Endocrine System Overview

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Questions and Answers

What physiological effect results from Trousseau’s sign?

  • Flexion of wrist and thumb with extension of fingers (correct)
  • Extension of the fingers and flexion of the wrist
  • Occlusion of blood flow to the heart
  • Contraction of facial muscles

Which hormone is released by the parafollicular cells of the thyroid gland?

  • Calcitonin (correct)
  • Parathyroid hormone (PTH)
  • Cholecalciferol
  • 1,25-dihydroxycholecalciferol

Which of the following best describes the function of calcitonin?

  • It increases calcium absorption in the intestine.
  • It lowers serum calcium and phosphate levels. (correct)
  • It stimulates the release of parathyroid hormone.
  • It raises calcium and phosphate levels in the blood.

What are the key organs involved in the activation of vitamin D3?

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

What is the primary effect of parathyroid hormone (PTH) on calcium levels?

<p>It increases calcium levels in blood. (D)</p> Signup and view all the answers

In which conditions does hyperparathyroidism lead to tetany?

<p>Due to increased calcium levels (hypercalcemia). (B)</p> Signup and view all the answers

What is the source of vitamin D3 in the human body?

<p>Diet and UV light action on skin (B)</p> Signup and view all the answers

Which statement accurately describes the function of vitamin D3?

<p>It helps increase calcium levels by acting on intestine, kidney, and bone. (B)</p> Signup and view all the answers

What is the primary function of Parathyroid Hormone (PTH)?

<p>To regulate the Ca$^{2+}$ concentration in the extracellular fluid (B)</p> Signup and view all the answers

Which of the following actions describes the immediate effect of PTH on the skeleton?

<p>Stimulates the release of calcium from the labile pool in bone fluid (C)</p> Signup and view all the answers

What is the role of PTH in the kidney?

<p>It enhances the reabsorption of calcium and magnesium while excreting phosphate (A)</p> Signup and view all the answers

How does PTH indirectly influence calcium absorption in the intestine?

<p>By increasing vitamin D3 (calcitriol) production in the kidneys (C)</p> Signup and view all the answers

What long-term effect does PTH have on bone structure?

<p>It leads to the activation of osteoclasts, resulting in bone resorption (C)</p> Signup and view all the answers

What effect does PTH have on plasma phosphate levels?

<p>It decreases plasma phosphate levels through renal action (D)</p> Signup and view all the answers

Which cells in the parathyroid glands secrete Parathyroid Hormone (PTH)?

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

What is the consequence of increased osteoclast activity due to PTH?

<p>Increased calcium release into plasma and localized bone dissolution (A)</p> Signup and view all the answers

What primarily regulates the secretion of parathyroid hormone (PTH)?

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

What occurs when plasma Ca2+ levels are high?

<p>PTH secretion is inhibited (A)</p> Signup and view all the answers

Which statement about hypercalcemia in primary hyperparathyroidism is true?

<p>It leads to bone deformation due to replacement by fibrous tissue. (B)</p> Signup and view all the answers

What is the effect of increased PTH secretion on calcium resorption?

<p>It increases calcium resorption from bones. (D)</p> Signup and view all the answers

Which condition is characterized by osteitis fibrosa cystica?

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

What is the primary consequence of renal stone formation due to primary hyperparathyroidism?

<p>Renal colic and hematuria (C)</p> Signup and view all the answers

What is the relationship between plasma calcium and phosphorus concentrations?

<p>They are inversely related. (A)</p> Signup and view all the answers

What physiological response occurs with low ionized plasma calcium levels?

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

What physiological effect does hypercalcemia have on neuromuscular excitability?

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

Which gastrointestinal disorder is associated with prolonged hypercalcemia?

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

What is the most common cause of hypoparathyroidism?

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

What triggers manifest tetany in hypoparathyroidism?

<p>Decreased ionized plasma calcium level below 7 mg% (D)</p> Signup and view all the answers

Which of the following symptoms is NOT a manifestation of hypoparathyroidism?

<p>Increased intestinal motility (D)</p> Signup and view all the answers

What condition is characterized by hypocalcemia and hyperphosphatemia?

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

Which of these conditions can lead to the development of hypocalcemia?

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

Which condition results from accidental removal or damage to parathyroid glands during surgery?

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

Flashcards

Trousseau's Sign

A medical sign where occluding blood flow in the forearm for a few minutes causes hand flexing and finger extending, indicating low calcium levels.

