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Questions and Answers
What is a key function of vitamin D in relation to calcium?
What is a key function of vitamin D in relation to calcium?
Which condition is characterized by muscle spasms and potential cardiac complications?
Which condition is characterized by muscle spasms and potential cardiac complications?
What results from primary hyperparathyroidism?
What results from primary hyperparathyroidism?
How do calcimimetics affect PTH secretion?
How do calcimimetics affect PTH secretion?
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What is a primary cause of postmenopausal osteoporosis?
What is a primary cause of postmenopausal osteoporosis?
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What is the primary function of parathyroid hormone (PTH) in calcium homeostasis?
What is the primary function of parathyroid hormone (PTH) in calcium homeostasis?
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How does parathyroid hormone (PTH) affect the kidneys?
How does parathyroid hormone (PTH) affect the kidneys?
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What role does vitamin D play in calcium absorption as influenced by parathyroid hormone?
What role does vitamin D play in calcium absorption as influenced by parathyroid hormone?
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Where is the majority of calcium located in the human body?
Where is the majority of calcium located in the human body?
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Which of the following actions is NOT associated with parathyroid hormone (PTH)?
Which of the following actions is NOT associated with parathyroid hormone (PTH)?
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What is the effect of low serum calcium levels on parathyroid hormone secretion?
What is the effect of low serum calcium levels on parathyroid hormone secretion?
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What are the primary sources of calcium in humans?
What are the primary sources of calcium in humans?
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What can occur if calcium concentration deviates from the normal range?
What can occur if calcium concentration deviates from the normal range?
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What role does vitamin D play in calcium absorption?
What role does vitamin D play in calcium absorption?
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What is the effect of parathyroid hormone (PTH) on calcium levels?
What is the effect of parathyroid hormone (PTH) on calcium levels?
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What can result from high calcium and phosphate levels in the body?
What can result from high calcium and phosphate levels in the body?
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What is the primary storage form of calcium in bones?
What is the primary storage form of calcium in bones?
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How does calcitonin function in the body?
How does calcitonin function in the body?
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What is the usual dietary absorption efficiency of calcium?
What is the usual dietary absorption efficiency of calcium?
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What effect does sustained elevation of PTH have on bones?
What effect does sustained elevation of PTH have on bones?
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Which channel is enhanced by vitamin D for intestinal calcium absorption?
Which channel is enhanced by vitamin D for intestinal calcium absorption?
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What is the role of the calcium-sensing receptor (CaR) in calcium homeostasis?
What is the role of the calcium-sensing receptor (CaR) in calcium homeostasis?
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Which process predominantly activates vitamin D to its final form?
Which process predominantly activates vitamin D to its final form?
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How does parathyroid hormone (PTH) affect serum calcium levels?
How does parathyroid hormone (PTH) affect serum calcium levels?
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What effect does 1,25(OH)₂D₃ have on the intestines?
What effect does 1,25(OH)₂D₃ have on the intestines?
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What is the transport mechanism of vitamin D in the bloodstream?
What is the transport mechanism of vitamin D in the bloodstream?
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What effect does calcitonin have on blood calcium levels?
What effect does calcitonin have on blood calcium levels?
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Which statement best describes the regulation of PTH secretion?
Which statement best describes the regulation of PTH secretion?
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Where are vitamin D receptors (VDRs) primarily located?
Where are vitamin D receptors (VDRs) primarily located?
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What is the primary role of vitamin D receptors (VDRs) in relation to gene expression?
What is the primary role of vitamin D receptors (VDRs) in relation to gene expression?
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What complex forms after the active form of vitamin D binds to the VDR?
What complex forms after the active form of vitamin D binds to the VDR?
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Which proteins are crucial for intestinal calcium absorption regulated by VDRs?
Which proteins are crucial for intestinal calcium absorption regulated by VDRs?
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What occurs as a result of insufficient VDR activity?
What occurs as a result of insufficient VDR activity?
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What characteristic defines Vitamin D-dependent rickets type II (VDDR II)?
What characteristic defines Vitamin D-dependent rickets type II (VDDR II)?
