What is Parathyroid Gland?
- There are four parathyroid glands distributed as two glands on either side of the thorax.
- The number of parathyroid glands in humans can vary between people. Up to eight parathyroid glands have been reported, some of which may be in other areas of the neck.
- The parathyroid gland releases the parathyroid hormone, also called parathyroid hormone, which is responsible for regulating the calcium balance in the blood.
- The parathyroid is directly involved in the functioning of various organs in the body such as the kidneys, bones, and small intestine.
- The regulation of the calcium level in the blood is maintained by influencing the calcium intake from food or by osteoporosis to increase the calcium level in the blood.
Structure of Parathyroid Gland
- Parathyroid glands appear as nodular structures that originate from the endodermal tissues that are present on the dorsal side of the thyroid gland.
- The size of the glands differs in different people, but the average weight of each of the glands is around 50 grams.
- Each of the glands is surrounded by capsules, which are made of fine connective tissue and enclose spherical cells arranged in columns of blood-containing sinusoids.
- The parathyroid glands are made up of two different cell types; Main cells and oxyphilic cells.
- The main cells are the functional cells of the parathyroid gland, which are responsible for both synthesis and secretion of the parathyroid hormone.
- The regulation of hormone synthesis and release depends on serum calcium levels.
- The surface of the main cells contains G-protein-coupled transmembrane receptors, so-called calcium-sensing receptors (CaSR), which respond to low calcium levels in the blood.
- The oxyphilic cells, also called oxyntic cells, are also located in the parathyroid but have no endocrine function. The number of oxyphilic cells in the parathyroid increases with age.
Hormones of Parathyroid Gland
- The parathyroid gland produces the parathyroid hormone, or parathyroid hormone, which is the main hormone that controls calcium levels in the blood.
- Controlling the Ca2 + level in the blood is important because Ca2 + homeostasis is involved in the transmission of nerve impulses, muscle contraction, and blood clotting.
- The decrease in calcium levels in the blood is recognized by the receptors on the main cells, which then stimulate the cell to release the parathyroid hormone.
- The release of parathyroid hormone causes cells in the skeletal system, digestive system, and kidney to use a different mechanism to hold calcium in the blood.
- The process of osteoporosis takes place in the bones, in which the osteoclasts break down the calcium in the bone so that the calcium level in the blood can be maintained.
- In the kidneys, the hormone stimulates calcium retention during filtration, while vitamin D is activated.
- The activated vitamin D is important for the reabsorption of calcium in the distal tubule of the nephrons, as it is controlled by a cytosolic vitamin D-dependent calcium-binding protein.
Functions of Parathyroid Gland
The following are some of the functions of the parathyroid gland;
- The primary function of the parathyroid is to synthesize and release parathyroid hormone, which is essential for maintaining calcium homeostasis in the body.
- The release of parathyroid hormone from the gland inhibits osteoclastic activity and stimulates osteoclastic activity, which causes calcium to break down and is released into the bloodstream.
- The parathyroid hormone also affects the nephrons of the kidney, where it induces reabsorption of calcium by regulating the calcium transporter.
- The parathyroid gland has no direct effect on the gastrointestinal tract, but it does increase vitamin D synthesis, which then increases calcium and phosphate reabsorption from the intestine.
Diseases and Disorders of Parathyroid Gland
The following are some of the disorders and diseases associated with the parathyroid gland;
- Primary hyperparathyroidism is a common condition affecting approximately 2% of the population over 55 years of age, particularly in women than men.
- It results from adenoma, hypertrophy of the glands, and carcinoma. The hypersecretion of the hormone leads to hypercalcemia and weak bones.
- Primary hyperparathyroidism is easier to diagnose because it can be detected by an increased level of calcium ions in the blood.
- Secondary hyperparathyroidism is characterized by adequate secretion of parathyroid hormone as a result of low calcium levels.
- However, the increased secretion can lead to hypercalcemia followed by primary hyperparathyroidism.
- The symptoms of secondary hyperparathyroidism are kidney stones, bone pain, and gastroesophageal reflux.
- Hypoparathyroidism is a condition characterized by a decreased release of parathyroid hormone.
- The condition leads to hypocalcemia, hyperphosphatemia, and elevated calcium ions.
- This can be due to various factors that can be genetic, autoimmune diseases, or other diseases.
- It has been observed that chronic hypoparathyroidism can lead to tetany, seizures, as well as distorted bone microarchitecture.
- Parathyroid cancer is a rare malignancy that leads to other conditions such as primary hyperparathyroidism in middle-aged adults.
- The carcinoma can lead to both kidney and skeletal symptoms such as renal colic, polyuria, fractures, and osteopenia.
- The final diagnosis of parathyroid cancer can be made by surgical resection with subsequent histological analysis.