Anatomy
The parathyroid glands are four or more small glands, about the size of a grain of rice, located on the posterior surface (back side) of the thyroid gland. The parathyroid glands usually weigh between 25 mg and 40 mg in humans. There are typically two, one above the other, on the left lobe of the thyroid and similarly on the right. The two parathyroid glands on each side which are positioned higher (closer to the head) are called the superior parathyroid glands, while the lower two are called the inferior parathyroid glands. Occasionally, some individuals may have six, eight, or even more parathyroid glands.
The parathyroid glands are named for their proximity to the thyroid but serve a completely different role than the thyroid gland. The parathyroid glands are quite easily recognizable from the thyroid as they have densely packed cells, in contrast with the follicle structure of the thyroid. However, at surgery, they are harder to differentiate from the thyroid or fat.
Because the inferior thyroid arteries provide the primary blood supply to the posterior aspect of the thyroid gland where the parathyroid glands are located, branches of these arteries usually supply the parathyroid glands. However they may also be supplied by the branches of the superior thyroid arteries. thyroid ima artey or the laryngeal, tracheal or esopahgeal artery. Parathyroid veins drain into thyroid plexus of veins of the thyroid gland.
Lymphatic vessels from the parathyroid glands drain into deep cervical lymph nodes and paratracheal lymph nodes.
In the histological sense, they distinguish themselves from the thyroid gland, as they contain two types of cells:
| Name | Staining | Quantity | Size | Function |
| parathyroid chief cells | darker | many | smaller | manufacture PTH (see below). |
| oxyphil cells | lighter | few | larger | function unknown. |
Read more about this topic: Parathyroid Gland
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“Man is a shrewd inventor, and is ever taking the hint of a new machine from his own structure, adapting some secret of his own anatomy in iron, wood, and leather, to some required function in the work of the world.”
—Ralph Waldo Emerson (1803–1882)