Chvostek's Sign

A medical sign where tapping on the facial nerve near the jaw causes muscle contractions, indicating low calcium levels.

Parathyroid Hormone (PTH)

A hormone produced by the parathyroid glands that increases blood calcium levels. It acts by promoting calcium release from bones, reabsorption in kidneys, and absorption in the intestines.

1, 25-dihydroxycholecalciferol (Calcitriol)

The active form of vitamin D3, it increases blood calcium levels. It stimulates calcium absorption in the intestines, reabsorption in the kidneys, and calcium release from bones.

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Calcitonin

A hormone released from the thyroid gland that lowers blood calcium levels, acting primarily on bones to reduce calcium release, and to a lesser extent on the kidneys to reduce reabsorption.

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Hypocalcemia

A condition characterized by low blood calcium levels, often caused by low parathyroid hormone. This can cause muscle spasms and cramps.

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Hypercalcemia

A condition characterized by high blood calcium levels, often caused by excessive parathyroid hormone production. It can lead to various symptoms including fatigue, weakness, and kidney stones.

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Bone Resorption

The process of calcium moving from bones into the blood, promoted by parathyroid hormone.

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Parathyroid Glands

Four small glands located on the posterior aspect of the thyroid gland, responsible for secreting parathyroid hormone (PTH).

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PTH's Primary Function

The major action of PTH is to increase the concentration of calcium in the blood by mobilizing it from bones, promoting its reabsorption in the kidneys, and indirectly increasing its absorption in the intestines.

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PTH's Effect on Skeleton

PTH stimulates the breakdown of bone, releasing both calcium and phosphates into the bloodstream. This process can be immediate or delayed.

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PTH's Immediate Effect on Bone

The rapid effect of PTH on bone, taking minutes to hours, involves stimulating calcium pumps on bone cell membranes, leading to direct release of calcium into the blood.

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PTH's Delayed Effect on Bone

The long-term effect of PTH on bone, taking days to weeks, involves increasing the activity of osteoclasts, which break down bone, releasing calcium in a more sustained manner.

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PTH's Effect on Kidneys

PTH stimulates reabsorption of calcium and magnesium, and promotes excretion of phosphate in the kidneys, contributing to the overall regulation of calcium in the blood.

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PTH's Effect on Intestines

PTH indirectly increases calcium absorption in the intestines by stimulating the kidney to produce active vitamin D3 (calcitriol).

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High Blood Calcium, PTH Role

When blood calcium levels are high, PTH secretion is inhibited, leading to calcium deposition in bones. This promotes bone building.

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Low Blood Calcium, PTH Role

When blood calcium levels are low, PTH secretion is increased, leading to calcium resorption from bones. This promotes bone breakdown.

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Solubility Product

The product of calcium and phosphate concentrations in the blood. This product remains relatively constant, meaning an increase in one usually means a decrease in the other.

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Hyperparathyroidism

A condition characterized by high blood calcium levels, often caused by excessive parathyroid hormone production. It can lead to symptoms like weak bones, kidney stones, and fatigue.

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Hypoparathyroidism

A condition characterized by low blood calcium levels, often caused by low parathyroid hormone production. It can lead to symptoms like muscle spasms and cramps.

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Osteitis Fibrosa Cystica

A bone disease associated with hyperparathyroidism. Bones soften and deform as their mineral salts are replaced by fibrous connective tissue.

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Renal Stones in Hyperparathyroidism

A condition where kidney stones form due to excess calcium being filtered by the kidneys. This can cause pain and blood in urine.

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Primary Hyperparathyroidism

A condition where the parathyroid glands produce too much parathyroid hormone (PTH), leading to high blood calcium levels.

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Peptic Ulcer in Primary Hyperparathyroidism

A symptom of primary hyperparathyroidism where the stomach produces excess acid, potentially leading to a peptic ulcer.

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Tetany

A state of uncontrolled muscle contractions caused by low calcium levels in the blood, leading to increased neuromuscular excitability.

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Neuromuscular Excitability in Hypocalcemia

An increased sensitivity to stimuli that can cause tetany (muscle spasms) in the presence of low blood calcium levels.

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Latent Tetany

A state of hypocalcemia that doesn't exhibit obvious signs of tetany at rest, but can be triggered by certain situations like stress, hyperventilation, or pregnancy.

