12
Parathyroid Gland
There are four parathyroid glands which are trivial, subtle clumps that project from
the surface of the thyroid gland. They are of butterfly shape and are situated inside
of neck, more precisely on either side of trachea. Parathyroid glands majorly play a
role in controlling amount of phosphorus as well as calcium in body [17, 18].
Parathyroid glands are also involved in release of parathyroid hormones that are
responsible for removal of calcium from bones into extracellular fluid by inhibiting
the synthesis of osteoblasts (particular cells responsible for bone formation) and the
stimulation of osteoclasts(specialized cells responsible for the removal of the
bone) [19].
There are two principal cells that constitute the parathyroid tissue which are
chief cells (secrete parathyroid hormone) as well as oxyphil. Morphologically parathyroid glands are largely dissimilar to thyroid gland. The main parathyroid hormone releasing cells are organized in a compact nest surrounding the small blood
vessels. It is completely different from the thyroid hormone releasing cells, which
are organized in spheres referred to as thyroid follicles [20, 21].
Parathyroid Hormone (PTH)
Four parathyroid glands directly release parathyroid hormone (PTH) into the blood
that reaches to its targeted areas, usually located at distance. Then binding takes
place between PTH and receptors present superficially or inside relevant cells.
Primary target cells of PTH are present in the bone, gastrointestinal systems, and
kidney. Calcitonin counteracts the production of calcium by PTH [22].
PTH opposes the action of thyrocalcitonin by eliminating calcium from the calcium storage site in the bone into the blood. In addition, PTH stimulates small
intestine as well as kidneys to reabsorb extra calcium and transport it to the bloodstream. Calcium is essential for the body’s metabolism, blood clotting, and skeletal
muscle’s contraction. Lack of PTH can cause muscle weakness and tetany due deficiency of available calcium in the blood [23, 24]. Calcium-phosphate balance
between blood as well as other tissues is controlled by parathormone or PTH. Level
of calcium in extracellular fluid bathing these glandular cells directly regulates
secretion of this hormone (Fig. 1.4). Parathormone has the following functions:
1. It rises the absorption of calcium in GIT and transfers calcium from the intestinal
lumen into the bloodstream by stimulating the active transport system.
2. It rises translocation of phosphate as well as calcium from bones to extracellular
fluid by activating osteoclasts that involve in destruction of bone structure and
hence rising calcium and phosphate levels in blood. As a result, the amount of
calcium confined in the bone can be excavated.
3. It causes renal tubules to reabsorb more calcium thus reducing urinary elimination of calcium.
A. Ahsan et al.
Parathyroid Gland
There are four parathyroid glands which are trivial, subtle clumps that project from
the surface of the thyroid gland. They are of butterfly shape and are situated inside
of neck, more precisely on either side of trachea. Parathyroid glands majorly play a
role in controlling amount of phosphorus as well as calcium in body [17, 18].
Parathyroid glands are also involved in release of parathyroid hormones that are
responsible for removal of calcium from bones into extracellular fluid by inhibiting
the synthesis of osteoblasts (particular cells responsible for bone formation) and the
stimulation of osteoclasts(specialized cells responsible for the removal of the
bone) [19].
There are two principal cells that constitute the parathyroid tissue which are
chief cells (secrete parathyroid hormone) as well as oxyphil. Morphologically parathyroid glands are largely dissimilar to thyroid gland. The main parathyroid hormone releasing cells are organized in a compact nest surrounding the small blood
vessels. It is completely different from the thyroid hormone releasing cells, which
are organized in spheres referred to as thyroid follicles [20, 21].
Parathyroid Hormone (PTH)
Four parathyroid glands directly release parathyroid hormone (PTH) into the blood
that reaches to its targeted areas, usually located at distance. Then binding takes
place between PTH and receptors present superficially or inside relevant cells.
Primary target cells of PTH are present in the bone, gastrointestinal systems, and
kidney. Calcitonin counteracts the production of calcium by PTH [22].
PTH opposes the action of thyrocalcitonin by eliminating calcium from the calcium storage site in the bone into the blood. In addition, PTH stimulates small
intestine as well as kidneys to reabsorb extra calcium and transport it to the bloodstream. Calcium is essential for the body’s metabolism, blood clotting, and skeletal
muscle’s contraction. Lack of PTH can cause muscle weakness and tetany due deficiency of available calcium in the blood [23, 24]. Calcium-phosphate balance
between blood as well as other tissues is controlled by parathormone or PTH. Level
of calcium in extracellular fluid bathing these glandular cells directly regulates
secretion of this hormone (Fig. 1.4). Parathormone has the following functions:
1. It rises the absorption of calcium in GIT and transfers calcium from the intestinal
lumen into the bloodstream by stimulating the active transport system.
2. It rises translocation of phosphate as well as calcium from bones to extracellular
fluid by activating osteoclasts that involve in destruction of bone structure and
hence rising calcium and phosphate levels in blood. As a result, the amount of
calcium confined in the bone can be excavated.
3. It causes renal tubules to reabsorb more calcium thus reducing urinary elimination of calcium.
A. Ahsan et al.