Parathyroid hormone is an endocrine hormone secreted by the parathyroid gland. The parathyroid glands are 4 in number located just behind the thyroid gland. This hormone is extremely important for the calcium metabolism of the body. This hormone is mainly protein in nature which contains 84 amino acids polypeptide. The half life of this hormone is about 4 minutes. Parathyroid hormone helps to maintain the right needed level of calcium in the body. This hormone should be present in the body at the normal levels, its deficiency or its presence in excess would show adverse effects on the body.
The synthesis of this hormone takes place in the preprohormone. The hormone after being processed is secreted into the secretory vesicles.
Function of the parathyroid hormone:
The main function of the parathyroid hormone is to maintain normal calcium levels in the body. When the calcium levels in the body falls, the parathyroid hormone compensates for the loss of calcium in the following ways-
- · calcium mobilization from the bones
- · facilitates calcium absorption from the intestine
- · calcium loss in the urine is suppressed
a) Calcium mobilization from the bones:
The bones of the body act as a large reservoir of calcium. So in cases when there is a calcium level fall in the body, the osteoclasts get stimulated and cause the resorption of the bone in order to bring back the calcium level in the body to normal. This causes the release of both calcium and phosphorus from the bones of the body into circulation.
b) Facilitates calcium absorption from the intestine:
This is done by the activation of the vitamin D. vitamin D in its active form is known as 1,25 dihydroxy vitamin D. The active form of vitamin D helps in the absorption of calcium from the intestine, when the level of calcium falls in the body.
c) Calcium loss in the urine is suppressed:
This process mainly occurs in the kidney. The calcium and the magnesium reabsorption take place in distal part on the tubule and the ascending tubule. Since calcium and phosphorus both are released from the body, the parathyroid hormone also facilitates the secretion of phosphorus from the body. By this there is more amount of free calcium which circulates in the body.
In the deficiency of the parathyroid hormone there can be symptoms such as:
- · paresthesia of the finger tips, toe nails and sometimes the perioral areas
- · disturbance of the normal personality of an individual like anxiety, mood swings
- · cramping of the muscles
- · seizures
- · fatigue and hyperirritability
- · spasm of the larynx and the bronchus
- · overall metabolic disturbances
In certain situations the parathyroid hormone is secreted in excess, this condition is known as hyperparathyroidism. In such cases the following symptoms are seen:
- · pain in the back, eyes and bone
- · easy fracture of bones
- · increase in thirst and the urine output
- · fatigue
- · abdominal pain
Hyperparathyroidism can be of two types:
- · Primary hyperparathyroidism- this condition arises when there is a defect in the gland itself.
- · Secondary hyperparathyroidism- this condition arises when there is a defect which lies outside the gland.
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