Parathyroid Gland Functions
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Parathyroid Gland Functions

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Questions and Answers

What is the primary physiological effect of Trousseau's sign?

  • It reflects secretion of parathyroid hormone.
  • It indicates an increase in blood flow to the extremities.
  • It involves flexion of the wrist and thumb with extension of the fingers. (correct)
  • It measures the contraction of facial muscles.

    • Which hormone is primarily responsible for lowering serum calcium levels?

  • Cholecalciferol
  • Parathyroid hormone
  • Calcitonin (correct)
  • Calcitriol

    • Which of the following statements about Vitamin D3 is correct?

  • Vitamin D3 decreases calcium absorption in the intestines.
  • It is formed in the skin by the action of ultraviolet light. (correct)
  • Vitamin D3 can only be obtained from dietary sources.
  • It is activated solely in the kidneys.

    • What is the role of parathyroid hormone regarding calcium levels?

    <p>It increases calcium levels in the bloodstream.</p> Signup and view all the answers

    Which organ is NOT involved in the activation of vitamin D3?

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

    Which statement accurately describes the effect of calcitonin on phosphate levels?

    <p>It lowers phosphate levels similar to calcium.</p> Signup and view all the answers

    How does hyperparathyroidism affect calcium levels in the body?

    <p>It results in hypercalcemia.</p> Signup and view all the answers

    What is the antagonistic relationship between calcitonin and parathyroid hormone primarily regarding?

    <p>Calcium and phosphate levels in the body.</p> Signup and view all the answers

    What is the primary role of Parathyroid Hormone (PTH) in the body?

    <p>Regulates calcium concentration in the extracellular fluid</p> Signup and view all the answers

    Which of the following organs does PTH primarily target to increase plasma calcium levels?

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

    What immediate effect does PTH have on bone?

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

    How does PTH affect the kidneys?

    <p>Increases calcium reabsorption and magnesium retention</p> Signup and view all the answers

    What is the delayed (chronic) effect of PTH on bone?

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

    What is the relationship between PTH and vitamin D3?

    <p>PTH increases vitamin D3 production in the kidneys, which enhances calcium absorption</p> Signup and view all the answers

    Which of the following statements about PTH's action on the intestine is accurate?

    <p>Calcium absorption is enhanced indirectly via vitamin D3</p> Signup and view all the answers

    What type of calcium pool does PTH mobilize from the bones for immediate effect?

    <p>Ionic calcium pool</p> Signup and view all the answers

    What primarily regulates the secretion of PTH?

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

    What happens to PTH secretion when plasma calcium levels are high?

    <p>It is inhibited to prevent further calcium deposition.</p> Signup and view all the answers

    What is the condition characterized by the replacement of bone mineral salts with fibrous tissue leading to deformities?

    <p>Osteitis fibrosa cystica</p> Signup and view all the answers

    In primary hyperparathyroidism, what is typically associated with increased calcium levels?

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

    What is the consequence of excess calcium salts being filtered through the kidneys in primary hyperparathyroidism?

    <p>Formation of renal stones and colic</p> Signup and view all the answers

    What result occurs when there is a decrease in plasma calcium levels?

    <p>Increased secretion of PTH</p> Signup and view all the answers

    Which of the following is NOT a manifestation of primary hyperparathyroidism?

    <p>Elevated phosphorus levels</p> Signup and view all the answers

    What is indicated by the term 'solubility product' in relation to calcium and phosphate?

    <p>The product of calcium and phosphate concentrations must remain constant</p> Signup and view all the answers

    What is a common gastrointestinal disorder associated with prolonged hypercalcemia?

    <p>Peptic ulcer</p> Signup and view all the answers

    Which symptom is indicative of manifest tetany?

    <p>Tonic contractions</p> Signup and view all the answers

    What is the most common cause of hypoparathyroidism?

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

    What condition can lead to hypocalcemic tetany?

    <p>Complete absence of parathyroid hormone</p> Signup and view all the answers

    Which of the following is NOT a cause of hypocalcemia?

    <p>HbA1c elevation</p> Signup and view all the answers

    What distinguishes latent tetany from manifest tetany?

    <p>Provocative tests causing contractions</p> Signup and view all the answers

    What effect does hypercalcemia have on neuromuscular excitability?

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

    What is a possible consequence of untreated hypoparathyroidism?

