Parathyroid

Parathyroid Gland

Location & Definition

* Small yellowish brown, ovoid structures

* 6 x 3-4 x 1-2 mm

* Weighs 50mg

* Related posterior border of thyroid gland within its fascial (fibrous) capsule

* Stimulates the activityof osteoclasts

* Chief cells that produce parathyroid hormone/ parathormone

* parathyroid hormone/ parathormone

* Stimulates osteoclastic activity in bone thus, mobilizing bone calcium

* Increases calcium levels in blood

* Secretion of parathyroid hormone is controlled by calcium levels in the blood

* Stimulates absorption of dietary calcium from small intestine

* Also, stimulates reabsorption of calcium in proximal convulated tubules of the kidney

* Strongly diminishes the reabsorption of phosphate in the proximal tubules of kidney disease

* 4 in number = 2 superior, 2 inferior

Embryological Development

* Endoderm

* 3rd and 4th pharyngeal arches/pouch

* Proliferation of entodermal cells of the 3rd pharyngeal arch/pouch = inferior parathyroid gland pair (Parathyroid III)

* Proliferation of entodermal cells of the 4th pharyngeal arch/pouch = superior parathyroid gland pair (Parathyroid IV)

* Earliest stages, consists of solid mass of clear cells (chief cells)

* Late Childhood, oxyphil cells (acidophilic) appear

* Oxyphil cells – thought to be non-functioning chief cells

* Conditions

* Absence and Hypoplasia of Parathyroid Glands

* Incomplete development or agenesis is demonstrated in individuals with idiopathic hypoparathyroidism.

* Ectopic Parathyroid Glands

* Finding of the parathyroid tissue in the superior mediastinum of the thorax

* If the parathyroid glands remain attached to the thymus, they may be pulled inferiorly into the lower part of the neck or thoracic cavity.

* Explains the variable position of the inferior parathyroid glands in...