6.2.3 Parathyroid Glands

The parathyroid glands are four small endocrine glands located on the posterior surface of the thyroid gland. They secrete parathyroid hormone (PTH), also called parathormone, which is the single most important hormone controlling the calcium balance of the blood.

Definition

Parathyroid Glands: In human, there are four parathyroid glands. All four glands are located on the thyroid gland. They are small, light coloured masses that stick out from the posterior surface of the thyroid gland.

Parathormone: The parathormone is the single most important hormone of parathyroid controlling the calcium balance of the blood.

Main Idea

• There are four parathyroid glands in humans.
• They are located on the posterior surface of the thyroid gland.
• They are small, light coloured masses.
• They secrete parathyroid hormone (PTH) or parathormone.
• Parathormone controls the calcium balance of the blood.
• Its release is triggered by low blood calcium levels.
• Its release is inhibited by high blood calcium levels.
• Parathormone works antagonistically to calcitonin.

Core Concept

• Parathyroid glands = four small glands
• Location = posterior surface of thyroid gland
• Hormone = parathyroid hormone (PTH) or parathormone
• Function = controls calcium balance of blood
• Stimulus = low blood calcium
• Inhibition = high blood calcium
• **Antagonist** = calcitonin
• Over secretion = hypercalcemia
• Under secretion = hypocalcemia

Detailed Explanation

Parathyroid Glands

• In human, there are four parathyroid glands.
• All four glands are located on the thyroid gland.
• They are small, light coloured masses that stick out from the posterior surface of the thyroid gland.
• The parathormone is the single most important hormone of parathyroid controlling the calcium balance of the blood.
• Its release is triggered by low blood calcium levels and inhibited by high blood calcium levels.
• Parathormone works antagonistically to the calcitonin.

Over Secretion of Parathormone

• Over secretion of parathormone is usually a result of a parathyroid gland tumour.
• Calcium is released from the bones and bones deform, soften and tend to fracture spontaneously.
• Blood calcium level elevates (hypercalcemia) which depresses nervous system and causes weakness of muscles.
• Excess calcium salts precipitate in the kidneys leading to stone formation.

Under Secretion of Parathormone

• Under secretion of parathormone causes hypocalcemia.
• This increases the excitability of neurons.
• Also it can lead to tetany in which muscles remain in contracted state.
• If untreated, it can be fatal.

Summary Table of Parathormone

Summary Table of Disorders

Intermediate Level

Parathyroid Glands

Regulation of Parathormone Secretion

Effects of Parathormone

Disorders of Parathyroid Gland

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. There are four parathyroid glands.
• 2. They are located on the posterior surface of the thyroid gland.
• 3. They are small, light coloured masses.
• 4. They secrete parathyroid hormone (PTH).
• 5. PTH is also called parathormone.
• 6. PTH controls calcium balance of the blood.
• 7. PTH release is triggered by low blood calcium.
• 8. PTH release is inhibited by high blood calcium.
• 9. PTH works antagonistically to calcitonin.
• 10. Over secretion of PTH causes hypercalcemia.
• 11. Hypercalcemia causes bones to deform, soften, and fracture.
• 12. Hypercalcemia causes muscle weakness.
• 13. Hypercalcemia causes kidney stones.
• 14. Under secretion of PTH causes hypocalcemia.
• 15. Hypocalcemia increases neuron excitability.
• 16. Hypocalcemia can lead to tetany.
• 17. Tetany is a condition where muscles remain contracted.
• 18. If untreated, hypocalcemia can be fatal.
• 19. PTH increases calcium release from bones.
• 20. PTH increases calcium absorption in intestines.

Remember

• - Parathyroid glands = four small glands
• - Location = posterior surface of thyroid gland
• - Hormone = parathyroid hormone (PTH) or parathormone
• - Function = controls calcium balance of blood
• - Stimulus = low blood calcium
• - Inhibition = high blood calcium
• - **Antagonist** = calcitonin
• - Over secretion = hypercalcemia
• - Under secretion = hypocalcemia
• - Hypercalcemia = bones deform, soften, fracture; muscle weakness; kidney stones
• - Hypocalcemia = increased neuron excitability; tetany; may be fatal

Common Mistakes

• 1. Confusing parathyroid and thyroid glands — Parathyroid = on thyroid; thyroid = in neck.
• 2. Mixing up the hormones — Parathyroid secretes PTH; thyroid secretes T₃, T₄, calcitonin.
• 3. Forgetting the number of glands — Four parathyroid glands.
• 4. Confusing hypercalcemia and hypocalcemia — Hyper = high calcium; hypo = low calcium.
• 5. Mixing up the causes — Hypercalcemia = over secretion of PTH; hypocalcemia = under secretion.
• 6. Forgetting the role of calcitonin — Calcitonin is the antagonist of PTH.
• 7. Thinking PTH decreases blood calcium — PTH increases blood calcium.
• 8. Mixing up the symptoms — Hypercalcemia: bone problems, kidney stones; hypocalcemia: tetany.
• 9. Believing tetany is caused by high calcium — Tetany is caused by low calcium.
• 10. Forgetting the role of the kidneys — PTH increases calcium reabsorption in kidneys.

Quick Revision

In human, there are four parathyroid glands. All four glands are located on the thyroid gland. They are small, light coloured masses that stick out from the posterior surface of the thyroid gland. The parathormone is the single most important hormone of parathyroid controlling the calcium balance of the blood. Its release is triggered by low blood calcium levels and inhibited by high blood calcium levels. Parathormone works antagonistically to the calcitonin. Over secretion of parathormone is usually a result of a parathyroid gland tumour. Calcium is released from the bones and bones deform, soften and tend to fracture spontaneously. Blood calcium level elevates (hypercalcemia) which depresses nervous system and causes weakness of muscles. Excess calcium salts precipitate in the kidneys leading to stone formation. Under secretion of parathormone causes hypocalcemia. This increases the excitability of neurons. Also it can lead to tetany in which muscles remain in contracted state. If untreated, it can be fatal.

60-Second Revision

• Parathyroid glands = four small glands
• Location = posterior surface of thyroid gland
• Hormone = parathyroid hormone (PTH) or parathormone
• Function = controls calcium balance of blood
• Stimulus = low blood calcium
• Inhibition = high blood calcium
• Antagonist = calcitonin
• Over secretion = hypercalcemia
• Under secretion = hypocalcemia
• Hypercalcemia = bones deform, soften, fracture; muscle weakness; kidney stones
• Hypocalcemia = increased neuron excitability; tetany; may be fatal
• Warning: PTH increases blood calcium; calcitonin decreases blood calcium

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• Chapter:
• 6. Endocrine System of Man

• Topic:
• 6.2.4 PANCREAS

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