Overview
There are four
parathyroid glands located in the anterior neck. They are yellow, oval glands
that secrete parathyroid hormone (PTH), which increases serum calcium levels.
Gross Anatomy
The two pairs of
parathyroid glands lie on the posterior surface of the lateral lobes of the
thyroid gland, within the same fascicular corpuscle. Their location is
variable, with the two superior parathyroid glands usual level with the middle
of the posterior thyroid border and the two inferior parathyroid glands on the
inferior poles of the thyroid.
During development
the superior parathyroid glands are derived from the third pharyngeal pouch and
the inferior parathyroid glands from the fourth pharyngeal pouch. They
translocation during development to their adult location.
The chief cells of
the parathyroid gland produce PTH, which increases the activity of osteoclasts
in bones, the resorption of calcium in the kidneys and increases calcium from
the small intestine to increase serum calcium levels. PTH also decreases
reabsorbtion of phosphate in the kidneys. Oxyphil cells are also found in the
parathyroid gland, their function is not known.
The main artery
supplying the posterior thyroid and parathyroid glands is the inferior thyroid
artery. There is also some collateral arterial supply from the superior thyroid
artery. The venous drainage of the parathyroid glands is into the thyroid
venous plexus.
Fibres innervating
the parathyroid glands arise from the superior and middle cervical sympathetic
ganglia. The nervous supply is vasomotor in nature, the endocrine secretions of
the parathyroid glands are regulated hormonally. Lymphatic drainage of the parathyroid glands is the
same as the thyroid gland, into the cervical and paratracheal nodes.
Clinical Anatomy
Ectopic
parathyroid glands - As the parathyroid
gland have a highly variable location and develop from the pharyngeal pouches
they sometimes can be situated in adults high in the neck or the thorax. These
adenomas can be found using a SPECT scan.
Parathyroid
damage during surgery - The variable
location of the parathyroid glands increases the risk of them being removed or
damaged during surgery. During a thyroidectomy surgeons may preserve some of
the posterior thyroid gland to prevent damage to the parathyroid glands.
Without the parathyroid glands the patient would become hypocalaemic leading to
tetany, which can be fatal without urgent medical treatment.
Quick Anatomy
Key Facts
|
Developmental
precursor |
Arterial
supply |
Venous
drainage |
Nervous
supply |
Lymphatic
drainage |
|
Third
pharyngeal pouch (inferior parathyroid glands), fourth pharyngeal pouch
(superior parathyroid glands). |
Superior
and inferior thyroid arteries. |
Superior,
middle and inferior thyroid veins. |
Superior
and middle cervical sympathetic ganglia. |
Mainly
deep cervical nodes. Some into paratracheal nodes. |
Aide-Memoire
Summary
The four
parathyroid glands lie deep on the posterior surface of the thyroid gland.
Parathyroid chief cells produce PTH, which acts on the proximal convoluted
tubules of the kidney, the small intestines and osteoclasts to increase serum
calcium. Their variable location and translocation during embryological
development can lead to problems in surgery or ectopic parathyroid glands. The
blood supply, drainage and innervation to the parathyroid glands is similar to
the posterior thyroid gland.