Transcript VIII. Calcium Homeostasis

VIII. Calcium Homeostasis
A. Bone Composition
1. Contains 500-1000x’s more calcium
than all other tissues combined
2. In blood level of Ca is monitored
extremely close
a. If it is too high the heart stops
b. If it is too low breathing stops
c. Needed for enzyme function
and blood clotting
3. Bones release and absorb calcium by
hormone control to help with all these
processes
B. Process
1. Main hormone involved is
parathyroid hormone (PTH)
a. Linked by a negative feedback
loop
2. Ca falls in blood due to stress
3. Detected by parathyroid gland cells
4. Causes an increase of cyclic AMP in
cell
5. This turns of PTH gene which
increases the PTH production
6. PTH increases the number and
activity of osteoclasts and bone
resorption occurs
7. Also affects kidneys
a. Promotes Ca to not be lost in
urine
b. Eliminates P in urine
c. Forms calcitrol (vitamin D)
8. Hormone calcitonin is involved when
Ca is too high
a. Secreted by thyroid
b. Inhibits osteoclasts, making
bones take up Ca
c. So promotes new bone
formation, too