29 Calcium metabolism (HOT TOPIC) Flashcards
Total plasma [Ca2+]
= 45% ? + 45%? + 10%?
45% ionized calcium
45% calcium bound to serum proteins
10 %calcium complexed with anions (PO43-,lactate, HCO3-)
What are the 3 hormones that control the equilibrium between ionized and protein bound Ca2+?
Other than that, suggest 3 factors that will also produce transient changes in Ca2+m and briefly describe why.
Calcitriol, PTH, calcitonin;
- pH: H+ will cause a rise in Ca2+ as H+ will attach to plasma albumin and release Ca2+
- FFA, citrate, muscle protein… bind to Ca2+
What is the equation of albumin corrected Ca2+ (in mmol/L)?
Measured Ca2+ + [40 – serum albumin (g/L)] x (0.02)
Which of the following are not functions of calcium?
A. Formation of bones and teeth B. Cofactor for blood clotting C. Cell adhesion D. Membrane excitability E. Transmission of nerve impulse F. Contraction of muscles
None of the above
State a sign of hypocalcemia.
Increased neuromuscular excitability (Chvostek's sign + Trousseau's sign)// Hypocalcemia tetany (muscle spasm)
Which of the following is false about hypercalcemia?
A. Increased muscle excitability (muscle spasm)
B. Polyuria
C. Altered CNS (impaired concentration/memory/confusion/stupor)
D. Hypercalcemia-induced ileus (constipation, nausea, vomiting
A
should be decreased neuromuscular excitability (muscle weakness)
B: calciuresis, nephrogenic DI, renal stones (nephrolithiasis)
C: peptic ulcer too (due to increased gastrin secretion)
With a fall in plasma Ca, what hormone(s) will increase?
What is/are its/their functions?
PTH and calcitriol will increase Ca2+ by increasing bone resorption, renal Ca2+ reabsorption and also intestinal Ca2+ absorption
With a rise in plasma Ca, what hormone(s) will increase? What is/are its/their functions?
Calcitonin
It will decrease bone resorption, renal reabsorption of Ca2+ and intestinal absorption of Ca+
The rise in calcium is sensed by _______________ cells of __________;
while the decrease in Ca2+ (hypocalcemia) is sensed by __________ cells of _________.
Parafollicular cells of thyroid;
(to secrete calcitonin)
Chief cells in parathyroid gland (to secrete PTH/calcitriol)
What is the major effect of calcitonin?
Major effect:
- act directly on osteoclasts to inhibit osteoclastic bone resorption
- act directly on osteocytes to inhibit osteocytic osteolysis
Why can sunbathing increase in bone resorption?
Sunbathing increases vitamine D in body, which is used to make calcitriol
What are the 2 major effects of PTH?
Briefly describe its effects on bones.
Increase plasma [Ca2+] and decrease plasma [PO43-].
It stimulate osteocytic osteolysis by direct action on osteocytes;
it also stimulates bone remodelling by direct action on osteoblast and indirect action on osteoclast
Which of the following is false in primary hyperparathyroidism?
A. increased Ca2+ in serum
B. decreased phosphorus in serum
C. increased or inappropriately normal PTH in serum
D. increased or normal alkaline phosphate
E. decrease Ca2+ in urinary Ca2+
E
normally, PTH will increase reabsorption of Ca2+ in kidneys, thus there should be low levels in urinary Ca2+. However, it is not a result in primary hyperparathyroidism due to change in Ca2+ receptors insensitivity.
Suggest treatment for secondary hyperparathyroidism.
Calcimimetics: orally active, allosteric activators of CaSR > thus body thinks that there is high [Ca2+] > fall in PTH secretion
*The circulating [Ca2+] is detected by a unique G-protein coupled calcium-sensing receptor (CaSR) on the surface of chief cells
Which of the following about PTH is wrong?
A. In low intermittent doses of PTH injections, there is a net increase in bone mass
B. It stimulate the recruitment of osteoprogenitor cells (pro-osteoblasts) into forming osteoblast
C. It has significant effect on osteoclast formation
D. It is used in treating osteoporosis
E. The use of it may increase risk of osteosarcoma
C: no significant effect on OSTEOCLAST!!
A: In low intermittent doses of PTH injections (subcutaneously), PTH has anabolic actions (rather than osteoporotic effect) on bone, and increases bone formation more than bone resorption , leading to net increase in bone mass
