucosal (lumen) side of the epithelium has been demonstrated in in vitro preparations of isolated rat colon mucosa. Serosal-to-mucosal transfer was observed to be completely... 

It is now clear that the vitamin D endocrine system is a major factor in the control of plasma calcium and the overall calcium economy of terrestial vertebrates The parathyroid glands monitor calcium concentration of the plasma (Fig. 5) and in response to low blood calcium secrete the parathyroid hormone Parathyroid hormone is taken up by the kidney and bone In the kidney, parathyroid hormone stimulates production of 1,25-(OH)2D3 The 1,25 (OH)2D3 then... 

A Thiery Vella fistula was made of the entire colon, the distal part of the ileum was anastomosed with the rectum. The reduced intestinal tract was found to give just as much fecal calcium as the intact one. Again Ca injections were followed by extra increase of Ca in the urine, but not in the feces. Rich calcium diet and the injections of calcium produced no measurable amount of calcium secretion into the colon. 

C call (parafollicular cell) Anyone of a group of calcium-secreting cells in vertebrates that are derived from the terminal pair of gill pouches. In mammals these cells are incorporated into the thyroid gland and the parathyroid gland. 

This problem, however, is far from being fully defined and we still need to know much more about the effect of bile acids on biliary calcium secretion and about the solubility of calcium salts in bile during cholelitholytic treatment. 

Other Calcium Disorders. In addition to hypocalcemia, tremors, osteoporosis, and muscle spasms (tetary), calcium deficiency can lead to rickets, osteomalacia, and possibly heart disease. These, as well as Paget s disease, can also result from faulty utilization of calcium. Calcium excess can lead to excess secretion of calcitonin, possible calcification of soft tissues, and kidney stones when combined with magnesium deficiency. 

The main role of the human thyroid gland is production of thyroid hormones (iodinated amino acids), essential for adequate growth, development, and energy metaboHsm (1 6). Thyroid underfunction is an occurrence that can be treated successfully with thyroid preparations. In addition, the thyroid secretes calcitonin (also known as thyrocalcitonin), a polypeptide that lowers excessively high calcium blood levels. Thyroid hyperfunction, another important clinical entity, can be corrected by treatment with a variety of substances known as antithyroid dmgs. 

Calcitonin is secreted when abnormally high calcium levels occur in plasma. Although plasma concentrations are normally minute (<100 pg/mL), they increase two- to threefold after calcium infusion. Calcitonin has a short plasma half-life (ca 10 min). Certain thyroid tumors are the result of CT concentrations 50—500 times normal. The mechanism of action is a direct inhibition of bone resorption. Calcitonin is used clinically in various diseases in which hypercalcemia is present, eg, Paget s disease (46). 

Although it is being found that vitamin D metaboUtes play a role ia many different biological functions, metaboHsm primarily occurs to maintain the calcium homeostasis of the body. When calcium semm levels fall below the normal range, 1 a,25-dihydroxy-vitainin is made when calcium levels are at or above this level, 24,25-dihydroxycholecalciferol is made, and 1 a-hydroxylase activity is discontiaued. The calcium homeostasis mechanism iavolves a hypocalcemic stimulus, which iaduces the secretion of parathyroid hormone. This causes phosphate diuresis ia the kidney, which stimulates the 1 a-hydroxylase activity and causes the hydroxylation of 25-hydroxy-vitamin D to 1 a,25-dihydroxycholecalciferol. Parathyroid hormone and 1,25-dihydroxycholecalciferol act at the bone site cooperatively to stimulate calcium mobilization from the bone (see Hormones). Calcium blood levels are also iafluenced by the effects of the metaboUte on intestinal absorption and renal resorption. 

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

The above series of alcohols are exceedingly difficult to manufacture, hence their expense. The general method of their preparation would theoretically be by distilling the calcium salts of the corresponding fatty acid with calcium formate, in vacuo. This would yield the corresponding aldehyde, which on reduction would yield the corresponding alcohol. In practice, however, many technical difficulties arise, and special processes have to be used which are kept carefully as trade secrets. 

