Parathyroids
Location
The parathyroid glands are endocrine glands
Oval structures
30 mgs each
Four
Lie on the posterior surface of the thyroid gland.
Symmetrically arranged
Two superior parathyroids lying about 1cm above the point where the inferior thyroid artery enters the thyroid.
The two inferior parathyroids lie 1cm below.
There is variation in the number and location of glands.
Situated within the fibrous capsule of the thyroid (intracapsular), or outside it (extracapsular).
Blood supply
Inferior thyroid artery
Superior thyroid artery
Thyroid ima artery
Lryngeal arteries
Tracheal arteries
Oesophageal arteries
Venous drainage into the plexus of veins : the superior, middle and inferior thyroid veins.
Nerve supply
Thyroid branches of the cervical sympathetic ganglia
Embryology
The superior parathyroids are derived from the fourth branchial pouches
The inferior parathyroids from the third branchial pouches.
Development begins fifth or sixth week of development.
The inferior glands form above the superior glands but descend below them.
Histology
The glands are made up of four types of cell:
1. Chief cells - these are the cells which secrete the parathyroid hormone (PTH).
2. Oxyphil cells - these have a secretory function but their precise role is not clear.
3. Adipose tissue - these are fat cells which add bulk to the glands.
4. Fibrovascular stroma - this is fibrous tissue that gives form to the glands containing the capillaries supplying them with blood.
Applied Anatomy
Accidental removal during total thyroidectomy - parathormone deficiency
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