This document discusses calcium regulation in the body. It notes that around 50% of calcium in the extracellular fluid is free and involved in important cellular processes like muscle contraction and hormone secretion. Another 40% is bound to proteins like albumin and not involved in these processes. Vitamin D, parathyroid hormone, and calcitonin help regulate calcium and phosphate levels in the blood and extracellular fluid between 2.25-2.75 mmol/L and 0.8-1.6 mmol/L respectively. The active form of vitamin D increases calcium and phosphate absorption in the intestines and kidneys while decreasing their excretion, and also promotes bone calcification.

1. Diffusible Non-diffusible
Ca2+ concentration in ECF
(bood and interstitium)
• Free Ca2+ (50%)
• Action
potentials
• Contraction
muscles
• Hormon
secretion
• Blood
coagulation
• Ca2+ linked with
oxalate/phospate
• Electricallyneutral
• Not useful for
celluarprocesses
• Ca2+ bound
protein (40%)
• Albumin
• Large
• Charged
• Unenvolved in
cellular
processes

3. • Low • High
Ca2+ level
PTH Vitamin Dcalcitonin
2.25 - 2.75 mmol/L
phosphateconcentrationin plasma
0.8 - 1.6 mmol/L

4. Vitamin D

8. Vitamin D active form (1,25-OHVD)
• Increases
• calcium and phosphate levels
• In the ECF of
• Intestines,
• Kidneys
• bones

9. Vitamin D active form (1,25-OHVD)
• Increases
• calcium and phosphate
absorptionfrom the intestine
• Decreases
• their excretion with the urine

10. Vitamin D active form (1,25-OHVD)
• Promotes
• Bone calcification
• Stimulates
• calcium release from the bones
• Increases
• the production of calmodulin