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Questions and Answers
What is converted to the active form of vitamin D in the kidneys?
What is converted to the active form of vitamin D in the kidneys?
- 25-hydroxy cholecalcifrol
- Calcidiol
- 1,25-dihydroxy cholecalcifrol (correct)
- Calcitonin
Which consequence is primarily associated with vitamin D deficiency in children?
Which consequence is primarily associated with vitamin D deficiency in children?
- Hypercalcemia
- Rickets (correct)
- Osteoporosis
- Hypocalcemia
What mechanism does calcitonin use to decrease plasma calcium levels?
What mechanism does calcitonin use to decrease plasma calcium levels?
- Decrease in osteoclast activity (correct)
- Stimulating parathyroid hormone secretion
- Increase in osteoclast activity
- Inhibition of intestinal calcium absorption
What clinical condition can result from hypercalcemia?
What clinical condition can result from hypercalcemia?
Which hormone is primarily secreted in response to elevated calcium levels?
Which hormone is primarily secreted in response to elevated calcium levels?
What does hypocalcemia primarily lead to in terms of neuromuscular symptoms?
What does hypocalcemia primarily lead to in terms of neuromuscular symptoms?
What can cause abnormal calcium levels in patients?
What can cause abnormal calcium levels in patients?
Which of the following is NOT a consequence of vitamin D deficiency?
Which of the following is NOT a consequence of vitamin D deficiency?
Which of the following statements about the forms of calcium in plasma is correct?
Which of the following statements about the forms of calcium in plasma is correct?
What role does parathyroid hormone (PTH) play in calcium homeostasis?
What role does parathyroid hormone (PTH) play in calcium homeostasis?
Which statement accurately describes the process of bone remodeling?
Which statement accurately describes the process of bone remodeling?
What is the primary physiological function of calcium in the human body?
What is the primary physiological function of calcium in the human body?
How do dietary phosphorus levels affect its absorption in the human body?
How do dietary phosphorus levels affect its absorption in the human body?
Which of the following hormones primarily decreases blood calcium levels?
Which of the following hormones primarily decreases blood calcium levels?
Which location in the kidneys is responsible for the majority of calcium reabsorption?
Which location in the kidneys is responsible for the majority of calcium reabsorption?
What is the role of 1,25 dihydroxycholecalciferol in the body?
What is the role of 1,25 dihydroxycholecalciferol in the body?
What triggers the secretion of parathormone (PTH)?
What triggers the secretion of parathormone (PTH)?
What is one primary consequence of primary hyperparathyroidism?
What is one primary consequence of primary hyperparathyroidism?
Which effect does parathormone have on the kidneys?
Which effect does parathormone have on the kidneys?
What condition results from the hyper-excitability of excitable tissues due to decreased calcium levels after parathyroidectomy?
What condition results from the hyper-excitability of excitable tissues due to decreased calcium levels after parathyroidectomy?
What is the role of vitamin D in calcium absorption?
What is the role of vitamin D in calcium absorption?
What process is primarily affected by chronic renal failure in relation to phosphate levels?
What process is primarily affected by chronic renal failure in relation to phosphate levels?
Which vitamin D form is synthesized in the skin upon exposure to sunlight?
Which vitamin D form is synthesized in the skin upon exposure to sunlight?
Which statement regarding secondary hyperparathyroidism is correct?
Which statement regarding secondary hyperparathyroidism is correct?
Flashcards
Parathyroid hormone (PTH)
Parathyroid hormone (PTH)
A peptide hormone produced by the parathyroid glands that helps regulate blood calcium levels.
Regulation of PTH Secretion
Regulation of PTH Secretion
Secretion of PTH is stimulated by low blood calcium levels and inhibited by high blood calcium levels, creating a negative feedback loop.
PTH's Effect on Bone
PTH's Effect on Bone
PTH increases bone resorption by stimulating osteoclasts, leading to the release of calcium into the blood.
PTH's Effect on Kidneys
PTH's Effect on Kidneys
PTH promotes calcium reabsorption in the kidneys and phosphate excretion, helping maintain calcium balance.
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PTH's Effect on Intestines
PTH's Effect on Intestines
PTH indirectly enhances intestinal calcium absorption via its activation of vitamin D.
