Calcium Absorption and Vitamin D
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Questions and Answers

What is the role of vitamin D in calcium absorption?

  • It inhibits active calcium transport
  • It promotes passive absorption in the jejunum and ileum
  • It is essential for the biosynthesis of calbindin protein (correct)
  • It increases calcium excretion in the kidneys

    • What happens to calcium absorption in the duodenum when calcium intake is low?

  • It remains the same
  • It becomes passive
  • It increases (correct)
  • It decreases

    • Where does most of the calcium absorption take place?

  • Duodenum
  • Jejunum and ileum (correct)
  • Large intestine
  • Kidneys

    • What inhibits calcium absorption?

    <p>Phosphates and oxalates</p> Signup and view all the answers

    What percentage of filtered calcium is reabsorbed in the kidneys?

    <p>99%</p> Signup and view all the answers

    Where is calcium reabsorption regulated by parathyroid hormone?

    <p>Distal tubule</p> Signup and view all the answers

    What is critical for normal cell function, neural transmission, and bone structure?

    <p>Regulation of plasma Ca2+ levels</p> Signup and view all the answers

    What percentage of total calcium absorption takes place in the large intestine?

    <p>10%</p> Signup and view all the answers

    Which hormone increases calcium excretion in the urine?

    <p>Growth hormone</p> Signup and view all the answers

    What is the effect of oestrogens on osteoporosis?

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

    What is the role of calcitonin in calcium homeostasis?

    <p>Inhibits bone resorption and increases calcium in the urine</p> Signup and view all the answers

    What is the effect of parathyroid hormone on bone?

    <p>Mobilizes calcium from bone</p> Signup and view all the answers

    What is similar in structure to Parathyroid Hormone (PTH) receptor?

    <p>Other G-protein coupled receptors</p> Signup and view all the answers

    What is the result of excessive secretion of parathyroid hormone in primary hyperparathyroidism?

    <p>Decalcification of bone and kidney stones</p> Signup and view all the answers

    What is the role of 1, 25-dihydroxycholecalciferol in calcium homeostasis?

    <p>Increases calcium absorption from the intestine</p> Signup and view all the answers

    What can cause secondary hyperparathyroidism?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of thyroid hormones on calcium levels?

    <p>Increase calcium levels</p> Signup and view all the answers

    What is the common cause of secondary hyperparathyroidism?

    <p>Kidney disease</p> Signup and view all the answers

    Which receptor plays an important role in regulation of extracellular calcium?

    <p>Calcium-sensing receptor (CASR)</p> Signup and view all the answers

    What is the effect of secondary hyperparathyroidism on bones?

    <p>Decalcification leading to pathologic fractures</p> Signup and view all the answers

    What is the effect of insulin on bone?

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

    What is the result of inadequate production of parathyroid hormone?

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

    What is the primary function of parathyroid hormone?

    <p>Regulation of calcium and phosphorus concentration in extracellular fluid</p> Signup and view all the answers

    What is a common cause of hypoparathyroidism?

    <p>Surgical removal of the parathyroid glands</p> Signup and view all the answers

    Where are the parathyroid glands located?

    <p>In the neck near the thyroid gland</p> Signup and view all the answers

    What is the result of hypocalcemia in hypoparathyroidism?

    <p>Tetany and convulsions</p> Signup and view all the answers

    What is the precursor of parathyroid hormone that is formed in polysomes?

    <p>Pre-Pro PTH</p> Signup and view all the answers

    What is the major target of parathyroid hormone?

    <p>Bone and kidney</p> Signup and view all the answers

    What is the response to low extracellular concentrations of free calcium?

    <p>Increase in parathyroid hormone secretion</p> Signup and view all the answers

    What happens to Pre-Pro PTH in the rough ER?

    <p>A single peptidase of rough ER membrane hydrolyzes the molecule to split off a 25 amino acid</p> Signup and view all the answers

    What is the role of the Golgi cisternae in parathyroid hormone biosynthesis?

    <p>Packaging and storage of PTH</p> Signup and view all the answers

    What is the relationship between parathyroid hormone secretion and blood calcium levels?

    <p>Parathyroid hormone secretion is inversely proportional to blood calcium levels</p> Signup and view all the answers

    What is the primary action of parathyroid hormone when calcium ion concentrations in extracellular fluid fall below normal?

