Calcium homeostasis

Calcium homeostasis

1. In the name of God

2. Calcium Homeostasis

3. Introduction Total plasma [ Ca ++] = 2.5mmol/L Range is 2.0 to 2.5 mmol /L Very tightly controlled Body content Bone intracellular extracellular Calcium 1300 gms 99% 1% 0.1%

4. Within cells, Ca ++ is sequestered in the endoplasmic reticulum and mitochondria, or it is bound to proteins. Approximately 50% of the Ca ++ in plasma is ionized, 45% is bound to plasma proteins (mainly albumin), and 5% is complexed to several anions, including HCO 3 - , citrate, P i , and SO 4 2- . Introduction

5. Factors affecting calcium concentration the plasma albumin concentration pH of plasma

6. Functions of Calcium Nerve and muscle functions Hypocalcemia Hypercalcemia

7. Neurotransmitter release Preserving bone and density important cofactor in many enzymatic reactions cell division and growth Hemostasis Functions of Calcium

8. Calcium Homeostasis Ca ++ homeostasis depends on two factors: 1.the total amount of Ca ++ in the body Total body [ Ca ++ ] is determined by the relative amounts of Ca ++ absorbed by the gastrointestinal tract and excreted by the kidneys 2.the distribution of Ca ++ between bone and ECF Three hormones ( [ PTH], calcitriol , and calcitonin ) regulate the distribution of Ca ++ between bone and ECF and thereby regulate plasma [ Ca ++ ].

9. The CaSR is a receptor expressed in the plasma membrane of cells involved in regulating Ca ++ homeostasis. Activation of the receptor results in inhibition of PTH secretion and calcitriol production and stimulation of calcitonin secretion. Calcium-Sensing Receptor

10. Parathyroid Hormone (PTH)

11. calcitriol

12. Calcitonin

13. Effect of plasma [ Ca ++ ] on plasma levels of PTH and calcitonin

14. Calcium handling in the nephron

15. Proximal Tubular Calcium Reabsorption approximately 80% of Ca ++ reabsorption is paracellular , and approximately 20% is transcellular in the proximal tubule. In the proximal tubule, calcium reabsorption usually parallels sodium and water reabsorption and is independent of PTH

16. Loop of Henle Calcium Reabsorption In the loop of Henle , calcium reabsorption is restricted to the thick ascending limb . approximately 50% of Ca ++ reabsorption is paracellular , and approximately 50% is transcellular in the proximal tubule.

17. Distal Tubule Calcium Reabsorption Reabsorption of Ca ++ by the distal tubule is exclusively transcellular . In the distal tubule, where the voltage in the tubule lumen is electrically negative with respect to blood, reabsorption of Ca ++ is entirely active

18. Regulation of Urinary Calcium Excretion PTH Calcitriol Calcitonin [ Ca ++ ] in ECF [P i ] in ECF Changes in ECF volume PH

19. Reference Berne & Levy Physiology Guyton and Hall Textbook of Medical Physiology Physiology by Linda S. Costanzo

20. Thank you for your attention