Regulation of Calcium Metabolism
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Questions and Answers

Which hormone is responsible for raising Ca2+ levels in the blood?

  • Vitamin D
  • Parathyroid Hormone (correct)
  • Albumin
  • Calcitonin

    • What percentage of total calcium in the body is found in soft-tissue cells and extracellular fluid?

  • 1% (correct)
  • 20%
  • 10%
  • 5%

    • What is the total Ca2+ concentration in blood?

  • 5 mg/dL
  • 10 mg/dL (correct)
  • 20 mg/dL
  • 15 mg/dL

    • What is the function of albumin in calcium regulation?

    <p>To transport calcium ions</p> Signup and view all the answers

    Which of the following is biologically active?

    <p>Free, ionized Ca2+</p> Signup and view all the answers

    What is the primary function of osteoclasts in calcium regulation?

    <p>To break down bone tissue</p> Signup and view all the answers

    What is a major consequence of hypocalcemia?

    <p>Muscle spasms</p> Signup and view all the answers

    Which of the following processes does not involve Ca2+?

    <p>Protein synthesis</p> Signup and view all the answers

    What is the effect of hypercalcemia on membrane excitability?

    <p>Decreases membrane excitability</p> Signup and view all the answers

    What is the primary function of the organs that play a central role in regulating the movement of calcium between stores?

    <p>To regulate calcium homeostasis</p> Signup and view all the answers

    What is the consequence of inadequate calcium in the body?

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

    Which of the following is a consequence of calcium's role in enzyme regulation?

    <p>Increased enzyme activity</p> Signup and view all the answers

    What is the effect of acidemia on the free ionized Ca2+ concentration?

    <p>It decreases the binding of Ca2+ to albumin, increasing the free ionized Ca2+ concentration.</p> Signup and view all the answers

    What is the role of Parathyroid Hormone in bone remodeling?

    <p>It stimulates bone resorption.</p> Signup and view all the answers

    What is the effect of alkalemia on the free ionized Ca2+ concentration?

    <p>It decreases the free ionized Ca2+ concentration.</p> Signup and view all the answers

    What is the role of Vitamin D in Ca2+ balance?

    <p>It stimulates Ca2+ absorption from the gastrointestinal tract.</p> Signup and view all the answers

    What is the role of phosphate in the body?

    <p>It serves as a biologic buffer and modifier of proteins.</p> Signup and view all the answers

    What is the result of net excretion of Ca2+ by the kidney?

    <p>It is equal to net absorption of Ca2+ from the gastrointestinal tract.</p> Signup and view all the answers

    Where are the receptors for Parathyroid Hormone located in bone?

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

    What is the initial effect of PTH on bone formation?

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

    What is the role of osteoblasts in PTH-induced bone resorption?

    <p>They release osteoclast-stimulating factors</p> Signup and view all the answers

    What is the result of osteoclast resorption of bone?

    <p>Ca++ is released from bone</p> Signup and view all the answers

    What is the effect of PTH on Ca++ reabsorption in the kidney?

    <p>Increased reabsorption</p> Signup and view all the answers

    What is the role of vitamin D in the intestine with regards to PTH?

    <p>It activates Ca++ absorption</p> Signup and view all the answers

    What is the primary effect of parathyroid hormone on the kidney?

    <p>Inhibiting phosphate reabsorption and stimulating calcium reabsorption</p> Signup and view all the answers

    Which of the following activities can lead to bone loss?

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

    What is the primary mechanism by which calcitonin decreases plasma Ca2+ concentration?

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

    What is the primary stimulus for calcitonin secretion?

    <p>Increased plasma Ca2+ concentration</p> Signup and view all the answers

    What is the effect of parathyroid hormone on bone resorption?

    <p>Stimulating bone resorption</p> Signup and view all the answers

    Which of the following hormones has an effect on bone resorption that opposes that of parathyroid hormone?

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

    Which of the following activities is most likely to promote bone loss?

