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Phosphorus and Calcium Metabolism
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Phosphorus and Calcium Metabolism

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@RadiantHyena

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Questions and Answers

What is the primary function of calcitonin in mammals?

  • To stimulate the thyroid gland
  • To increase plasma calcium levels
  • To decrease plasma calcium levels (correct)
  • To regulate plasma phosphate levels

    • Which of the following stimuli can increase calcitonin secretion?

  • β-Adrenergic agonists (correct)
  • β-Adrenergic antagonists
  • Insulin
  • Glucocorticoids

    • Where are receptors for calcitonin primarily found?

  • In the thyroid gland and heart
  • In the lungs and brain
  • In bones and the kidneys (correct)
  • In the liver and pancreas

    • What is the approximate plasma calcium level that triggers increased calcitonin secretion?

    <p>9.5 mg/dL</p> Signup and view all the answers

    What is the approximate half-life of calcitonin in humans?

    <p>Less than 10 min</p> Signup and view all the answers

    Which syndrome is associated with elevated plasma calcitonin levels?

    <p>Zollinger–Ellison syndrome</p> Signup and view all the answers

    What is the primary effect of calcitonin on calcium levels in the body?

    <p>It lowers calcium levels by inhibiting bone resorption</p> Signup and view all the answers

    What is the effect of calcitonin on osteoclast activity?

    <p>It inhibits osteoclast activity</p> Signup and view all the answers

    What is the role of calcitonin in phosphate homeostasis?

    <p>It has no effect on phosphate levels</p> Signup and view all the answers

    What is the effect of thyroidectomy on calcium and phosphate levels in individuals with intact parathyroid glands?

    <p>Calcium and phosphate levels remain normal</p> Signup and view all the answers

    What is a characteristic of patients with medullary carcinoma of the thyroid?

    <p>They have high circulating calcitonin levels and normal bones</p> Signup and view all the answers

    What is the potential role of calcitonin in skeletal development?

    <p>It may play a role in skeletal development in young individuals</p> Signup and view all the answers

    What is the purpose of elevated plasma concentrations of 1,25dihydroxycholecalciferol in pregnancy?

    <p>To support bone formation in the infant and lactation</p> Signup and view all the answers

    What is the effect of PTH on plasma Ca2+ concentration?

    <p>Increases Ca2+ by mobilizing it from bone</p> Signup and view all the answers

    What is the effect of calcitonin on bone resorption?

    <p>Inhibits bone resorption to prevent calcium loss</p> Signup and view all the answers

    What is the additional effect of 1,25dihydroxycholecalciferol on calcium metabolism?

    <p>Increases calcium reabsorption in the kidneys</p> Signup and view all the answers

    What is the role of PTH in the regulation of calcium reabsorption in the kidneys?

    <p>Increases calcium reabsorption to maintain calcium homeostasis</p> Signup and view all the answers

    What is the effect of calcitonin on urinary calcium excretion?

    <p>Increases urinary calcium excretion</p> Signup and view all the answers

    What is the effect of glucocorticoids on osteoclast formation and activity?

    <p>Inhibiting osteoclast formation and activity</p> Signup and view all the answers

    How do glucocorticoids decrease bone formation?

    <p>By inhibiting protein synthesis in osteoblasts</p> Signup and view all the answers

    What is the effect of growth hormone on calcium balance?

    <p>It may result in a positive calcium balance</p> Signup and view all the answers

    What is the effect of insulin-like growth factor I (IGF-I) on bone?

    <p>It stimulates protein synthesis in bone</p> Signup and view all the answers

    What is the effect of estrogens on osteoporosis?

    <p>They prevent osteoporosis</p> Signup and view all the answers

    What is the effect of insulin on bone formation?

    <p>It increases bone formation</p> Signup and view all the answers

    What is the primary function of the epiphysial plate during growth?

    <p>To lay down new bone on the end of the shaft</p> Signup and view all the answers

    Which hormone has the most significant impact on the width of the epiphysial plate?

