12 - Calcium Metabolism Flashcards
1
Q
How does PTH increase calcium release from bone?
A
- PTH makes osteoblasts produce osteoclast activating factors (RANKL)
- OAFs bind to receptors on osteoclasts
- stimulates break down of bone matrix to release calcium
2
Q
What are the functions of calcium?
A
- neuromuscular excitability
- muscle contraction
- strength in bones
- intracellular second messenger
- intracellular co-enzyme
- hormone/neurotransmitter stimulus-secretion coupling
- blood coagulation (factor IV)
3
Q
What are the causes of hypocalcaemia?
A
- hypoparathyroidism
- pseudohypoparathyroidism
- vitamin d deficiency
4
Q
What are the features of hypoparathyroidism?
A
INSUFFICIENT PTH
- reduced calcium
- reduced PTH
- increased PO4
5
Q
What are the features of pseudohypoparathyroidism?
A
RESISTANCE TO PTH
- reduced calcium
- increased PTH
- reduced PO4
6
Q
What are the features of vitamin D deficiency?
A
- reduced calcium
- increased PTH
- reduced PO4
RICKETS AND OSTEOMALACIA
7
Q
What are the signs of hypocalcaemia?
A
- Trousseau’s sign
- Chvostek’s sign
8
Q
What are the causes of hypercalcaemia?
A
- primary hyperparathyroidism
- tertiary hyperparathyroidism
- vitamin d toxicosis
9
Q
What are the symptoms of hypercalcaemia?
A
- painful bones
- renal stones
- abdominal groans
- psychic moans
10
Q
How is Ca2+ regulated?
A
- increased by parathyroid hormone (PTH - secreted by parathyroid gland)
- increased by 1,25(OH)2 vitamin D3 (calcitriol - produced by kidneys)
- decreased by calcitonin (produced by parafollicular cells in thyroid)
11
Q
How is PTH regulated?
A
- stimulates enzyme leading to calcitriol synthesis
- increased calcitriol synthesis leads to increased plasma calcium concentration
- parathyroid cells respond to changes in plasma calcium concentration (have Ca2+ receptors)
- Ca2+ receptors activated with fall in calcium concentration
- calcitriol has negative feedback on PTH
- β receptors on cells producing PTH stimulated by catecholamines to secrete PTH (positive feedback)
12
Q
What are the actions of PTH on kidneys, bone, small intestine and blood?
A
- kidneys: increases Ca2+ reabsorption, PO43- excretion and stimulates 1 α hydroxylase activity (increases calcitriol synthesis)
- bone: increases Ca2+ mobilisation (osteoclasts stimulated, osteoblasts inhibited) and increases bone resorption
- small intestine: increases Ca2+ and PO43- absorption
- [Ca2+] in blood increases
13
Q
What are the actions of calcitriol on the kidneys, small intestine and bone?
A
- kidneys: increased Ca2+ and PO43- reabsorption
- small intestine: increased Ca2+ and PO43- absorption
- bone: increased osteoblast activity
14
Q
How is calcitriol regulated?
A
- cholecalciferol sourced from diet and sunlight (taken up by liver)
- 25-hydroxylase converts cholecalciferol to 25-hydroxy-cholecalciferol (stored in liver)
- 1 α hydroxylase converts 25-hydroxy-cholecalciferol to calcitriol (in kidneys)
15
Q
How is calcitonin regulated?
A
- stimulated by increase in plasma calcium conc.
- gastrin also stimulates production