    <p>Prolonged periods of inactivity</p> Signup and view all the answers

    What is the primary effect of Parathyroid Hormone on the kidney?

    <p>Inhibiting phosphate reabsorption</p> Signup and view all the answers

    Which of the following hormones has an effect on bone resorption that opposes that of calcitonin?

    <p>Parathyroid Hormone</p> Signup and view all the answers

    What is the primary action of calcitonin in the bone?

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

    What is the primary stimulus for Parathyroid Hormone secretion?

    <p>Low plasma Ca2+ concentration</p> Signup and view all the answers

    What is the effect of Parathyroid Hormone on calcium reabsorption in the kidney?

    <p>Stimulating calcium reabsorption</p> Signup and view all the answers

    What is the primary function of osteoclast cells in the bone?

    <p>Resorbing bone tissue</p> Signup and view all the answers

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

    <p>Decreases plasma Ca2+ concentration</p> Signup and view all the answers

    What is the primary action of Parathyroid Hormone on the small intestine?

    <p>No direct action on the small intestine</p> Signup and view all the answers

    What is the primary mechanism by which Parathyroid Hormone promotes bone resorption?

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

    Study Notes

    Calcium Metabolism

    • Calcium is crucial for various physiological processes, including muscular contraction, membrane permeability, endocrine and exocrine secretions, enzyme regulation, and coagulation.
    • Calcium stabilizes membrane potentials, and its imbalance can lead to manifestations such as muscle spasms, cardiac arrhythmias, and seizures.

    Regulation of Calcium Metabolism

    • Three tissues play a central role in calcium regulation: bone (and teeth), intestine, and kidney.
    • Three hormones are involved in calcium regulation: parathyroid hormone (PTH), calcitonin, and activated vitamin D3.
    • Three cell types are involved in calcium regulation: osteoblasts, osteocytes, and osteoclasts.

    Parathyroid Hormone (PTH)

    • PTH is produced by the parathyroid gland and raises calcium levels in the blood.
    • PTH regulates blood calcium levels by promoting bone resorption, increasing calcium reabsorption in the kidney, and stimulating vitamin D activation in the intestine.

    Calcitonin

    • Calcitonin is produced by the thyroid gland and lowers calcium levels in the blood.
    • Calcitonin is secreted in response to elevated calcium levels and opposes the effects of PTH in the bone and renal tubule.
    • Calcitonin's main action is to inhibit osteoclastic bone resorption, decreasing plasma calcium concentration.

    Calcium Stores in the Body

    • The adult human body contains approximately 1-1.3 kg of calcium, with 99% stored in bones and teeth.
    • The remaining 1% is distributed between soft-tissue cells and extracellular fluid.

    Forms of Calcium in Blood

    • Total calcium concentration in blood is 10 mg/dL.
    • 40% of calcium is bound to plasma proteins, mainly albumin.
    • Free, ionized calcium is the only biologically active form of calcium.

    Acid-Base Abnormalities and Calcium

    • Acid-base abnormalities alter ionized calcium concentration by changing the fraction of calcium bound to plasma albumin.
    • In acidemia, free ionized calcium concentration increases.
    • In alkalemia, free ionized calcium concentration decreases.

    Roles of Calcium in the Body

    • Calcium plays a role in signal transduction, neurotransmitter release, and muscle contraction.
    • Calcium is a structural component in bone matrix and is involved in bone formation.

    Calcium Balance

    • Renal and gastrointestinal systems maintain a balance of calcium, with net excretion of calcium by the kidney equal to net absorption from the gastrointestinal tract.
    • Bone remodeling involves the simultaneous formation of new bone and resorption of old bone.

    Role of Phosphate in the Body

    • Phosphate is involved in the formation of ATP, serves as a biologic buffer, and can modify protein functions.
    • Phosphate can act as a biologic buffer and modulate protein functions.