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Study Notes

Endocrine System Overview

  • The endocrine system is a complex network of glands responsible for producing and releasing hormones into the bloodstream.

Parathyroid Gland

  • Typically, four small glands located on the posterior aspect of the thyroid gland.
  • Contains chief cells that secrete parathyroid hormone (PTH).
  • PTH's primary function is regulating calcium (Ca²⁺) concentration in the extracellular fluid (ECF).
  • Essential for life due to its role in calcium regulation.
  • This hormone increases plasma calcium levels and decreases plasma phosphate levels.

PTH's Action on Target Organs

  • 1. Skeleton: PTH directly affects bone, increasing bone resorption and releasing ionic calcium and phosphates into the bloodstream.
    • Immediate effect: occurs within minutes, PTH stimulates calcium pumps in the bone to release calcium.
    • Delayed effect: takes days to weeks, PTH increases osteoclast activity to break down bone and release Ca2+ into the bloodstream.
  • 2. Kidneys: PTH directly stimulates calcium reabsorption and phosphate excretion in the kidneys.
    • It also increases the formation of active vitamin D3 (calcitriol).
  • 3. Intestine: PTH indirectly increases calcium absorption via vitamin D3 formation.
    • Vitamin D3, in turn, increases calcium absorption from the intestine through increasing calbindin production.

Regulation of PTH Levels

  • PTH levels are primarily regulated by blood calcium levels, not other glands.
  • A calcium sensing receptor on parathyroid cells monitors blood calcium levels.
  • High calcium levels inhibit PTH secretion, while low calcium levels increase it.
  • This is a negative feedback mechanism.

Relationship between Calcium and Phosphorus

  • Plasma phosphorus concentration is inversely related to calcium concentration.
  • Their product (Ca²⁺ × PO₄⁻³) remains relatively constant, this is called the solubility product.

Abnormalities of Parathyroid Hormone Secretion

  • Hyperparathyroidism
    • Causes: Typically a parathyroid gland tumor (adenoma). Compensatory hypertrophy can occur due to vitamin D deficiency or renal failure.
    • Manifestations: Bone disease (weak bones, spontaneous fractures), kidney stones, neuromuscular issues (muscle weakness, decreased alertness, poor memory), abdominal pain, nausea, vomiting & constipation, and cardiac arrhythmias.
  • Hypoparathyroidism
    • Cause: Accidental removal or injury of parathyroid glands during thyroid surgery (thyroidectomy).
    • Manifestations: Hypocalcemia, hyperphosphatemia, and tetany (spastic muscle contractions).

Hypocalcemia Causes

  • Hypoparathyroidism
  • Renal failure
  • Alkalemia (decreased ionized Ca²⁺)
  • Vitamin D deficiency

Manifestations of Hypocalcemic Tetany (Symptoms)

  • Manifest tetany: Occurs when blood calcium levels fall below 7 mg%. Characterized by muscle twitching, tonic and clonic spasms, and generalized convulsions.
  • Latent tetany: Blood calcium levels are between 7-8.5 mg%. Tetanic contractions are absent at rest but may occur in stress, hyperventilation, or pregnancy; manifested by provocative tests.

Hypoparathyroidism Treatment

  • Manifest tetany: Calcium gluconate via intravenous injection
  • Latent tetany: Calcium rich diet and vitamin D3 supplementation.

Calcium Homeostasis

  • The interconnected roles of bone, small intestine, and kidneys in calcium regulation.

Role of Calcium in Physiologic Processes

  • Bone and teeth formation, neuromuscular excitability, muscle contraction, synaptic transmission, hormone secretion, intracellular communication, blood clotting, and maintenance of tight junctions.

Hormonal Control of Calcium

  • Parathyroid hormone (PTH), 1,25-dihydroxycholecalciferol (vitamin D3), and calcitonin play a key role in regulating blood calcium levels.

Vitamin D3

  • Obtained from diet (e.g., fatty fish, egg yolks) and formed in the skin from UV light.
  • Activated in the liver and kidneys.
  • Increases calcium absorption in the intestine, kidneys, and bone.

Calcitonin

  • Released by parafollicular cells of the thyroid gland
  • Primarily regulates calcium absorption and excretion through it's interaction with the bone and kidneys.
  • Antagonistic to PTH (regarding calcium) but similar to PTH (regarding phosphorus).

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