40 Questions
What is the result of calcitonin binding to receptors through cAMP?
Activation of phospholipase C pathway
What is the effect of sex steroids on bone metabolism?
Increased 1α-hydroxylase activity and osteoprotegerin synthesis
What is the overall effect of glucocorticoids on bone metabolism?
Catabolic role, increasing bone resorption and decreasing bone synthesis
What is not mentioned as a regulator of calcium and bone metabolism?
Parathyroid hormone
What is the result of phospholipase C pathway activation?
Increased release of calcium from intracellular stores
What is the primary response to hypocalcemia in terms of PTH release?
Increased PTH release
How does vitamin D influence PTH gene expression?
Vitamin D represses PTH gene expression
What is the result of decreased calcium levels on PTH production?
Increased PTH production
What is the effect of hypercalcemia on PTH release?
PTH release is decreased
How does the calcium sensing receptor (CaSR) gene expression respond to vitamin D?
CaSR gene expression is increased by vitamin D
What is the primary role of 1,25-Dihydroxy-Vitamin D in the kidneys?
Increase the absorption of dietary calcium
What is the effect of excess thyroid hormone levels on bone metabolism?
Increased bone resorption
What is the role of PTH and Vitamin D in the body?
To maintain normal blood calcium and phosphate levels
What is the effect of growth hormone on bone formation?
Stimulates bone formation
What is the role of calcitonin in the body?
To inhibit osteoclast differentiation
What are the two primary sources of circulating phosphate?
Diet and skeleton
What is the effect of high calcium levels in blood on PTH release?
Decrease PTH release
What hormone is involved in the regulation of calcium levels?
Parathyroid hormone
What is the source of calcitonin?
Thyroid gland
What inhibits PTH synthesis?
Vitamin D
What is the function of vitamin D in calcium metabolism?
Regulating calcium levels
What is the consequence of low magnesium levels in response to hypocalcemia?
PTH release is prevented
What happens to osteoclast activity when calcitonin is released?
It decreases
What is the result of hypocalcemia?
Increased PTH production
What is the result of activating the Parathyroid-Calcium Sensing Receptor?
Activation of phospholipase A2
What is the role of the parathyroid gland in calcium metabolism?
Regulating calcium levels
What is the effect of calcitonin on renal calcium excretion?
It increases
How is the release of calcitonin regulated?
By plasma calcium levels
What is the effect of acute decreases in Ca2+ levels on PTH release?
Immediate release of preformed PTH
What is the role of calcitonin in calcium homeostasis?
It has a minor effect on calcium levels
What is the primary function of calcium in the body?
Maintenance of bone structure and teeth
What is the normal range of calcium levels in the blood?
1.0-1.3 mmol/L
What is the role of phosphate in the body?
Formation of bones and teeth
What is the result of maintaining calcium levels in the blood?
All of the above
What is the function of calcium in metabolic and signaling pathways?
All of the above
What is the importance of maintaining calcium levels in the blood?
Maintenance of critical processes
What is the role of phosphate in ATP molecules?
Part of the adenosine triphosphate molecule
What is the effect of fluctuating phosphate levels in the blood?
Fluctuation throughout the day, particularly after meals
What is the result of maintaining normal plasma calcium values?
All of the above
What is the function of calcium in the body's signaling pathways?
All of the above
Study Notes
Calcium Metabolism and Hormonal Regulation
- Calcium homeostasis is maintained by the interaction of three main calciotropic hormones: Parathyroid Hormone (PTH), Vitamin D, and Calcitonin.
- These hormones regulate calcium levels by acting on three important organs: kidneys, bones, and the gastrointestinal tract.
Parathyroid Hormone (PTH)
- PTH is released in response to low calcium levels in the blood.
- PTH stimulates bone resorption, increases calcium reabsorption in the kidneys, and stimulates the production of active Vitamin D.
- PTH gene expression is repressed by Vitamin D in a negative feedback loop.
- Decreased calcium levels lead to the production of proteins that stabilize PTH mRNA, increasing PTH translation.
Vitamin D
- Vitamin D increases calcium absorption in the gut, promotes bone formation, and maintains calcium levels in the body.
- Vitamin D suppresses PTH gene expression and production.
- Vitamin D also regulates calcium sensing receptor (CaSR) gene expression.
Calcitonin
- Calcitonin is a 32-amino acid peptide hormone produced by parafollicular cells in the thyroid gland.
- Calcitonin is released in response to high calcium levels in the blood (>9mg/dl).
- Calcitonin inhibits osteoclast activity, decreasing bone resorption, and increases renal calcium excretion, resulting in decreased free ionized calcium levels.
Other Hormones and Calcium Metabolism
- Sex steroids (androgens and estrogens) increase 1α-hydroxylase activity and osteoprotegerin synthesis, decreasing bone resorption.
- Glucocorticoids have an overall catabolic role in bone metabolism, increasing bone resorption and decreasing bone synthesis.
- Growth Hormone and Insulin-Like Growth Factor-1 (IGF-1) stimulate bone formation by increasing the proliferation of osteoblast precursors.
- Thyroid Hormone inhibits osteoclast differentiation and stimulates bone formation.
Regulation of PTH Release
- PTH release is regulated by a negative feedback mechanism.
- PTH synthesis is inhibited by Vitamin D, decreasing PTH release.
- Low calcium levels activate the Parathyroid-Calcium Sensing Receptor (PTH-CSR), leading to the release of preformed PTH and stimulation of new PTH synthesis.
- Hypomagnesemia prevents PTH release in response to hypocalcemia.
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