Correction.Nutrition & Dietetics 2003;60 Continuing education, pages 266-7 3. Which of the following proteins and peptides is integral to the process of calcium absorption? a. calcitriol b. calmodulin calmodulin /cal·mod·u·lin/ (kal-mod´u-lin) a calcium-binding protein present in all nucleated cells; it mediates a variety of cellular reponses to calcium. cal·mod·u·lin n. c. calbindin d. calcitonin calcitonin /cal·ci·to·nin/ (-to´nin) a polypeptide hormone secreted by C cells of the thyroid gland, and sometimes of the thymus and parathyroids, which lowers calcium and phosphate concentration in plasma and inhibits bone resorption. 3 c Calcitriol or 1.25-dihydroxyvitamin D is the active form of vitamin D. Calcitriol together with parathyroid hormone (PTH) regulates plasma calcium concentrations by interacting at three major sites; the small intestine, bone and kidneys. Hypocalcaemia Noun 1. hypocalcaemia - abnormally low level of calcium in the blood; associated with hypoparathyroidism or kidney malfunction or vitamin D deficiency hypocalcemia triggers secretion of PTH which in turn stimulates synthesis of calcitriol in the kidney. Calcitriol interacts with receptors in the enterocyte enterocyte the predominant cells in the small intestinal mucosa. They are tall columnar cells and responsible for the final digestion and absorption of nutrients, electrolytes and water. and upregulates the synthesis of calcium-binding protein, calbindin, which facilitates absorption of calcium. PTH and calcitriol also act on bone to mobilise calcium, and in the distal renal tubule, to stimulate calcium reabsorption reabsorption /re·ab·sorp·tion/ (re?ab-sorp´shun) 1. the act or process of absorbing again, as the absorption by the kidneys of substances (glucose, proteins, sodium, etc.) already secreted into the renal tubules. 2. . When calcium concentrations begin to rise above normal, calcitonin is released from the thyroid gland and acts rapidly to promote deposition of calcium in bone, thereby restoring calcium levels. The concentration of plasma calcium is therefore tightly regulated, reflecting the critical role of ionised calcium in muscle contraction. Hypocalcaemia results in tetany tetany (tĕt`ənē), condition of mineral imbalance in the body that results in severe muscle spasms. Tetany occurs when the concentration of calcium ions (Ca++) in extracellular fluids such as plasma falls below normal. due to increased neuromuscular excitability, while hypercalcaemia results in depressed neuromuscular excitability with cardiac arrhythmias and muscular weakness. Calmodulin, a calcium-binding peptide regulates many calcium dependent enzymes (1). |
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