PTH is the most important regulator of bone remodelling and calcium homeostasis. PTH is an 84-amino acid polypeptide and is secreted by the parathyroid glands in response to reductions in blood levels of ionised calcium. The primary physiological effect of PTH is to increase serum calcium. To this aim, PTH acts on the kidney to decrease urine calcium, increase mine phosphate, and increase the conversion of 25-OH-vitamin D to l,25-(OH)2-vitamin D. PTH acts on bone acutely to increase bone resorption and thus release skeletal calcium into the circulation. However, due to the coupling of bone resorption and bone formation, the longer-term effect of increased PTH secretion is to increase both bone resorption and bone formation. 

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

PTH has a dual effect on bone cells, depending on the temporal mode of administration given intermittently, PTH stimulates osteoblast activity and leads to substantial increases in bone density. In contrast, when given (or secreted) continuously, PTH stimulates osteoclast-mediated bone resorption and suppresses osteoblast activity. Further to its direct effects on bone cells, PTH also enhances renal calcium re-absorption and phosphate clearance, as well as renal synthesis of 1,25-dihydroxy vitamin D. Both PTH and 1,25-dihydroxyvitamin D act synergistically on bone to increase serum calcium levels and are closely involved in the regulation of the calcium/phosphate balance. The anabolic effects of PTH on osteoblasts are probably both direct and indirect via growth factors such as IGF-1 and TGF 3. The multiple signal transduction... 

Oral calcium has long been used for the treatment of osteoporosis, both in the form of dietary and pharmacological supplements. In patients with calcium deficiency, oral calcium at doses of 1000-1500 mg/day corrects a negative calcium balance and suppresses PTH secretion. Sufficient calcium intake is most important for the acciual of peak bone mass in the young, but is also considered the basis of most anti-osteoporotic regimens. In the elderly, supplementation with oral calcium and vitamin D reduces the risk of hip fracture by about 30 4-0%. 

The CaR regulates numerous biological processes, including the expression of various genes (e.g., PTH) the secretion of hormones (PTH and calcitonin), cytokines (MCP-1), and calcium (e.g., into breast milk) the activities of channels (potassium channels) and transporters (aquaporin-2) cellular shape, motility (of macrophages), and migration cellular adhesion (of hematopoietic stem cells) and cellular proliferation (of colonocytes), differentiation (of keratinocytes), and apoptosis (of H-500 ley dig cancer cells) [3]. 

More recent analysis of tissue specific gene deletions showed that the Cav1.2 channel is involved in a wide variety of function including hippocampal learning, insulin secretion, intestine and bladder motility. Further analysis will be required to unravel the functional significance of voltage-dependent calcium channels for specific cellular functions. 

Nerve growth factor snake venoms zinc, 6, 613 Neurospora crassa calcium transport, 6, 571 cation transport, 6, 559 Neurosporin, 6, 676 Neurotransmitters secretion calcium, 6, 595 Neutral complexes electrical properties, 6, 143 Neutron absorbers... 

Neutrophils represent an ideal system for studying osmotic effects on exocytosis. Stimulation of cytochalasin-B-treated neutrophils with the chemotactic peptide Jlf-formylmethionyl-leucyl-phenyl-alanine (FMLP) results in a rapid compound exocytosis up to 80% of lysosomal enzymes are released within 30 s (9-14). Secretion appears to be triggered by a rise in the level of cytosolic free calcium (15-18) promoted in part by entry of extracellular calcium through receptor-gated channels and in part by release of calcium that is sequestered or bound at some intracellular site (19-21). In this presentation, we augment our previously published data (22,23), which demonstrates that lysosomal enzyme release from neutrophils is inhibited under hyperosmotic conditions and that the rise in cytosolic calcium preceding secretion is inhibited as well. 

Liu PS, Kao LS, Lin MK. 1994. Organophosphates inhibit catecholamine secretion and calcium influx in bovine adrenal chromaffin cell. Toxicology 90 81-91. 

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