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Questions and Answers
What is one potential complication of prolonged hypercalcemia in cases of primary hyperparathyroidism?
What is one potential complication of prolonged hypercalcemia in cases of primary hyperparathyroidism?
Which of the following conditions is most likely caused by accidental removal of parathyroid glands during surgery?
Which of the following conditions is most likely caused by accidental removal of parathyroid glands during surgery?
Which symptom is associated with latent tetany due to hypocalcemia?
Which symptom is associated with latent tetany due to hypocalcemia?
What physiological change occurs in hypoparathyroidism due to decreased PTH levels?
What physiological change occurs in hypoparathyroidism due to decreased PTH levels?
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Which of the following is a manifestation of hypocalcemia in hypoparathyroidism?
Which of the following is a manifestation of hypocalcemia in hypoparathyroidism?
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Which of the following statements about provocation tests for tetany is accurate?
Which of the following statements about provocation tests for tetany is accurate?
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In the context of hypoparathyroidism, what happens when calcium levels drop below 7 mg%?
In the context of hypoparathyroidism, what happens when calcium levels drop below 7 mg%?
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Which treatment option is primarily utilized for primary hyperparathyroidism?
Which treatment option is primarily utilized for primary hyperparathyroidism?
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What is the primary effect of elevated plasma calcium levels on parathyroid hormone (PTH) secretion?
What is the primary effect of elevated plasma calcium levels on parathyroid hormone (PTH) secretion?
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Which of the following is NOT a manifestation of primary hyperparathyroidism?
Which of the following is NOT a manifestation of primary hyperparathyroidism?
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What is the expected physiological response when plasma calcium levels are low?
What is the expected physiological response when plasma calcium levels are low?
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Which of the following best describes the solubility product of calcium and phosphate?
Which of the following best describes the solubility product of calcium and phosphate?
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What is a key symptom of hypocalcemic tetany?
What is a key symptom of hypocalcemic tetany?
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Which of the following complications is primarily associated with prolonged primary hyperparathyroidism?
Which of the following complications is primarily associated with prolonged primary hyperparathyroidism?
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What happens to the calcium sensing receptor in parathyroid glands when blood calcium levels are high?
What happens to the calcium sensing receptor in parathyroid glands when blood calcium levels are high?
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What laboratory finding is typically expected in patients with primary hyperparathyroidism?
What laboratory finding is typically expected in patients with primary hyperparathyroidism?
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Which of the following hormones is primarily responsible for increasing calcium levels in the blood?
Which of the following hormones is primarily responsible for increasing calcium levels in the blood?
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What is the primary effect of calcitonin in relation to calcium levels?
What is the primary effect of calcitonin in relation to calcium levels?
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Which provocative test involves the occlusion of circulation in the forearm to assess latent tetany?
Which provocative test involves the occlusion of circulation in the forearm to assess latent tetany?
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What condition can lead to tetany due to enhanced calcium levels in the bloodstream?
What condition can lead to tetany due to enhanced calcium levels in the bloodstream?
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Which of the following statements about vitamin D3 is correct?
Which of the following statements about vitamin D3 is correct?
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Which factor is NOT a direct action of parathyroid hormone (PTH)?
Which factor is NOT a direct action of parathyroid hormone (PTH)?
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Which sign is associated with the contraction of facial muscles upon tapping over the facial nerve?
Which sign is associated with the contraction of facial muscles upon tapping over the facial nerve?
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Which hormone is released from the parafollicular cells of the thyroid gland?
Which hormone is released from the parafollicular cells of the thyroid gland?
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Study Notes
Provocative Tests for Latent Tetany
- Trousseau's sign: Occluding blood flow in the forearm for a few minutes causes ischemia of peripheral nerves, resulting in wrist flexion, thumb flexion, and finger extension.
- Chvostek's sign: Tapping over the facial nerve at the angle of the jaw causes a quick contraction of facial muscles.
