Calcium

Question 1

Explain the significance if maintaining serum calcium levels within set limit

Answer 1

Calcium plays critical role in many cellular processes. CA2+ also serves as an intracellular second messenger by carrying information from the cell membrane into the interior of the cell. It’s not surprising that the body carefully regulates plasma concentration of free ionised calcium. It maintains free plasma Ca2+ within a narrow range (between 1.0 and 1.3 mmol/L.

Question 2

Describe the hormonal regulation of serum calcium

Answer 2

Calcium and phosphate homeostasis are linked go two reasons:
- Both are principle components of hydroxyapatite crystals which constitute the major portion of mineral phase of bone
- Regulated by the same hormones primarily parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D. These hormones act on 3 organ system, Bone, Kidney and Gastrointestinal tract. However, the actions of these hormones on calcium and phosphate are typically opposed in that a hormone may elevate the level of ion ion whilst lowering the other.

Question 3

Explain the regulation of parathyroid hormone and vitamin D

Question 4

Explain the significance of renal function on calcium metabolism.

Answer 4

The kidneys filter about 10 times the total extracellular pool of calcium per day (10,000mg/day). More than 98% of this Ca2+ is reabsorbed and therefore the net renal excretion of Ca2+ is less than 2% of the filtered load. In a person in Ca2+ balance, urinary excretion (around 175mg/day) is the same as net absorption by the GI tract