Parathyroid Gland – Class 11 | Chapter – 22 | Biology Short Notes Series PDF

Parathyroid Gland: The parathyroid glands are small endocrine glands situated just below the thyroid glands in the neck. They are usually four in number, two behind each thyroid gland. They are very small, pea-sized and weigh about 50 mg. The glands function to maintain the calcium and phosphorus levels in our bodies.

Functions of Parathyroid Gland

The parathyroid gland’s main role is in secreting parathyroid hormone (PTH). PTH acts by raising the levels of calcium in the blood. This is accomplished by PTH’s ability to do three things. First, PTH can stimulate the breakdown of bone, which inherently releases calcium from the stores held within the bone.

Second, PTH can also increase the reabsorption of calcium from food by influencing the permeability of the intestinal membrane. In doing so, more calcium is absorbed directly into the bloodstream, raising overall calcium levels.

Third, PTH can increase retention of calcium in the kidneys that would otherwise be lost in the urine. This tight control of blood calcium levels earns the parathyroid gland’s status as a kind of thermostat. When the blood’s calcium becomes too low, the body will release more PTH which will bring the calcium levels back to normal.

In contrast, when calcium levels are too high, the parathyroid gland will stop releasing PTH. Maintenance of proper calcium levels goes a long way. A calcium balance will benefit the heart, the kidneys, the nervous system, and the bones. Low calcium levels can lead to heart, bone, and neural disease.

Location of Parathyroid Gland

Parathyroid Gland

The parathyroid gland is found in the neck behind, adjacent, or within the thyroid gland. Another landmark that gives its relative location is the Adam’s apple, which lies next to the parathyroid glands that grace either side of it. The number of glands can vary but most people are born with four.

They are about the size of a grain of rice where one lies above the other on each side of the neck. The parathyroid gland will be composed of epithelial cells that excrete parathyroid hormone, and the gland will be richly supplied by capillary beds. The superior, or top, parathyroid gland is supplied by the inferior thyroid arteries, while the inferior gland will receive supply from variable sources like the ascending branch of inferior thyroid artery or the thyroid inferior mesenteric artery. The parathyroid veins drain into a venal thyroid plexus.

Disorders of Parathyroid Gland

Hyperparathyroidism: This condition is developed when an individual produces too much of the PTH hormone. Overproduction of the hormone releases large amounts of calcium, which causes hypercalcemia. The symptoms include extreme thirst, more urine production, abdominal pain and mood changes. Undetected high levels of calcium lead to bone thinning or osteoporosis and can also cause stones in the kidneys.

Hypoparathyroidism: Low levels of PTH hormone causes hypoparathyroidism and hypocalcemia. The symptoms include tingling sensations, muscle cramps and spasms.

Hormones of Parathyroid Gland

The major hormone released by the parathyroid gland is parathyroid hormone (PTH). PTH has two very important functions within the body. First, PTH stimulates osteoclasts, a type of cell involved in the breakdown and buildup of bone tissue. When stimulated by PTH, these cells break down bone and release the calcium into the bloodstream. Calcium is needed in a wide variety of cellular processes, and the parathyroid gland is the main regulator of calcium.

PTH also functions by directing the kidneys to convert an inactive form of vitamin D into the active form, which has a hormone function. When active vitamin D reaches the intestine, it directs the intestine to take up more calcium, further increasing the calcium concentration.

Second, PTH acts to decrease the phosphate within the blood serum. While this is technically a second function, it is also related to blood calcium levels. Phosphate tends to form salts with calcium. So, when you decrease the amount of phosphate by excreting more from the kidneys, the calcium level in the blood is subsequently increased.

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By Team Learning Mantras