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Hyperparathyroidism
Hyperparathyroidism
A condition characterized by high levels of PTH, usually due to a tumor in the parathyroid glands.
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Hypoparathyroidism
Hypoparathyroidism
A condition characterized by low levels of PTH, often caused by surgery or autoimmune disorders.
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Vitamin D
Vitamin D
A fat-soluble vitamin that acts as a hormone and plays a crucial role in calcium absorption.
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Vitamin D Activation
Vitamin D Activation
The process where vitamin D is converted into its active form, calcitriol, which is essential for calcium absorption.
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Hypocalcemia
Hypocalcemia
A condition characterized by low levels of calcium in the blood, causing increased nerve excitability and potentially leading to muscle spasms (tetany).
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Hypercalcemia
Hypercalcemia
A condition marked by high blood calcium levels, which can lead to various complications including sluggish reflexes, decreased appetite, and increased risk of kidney stones.
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Calcitonin
Calcitonin
A hormone produced by the thyroid gland that helps regulate calcium levels by preventing bone breakdown and promoting calcium excretion in urine.
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Rickets
Rickets
A bone disease in children caused by calcium deficiency, leading to weak and deformed bones. Primarily due to vitamin D deficiency, hindering calcium absorption.
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Osteomalacia
Osteomalacia
A bone disease in adults caused by calcium deficiency, characterized by soft and weak bones, often leading to fractures.
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Osteoclasts
Osteoclasts
The specialized cells responsible for breaking down bone tissue, releasing calcium into the bloodstream.
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Osteoblasts
Osteoblasts
The specialized cells responsible for building new bone tissue, utilizing calcium from the bloodstream.
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Why is Calcium Important?
Why is Calcium Important?
Calcium is crucial for various bodily functions including muscle contraction, nerve impulse transmission, hormone release, blood clotting, and maintaining strong bones and teeth.
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What does Parathyroid Hormone do?
What does Parathyroid Hormone do?
Parathyroid hormone (PTH) is released when blood calcium levels are low. It increases calcium levels by stimulating bone resorption (breakdown), increasing calcium reabsorption in the kidneys, and promoting vitamin D activation, which further enhances calcium absorption from the gut.
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What does Calcitonin do?
What does Calcitonin do?
Calcitonin is a hormone produced by the thyroid gland. It lowers blood calcium levels by inhibiting bone resorption, increasing calcium excretion in the kidneys, and reducing calcium absorption in the gut.
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What is the role of Vitamin D in Calcium Homeostasis?
What is the role of Vitamin D in Calcium Homeostasis?
Vitamin D is a fat-soluble vitamin. It plays a crucial role in calcium homeostasis by increasing calcium absorption from the gut.
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What happens when there is insufficient parathyroid hormone?
What happens when there is insufficient parathyroid hormone?
Hypoparathyroidism refers to the condition where not enough parathyroid hormone is produced. This leads to low blood calcium levels, which can cause muscle cramps, spasms, and tingling sensations.
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What happens when there is excess parathyroid hormone?
What happens when there is excess parathyroid hormone?
Hyperparathyroidism occurs when there is an overproduction of parathyroid hormone. It leads to high blood calcium levels, which can cause bone weakness, kidney stones, and fatigue.
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What is Bone Resorption?
What is Bone Resorption?
Bone resorption is the process of breaking down bone tissue. It is carried out by osteoclasts, specialized cells that dissolve bone matrix.
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What are Osteoblasts?
What are Osteoblasts?
Osteoblasts are specialized cells responsible for building new bone tissue. They produce and secrete the matrix that forms bone.
