Calcium Homeostasis and the Parathyroid Gland Flashcards
How often in human skeleton replaced?
10-15 years, it is therefore very dynamic
What is the function of calcium in bone?
- protects vital organs
- supports muscles
- reservoir of calcium
What is the function soluble calcium?
- excitable tissues
- muscles/nerves
- cell adhesion
What is the percentage of the body’s calcium is in the bones?
> 99%
What are the 3 functions of the skeleton?
mechanical - support and muscle attachment
protective - vital organs and marrow
metabolic - calcium and phosphate
What organs and chemicals are involved in calcium homeostatsis?
bones can increase and decrease Ca, GI tract can only increase Ca, kidneys can increase and decrease Ca
Vit D, PTH, FGF23
What percentage of soluble calcium is free?
50% is free
50% is bound to albumin
What stimulates PTH to be secreted?
Low calcium or high potassium
What is the effect of PTH?
How does it bring about this effect?
Increase calcium reabsorption in renal distal tubule
Increases intensity calcium absoprtion (via activation of VitD)
Increases calcium release from bone by stimulating osteoclasts
Decreases phosphate reabsorption
How does PTH affect the kidneys?
Increases distal tubular reabsorption of calcium (and inhibits PO4 reabsorption)
PTH stimulates the activation of VitD to 1,25(OH)2D3
How does PTH affect bone?
Increases bone resorption by binding to GPCR’s on osteoclasts and stimulating their activity
Describe the negative feedback of PTH?
PTH transcription inhibited by 1,25D3
PTH translation inhibited by increased serum calcium
Describe the role of calcitonin?
Produced by parafollicular cells (c-cells) in hypercalcaemia
Direct affect of osteoclasts, decreases bone resorption
Plays small role, not essential to life
Describe what happens during hypocalcaemia or hyperphosphataemia
Increased PTH secretion:
- decreases urinary calcium
- increases urinary phosphate
- increases osteoclast activity
- increases activation of VitD to 1,25D3 in kidneys –> increased absorption of calcium of GI tract
Describe what happens during hypercalcaemia
PTH secretion decreased, calcitonin released
- Decreases bone resorption
- Decreases urinary phosphate
- Increases urinary calcium
- Decreases 1,25D3 production which decreases calcium and phosphate absorption in the GI tract