Calcium and Phosphate PDF

Calcium and Phosphate Select this paragraph to edit  Calcium Calcium is the most abundant mineral in the human body. the average adult body contains approximately 25 000 mmol (1 kg), of which 99% is bound in the skeleton. the total calcium content of the extrace...

Calcium and Phosphate Select this paragraph to edit  Calcium Calcium is the most abundant mineral in the human body. the average adult body contains approximately 25 000 mmol (1 kg), of which 99% is bound in the skeleton. the total calcium content of the extracellular fluid (ECF) is only 22.5 mmol, of which about 9 mmol is in the plasma. Cont. …. most of the calcium in bone is stable. In the kidneys, ionized calcium is filtered by the glomeruli (240 mmol/24 h).  Select this paragraph to edit Daily calcium fluxes in the body. Calcium functions Function Example Structural Bone Teeth Neuromuscular Control of excitability Release of neurotransmitter Initiation of muscle contraction Enzymic Co-enzyme of coagulation factors Signaling Intracellular second messenger Calcium-Regulating Hormones two hormones: parathyroid hormone (PTH) calcitriol (1,25- dihydroxycholecalciferol). Calcitonin probably has only a minor role in calcium homoeostasis. Parathyroid hormone PTH is secreted by the parathyroid glands in response to a fall in plasma (ionized) calcium concentration, and secretion is inhibited by hypercalcemia. these effects are mediated by the calcium-sensing receptor (CaSR). Cont. …… Calcitriol inhibits PTH synthesis. PTH acts on bone and kidneys, tending to increase the plasma concentration of calcium and reduce that of phosphate. Action of PTH Calcitriol this hormone is derived from vitamin D. the principal actions of calcitriol are: Gut: it stimulates absorption of dietary calcium and phosphate. Bone: promotes mineralization largely, through its role in the maintenance of ECF calcium and phosphate concentrations. Kidneys: calcitriol inhibits its own synthesis.  Select this paragraph to edit Calcitriol: principal actions and control of renal synthesis.  Calcium and Phosphate Homoeostasis Hypocalcaemia stimulates the secretion of PTH, which in turn increases the production of calcitriol. there is an increase in the uptake of both calcium and phosphate from the gut, and in their release from bone. Cont. …… PTH is phosphaturic, so the excess phosphate is excreted, but the fractional reabsorption of calcium by the kidney is increased, some of the mobilized calcium is retained and the plasma calcium concentration tends to rise towards normal.  Select this paragraph to edit Homoeostatic responses to hypocalcaemia. Cont. …… in hypophosphatemia, calcitriol secretion is increased but PTH is not. indeed, any tendency for calcitriol to increase the plasma calcium concentration should inhibit PTH secretion. Calcium and phosphate absorption from the gut are stimulated.  Select this paragraph to edit Homoeostatic responses in hypophosphatemia Causes of hypercalcemia two conditions account for up to 90% of cases: primary hyperparathyroidism malignancy. Select this paragraph to edit Select this paragraph to edit Investigation investigated is dependent on the clinical setting. the plasma phosphate concentration is of limited diagnostic value. plasma alkaline phosphatase activity can be elevated in either condition. Cont. …… Radiographic examination may occasionally reveal the characteristic subperiosteal bone reabsorption and bone cysts of hyperparathyroidism. measuremeis nt of PTH, using an assay for the intact hormone, essential.  Hypocalcaemia Causes  Artefactual (collection of blood in EDTA tube)  Associated with low PTH : Hypoparathyrodism. Hypomagnesaemia. Hungry bone syndrome. Neonatal hypocalcaemia. Cont. …… Associated with high PTH: Vit D deficiency(malabsorption Disorder vit D metabolism(renal impairment) Pseudohypoparathyrodism. Acute pancreatitis High phosphate intake(rare) Massive blood transfusion with citrate blood Acute rhabdomyolysis. Clinical features: behavior disturbance and stupor numbness and paresthesia muscle cramps and spasms (tetany) laryngeal stridor convulsions cataracts (chronic hypocalcaemia) basal ganglia calcification (chronic hypocalcaemia) papilleodema Cont. …… Chvostek’s sign (contraction of facial muscles on tapping facial nerve) Trousseau’s sign (carpal spasm when sphygmomanometer cuff applied to upper arm is inflated to midway between systolic and diastolic blood pressures for 3 min) may be positive before other signs are present (latent tetany). prolonged QT wave in ECG.  Hyperphosphataemia Causes i. Renal impairment. ii. Hypoparathyrodism and psedohypoparathyrodism iii. Acromegaly iv. Excessive phosphate intake/administration v. Vit D intoxication vi. Catabolic state eg, tumor lysis syndrome vii. Artefactual: delay separation or hemolysis  Hypophosphataemia this is a common biochemical finding. severe hypophosphataemia (