Factors Affecting Calcium Absorption
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Questions and Answers

What hormone is responsible for increasing calcium absorption?

  • Estrogen
  • Calcitonin
  • Calcitriol (correct)
  • Parathyroid hormone (PTH)

    • Which nutrient, when present in high amounts, can lead to the precipitation of calcium?

  • Fatty acids
  • Phosphate (correct)
  • Oxalic acid
  • Amino acids

    • What hormone decreases plasma calcium levels?

  • Calcitriol
  • Calcitonin (correct)
  • Estrogen
  • Parathyroid hormone (PTH)

    • In which conditions does the efficiency of calcium absorption increase by 50%?

    <p>Pregnancy, lactation, and adolescence</p> Signup and view all the answers

    Which acid is associated with decreased calcium absorption?

    <p>Phytic acid</p> Signup and view all the answers

    What is the function of Parathyroid hormone (PTH) in relation to serum calcium levels?

    <p>Increase Serum Ca2+ levels</p> Signup and view all the answers

    What is the main action of PTH on bones?

    <p>Promotes osteoclast differentiation</p> Signup and view all the answers

    Which receptor is upregulated by PTH in osteoblasts?

    <p>RANK receptor</p> Signup and view all the answers

    What is the function of osteoprotegerin (OPG) in bone metabolism?

    <p>Prevents osteoclast activation by blocking RANKL-RANK interaction</p> Signup and view all the answers

    How does PTH affect calcium reabsorption in the kidney?

    <p>Stimulates calcium reabsorption from DCT</p> Signup and view all the answers

    What effect does PTH have on urinary calcium levels?

    <p>Reduces urinary calcium levels within minutes</p> Signup and view all the answers

    How does PTH influence phosphate levels in the body?

    <p>Decreases serum phosphate levels</p> Signup and view all the answers

    Which of the following is NOT a symptom or sign of hypercalcaemia?

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

    What is the normal range for plasma ionised Ca2+?

    <p>1.1 - 1.3 mmol/L</p> Signup and view all the answers

    Which hormone is involved in calcium homeostasis that promotes calcium reabsorption in the kidneys?

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

    Why is alteration in calcium balance important for cells?

    <p>To affect excitability of cells</p> Signup and view all the answers

    What percentage of ionised Ca2+ is typically found in the extracellular fluid (ECF)?

    <p>~50%</p> Signup and view all the answers

    What is the main action of PTH on the small intestine?

    <p>Indirectly increases intestinal absorption of calcium through its influence on vitamin D3</p> Signup and view all the answers

    How does PTH affect phosphate reabsorption in the kidneys?

    <p>Inhibits phosphate reabsorption in the kidneys</p> Signup and view all the answers

    Which gland is involved in a negative feedback mechanism to regulate PTH release in response to hypocalcemia?

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

    In hyperparathyroidism, what is the primary cause of increased PTH levels?

    <p>Parathyroid gland adenoma or hyperplasia</p> Signup and view all the answers

    What is the consequence of long-term secondary hyperparathyroidism?

    <p>Parathyroid gland hyperplasia and loss of response to serum Ca2+ levels</p> Signup and view all the answers

    What action does active vitamin D3 have on intestinal calcium absorption?

    <p>Increases intestinal calcium absorption by inducing calbindin-D synthesis</p> Signup and view all the answers

    What is the main reason behind the symptoms and signs of hypocalcaemia related to nerve and muscular hyperexcitability?

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

    Which of the following is NOT a symptom of hypocalcaemia?

    <p>Muscular relaxation</p> Signup and view all the answers

    What is the sign called when carpopedal spasm occurs after 3 minutes of sphygmomanometer cuff inflation above systolic BP?

    <p>Trousseau sign</p> Signup and view all the answers

    Which of the following is a method used in Chvostek's sign to test for hypocalcaemia?

    <p>Tapping the facial nerve at the jaw</p> Signup and view all the answers

    What does a positive response in Chvostek's sign indicate?

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

    Why does ischemia worsen the condition in Trousseau sign?

    <p>It exacerbates neuromuscular hyperexcitability</p> Signup and view all the answers

    Study Notes

    • Calcitonin is the hormone responsible for increasing calcium absorption.
    • High amounts of phosphorus can lead to the precipitation of calcium.
    • Parathyroid hormone (PTH) decreases plasma calcium levels.

    Factors Affecting Calcium Absorption

    • Efficiency of calcium absorption increases by 50% during pregnancy and lactation.
    • Phytic acid is associated with decreased calcium absorption.

    Functions of Parathyroid Hormone (PTH)

    • PTH regulates serum calcium levels by promoting calcium release from bones, kidney reabsorption, and intestinal absorption.
    • The main action of PTH on bones is the stimulation of bone resorption by osteoclasts.
    • PTH upregulates the receptor activator of nuclear factor kappa-Β (RANKL) in osteoblasts.

    Bone Metabolism and Kidneys

    • Osteoprotegerin (OPG) inhibits RANKL, helping to regulate bone metabolism and prevent excessive bone destruction.
    • PTH enhances calcium reabsorption in the kidneys.
    • PTH leads to increased urinary calcium levels due to its mobilization from bones and reduced renal reabsorption.

    Effects on Phosphate Levels

    • PTH decreases phosphate reabsorption in the kidneys, leading to increased urinary phosphate excretion.

    Hypercalcemia Symptoms

    • Symptoms of hypercalcemia include nausea, vomiting, fatigue, and confusion, while muscle spasms and tetany are usually not present.
    • Normal range for plasma ionised Ca2+ is typically between 1.1 to 1.3 mmol/L.
    • The hormone associated with calcium homeostasis and promoting renal calcium reabsorption is calcitriol (active vitamin D).

    Importance of Calcium Balance

    • Calcium balance is critical for cellular functions including muscle contraction, blood clotting, and neurotransmitter release.

    Ionised Calcium in Extracellular Fluid

    • About 45% of ionised Ca2+ is typically found in the extracellular fluid (ECF).

    Main Actions of PTH

    • PTH promotes intestinal absorption of calcium indirectly by enhancing the activation of vitamin D3.
    • PTH decreases phosphate reabsorption in the kidneys, contributing to the overall management of phosphate levels.

    Feedback Mechanisms and Hyperparathyroidism

    • The thyroid gland is involved in a negative feedback mechanism to regulate PTH release in response to hypocalcemia.
    • In hyperparathyroidism, the primary cause of increased PTH levels is usually a parathyroid adenoma.

    Consequences of Secondary Hyperparathyroidism

    • Long-term secondary hyperparathyroidism can lead to bone loss and weakening.

    Active Vitamin D3 Role

    • Active vitamin D3 increases intestinal calcium absorption, enhancing overall calcium homeostasis.

    Symptoms of Hypocalcemia

    • Nerve and muscular hyperexcitability symptoms are mainly due to low extracellular calcium levels.
    • Symptoms of hypocalcemia include numbness, cramps, and seizures, excluding hypercalcemia signs.
    • The sign seen when carpopedal spasm occurs after three minutes of sphygmomanometer cuff inflation is called Trousseau’s sign.
    • Chvostek's sign tests for hypocalcemia by tapping the facial nerve and observing muscle twitching.
    • A positive response in Chvostek's sign indicates possible hypocalcemia.
    • Ischemia can worsen Trousseau's sign by increasing neuromuscular irritability.

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    Description

    This quiz covers various factors that influence the absorption of calcium in the body, including hormonal regulation, dietary components, and physiological conditions. Topics include the effects of hormones like calcitriol and estrogen, as well as issues like malabsorption and calcium demand during specific life stages.

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