8.3 Endocrine Regulation of Calcium Metabolism and Bone Health Flashcards
What substances can bind with calcium to make it no longer biologically active? Why do we care?
- Anions (e.g. phosphate)
- Proteins (e.g. calbindin)
What is more important: maintaining bone mass, or maintaining circulating Ca2+? What are the implications of this?
- Circulating calcium is more important
- Therefore, the body will sacrifice bone mass for the sake of short-term calcium levels, giving rise to pathologies such as osteoporosis
In response to PTH release, what is released from bone?
- Ca2+
- PO4-
What is the effect of PTH on the kidneys? What are the downstream effects of this on calcium metabolism?
- Increased conversion of calcidiol to calcitriol
- Calcitriol acts on the kidneys (increasing calcium resorption) and the GI tract (increasing calcium absorption)
Describe the difference between intestinal absorption of calcium in the presence/absence of calcitriol
Absence: passive diffusion (it’s a function of volume, but not very efficiently stored)
Presence: active absorption
We have stores of PTH; how long will they last us?
1 hour
How does the role of PTH-related protein (PTHrP) differ from that of PTH? What kinds of effects does it exert?
Plays longer-term roles:
- Growth
- Tooth eruption
- Breast development
What is the action of calcitonin?
Decrease osteoclast activity.
What is the precursor for Vitamin D3?
7-dehydrocholesterol
Describe Vitamin D Metabolism
- 7-dehydrocholesterol
(sunlight) - Vitamin D3
(Liver) - Calcidiol
(Kidney) - Calcitriol
A patient has high calcitriol, high calcium, but their bone density is very low. What other important factor are we forgetting about?
- Phosphate
- We need both Ca2+ and PO4- to produce bone
What is the effect of Calcitriol on osteoclast formation?
Increase
Effect of PTH on urinary excretion of phosphate
Increase
