Development of Endocrine Glands of Head & Neck

Question 1

[9-minute video]: the Thyroid Gland (embryology, blood supply, venous drainage, innervation, histology)

Answer 1

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Question 2

Develop the thyroid gland. It is the first endocrine gland to develop, beginning to form at approximately 24 days.

Answer 2

✓ Thyroid anlage arises from the dorsum of the tongue.
✓ The diverticulum descends in the neck anterior to the hyoid bone
✓ Cells from the ultimobranchial body invade the developing gland [why?]
✓ Thyroid primordium is hollow at first then it becomes a solid mass of cells. It divides into the 2 lobes connected by the isthmus.
✓ At 7 weeks, the thyroglossal duct has normally degenerated (and disappeared).
✓ The proximal opening of the duct persists as a small pit on the dorsum of the tongue called foramen cecum.
✓ A pyramidal lobe is also found in most people (from distal end of the thyroglossal duct).
[Diagram 1] [Diagram 2] [Diagram 3] [Diagram 4]

Question 3

Identify the congenital anomaly and state its embryological basis: [Click here]. State its embryological basis.

Answer 3

Ectopic thyroid tissue; failure of descent of thyroid gland

Question 4

Identify the congenital anomaly shown in the following diagram: [Diagram].

Answer 4

Thyroglossal duct cysts

Further notes:
✓ These cysts occur due to persistence of the remnants of the thyroglossal duct.
✓ They may form anywhere along the course of the thyroglossal duct (may occur in tongue, anterior neck, inferior to hyoid)
✓ These swellings are painless, progressively enlarging and movable.
✓ If infection of the cyst occurs, a perforation of the skin may develop forming a thyroglossal duct sinus that opens in the median plane of neck anterior to the laryngeal cartilages.

Question 5

State the embryological basis of thyroid hemiagenesis.

Answer 5

Unilateral failure of formation.

Question 6

Develop the parathyroid glands.

Answer 6

✓ The parathyroid glands develop from endoderm of the 3rd and 4th pharyngeal pouches.
✓ The superior parathyroid glands develop from 4th pouch.
✓ The inferior parathyroid glands develop from 3rd pouch (with the thymus).
✓ Vascular mesenchyme grows into the nodules.
✓ Chief/principal cells differentiate during embryonic period.
✓ Oxyphil cells differentiate 5 to 7 years after birth.

Question 7

Discuss DiGeorge syndrome, stating its embryological basis and symptoms.

Answer 7

Embryological basis: Failure of differentiation of 3rd and 4th pouch into thymus and parathyroid glands (due to breakdown in signalling between pharyngeal endoderm and adjacent neural crest cells).
Symptoms:
✓ Congenital hypoparathyroidism.
✓ Increased susceptibility to injections.
✓ Shortened philtrum.
✓ Cardiac abnormalities.
✓ Low-set and notched ears.
✓ Thyroid hypoplasia.
✓ Nasal clefts.
[Diagram]

Question 8

Briefly discuss ectopic parathyroid glands.

Answer 8

✓ Inferior parathyroid gland remains near bifurcation of common carotid artery.
✓ Intrathyroid parathyroid glands

Question 9

What leads to:
1. supernumerary parathyroid glands?
2. absence of parathyroid glands?

Answer 9

1. division of primordia of original glands.
2. • failure of primordia to differentiate
   • atrophy of gland in early development

Question 10

Develop the pituitary gland.

Answer 10

Answer: [Diagram]

Further notes:
2 sources:
✓ oral ectoderm: adenohypophysis [develops from an invagination of the oral ectoderm known as Rathke’s pouch]
✓ neuroectoderm: neurohypophysis

Hypophyseal diverticulum (Rathke’s pouch): upgrowth from ectodermal roof of the stomodeum
Neurohypophyseal diverticulum: downgrowth from the neuroectoderm of the diencephalon

Question 11

List two developmental anomalies of the pituitary gland.

Answer 11

✓ Pharyngeal pituitary gland/hypophysis
✓ Craniopharyngioma