    <p>Pituitary growth hormone</p> Signup and view all the answers

    What occurs to the cartilage cells after the epiphyses unite with the shaft of the bone?

    <p>They become hypertrophic and secrete VEGF</p> Signup and view all the answers

    What is the term for the process of the epiphyses uniting with the shaft of the bone?

    <p>Epiphysial closure</p> Signup and view all the answers

    What is the purpose of radiographing the skeleton in determining the bone age of a young individual?

    <p>To identify which epiphyses are open and which are closed</p> Signup and view all the answers

    What is the periosteum?

    <p>A dense fibrous, vascular, and innervated membrane that covers the surface of bones</p> Signup and view all the answers

    What is the primary source of stimulation for calcitonin secretion in the thyroid gland?

    <p>Hypercalcemia</p> Signup and view all the answers

    Which of the following hormones has the most potent stimulatory effect on calcitonin secretion?

    <p>Gastrin</p> Signup and view all the answers

    What is the effect of calcitonin on osteoclast activity in bones?

    <p>Inhibition</p> Signup and view all the answers

    What is the approximate duration of action of calcitonin in humans?

    <p>Less than 10 minutes</p> Signup and view all the answers

    In which syndrome is plasma calcitonin level elevated?

    <p>Zollinger-Ellison syndrome</p> Signup and view all the answers

    What is the effect of dietary calcium on calcitonin secretion?

    <p>No effect</p> Signup and view all the answers

    What is the approximate percentage of total body phosphorus that is found in the skeleton?

    <p>85-90%</p> Signup and view all the answers

    What is the primary mechanism of phosphorus reabsorption in the proximal tubule?

    <p>Active transport</p> Signup and view all the answers

    What is the effect of parathyroid hormone (PTH) on renal phosphorus reabsorption?

    <p>It decreases reabsorption</p> Signup and view all the answers

    What is the approximate amount of phosphorus that normally enters bone per kilogram of body weight per day?

    <p>3 mg (97 μmol)</p> Signup and view all the answers

    What is the primary site of phosphorus absorption in the gastrointestinal tract?

    <p>Duodenum and small intestine</p> Signup and view all the answers

    What is the effect of 1,25-dihydroxycholecalciferol on phosphorus absorption?

    <p>It increases absorption</p> Signup and view all the answers

    What is the primary purpose of haversian canals in compact bone?

    <p>To provide a pathway for blood vessels to supply nutrients</p> Signup and view all the answers

    What is the approximate percentage of type I collagen in bone matrix?

    <p>90%</p> Signup and view all the answers

    What is the unique structure of collagen in bone matrix?

    <p>A triple helix of three polypeptides</p> Signup and view all the answers

    How many collagen genes have been identified so far?

    <p>40</p> Signup and view all the answers

    What is the process by which bones are formed in cartilage models during fetal development?

    <p>Endochondral bone formation</p> Signup and view all the answers

    Which bones are formed directly from mesenchymal cells during fetal development?

    <p>Clavicles, mandibles, and certain skull bones</p> Signup and view all the answers

    What is the primary effect of increased plasma calcitonin levels during pregnancy?

    <p>Inhibiting bone resorption in the mother</p> Signup and view all the answers

    What is the net effect of PTH on Ca2+ reabsorption in the kidneys?

    <p>Increased Ca2+ reabsorption, but offset by increased filtered Ca2+</p> Signup and view all the answers

    How do elevations in plasma 1,25dihydroxycholecalciferol levels during pregnancy affect calcium metabolism?

    <p>Increase Ca2+ absorption from the intestine and increase Ca2+ reabsorption in the kidneys</p> Signup and view all the answers

    What is the primary mechanism by which PTH increases plasma Ca2+ concentrations?

    <p>By mobilizing Ca2+ from bone</p> Signup and view all the answers

    What is the effect of calcitonin on urinary Ca2+ excretion?

    <p>Increased urinary Ca2+ excretion</p> Signup and view all the answers

    What is the primary role of 1,25dihydroxycholecalciferol in regulating calcium metabolism?