    <p>Bring calcium ion concentrations back within the normal range</p> Signup and view all the answers

    What is the effect of parathyroid hormone on bone?

    <p>Increase osteoclastic activity</p> Signup and view all the answers

    How does parathyroid hormone enhance calcium absorption from the small intestine?

    <p>By stimulating production of the active form of vitamin D in the kidney</p> Signup and view all the answers

    What is the effect of parathyroid hormone on calcium excretion in urine?

    <p>Decrease calcium excretion in urine</p> Signup and view all the answers

    What is the effect of parathyroid hormone on phosphate ions in urine?

    <p>Stimulate phosphate ion loss in urine</p> Signup and view all the answers

    How does parathyroid hormone stimulate calcium release from bone?

    <p>By stimulating osteoclastic activity</p> Signup and view all the answers

    What is the net effect of parathyroid hormone on calcium ion concentrations in blood?

    <p>Increase calcium ion concentrations in blood</p> Signup and view all the answers

    What is the indirect mechanism by which parathyroid hormone enhances calcium absorption from the small intestine?

    <p>Stimulating production of the active form of vitamin D in the kidney</p> Signup and view all the answers

    Study Notes

    Calcium Absorption and Regulation

    • Calcium absorption is related to calcium intake and vitamin D.
    • Active transcellular calcium transport occurs in the duodenum and is increased when calcium intake is low.
    • Passive paracellular calcium transport occurs in the jejunum and ileum and is the dominant process when calcium intake is adequate or high.
    • Calcium absorption is inhibited by phosphates and oxalates, which form insoluble salts with calcium in the intestine.

    Calcium Reabsorption in the Kidneys

    • Around 99% of filtered calcium is reabsorbed in the kidneys.
    • 60% of reabsorption occurs in the proximal tubules, and the remainder occurs in the ascending limb of the loop of Henle and the distal tubule.
    • Distal tubule absorption is regulated by parathyroid hormone.

    Regulation of Calcium Homeostasis

    • The regulation of plasma Ca2+ levels is critical for normal cell function, neural transmission, membrane stability, bone structure, blood coagulation, and intracellular signaling.
    • The regulation relies on interactions among parathyroid hormone (PTH), dietary vitamin D, and calcitonin.

    Parathyroid Hormone (PTH)

    • PTH is secreted by the parathyroid glands and is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid.
    • PTH is secreted from cells of the parathyroid glands and finds its major target cells in bone and kidney.
    • Biosynthesis of PTH involves three stages: pre-Pro PTH, Pro-PTH, and PTH.
    • Control of PTH secretion is regulated by low extracellular concentrations of free calcium.

    Physiologic Effects of Parathyroid Hormone

    • PTH has direct action to bring calcium ion concentrations in extracellular fluid back within the normal range.
    • PTH accomplishes this by stimulating three processes:
      • Mobilization of calcium from bone
      • Enhancing absorption of calcium from the small intestine
      • Suppression of calcium loss in urine

    Parathyroid Hormone Receptor

    • PTH receptor structure is similar to that of other G-protein coupled receptors.

    Disease States

    • Primary hyperparathyroidism is caused by parathyroid gland disease, leading to excessive secretion of PTH.
    • Secondary hyperparathyroidism is caused by disease outside of the parathyroid gland, leading to excessive secretion of PTH.
    • Hypoparathyroidism is characterized by inadequate production of PTH, leading to decreased concentrations of calcium and increased concentrations of phosphorus in blood.

    Key Points in Calcium Homeostasis

    • Calcium homeostasis is regulated by three hormones: parathyroid hormone, vitamin D, and calcitonin.
    • Parathyroid hormone increases plasma calcium by mobilizing it from bone, increasing reabsorption from the kidney, and increasing the formation of 1, 25-dihydroxycholecalciferol.
    • 1, 25-dihydroxycholecalciferol increases calcium absorption from the intestine, mobilizes calcium from the bone, and increases calcium reabsorption in the kidneys.
    • Calcitonin inhibits bone resorption and increases the amount of calcium in the urine, thus reducing plasma calcium.
    • The calcium-sensing receptor (CASR) plays an important role in regulation of extracellular calcium.

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    Description

    This quiz covers the absorption of calcium in the body, specifically the role of vitamin D and the different processes of calcium transport in the intestines.

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