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 stopsb. If it is too low breathing stopsc. 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 stress3. Detected by parathyroid gland cells4. 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