5 Questions
What are the actions of PTH on blood calcium and phosphate levels?
PTH increases blood calcium and decreases phosphate levels by stimulating osteoclasts to breakdown bone, reabsorbing calcium from the kidney, and absorbing calcium from the GI tract.
What are the actions of calcitonin on bone resorption and bone formation?
Calcitonin inhibits bone resorption by inhibiting osteoclasts and promotes bone formation by stimulating osteoblasts.
Where is calcitonin secreted from and what stimulates its secretion?
Calcitonin is secreted from 'C' cells in the thyroid gland and its secretion is stimulated by increased serum calcium levels.
What role does vitamin D play in calcium absorption?
Vitamin D helps absorb intestinal and renal calcium.
What are the regulatory factors for PTH secretion?
Decreased plasma calcium levels lead to increased PTH secretion.
Study Notes
Parathyroid Hormone (PTH), Calcitonin, and Vitamin D in Calcium Homeostasis
- Calcium (Ca++) homeostasis is regulated by three key hormones: Parathyroid hormone (PTH), Calcitonin, and Vitamin D.
Parathyroid Hormone (PTH)
- Increases blood Calcium levels and decreases Phosphate levels.
- Actions:
- Indirectly stimulates osteoclasts, breaking down bone into Ca++ and Phosphate ions, which then enter the blood.
- Stimulates Ca++ reabsorption from the kidney.
- Stimulates Ca++ absorption from the GI tract.
- Phosphate is normally excreted by the kidney, resulting in a net increase in plasma Ca++.
Calcitonin
- Inhibits bone resorption by inhibiting osteoclasts.
- Promotes bone formation by stimulating osteoblasts.
- Osteoblasts build bone.
- Secreted from "C" cells in the thyroid gland in response to increased serum Ca2+.
Vitamin D
- Helps absorb intestinal and renal Ca+.
Regulation of PTH and Calcitonin
- PTH:
- Decreased plasma Ca++ levels increase PTH secretion.
- Calcitonin:
- Secretion is stimulated by increased serum Ca2+.
Test your knowledge on the regulation of bone and the role of parathyroid hormone, calcitonin, and vitamin D in maintaining calcium homeostasis. Learn about the actions of these hormones and their effects on blood calcium levels and bone breakdown.
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