Parathyroid Glands - Anatomy & Physiology
The Parathyroid Glands
The parathyroid glands are small glands vital for calcium homeostasis.
Anatomy
The parathyroid glands are multiple (generally four) small glands approximately 1-2mm in length are located about the cranial trachea. Generally there are two internal glands embedded within the Thyroid Glands, and two external glands are outside the thyroid tissue. However all of the parathyroid tissue may be embedded within the thyroid gland itself.
In the Horse, there are 'nests' of parathyroid tissue along the neck to the thoracic inlet.
Embryology
The parathyroid glands originate from the endoderm of pharyngeal pouches III and IV. The internal gland from pouch IV, external from pouch III.
Histology
Blood Supply and Innervation
| Arteries | Veins | Nerve | Precursor |
|---|---|---|---|
| Superior thyroid artery | Superior thyroid vein | Middle cervical ganglion | Neural crest mesenchyme |
| Inferior thyroid artery | Middle thyroid vein | Inferior cervical ganglion | 3rd and 4th pharyngeal pouch endoderm |
| .</white> | Inferior thyroid vein | .</white> | .</white> |
Physiology
- The sole function of the parathyroid gland is to maintain Calcium Homeostasis.
- When blood calcium levels drop below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood.
- The hormone produced by the parathyroid gland (Parathyroid Hormone) also has an effect on Phosphorus Homeostasis.