1. Bone Homeostasis

2. What is being regulated?
The amount of CALCIUM in the blood is being regulated.
Why is calcium needed in the blood?
1. Provides the hardness and strength of bones.
2. Muscle contraction, nerve impulse conduction, blood clotting, and other physiological processes.

3. When Blood Calcium Drops…
Parathyroid gland is stimulated to release: PTH (parathyroid hormone).
PTH causes:
a. Osteoclasts to break down bone matrix and release Ca2+ into bloodstream.
b. Urine loss of Ca2+ is reduced.
PTH causes kidneys to release CALCITRIOL which stimulates absorption of Ca2+ from intestines.

4. When Blood Calcium Rises…
Thyroid gland is stimulated to release: CALCITONIN
Calcitonin causes: Osteoblasts are stimulated to lay down more bone matrix, in order to take excess calcium out of the blood stream.

5. Calcitriol release increased
Osteoblasts
Osteoclasts
Calcitriol release increased

6. Necessary Vitamins
Vitamin D – involved in the formation of calcitriol for calcium absorption.
Vitamin A – Involved in stimulating activity of osteoblasts.
Vitamin C – Needed for collagen synthesis.

7. More activity or stress on the bones increases the bone density.
How is bone density regulated by mechanical factors instead of hormonal?
More activity or stress on the bones increases the bone density.
Couch potatoes beware!