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 HCO3
-, citrate, Pi, and SO4
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
• [Pi] 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