endocrine 4
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Questions and Answers

What is a potential effect of hypercalcemia on the body?

  • Increased cardiac contractility
  • Formation of bone fractures
  • Increased muscle strength
  • Mineralization of soft tissues (correct)

    • What percentage of total body calcium is found in bones and teeth?

  • 90%
  • 70%
  • 99% (correct)
  • 50%

    • Which physiological function is NOT regulated by calcium homeostasis?

  • Skeletal muscle contraction
  • Blood coagulation
  • Heart rate regulation
  • Protein synthesis (correct)

    • What condition may result from low calcium levels in the body?

    <p>Tetany in dogs and cats (C)</p> Signup and view all the answers

    Which hormone plays a key role in calcium regulation by acting on bones, the GI tract, and kidneys?

    <p>Parathyroid hormone (PTH) (C)</p> Signup and view all the answers

    What condition results in softening of bones in adults due to high PTH levels and vitamin D deficiency?

    <p>Osteomalacia (D)</p> Signup and view all the answers

    What physiological effect does high extracellular fluid [Ca2+] have on muscle and nerve excitability?

    <p>Depressed excitability (C)</p> Signup and view all the answers

    What is a possible consequence of high concentrations of calcium in renal filtrate?

    <p>Kidney stones (C)</p> Signup and view all the answers

    In hypocalcemia, what is the expected response of calcium regulatory hormones?

    <p>Increased Vitamin D synthesis (D)</p> Signup and view all the answers

    What is the typical calcium level in a lactating dairy cow experiencing hypocalcemia?

    <p>6.8 mg/dL (C)</p> Signup and view all the answers

    Which tissues express calcium sensing receptors (CasR)?

    <p>Parathyroid cells and kidneys (C)</p> Signup and view all the answers

    What effect does high serum calcium levels have on PTH secretion?

    <p>It decreases PTH secretion (D)</p> Signup and view all the answers

    Which receptor is classified as the classical PTH receptor?

    <p>PTH1R (A)</p> Signup and view all the answers

    How does PTH act on bone to increase plasma calcium levels?

    <p>By promoting bone resorption (A)</p> Signup and view all the answers

    Which of the following statements about PTH binding is correct?

    <p>PTH binds to PTH1R on target cells in bone and kidney (B)</p> Signup and view all the answers

    What percentage of total calcium in the body is free ionized calcium (Ca2+)?

    <p>45% (D)</p> Signup and view all the answers

    Which tissue is NOT involved in the regulation of total body calcium levels?

    <p>Liver (A)</p> Signup and view all the answers

    Which hormone primarily increases blood calcium levels?

    <p>Parathyroid hormone (PTH) (C)</p> Signup and view all the answers

    What is the primary function of calcitonin in relation to calcium levels?

    <p>Decrease blood calcium levels (C)</p> Signup and view all the answers

    What triggers the release of parathyroid hormone (PTH) from the parathyroid glands?

    <p>Low extracellular calcium levels (D)</p> Signup and view all the answers

    Which of the following processes is NOT a function of PTH?

    <p>Inhibition of vitamin D activation (A)</p> Signup and view all the answers

    How is parathyroid hormone (PTH) stored in the body?

    <p>In secretory vesicles of chief cells (C)</p> Signup and view all the answers

    Which statement best describes the complexed form of calcium in the body?

    <p>It is typically associated with anions like PO4 and SO3. (A)</p> Signup and view all the answers

    What is the primary function of parathyroid hormone (PTH) in bone?

    <p>To increase bone resorption (C)</p> Signup and view all the answers

    How does PTH increase calcium reabsorption in the kidneys?

    <p>By inhibiting the excretion of calcium in the distal tubules (B)</p> Signup and view all the answers

    What is the main effect of vitamin D on calcium levels in the body?

    <p>Promotes calcium absorption in the intestines and increases bone calcium release (C)</p> Signup and view all the answers

    Which of the following is NOT a direct stimulator of 1α-hydroxylase activity in the kidney?

    <p>High plasma phosphate (B)</p> Signup and view all the answers

    What is the role of calcitonin in the regulation of calcium homeostasis?

    <p>To decrease plasma calcium levels by inhibiting bone resorption and promoting calcium excretion (C)</p> Signup and view all the answers

    Which of the following factors is MOST likely to increase calcitonin secretion?

    <p>High plasma calcium levels (D)</p> Signup and view all the answers

    What is the primary mechanism by which calcitonin lowers blood calcium levels?

    <p>Inhibiting osteoclast activity and promoting calcium excretion (A)</p> Signup and view all the answers

    Which of the following conditions is MOST likely to result in hypocalcemia?

    <p>Vitamin D deficiency (D)</p> Signup and view all the answers

    Which of the following is a potential consequence of hypoparathyroidism?

    <p>Tetany (A)</p> Signup and view all the answers

    Which of the following is a primary mechanism by which active vitamin D increases calcium absorption in the intestines?

    <p>Activating the production of calcium-binding proteins like calbindin (A)</p> Signup and view all the answers

    Which of the following is TRUE about the regulation of 1α-hydroxylase activity by phosphate?

    <p>High phosphate levels inhibit 1α-hydroxylase (D)</p> Signup and view all the answers

    What are the primary stimuli for PTH secretion?

    <p>Low blood calcium and high phosphate levels (C)</p> Signup and view all the answers

    Which two of the following hormones directly promote bone resorption?

