The parathyroid glands, tiny organs behind the thyroid, play a crucial role in calcium regulation. They produce parathyroid hormone (PTH), which works to increase blood calcium levels by targeting bones, kidneys, and intestines.

Disorders of the parathyroid glands can lead to serious health issues. Hyperparathyroidism causes high calcium levels and weakened bones, while hypoparathyroidism results in low calcium, muscle cramps, and potentially dangerous complications like seizures.

Parathyroid Glands

Location and structure of parathyroid glands

• Embedded in the posterior surface of the thyroid gland typically four glands: two superior and two inferior
• Small, oval-shaped glands composed of chief cells and oxyphil cells
  • Chief cells secrete parathyroid hormone (PTH) which regulates calcium levels in the body
  • Oxyphil cells have an unknown function but are present in higher numbers in older individuals

Parathyroid hormone and calcium regulation

• Parathyroid hormone (PTH), also known as parathormone, functions to increase blood calcium levels when they fall below normal by targeting bones, kidneys, and intestines to maintain calcium homeostasis
• Effects on bones:
  1. Stimulates osteoclasts to break down bone matrix and release calcium into the bloodstream (bone resorption)
  2. Increases calcium reabsorption from bone fluid
• Effects on kidneys:
  1. Enhances reabsorption of calcium in the distal tubules and collecting ducts
  2. Reduces reabsorption of phosphate, leading to increased phosphate excretion
  3. Stimulates the production of active vitamin D (calcitriol) which increases intestinal absorption of calcium
• Effects on intestines: PTH indirectly increases calcium absorption through its effect on calcitriol production in the kidneys

Effects of parathyroid disorders

• Hyperparathyroidism involves excessive secretion of PTH due to enlargement or tumors of the parathyroid glands (primary) or as a compensatory response to chronic low blood calcium levels (secondary)
  • Effects include hypercalcemia (elevated blood calcium), weakened bones due to increased bone resorption, formation of kidney stones due to increased calcium excretion, and symptoms like fatigue, muscle weakness, and depression
  • Prolonged hyperparathyroidism can lead to osteoporosis, a condition characterized by decreased bone density and increased risk of fractures
• Hypoparathyroidism involves insufficient secretion of PTH often due to damage or removal of parathyroid glands during thyroid surgery, autoimmune disorders, or genetic factors
  • Effects include hypocalcemia (low blood calcium), muscle cramps, twitches, and spasms, tingling sensations in the fingers and toes, and in severe cases seizures and cardiac arrhythmias
  • In extreme cases, hypoparathyroidism can lead to tetany, a condition characterized by severe muscle spasms and convulsions

Calcium Homeostasis and the Endocrine System

• The parathyroid glands are part of the endocrine system, which regulates various bodily functions through hormone secretion
• Calcitonin, a hormone produced by the thyroid gland, works in opposition to PTH by lowering blood calcium levels
• The interplay between PTH and calcitonin helps maintain calcium homeostasis in the body