5.9.3 Parathyroid Glands

Introduction

The parathyroid glands are small endocrine glands located on the thyroid gland in the neck. Despite their small size, they play a crucial role in regulating calcium and phosphate balance in the body. This topic explains the structure, hormone, and function of the parathyroid glands.

Definition

The parathyroid glands are two pairs of very small structures located on the thyroid glands. They secrete the hormone called parathormone.

Main Idea

• Located on the thyroid glands are two pairs of very small structures called parathyroid glands.
• They secrete the hormone called parathormone.
• Parathormone has function opposite to the function of calcitonin.
• It controls the balance of calcium ions and phosphate in body.

Core Concept

Parathyroid Glands and Parathormone

Detailed Explanation

1. Structure of Parathyroid Glands

Located on the thyroid glands are two pairs of very small structures called parathyroid glands.

Simple explanation: The parathyroid glands are four tiny glands located on the back of the thyroid gland in your neck.

Why they are important:

• They regulate calcium levels in the blood.
• They regulate phosphate levels in the blood.
• They work with calcitonin to maintain calcium balance.

2. Parathormone (PTH)

What it is: Parathormone is the hormone secreted by the parathyroid glands.

Function:

• Parathormone has function opposite to the function of calcitonin.
• It controls the balance of calcium ions and phosphate in body.

Simple explanation: Parathormone raises blood calcium levels. It does the opposite of calcitonin, which lowers blood calcium levels.

How parathormone raises blood calcium:

• Stimulates osteoclasts: Breaks down bone tissue, releasing calcium into the blood.
• Increases intestinal absorption: Enhances absorption of calcium from the intestine.
• Increases renal reabsorption: Increases reabsorption of calcium in the kidneys.
• Increases phosphate excretion: Increases excretion of phosphate in the urine.

Why this is important:

• Calcium is essential for bone health, muscle contraction, nerve transmission, and blood clotting.
• Phosphate is essential for bone formation, energy metabolism, and DNA synthesis.

3. Opposing Actions of Calcitonin and Parathormone

Simple explanation: Calcitonin and parathormone work in opposite directions to keep blood calcium levels balanced.

How they work together:

• When blood calcium is high → calcitonin is secreted → calcium is deposited in bones → blood calcium decreases.
• When blood calcium is low → parathormone is secreted → calcium is released from bones → blood calcium increases.

4. Disorders of Parathyroid Glands

Simple explanation:

• Too much parathormone → too much calcium in blood → bone weakness, kidney stones.
• Too little parathormone → too little calcium in blood → muscle cramps, tetany.

Summary Table

Intermediate Level

The parathyroid glands are located on the thyroid gland and secrete parathormone.

Key points:

• Parathormone raises blood calcium levels.
• Calcitonin lowers blood calcium levels.
• Parathormone and calcitonin work together to maintain calcium balance.
• Parathormone also regulates phosphate balance.

Disorders:

Important Points

• - Located on the thyroid glands are two pairs of very small structures called parathyroid glands.
• - They secrete the hormone called parathormone.
• - Parathormone has function opposite to the function of calcitonin.
• - It controls the balance of calcium ions and phosphate in body.
• - Parathormone raises blood calcium levels.
• - Calcitonin lowers blood calcium levels.
• - Parathormone stimulates osteoclasts to release calcium from bones.
• - Parathormone increases calcium reabsorption in the kidneys.
• - Parathormone increases phosphate excretion in the urine.
• - Hyperparathyroidism causes high blood calcium; bone weakness, kidney stones.
• - Hypoparathyroidism causes low blood calcium; muscle cramps, tetany.

Remember

• - Parathyroid glands = two pairs (four glands)
• - Location = on the thyroid glands
• - Hormone = parathormone
• - Function = controls balance of calcium ions and phosphate
• - Parathormone = raises blood calcium
• - Calcitonin = lowers blood calcium
• - Opposing actions = maintain calcium balance
• - Disorders = hyperparathyroidism (high calcium), hypoparathyroidism (low calcium)

Common Mistakes

• 1. Confusing parathyroid glands with thyroid gland.
• - Thyroid gland = produces thyroxin and calcitonin.
• - Parathyroid glands = produce parathormone.
• 2. Mixing up parathormone and calcitonin.
• - Parathormone = raises blood calcium.
• - Calcitonin = lowers blood calcium.
• 3. Thinking the parathyroid glands are part of the thyroid gland.
• - They are separate glands located on the thyroid gland.
• 4. Forgetting the role of parathormone in phosphate balance.
• - Parathormone increases phosphate excretion in the urine.
• 5. Confusing hyperparathyroidism and hypoparathyroidism.
• - Hyperparathyroidism = too much parathormone → high blood calcium.
• - Hypoparathyroidism = too little parathormone → low blood calcium.
• 6. Believing calcium is only important for bones.
• - Calcium is also important for muscle contraction, nerve transmission, and blood clotting.
• 7. Thinking the parathyroid glands are not important.
• - The parathyroid glands are essential for calcium homeostasis.

Quick Revision

60-Second Revision

• Parathyroid glands = two pairs (four glands)
• Location = on the thyroid glands
• **Hormone** = parathormone
• Function = controls balance of calcium ions and phosphate
• Parathormone = raises blood calcium
• Calcitonin = lowers blood calcium
• Opposing actions = maintain calcium balance
• Disorders = hyperparathyroidism (high calcium), hypoparathyroidism (low calcium)
• Warning: Do not confuse parathormone (raises blood calcium) with calcitonin (lowers blood calcium).