    <p>Parathyroid hormone (A), Vitamin D (C)</p> Signup and view all the answers

    How does Vitamin D regulate calcium homeostasis?

    <p>It enhances the effects of PTH by promoting calcium absorption and bone resorption (B)</p> Signup and view all the answers

    Which of the following is NOT a role of calcitonin in calcium homeostasis?

    <p>Promoting bone formation by stimulating osteoblasts (D)</p> Signup and view all the answers

    What is the primary physiological role of calcitonin in regulating blood calcium?

    <p>Playing a more minor role in bone remodeling compared to PTH (D)</p> Signup and view all the answers

    Study Notes

    Parathyroid Glands and Calcium Regulation

    • Parathyroid glands are small, oval-shaped structures located on the posterior surface of the thyroid gland.
    • These glands produce parathyroid hormone (PTH).
    • Calcium homeostasis is crucial for various physiological functions, including bone and tooth formation, skeletal integrity, intracellular signaling, nerve and muscle function, and blood clotting.
    • Calcium levels in the body are tightly regulated within a narrow range (8.5-10.3 mg/dL) using various mechanisms to maintain the proper balance.
    • Calcium exists in three forms: 45% ionized calcium (Ca2+), 50% bound to plasma proteins (primarily albumin), and 5% combined with anions like phosphate and sulfate. Only the ionized form (Ca2+) is biologically active.
    • Ninety-nine percent of total body calcium is stored in bones and teeth; the remaining portion is found in soft tissues and extracellular fluid.

    Calcium Homeostasis

    • Calcium levels are tightly regulated by the interplay of several hormones: parathyroid hormone (PTH), vitamin D, and calcitonin.
    • These hormones influence calcium absorption, release, and excretion across different tissues, including the gastrointestinal tract, bone, and kidneys.

    Regulation of Calcium Levels (The Three 3's)

    • The regulation of calcium levels within the body relies on the coordinated actions of three principal components:
      • 3 Tissues: Gastrointestinal tract (dietary intake and fecal excretion), Bone (storage and release), and Kidneys (urinary excretion)
      • 3 Processes: Calcium absorption (GI tract), Calcium resorption/deposition (bone), and Calcium reabsorption (kidney)
      • 3 Principal Hormones: Parathyroid hormone (PTH), 1,25-dihydroxy Vitamin D3/Calcitriol (active vitamin D3), and Calcitonin

    Parathyroid Hormone (PTH)

    • PTH is a protein hormone (84 amino acids).
    • Its primary functions include maintaining calcium homeostasis by increasing blood calcium levels. This is achieved through:
      • Increasing bone resorption, releasing calcium from the bone matrix
      • Increasing renal calcium reabsorption and reducing renal phosphate reabsorption
      • Activating Vitamin D, enhancing calcium absorption in the intestines.

    Vitamin D

    • Vitamin D is a hormone, not a true vitamin, and is involved in calcium homeostasis.
    • Two main sources: Synthesis in the skin from UV light, and dietary sources.
    • Vitamin D must be converted to its active form, 1,25-dihydroxyvitamin D3 (calcitriol), through a two-step process occurring primarily in the liver and kidneys.
    • 1,25-(OH)2 Vitamin D3 (Calcitriol) binds to specific receptors, influencing target genes for calcium homeostasis within cells.

    Calcitonin

    • Calcitonin is a peptide hormone (32 amino acids) produced by the parafollicular cells (C cells) of the thyroid gland.
    • Calcitonin opposes the effects of PTH, helping regulate blood calcium levels by:
      • Inhibiting osteoclast activity preventing the breakdown of bone (bone resorption)
      • Decreasing the reabsorption rate of calcium in the kidneys to increase excretion
      • Reducing calcium absorption from the intestines. Calcitonin lowers plasma calcium levels.

    Disruption of Calcium Homeostasis

    • Hypoparathyroidism: Rare condition caused by autoimmune disease, resulting in low PTH secretion, causing hypocalcemia (low blood calcium) and neuromuscular excitability issues (e.g., muscle spasms).
    • Hyperparathyroidism: Usually due to a hypersecreting parathyroid tumor and high PTH levels, leading to hypercalcemia (high blood calcium). Chronic renal disease or vitamin D deficiency can sometimes cause hyperparathyroidism as well.

    Calcitonin Secretion Regulation

    • Plasma calcium level regulates calcitonin secretion. Low serum Ca2+ level inhibits calcitonin release, whereas high levels stimulate it.

    Clinical Problems

    • High PTH and Vitamin D Deficiency: Leading to bone demineralization. Rickets (in children) and osteomalacia (in adults) are common consequences.
    • Low Calcium: Can lead to decreased muscle and nerve excitability, an increased risk of fractures, and kidney stones.

    Actions in Response To Conditions

    • Low calcium levels (Hypocalcemia): PTH is released to increase calcium levels. Vitamin D activation is also stimulated.
    • High calcium levels (Hypercalcemia): Calcitonin is released to decrease calcium levels.

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    Parathyroid Glands and Calcium Regulation PDF

    Description

    This quiz explores the role of parathyroid glands in calcium regulation and homeostasis. Learn about the functions of parathyroid hormone, the importance of calcium levels, and how the body maintains proper calcium balance for physiological processes. Test your knowledge on this essential endocrine function and its impact on overall health.

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