    <p>Increasing Ca2+ absorption from the intestine</p> Signup and view all the answers

    What is the primary function of the epiphysial plate during growth?

    <p>To lay down new bone on the end of the shaft</p> Signup and view all the answers

    What is the most significant hormonal influence on the width of the epiphysial plate?

    <p>Pituitary growth hormone and IGF-I</p> Signup and view all the answers

    What is the consequence of the epiphyses uniting with the shaft of the bone?

    <p>Linear bone growth ceases</p> Signup and view all the answers

    What is the purpose of noting which epiphyses are open and which are closed in determining the bone age of a young individual?

    <p>To determine the age at which each epiphysis closes</p> Signup and view all the answers

    What is the characteristic of the periosteum?

    <p>It is a dense, fibrous, vascular, and innervated membrane</p> Signup and view all the answers

    What is the consequence of the cartilage cells becoming hypertrophic and secreting vascular endothelial growth factor (VEGF)?

    <p>Vascularization and ossification occur</p> Signup and view all the answers

    Study Notes

    Calcium and Phosphate Metabolism

    • Bone Growth: During fetal development, most bones are modeled in cartilage and then transformed into bone by ossification (enchondral bone formation).
    • Long Bone Growth: Specialized areas at the ends of each long bone (epiphyses) are separated from the shaft of the bone by a plate of actively proliferating cartilage, the epiphysial plate.
    • Epiphysial Plate: The width of the epiphysial plate is proportional to the rate of growth, affected by hormones, particularly pituitary growth hormone and IGF-I.
    • Linear Bone Growth: Can occur as long as the epiphyses are separated from the shaft of the bone, but ceases after the epiphyses unite with the shaft (epiphysial closure).
    • Epiphysial Closure: Cartilage cells stop proliferating, become hypertrophic, and secrete vascular endothelial growth factor (VEGF), leading to vascularization and ossification.
    • Bone Age: Determined by radiographing the skeleton and noting which epiphyses are open and which are closed, with the normal age at which each of the epiphyses closes known.

    Calcitonin

    • Origin and Secretion: Produced by parafollicular cells of the thyroid gland, stimulated by plasma calcium levels above 9.5 mg/dL.
    • Actions: Lowers circulating calcium and phosphate levels by inhibiting bone resorption, increases calcium excretion in the urine.
    • Receptors: Found in bones and kidneys.
    • Physiological Role: Uncertain, but may play a role in skeletal development and protecting the bones of the mother from excess calcium loss during pregnancy.

    Phosphorus Metabolism

    • Total Body Phosphorus: 500-800 g (16.1-25.8 moles), 85-90% of which is in the skeleton.
    • Plasma Phosphorus: 12 mg/dL, with two-thirds of this total in organic compounds and the remaining inorganic phosphorus (Pi).
    • Renal Reabsorption: 85-90% of filtered Pi is reabsorbed in the proximal tubule, involving two related sodium-dependent Pi cotransporters, NaPi-Iia and NaPi-IIc.
    • PTH Inhibition: PTH inhibits NaPi-IIa, reducing renal Pi reabsorption.

    Hormonal Regulation of Calcium Metabolism

    • PTH: Increases plasma Ca2+ by mobilizing this ion from bone, increases Ca2+ reabsorption in the kidney, and increases the formation of 1,25dihydroxycholecalciferol.
    • 1,25-Dihydroxycholecalciferol: Increases Ca2+ absorption from the intestine and increases Ca2+ reabsorption in the kidneys.
    • Calcitonin: Inhibits bone resorption and increases the amount of Ca2+ in the urine.
    • Other Hormones: Glucocorticoids, growth hormone, and insulin-like growth factor I (IGF-I) also affect calcium metabolism.

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    Endocrine Sys. , Calcium & Phosphate Metabolism (2).pdf

    Description

    Learn about the importance of phosphorus in the body, its role in ATP and protein regulation, and how it's closely tied to calcium metabolism. Understand how phosphorus is distributed in the body and its significance in cell function.

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