CHP 19 (552-553)
Ca triggers exocytosis of chemical messengers, stimulates secretion of substances, stimulates muscle
contractions, and increases the contractility of the heart and blood vessels. Important for bones.
Hypercalcemia results with muscle weakness, atrophy, lethargy, behavioral changes, hypertension, sontipatino,
Hypocalcemia causes numbness and tingling sensations, muscle cramps and spasms, exaggerated reflexes and
Ca can be added to the plasma from bone and absorbed via the digestive tract. It can be removed from the
plasma by bone and the kidneys.
The bone provides a reservoir of Ca through resorption. When plasma Ca levels are high, Ca can be deposited
RENAL HANDLING OF CA IONS
Ca is transported in blood by carrier proteins or is free in the plasma. Ca that is free in the plasma is freely
filtered at the glomerulus.
99% of filtered Ca is reabsorbed as the tubular fluid moves through the renal tubules.
70% of Ca is reabsorbed in the proximal tubules, 20% in the thick ascending limbs of the loops of Henle, and
10% in the distal tubules.
HORMONAL CONTROL OF PLASMA CA CONCENTRATIONS
EFFECTS OF PARATHYROID HORMONE
o PTH is a peptide hormone produced in the parathyroid glands and secreted in response to a decrease in
o It stimulates Ca reabsorption in the ascending lum