5 Ca/PO4 Regulation Flashcards
Why are calcium levels so tightly regulated?
Calcium is fundamentally important to ALL biologic systems
What is a normal level of blood calcium?
Total (free and bound) 8.6 to 10.6mg/dL with daily variation < 10%
How much of plasma calcium is bound?
50%
The unbound, ionized form is active (so about 5 mg/dL with daily variation <2%)
99% of Ca2+ is in …
Crystalline form found in teeth and bone (1 and 2 kg)
Of the 1%, remaining, 0.9% is contained in soft tissues and 0.1% is in the ECF (1/2 of that is free and diffusable)
What is the normal daily intake of calcium from diet?
1000mg
Of that, 800mg is excreted in feces and 200mg excreted in urine
What is the normal distribution of phosphate in the body?
85% in bone and teeth, 15% in muscle
In cells, >80% in mitochondria and remaining in cytosol
What is the normal dietary intake of phosphate?
1000mg
350mg excreted in feces, 650mg excreted in urine
If there’s a demand for phosphate, the kidney can reabsorbed a lot
Calcium and phosphate levels in the blood stream are regulated by..
Parathyroid hormone (PTH) and vitamin D
Involves the interaction of bone, intestine, and kidney (target organs for PTH)
PTH is released in response to a drop in blood calcium —> acts to normalize Ca by acting on these organs
Parathyroid glands release PTH from _________
Chief cells
Released in response to hypocalcemia (low blood Ca2+)
Effect of PTH on bone
Activates osteoclasts —> calcium and phosphate ions released to blood
Effect of PTH on Intestines
Increases calcium absorption from food
Effect of PTH on Kidneys
Promotes activation of Vitamin D (which increases calcium absorption from food)
Increases calcium reabsorption and phosphate secretion in kidney
What are the two pools of calcium in bone?
Stable pool - consists of mature mineralized bone, composed primarily of hydroxyapatite; undergoes resorption by SLOW breakdown of crystals to liberate Ca and PO4
Labile pool - consists of bone fluid, composed primarily of amorphous crystals; undergoes osteopathic osteolysis for FAST release of Ca and PO4
Which calcium pool in the bone is used for minute to minute adjustments to Calcium/phosphate levels?
Labile pool (can undergo osteolytic osteolysis)
What separates the bone itself from the plasma in the osteon canals?
Osteocytic-osteoblastic bone membrane
This is where fast exchange from labile pool occurs
Has large surface area —> large influx between bone fluid and plasma