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How does VDR activity relate to geographical factors?
How does VDR activity relate to geographical factors?
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What are potential therapeutic applications mentioned for VDR agonists?
What are potential therapeutic applications mentioned for VDR agonists?
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What role does 1,25-dihydroxyvitamin D₃ play in calcium absorption?
What role does 1,25-dihydroxyvitamin D₃ play in calcium absorption?
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Study Notes
Calcium Homeostasis
- Calcium is crucial for bone formation, muscle function, and cell signalling
- 99% of calcium is stored in bones and teeth, 1% in blood and extracellular fluid
- Intracellular calcium levels are tightly regulated within organelles like ER and mitochondria
- Normal calcium levels are vital for healthy neuromuscular function and cardiac function
- Deviations from the normal range can cause serious neuromuscular and cardiac issues
Primary Hormones in Calcium Homeostasis
-
Parathyroid Hormone (PTH):
- Secreted by parathyroid glands in response to low blood calcium
- Stimulates osteoclast activity increasing bone resorption and calcium release into the bloodstream
- Enhances calcium reabsorption in the kidneys, reducing phosphate excretion
- Stimulates vitamin D conversion to calcitriol, increasing intestinal calcium absorption
- Overall, PTH acts synergistically to elevate serum calcium levels, counteracting hypocalcemia
-
Vitamin D (1,25(OH)2D3):
- Synthesized in skin (UVB) or obtained from diet, requires liver and kidney activation
- Increases serum calcium by promoting intestinal calcium absorption and bone resorption
- 1,25(OH)2D3 is essential for calcium uptake and absorption
Calcium Regulation Mechanisms
- Ca2+-sensing receptor (CaR): Monitors blood calcium levels and regulates PTH release. High calcium inhibits PTH; low calcium causes PTH release
- Vitamin D activation pathway: UVB converts 7-dehydrocholesterol to pre-vitamin D3, converted in the liver to 25(OH)D3, then to active 1,25(OH)2D3 in the kidneys
Effects of PTH
- Increases blood calcium levels
- Stimulates osteoclast activity
- Enhances renal calcium reabsorption
Mechanism of Action and Function of Vitamin D:
- Vitamin D is necessary for calcium absorption; its active form (1,25(OH)2D3) binds to VDRs, activates gene expression, and ensures calcium absorption, bone mineralization, and cell differentiation
- Vitamin D receptor (VDR) plays a role in calcium absorption in intestines, and renal calcium reabsorption
Intestinal Calcium Absorption
- 90% of dietary calcium is absorbed in the duodenum
- Both paracellular (passive) & transcellular (active) absorption
- Active transport via TRPV6, calbindin & PMCA requires 1,25(OH)2D3
Clinical Relevance of Calcium Imbalances
- Hypocalcemia: Neuromuscular excitability (e.g., tetany, Trousseau's or Chvostek's sign)
- Hypercalcemia: Reduced neuromuscular excitability, lethargy, cardiac arrhythmias, risk of death
Disorders of Calcium Homeostasis
- Hypocalcemia: Muscle spasm, tetany
- Hypercalcemia: Lethargy, arrhythmias, death
Role of PTH in Calcium Metabolism
- Key regulator of calcium homeostasis and is crucial for maintaining normal serum calcium levels
Effects of Calcium regulation
- PTH: PTH regulates blood calcium levels
- Vitamin D: Vitamin D enhances intestinal calcium absorption
- Calcitonin: Lowers blood calcium by suppressing osteoclast activity
Osteoporosis
- Postmenopausal osteoporosis disrupts bone remodelling, increasing osteoclast activity and decreasing osteoblast function
- Results in weakened bones prone to fractures (especially in the hip, spine, wrist)
- Treatment includes anti-resorptive agents (bisphosphonates) and anabolic therapies (teriparatide). Calcium and vitamin D supplementation are important in maintaining bone health.
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Description
Test your knowledge on calcium homeostasis, a crucial process for bone health, muscle function, and cellular signaling. This quiz covers the role of calcium in the body, the primary hormones involved, and the consequences of calcium level deviations. Perfect for students studying biology and health sciences.
