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 Of The Parathyroid Glands:

• 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 On Bone, Kidney, And Intestine:

• Bone: The osteoclasts get stimulated to release calcium.

• Kidney: Increased calcium reabsorption and phosphate excretion

• Intestine: Calcium absorption is increased indirectly due to active 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 Of Calcium And Phosphate Excretion

• Increases reabsorption of calcium in renal tubules.

• Promotes phosphate excretion to maintain its levels.

Intestinal Absorption Of Calcium

• Increases absorption indirectly through stimulation of vitamin D.

Parathyroid Hormone Disorders

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

Hyperparathyroidism (Primary, Secondary, And Tertiary):

• 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.

Hypoparathyroidism:

• Insufficient production of PTH resulting in hypocalcemia.

Symptoms And Complications Of Pth Disorders:

• Hyperparathyroidism: Bone pain, kidney stones, fatigue.

• Hypoparathyroidism: Muscle cramps, tetany, seizures.

Parathyroid Hormone Levels Diagnostic Tests

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

Blood Tests For PTH Levels:

• Serum PTH levels

• Serum calcium and phosphate levels

Imaging Studies (Ultrasound, Sestamibi Scan):

• Ultrasound: Visualization of parathyroid glands

• Sestamibi Scan: Nuclear medicine scan to detect overactive glands

Treatment Options For Parathyroid Hormone Imbalances

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

• Vitamin D and calcium supplements in hypoparathyroidism.

• Calcimimetics in hyperparathyroidism.

Surgical Options

• Parathyroidectomy involves removing the overactive glands in hyperparathyroidism.

Lifestyle And Dietary Changes

• Adequate intake of calcium and vitamin D.

• Regular check on calcium levels.