In blood, most phosphate exists in the ionized form of phosphoric acid, which is called inorganic phosphate (Pi). calcium phosphate . Start studying Calcium and phosphate regulation. Calcitriol regulates the levels of calcium and phosphorus in the blood and helps maintain a healthy skeletal system. The maintenance of calcium and phosphate homeostasis involves intestinal, bone, and renal handling of these ions. Vitamin D, calcium or phosphate deficiency can cause weak bones or rickets. Hypocalcemia refers to low blood calcium concentration. Mechanistically, parathyroid hormone preserves blood calcium by several major effects: Vitamin D acts also to increase blood concentrations of calcium. In these patients the CaSR fails to appropriately inhibit PTH secretion in response to high blood levels of Ca++. The structure, synthesis, and secretion of these two hormones and their receptors will be discussed first. It makes up, together with phosphate, the main strength in the bones. What percentage of Phosphate is protein bound? Because soft tissues contain 10-fold more Pi than Ca++, tissue damage (e.g., crush injury with massive muscle cell death) can result in hyperphosphatemia, whereupon the increased Pi complexes with Ca++ to cause acute hypocalcemia. Figure 39-5 Biosynthesis of 1,25-dihydroxyvitamin D. Vitamin D3 (also called cholecalciferol) is synthesized via the conversion of 7-dehydrocholesterol by ultraviolet B light (UVB) in the more basal layers of the skin (Fig. Either too little Ca++ (hypocalcemia; total serum [Ca++] below 8.5 mg/dL [4.2 mEq/L]) or too much Ca++ (hypercalcemia; total serum [Ca++] above 10.5 mg/dL [5.2 mEq/L]) in blood can lead to a broad range of pathophysiological changes, including neuromuscular dysfunction, central nervous system dysfunction, renal insufficiency, calcification of soft tissue, and skeletal pathology. 39-3). Title: Calcium and Phosphate regulation 1 Calcium and Phosphate regulation. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), on Hormonal Regulation of Calcium and Phosphate Metabolism, CRUCIAL ROLES OF CALCIUM AND PHOSPHATE IN CELLULAR PHYSIOLOGY, Calcium is an essential dietary element. Calcium and Phosphate levels are regulated through the coordinated action of three hormonal systems that include Vitamin D, Parathyroid Hormone (PTH), and Calcitonin. IUPAC names . It is secreted in response to hypercalcemia and has at least two effects: Although calcitonin has significant calcium-lowing effects in some species, it appears to have a minimal influence on blood calcium levels in humans. Thus, the signaling pathway that is activated by binding of Ca++ to the CaSR ultimately leads to repression of PTH gene expression and synthesis. C alcium (Ca ++) and phosphate are essential to human life because they play important structural roles in hard tissues (i.e., bones and teeth) and important regulatory roles in metabolic and signaling pathways. The 30 amino acids at the N-terminus of PTHrP have significant structural homology with PTH. For kidney tubules, PTH and FGF23 are the key regulators for the transport of calcium and phosphate (1,5,10). Calcium is vital for several biological processes including neurotransmission, muscle contraction, hormone secretion and blood coagulation. In addition to obtaining Ca++ from the diet, humans contain a vast store (i.e., > 1 kg) of Ca++ in their bones, which can be called on to maintain normal circulating levels of Ca++ in times of dietary restriction and during the increased demands of pregnancy and nursing. Other . Regulation of Calcium, Magnesium, and Phosphate Metabolism Murray J. Favus,1 David A. Bushinsky,2 and Jacob Lemann Jr.3 1Section of Endocrinology, University of Chicago, Chicago, Illinois; 2Nephrology Unit, University of Rochester School of Medicine, Rochester, New York; and 3Nephrology Section, Tulane University School of Medicine, New Orleans, Louisiana Phosphoric acid, calcium salt . A 0.2-mEq/L drop in blood [Ca++] produces an increase in circulating PTH levels from basal (5% of maximum) to maximum levels (Fig. The primary processes for removal of Ca++ and Pi from blood are renal excretion and bone formation (Fig. Hypercalcemia, or too much blood calcium, is relatively rare, but lethargy and muscle weakness are among possible symptoms. The normal concentration of calcium and phosphate in blood and extracellular fluid is near the saturation point; elevations can lead to diffuse precipitation of calcium phosphate in tissues, leading to widespread organ dysfunction and damage. Thus, PTHrP binds to and signals through the PTH/PTHrP receptor. As such, they are referred to as calciotropic hormones. Suppression of renal tubular reabsorption of calcium. Circulating Ca++ exists in three forms (Table 39-1): free ionized Ca++, protein-bound Ca++, and Ca++ complexed with anions (e.g., phosphates, HCO3−, citrate). In other words, calcitonin enhances excretion of calcium into urine. CHAPTER 35 Potassium, Calcium, and Phosphate Homeostasis K+ HOMEOSTASIS Potassium (K+) is one of the most abundant cations in the body, and it is critical for many cell functions, including regulation of cell volume, regulation of intracellular pH, synthesis of DNA and protein, growth, enzyme function, resting membrane potential, and cardiac and neuromuscular activity. We first discuss the contributions of each hormone to calcium and phosphate regulation independently and then describe how all three hormones are coordinated in an integrated fashion to achieve stable levels of calcium and phosphate. 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