Control of Blood Ca

Why is Calcium important?

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)

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

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

Parathyroid Hormone• PTH stimulates ‘osteoclasts’ (bone cells) to

break down bone material and release Ca (and phosphate) to the blood

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)

Negative feedback (HOMEOSTASIS!)

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?

Homework that I WANT YOU to do

• Read the second handout

• Finish the homeostasis worksheet (front and back)