This document discusses calcium regulating hormones and homeostasis. It outlines the physiological roles of calcium and phosphate. The key tissues involved in calcium regulation are the intestine, kidney, and bone. The major hormones that regulate calcium levels are parathyroid hormone (PTH), vitamin D, and calcitonin. PTH increases calcium reabsorption in the kidneys and intestine and signals bone resorption to elevate calcium levels when they decrease in the blood.

1. Calcium Regulating Hormones
By Dr.Sara Sadiq

2. Physiological Action Of Calcium
• Maintenance of normal Na permeability in nerves
• Release of acetylcholine from nerve ending at
neuromuscular junction
• Excitation-contraction coupling in muscle cells
• Intracellular signal for some hormones
• Required by some enzymes for normal activity
• Required for protein secretion
• Required for blood clotting
• Constituent of bone

3. Distribution of calcium

4. Physiological Action Of Phosphate
• Intracellular buffer system
• Important constituent of macromolecules
Nucleic acid
Phospholipids
Phosphoproteins
• Constituent of bone

5. Distribution of phosphate

6. Tissues involved in Calcium
regulation in blood
• Intestine
• Kidney
• Bone

7. Hormones Involved In
Calcium Regulation In
Blood
PTHVit: DCalcitonin

8. Calcium Homeostasis

10. PTH
• Provides a powerful mechanism for controlling extracellular
calcium and phosphate concentrations by regulating
intestinal reabsorption,
renal excretion
exchange between extracellular fluid and bone of
these ions.
• Excess activity of parathyroid gland causes rapid absorption
of calcium salts from the bones with resultant hypercalcemia
in the ECF.

13. PTH effect on kidneys
• PTH increases renal tubular reabsorption of calcium,
mainly in late distal tubules, collecting tubules, the early
collecting ducts and possibly the ascending loop of Henle
to a lesser extent.
• Causes rapid loss of phosphate in the urine as it
diminishes proximal tubular reabsorption of phosphate
ions.

15. PTH effect on intestine
• PTH greatly enhances both calcium and phosphate
absorption from intestines by increasing the
formation of 1,25 dihdroxycholecalciferol from
Vitamin D in the kidney.
• cAMP mediates the effects of PTH.

16. PTH
PTH administration
↑ conc. of CAMP in osteocytes and osteoclasts
Osteoclastic secretion of enzymes and acids to cause bone
resorption and formation of 1,25 dihydroxycholecalciferol in
kidneys

17. Activation of osteoclasts
• Occurs in two stages:
• 1) immediate activation of osteoclasts that are
already formed and
• 2) formation of new osteoclasts

18. Control of parathyroid secretion
decrease in Ca + conc.in ECF
PTH secretion increases
Parathyroid gland hypertrophy occurs in:
• Rickets,
• pregnancy,
• lactation