Hormonal Control of Calcium Ion Concentration
-
Parathyroid Hormone (PTH):
- Increases calcium levels in the blood.
- Acts on intestines, kidneys, and bone.
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1, 25- Dihydroxycholecalciferol (Calcitriol) (Active Vitamin D3):
- Can be obtained from diet (fat fish & egg yolk).
- Formed in the skin by ultraviolet light.
- Activated in the liver and kidney.
- Increases calcium levels in the blood by acting on intestines, kidneys, and bone.
-
Calcitonin (Thyrocalcitonin):
- Released from parafollicular cells of the thyroid gland.
- A polypeptide hormone (32 amino acids).
- Lowers serum calcium and phosphate levels.
- Antagonistic to PTH regarding calcium but similar to PTH regarding phosphate.
- Lower blood calcium by acting on bones and kidneys.
Regulation of Parathyroid Hormone (PTH)
- PTH is primarily regulated by blood calcium levels.
- Parathyroid glands and many tissues contain a cell membrane calcium-sensing receptor.
- Circulating ionized calcium acts directly on the parathyroid glands in a negative feedback fashion to regulate PTH secretion.
- When plasma calcium is high, PTH secretion is inhibited, leading to calcium deposition in bones.
- When plasma calcium is low, PTH secretion is increased, leading to calcium resorption from bones.
Factors Increasing PTH Secretion
- Decreased ionized plasma calcium levels
- Decreased plasma magnesium levels
- Increased plasma phosphate levels
- Decreased vitamin D3 levels
Abnormalities of Parathyroid Hormone Secretion
- Calcium is crucial for life, requiring precise control of ionic calcium levels in body fluids (8.5-10.5 mg/dl).
- Hyperfunction (Hyperparathyroidism): Leads to hypercalcemia.
- Hypofunction (Hypoparathyroidism): Leads to hypocalcemic tetany.
Hyperparathyroidism
- A disease of bones, stones, and abdominal groans.
- Characterized by hypercalcemia and hypophosphatemia.
-
Manifestations:
- Bones: Softening and deformation of bones due to replacement of mineral salts with fibrous connective tissue. Multiple bone cysts form (osteitis fibrosa cystica), leading to spontaneous fractures and deformities.
- Stones: Formation of renal stones from excess calcium salts filtered through the kidneys, leading to renal colic and hematuria. Calcium salts can deposit within kidney tissue, leading to renal failure.
- Abdominal Groans: Gastrointestinal disorders like peptic ulcers (prolonged hypercalcemia stimulates gastric acid secretion) and acute pancreatitis. Nausea, vomiting, and constipation (decreased intestinal motility) can occur.
- Cardiac Arrhythmias: Irregular heart rhythms.
- Treatment: Surgical removal of the tumor in primary hyperparathyroidism, treatment of the cause in secondary hyperparathyroidism.
Hypoparathyroidism
- Cause: Most common cause is accidental removal or injury of parathyroid glands during thyroid surgery (thyroidectomy), leading to hypocalcemic tetany.
- Characteristics: Hypocalcemia and hyperphosphatemia.
- Complete Absence of PTH: Leads to death.
- Relative Deficiency: Manifested by tetany.
- Tetany: A state of spastic contraction of the skeletal muscle caused by increased neuromuscular excitability due to decreased ionized plasma calcium levels.
Causes of Hypocalcemia
- Hypoparathyroidism
- Renal failure
- Alkalemia (decreased ionized calcium)
- Vitamin D deficiency
Symptoms of Hypocalcemia
- Manifest tetany: Appears during rest when blood calcium levels decrease below 7mg%. It is characterized by muscular twitches and attacks of tonic and clonic contractions, leading to generalized convulsions. Between attacks, muscles are stiff with carpopedal spasm.
- Latent tetany: Occurs when blood calcium levels are between 7 - 8.5 mg%. Tetanic contractions are absent at rest but appear in certain situations (stress, hyperventilation, pregnancy). This can be made manifest by provocative tests.
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