1. Control of Blood Ca

2. Why is Calcium important?

3. Ca is essential for healthy teeth and skeletal development It is also involved in: Blood clotting (Ca works with other factors to stimulate platelets) Nerve conduction (“Ca-gated channels” for Na,K) Muscle contraction (Calcium binds to certain areas of the muscle fibers to allow actin and myosin interaction)

4. Blood Ca is regulated by a HORMONE called calcitonin Non-steroid hormone (note the absence of C- rings) Released by the thyroid gland when blood [Ca] concentration is too high Stimulates Ca uptake into bones, limits intestinal Ca absorption

5. What happens when blood Ca is too low? Parathyroid = 4 small glands attached to the thyroid When blood [Ca] is low, PTH (parathyroid hormone) is synthesized and released

6. Parathyroid Hormone PTH stimulates ‘osteoclasts’ (bone cells) to break down bone material and release Ca (and phosphate) to the blood

7. Other PTH functions Stimulate kidneys to reabsorb Ca from urine Simultaneously activates production of Vitamin D (at the kidney) as a cofactor to stimulate absorption of calcium from digested food (in the small intestine)

8. Negative feedback (HOMEOSTASIS!)

9. What do YOU think? After normal [Ca] is reached, will calcitonin/PTH still be produced? What symptoms could accompany an underactive parathyroid? Overactive? What about an under/over-active thyroid?

10. Homework that I WANT YOU to do Read the second handout Finish the homeostasis worksheet (front and back)