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Calcium Homeostasis & Balance
- Calcium is 1.5% of adult human body weight
- 99% of calcium is in bones
- 98-99% of filtered calcium in the kidney is reabsorbed, with 60% occurring in the proximal tubule
- Plasma calcium is approximately 9-10.5 mg/dL and exists in three forms:
- 50% ionized calcium (Ca2+), freely diffusible
- 10% non-ionized or complexed with organic ions (citrate, phosphate)
- 40% protein-bound calcium (primarily to albumin), non-diffusible through capillary membranes
Calcium Functions
- Muscle contraction and nerve excitability
- Neurotransmitter and hormonal release
- Enzyme function
- Blood coagulation
- Maintaining healthy bones and strong teeth
- Maintaining membrane integrity and permeability
Phosphorus
- About 90% of phosphorus is found in the skeleton
- Plasma phosphates are approximately 2.48-4.34 mg/dL
- Phosphorus absorption occurs in the duodenum and small intestine via active transport and passive diffusion
- Absorption is directly correlated with dietary intake
- Vitamin D increases phosphorus absorption
- 85-90% of filtered phosphorus is reabsorbed in the proximal tubules
- Parathyroid hormone (PTH) inhibits phosphorus absorption
Bone Structure and Physiology
- Bone is a connective tissue composed of microscopic calcium phosphate crystals in a collagen matrix
- Osteoblasts and osteoclasts, derived from bone marrow, are primarily involved in bone formation and resorption
- Bone growth occurs at the ends of long bones (epiphyses), separated from the shaft by epiphyseal plates
- Bone remodeling is a local process where bone is resorbed and replaced by osteoclasts and osteoblasts, respectively, in concentric circles (lamellae)
- Remodeling adjusts bone shape and strength in response to stress
Calcium Homeostasis Regulation
- Blood calcium is regulated by:
- Principle organ systems: intestines, bone, kidney
- Hormones: parathyroid hormone (PTH), vitamin D, calcitonin
Parathyroid Hormone (PTH)
- There are four parathyroid glands on the dorsal side of the thyroid
- Blood supply to the glands comes from thyroid arteries
- Chief cells secrete PTH
- Oxyphil cells' function is unknown and they are possibly degenerated chief cells
- PTH is a peptide hormone derived from preproparathyroid hormone
- PTH secretion is stimulated by low blood calcium levels and inhibited by high blood calcium levels
PTH Mechanism of Action
- Bone: Stimulates osteoclast activity, increasing bone resorption and calcium release
- Kidney: Increases calcium reabsorption in renal tubules, promotes phosphate excretion, and stimulates Vitamin D conversion to calcitriol
- Intestines: Enhances intestinal calcium absorption indirectly via calcitriol
Vitamin D
- Fat-soluble vitamin that functions as a hormone
- Two forms: vitamin D2 (ergocalciferol), vitamin D3 (cholecalciferol)
- Vitamin D2 comes from dietary sources and supplements
- Vitamin D3 is synthesized in the skin upon exposure to sunlight
Vitamin D Synthesis and Activation
- Synthesis: 7-dehydrocholesterol converts to cholecalciferol via UVB radiation in the skin
- Activation:
- Liver: Converts vitamin D to 25-hydroxy cholecalciferol (calcidiol).
- Kidney: Converts calcidiol to 1,25-dihydroxy cholecalciferol (calcitriol).
Vitamin D Actions
- Bone: Promotes bone resorption and increases calcium and phosphate release
- Kidney: Increases calcium and phosphate reabsorption
- Intestine: Increases calcium and phosphate absorption
Calcitonin
- Protein hormone produced by parafollicular cells (C cells) of the thyroid gland
- Secreted in response to hypercalcemia
- Inhibitory feedback by low calcium levels
- Calcitonin secretion increases with increasing calcium levels
- Calcitonin receptor mainly in bones and kidney
Calcitonin Mechanism of Action
- Direct effect: Inhibits osteoclast activity inhibiting bone resorption
- Indirect effect: Reduces the formation of new osteoclasts
- Increases calcium and phosphate excretion in urine
Clinical Significance
- Deficiency: Inadequate sunlight exposure or poor dietary intake, leading to rickets in children and osteomalacia in adults
- Excess: Can result in hypercalcemia and complications
- Hypocalcemia: A decrease in plasma calcium, leading to muscle tetany and laryngeal spasm
- Hypercalcemia: An increase in plasma calcium associated with nervous system depression, ECG changes, and increased risk for kidney stones
Bone Diseases
- Rickets and osteomalacia: Caused by vitamin D deficiency
- Osteoporosis: Loss of bone mass and strength, with increased fracture risk; may be related to age, menopause, lack of activity, malnutrition, Vitamin C deficiency, or excess glucocorticoids
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