    <p>Fatal hypocalcemia</p> Signup and view all the answers

    Study Notes

    Parathyroid Gland

    • Four small glands located on the posterior aspect of the thyroid gland.
    • Contain Chief cells that secrete Parathyroid Hormone (PTH).
    • PTH is essential for life, regulating calcium concentration in the extracellular fluid.

    PTH Action on Target Organs

    • Skeleton:
      • Increases bone resorption and mobilizes calcium and phosphate into the blood.
        • Immediate Effect: PTH stimulates membrane-bound calcium pumps, transferring soluble calcium from bone fluid to plasma.
        • Delayed (Chronic) Effect: PTH increases osteoclast activity, breaking down calcium crystals and releasing calcium into plasma.
    • Kidneys:
      • Stimulates calcium and magnesium reabsorption and phosphate excretion.
      • Increases formation of active vitamin D3 (calcitriol).
    • Intestine:
      • Increases calcium absorption through indirect action via vitamin D3.
      • PTH increases calcitriol formation, which enhances calcium binding proteins (calbindin D) in the intestinal mucosa, increasing calcium absorption.

    Regulation of PTH

    • Primarily regulated by blood calcium levels through a cell membrane calcium sensing receptor.
    • High calcium levels negatively feedback to inhibit PTH secretion, depositing calcium into bones.
    • Low calcium levels stimulate PTH secretion, increasing calcium resorption from bones.
    • PTH secretion is also affected by factors including magnesium levels, phosphate levels, and vitamin D levels.
    • Plasma phosphorus concentration is inversely related to calcium concentration, maintaining a constant solubility product.

    Abnormalities of Parathyroid Hormone Secretion

    • Precise regulation of calcium levels is crucial for life (8.5-10.5 mg/dl).
    • Hyperfunction (hyperparathyroidism) leads to hypercalcemia.
    • Hypofunction (hypoparathyroidism) leads to hypocalcemic tetany.

    Hyperparathyroidism

    • Often characterized by hypercalcemia and hypophosphatemia, resulting in:

      • Skeletal Issues: Bones soften and deform as mineral salts are replaced by fibrous connective tissue, leading to multiple cysts (osteitis fibrosa cystica) and increased risk of fractures and deformities.
      • Renal Issues: Excess calcium filtered through the kidneys leads to stone formation, potential for renal colic and hematuria, and calcium deposition in the kidney tissue, potentially resulting in renal failure.
      • Neuromuscular Issues: Decreased neuromuscular excitability manifests as muscle weakness, decreased alertness, and memory impairment.
      • Gastrointestinal Issues: Hypercalcemia stimulates gastric acid secretion, potentially leading to peptic ulcers, while decreased intestinal motility can cause nausea, vomiting, and constipation.
      • Cardiac Issues: Cardiac arrhythmias can occur.

    • Treatment involves surgical removal of the tumor in primary hyperparathyroidism or addressing the underlying cause in secondary cases.

    Hypoparathyroidism

    • Primarily caused by accidental removal or damage of parathyroid glands during thyroid surgery.
    • Characterized by hypocalcemia and hyperphosphatemia.
    • Complete absence of PTH is lethal, while relative deficiency causes tetany.

    Tetany

    • A state of spastic skeletal muscle contractions due to increased neuromuscular excitability from decreased ionized calcium levels.

    Causes of Hypocalcemia

    • Hypoparathyroidism
    • Renal failure
    • Alkalemia (decreased ionized calcium)
    • Vitamin D deficiency

    Manifestations of Hypocalcemia

    • Manifest Tetany:

      • Occurs during rest when calcium levels are below 7 mg%.
      • Characterized by muscular twitches, tonic and clonic muscle contractions, and potential for generalized convulsions.
      • Muscle stiffness between attacks.

    • Latent Tetany:

      • Occurs when calcium levels are between 7-8.5 mg%.
      • Tetanic contractions are absent at rest but appear during specific situations (stress, hyperventilation, pregnancy).
      • Latent tetany can progress to manifest tetany with provocative tests.
      • Carpopedal spasm can occur.

    Provocative Tests for Latent Tetany

    • Trousseau's Sign: Occluding forearm circulation for a few minutes using a sphygmomanometer induces ischemia, leading to wrist flexion, thumb flexion, and finger extension.
    • Chvostek's Sign: Tapping over the facial nerve at the angle of the jaw causes quick contraction of facial muscles.

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    Description

    Explore the essential roles of the parathyroid gland and its hormone in regulating calcium levels. This quiz delves into the actions of parathyroid hormone (PTH) on the skeleton, kidneys, and intestines. Test your understanding of this crucial aspect of human physiology.

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