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Control of Blood Ca
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Why is Calcium important?
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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)
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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
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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
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Parathyroid Hormone• PTH stimulates ‘osteoclasts’ (bone cells) to
break down bone material and release Ca (and phosphate) to the blood
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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)
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Negative feedback (HOMEOSTASIS!)
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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?
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Homework that I WANT YOU to do
• Read the second handout
• Finish the homeostasis worksheet (front and back)