The parathyroid is originated from endodermal germ layer cells of the early embryo.
These glands are yellowish-brown in color and oval in shape which remains embedded in the dorsal surface of the thyroid gland within the thyroid capsule where they continuously check and regulate the blood calcium levels. They are two pairs in number.
These glands secrete only one hormone that is Parathormone or Collip’s hormone or PTH.
It was isolated in 1923 by Adolph M. Hanson and in 1925 by James B. Collip in its pure form.
This hormone is proteinaceous in nature or chain of amino acid or polypeptide hormone.
Parathormone is essential for survival because it significantly contributes to homeostasis by regulating the amount of calcium and phosphate ions in ECF.
Calcium is a key element in many physiological functions like motility of sperm, proper permeability of cell membrane, muscular activities, nerve impulse conduction, the beating of heart, blood coagulation, bone formation, and fertilization of ova.
Calcium is the most abundant of all minerals found in the body and about 99% of calcium and phosphorus are contained in the bones and only 1% calcium is found in ECF.
Maintenance of proper calcium level and “homeostasis” is in fact, a combined function of parathormone, thyrocalcitonin, and vitamin D3 or cholecalciferol.
Parathormone is a hyperglycemic hormone that increases blood calcium levels by
- Stimulating the process of bone reabsorption/dissolution and demineralization
- Promoting the absorption of calcium from food in the intestine
- Promoting that reabsorption from the nephrons in the Kidneys
This calcium is then utilized by bone-forming cells which is osteoblast cell, in the formation of bone under the influence of vitamin D3.
Parathormone stimulates the osteoclast cells to feed upon bones, these cells remove the unnecessary parts of bones by dissolving and phagocytosis.
Thus, change asymmetrical bone into symmetrical in shape. The remolding of bone is done by these cells lifelong.
As a result of this, the amount of calcium remains constant in the blood in normal conditions. Every 100 mL of blood contains 12 mg of calcium (Ca+2).
Parathormone maintains the activity of muscles.
Just opposite to it, thyrocalcitonin (TCT) hormone works antagonistically to oppose the parathormone.
Thyrocalcitonin reduces the amount of calcium in the blood by increasing the excretion of calcium in the urine and by reducing the destruction of bone.
Due to hyposecretion of parathormone or PTH, the amount of calcium decreases in ECF, it is known as hypocalcemia, and the amount of phosphate is increased.
Due to deficiency of calcium in the blood, muscles, and nerves get unnecessarily irritated in start conversion and cramping. Sometimes voluntary muscles remain contracted for a long time, this condition is known as Tetany disease.
If this tetany happens in intercostal muscles and diaphragm, then the animal dies due to Asphyxia.
Due to the hypersecretion of PTH, osteoclast cells feed an excess amount of bone unnecessarily. As a result of these bones become brittle, weak, and easily destructible. This condition is called osteoporosis.
When the quantity of calcium is increases in ECF and the level of phosphate is reduced, this condition is known as hypercalcemia and hypophosphatemia respectively.
Due to Excess deposition of calcium in the kidneys and gallbladder, Stones are formed. This condition is known as Renal lithiasis and Cholelithiasis.
Hyperparathyroidism is the condition when one or more of the four parathyroid glands grows in size and developed into a tumor and behaves inappropriately by excessively making parathyroid hormone.
The tumor of the parathyroid gland is known as a parathyroid adenoma.
Know more from endocrinology:
|Chemical control and coordination||Thyroid Gland and its hormones|
|What are hormones? Types of Hormones, how they work?||Hypothalamus and Hypothalamic hormones|
|Pituitary Gland – Its Hormones, functions, and disorders||Complete Endocrinology|