Parathyroid Hormone: What It Is, Function, Levels, Symptoms & Treatment

Definition of Parathyroid Hormone (PTH)

Parathyroid hormone is one of the peptide hormones produced by the parathyroid glands, which have a crucial role in maintaining the calcium and phosphate levels within the blood. PTH is involved in the maintenance of calcium homeostasis by its action on bone remodelling, renal reabsorption of calcium, and intestinal calcium absorption.

Anatomy of the Parathyroid Glands

These are small endocrine glands located near the thyroid gland and have an important function in maintaining calcium levels within the body.

Structure and Location

• Four small glands on the posterior surface of the thyroid gland.

• Typically, two superior and two inferior glands.

• Each gland is about the size of a grain of rice.

Synthesis and Secretion of Parathyroid Hormone

Synthesis and secretion are tightly regulated processes crucial for calcium homeostasis.

PTH Synthesis Process

• PTH is synthesised as a preprohormone.

• Cleaved to form prohormone and then active PTH.

Factors Influencing PTH Secretion

• Serum calcium levels: Low levels stimulate secretion.

• Serum phosphate levels: High levels stimulate secretion.

• Vitamin D levels: Inhibit secretion.

Regulation of Calcium and Phosphate Homeostasis

PTH is integral in the regulation of calcium and phosphate balance in the body.

Role of PTH in Calcium Regulation

• Increases calcium release from bones.

• Increases calcium reabsorption in the kidneys.

• Stimulates calcium absorption in the intestines by facilitating the action of vitamin D.

Mechanism of Action of PTH

Mechanism of action of PTH is discussed below:

Action on Bone

• The osteoclasts get stimulated to release calcium.

• Promotes bone resorption.

Action on Kidneys

• Increased calcium reabsorption in renal tubules

• Promotes phosphate excretion

Action on Intestine

• Calcium absorption is increased indirectly

• Achieved through activation of vitamin D

Physiological Effects of Parathyroid Hormone

PT H has several physiological effects that are of importance to calcium equilibrium and bone health.

Bone Remodeling and Calcium Mobilisation

• Stimulates the activity of osteoclasts to resorb the bone, thereby making calcium available.

Renal Reabsorption and Phosphate Balance

• Increases reabsorption of calcium in renal tubules.

• Promotes phosphate excretion to maintain its levels.

Intestinal Calcium Absorption

• Increases absorption indirectly through stimulation of vitamin D.

Parathyroid Hormone Disorders

An abnormal concentration of PTH can result in several clinical disorders.

Hyperparathyroidism

Types:

• Primary: Gland overproduction due to adenoma or hyperplasia.

• Secondary: Compensation due to low calcium as seen in chronic renal failure.

• Tertiary: Autonomous PTH secretion following long-standing secondary hyperparathyroidism.

Symptoms:

• Bone pain

• Kidney stones

• Fatigue

Hypoparathyroidism:

• Insufficient production of PTH

• Leads to hypocalcemia.

Symptoms:

• Muscle cramps

• Tetany

• Seizures

Diagnostic Tests for PTH Disorders

For an accurate diagnosis of disorders related to the parathyroid hormone, the following tests are necessary.

Blood Tests

• Serum PTH levels

• Serum calcium and phosphate levels

Imaging Studies

• Ultrasound of parathyroid glands

• Sestamibi Scan to detect overactive glands

Treatment Options for PTH Imbalances

Treatment will depend on the type and degree of PTH imbalance.

Medical Management

• Vitamin D and calcium supplements in hypoparathyroidism.

• Calcimimetics (hyperparathyroidism).

Surgical Options

• Parathyroidectomy for hyperparathyroidism.

• Removing of overactive glands

Lifestyle And Dietary Changes

• Adequate intake of calcium and vitamin D.

• Regular check on calcium levels.

Parathyroid Hormones (PTH) NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Functions of parathyroid hormones

• Disorders related to PTH

Practice Questions for NEET

Q1. The blood calcium level is lowered by the deficiency of

1. Thyroxine

2. Calcitonin

3. Parathormone

4. Both 1 and 2

Correct answer: 3) Parathormone

Explanation:

The parathyroid glands secrete a peptide hormone called parathyroid hormone (PTH), which plays a crucial role in regulating calcium levels in the blood. The secretion of PTH is primarily controlled by the circulating levels of calcium ions. When blood calcium levels drop, the parathyroid glands increase the release of PTH to stimulate the release of calcium from bones, increase calcium reabsorption by the kidneys, and promote the activation of vitamin D, which enhances calcium absorption from the intestines. Conversely, when calcium levels rise, the secretion of PTH is reduced, maintaining a balanced calcium concentration in the body.

Hence the correct answer is option 3) Parathormone.

Q2. Tetany is caused by

1. Hyperparathyroidism

2. Hypoparathyroidism

3. Hypothyroidism

4. Hyperthyroidism

Correct answer: 2) Hypoparathyroidism

Explanation:

The clinical complications associated with hypoparathyroidism can result in a disorder termed parathyroid tetany or hypocalcemic tetany, characterized by involuntary muscle contractions that can be distressing and potentially dangerous. Proper diagnosis and management of this condition are essential to restore calcium balance and reduce symptoms.

Hence, the correct answer is option 2) Hypoparathyroidism.

Q3. Which of the following hormones can play a significant role in osteoporosis?

1. Estrogen and Parathyroid hormone

2. Progesterone and Aldosterone

3. Aldosterone and Prolactin

4. Parathyroid hormone and Prolactin

Correct answer: 1) Estrogen and Parathyroid hormone

Explanation:

Estrogen: By preventing bone resorption, or breakdown, this hormone aids in maintaining bone density. Osteoporosis is a disorder in which bones become weak and can be exacerbated by a reduction in estrogen levels, such as occurs after menopause.

Parathyroid hormone (PTH): PTH affects bone metabolism and controls blood calcium levels. Increased bone resorption brought on by high PTH levels can erode bones even more and exacerbate osteoporosis. PTH promotes bone breakdown to release calcium into the bloodstream when blood calcium levels are low.

Hence, the correct answer is option 1)Estrogen and Parathyroid hormone.

Also Read:

• MCQs on Parathyroid Gland

• Mechanism of Hormone Action

• Adrenal Gland