    Regulation of Calcium Metabolism

    • The body maintains homeostasis of calcium and phosphate concentrations through various mechanisms.
    • Calcium and phosphate are essential for various physiological processes, including muscular contraction, membrane permeability, endocrine and exocrine secretions, enzyme regulation, and coagulation.

    Physiological Processes Involving Ca2+

    • Muscular contraction
    • Membrane permeability
    • Endocrine and exocrine secretions
    • Enzyme regulation
    • Coagulation

    Calcium Stabilizes Membrane Potentials

    • Hypocalcemia (low calcium levels) can lead to muscle spasms, cardiac arrhythmias, and seizures due to enhanced membrane excitability.
    • Hypercalcemia (high calcium levels) reduces membrane excitability, leading to muscle weakness and stupor.

    Acid-Base Abnormalities and [Ca2+]

    • Acid-base abnormalities alter the ionized Ca2+ concentration by changing the fraction of Ca2+ bound to plasma albumin.
    • In acidemia, the free ionized Ca2+ concentration increases due to the excess of H+ ions binding to albumin.
    • In alkalemia, the free ionized Ca2+ concentration decreases due to the deficit of H+ ions binding to albumin.

    Roles of Calcium in the Body

    • Signal transduction (neurotransmitter release)
    • Second messenger
    • Structural component in bone matrix
    • Muscle contraction
    • Bone formation

    Calcium Balance

    • Renal and GI: Net excretion of Ca2+ by the kidney equals net absorption of Ca2+ from the gastrointestinal tract.
    • Bone remodeling: new bone is formed, and old bone is resorbed. Bone resorption is stimulated by parathyroid hormone.

    Role of Phosphate in the Body

    • Formation of adenosine triphosphate (ATP)
    • Phosphate can serve as a biologic buffer
    • Phosphate can act as a modifier of proteins, altering their functions.

    Calcium and Phosphate Reabsorption

    • PTH inhibits phosphate reabsorption in the proximal convoluted tubule of the nephron (phosphaturic action of PTH).
    • Phosphaturia: the phosphaturic action of PTH causes the phosphate resorbed from bone to be excreted in the urine, allowing the plasma ionized Ca2+ concentration to increase.

    Actions of Parathyroid Hormone (PTH)

    • Inhibits phosphate reabsorption
    • Stimulates Ca2+ reabsorption
    • Stimulates Vitamin D synthesis

    PTH and Small Intestine

    • PTH indirectly stimulates intestinal Ca2+ absorption via activation of vitamin D.

    Vitamin D Synthesis

    • Renal cells produce 1,25-dihydroxycholecalciferol (active metabolite) or 24,25-dihydroxycholecalciferol (inactive metabolite) depending on the status of Ca2+ in the body.
    • 1α-Hydroxylase activity is regulated by changing the activity of the 1α-hydroxylase enzyme.

    Actions of Vitamin D

    • Increases plasma levels of both Ca2+ and phosphate
    • Promotes mineralization of new bone
    • Has coordinated actions on the:
      • Intestine: increases both Ca2+ and phosphate absorption
      • Kidney: stimulates both Ca2+ and phosphate reabsorption
      • Bone: stimulates osteoclast activity and bone resorption

    Pathophysiology of Vitamin D

    • Rickets: vitamin D deficiency causes rickets in children, leading to softening of bones
    • Osteomalacia: new bone fails to mineralize in adults, resulting in bending and softening of weight-bearing bones

    Bone Mass in Balance

    • Osteoblasts deposit new bone
    • Weight-bearing activities
    • Calcium/Vitamin D
    • Estrogen/Testosterone

    Resorption/Bone Loss

    • Osteoclast cells digest bone
    • Inactivity
    • Deficient nutrition
    • Low Estrogen/Low Testosterone

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    Description

    Understand the mechanisms of maintaining homeostasis of body calcium and phosphate concentrations, including body stores, absorption, excretion, and hormone regulation. Learn about the organs involved and their roles in regulating calcium movement.

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