Thyroid Gland Development And Anomalies: From Embryo To Adult

Thyroid Gland Development And Anomalies: From Embryo To Adult

Question 1. Development of thyroid gland and its anomalies.
Answer:

Development Thyroid Gland :

• The thyroid gland develops mainly from the thyroglossal duct.
• The medial ends of the two mandibular arches are separated by a midline swelling called the tuberculum impar.
• Behind the tuberculum, the epithelium is thickened which soon gets depressed to form a diverticulum called thyroglossal duct
• The diverticulum grows down in the midline into the neck.
• Its tip soon bifurcates.
• Proliferation of the cells of the bifid end gives rise to the two lobes of the thyroid gland.
• Parafollicular cells are derived from the caudal pharyngeal complex which is derived from the fourth and fifth pharyngeal pouches.

Thyroid Gland Anomalies:

1. Anomalies of shape.

• Pyramidal lobe arises from the isthmus or from one of the thyroid lobes.
• Isthmus may be absent.
• One of the lobes may be small or absent.

2. Anomalies of Position.

• Lingual thyroid – under tongue mucosa.
• Intra-lingual thyroid – embedded in tongue musculature.
• Suprahyoid thyroid – above the hyoid bone.
• Infrahyoid thyroid – below the hyoid bone.
• Intrathoracic thyroid – lie in the thorax.

3. Ectopic Thyroid Tissue.

• Thyroid tissue has been observed in the larynx, trachea, oesophagns, pons, pleura, pericardium and ovaries.

4. Remnants of the Thryoglassal Duct.

• Thyroglossal cyst- occur along the course of the duct.
• Thyroglossal fistula – opening at foramen caecum.
• Carcinoma of the thyroglossal duct.

Question 2. Development of Mandible.
Answer:

• About 4th week of intrauterine life, pharyngeal arches are laid down on the lateral and ventral aspects of foregut.
• Mandible is developed from first pharyngeal arch is called mandibular arch.
• The mandibular processes of both sides grow towards each other and fuse in the midline.
• This results in formation of lower lip and lower jaw.

Development of Condylar Process:

• It occurs of 5thwek of intrauterine life.
• Mesenchymal condensation occurs above the ventral side of developing mandible.
• Cartilage is formed at 10th week which undergoes ossification to form condylar process.

Development of Coronoid Process:

• At 10-14 week of interauterine life, secondary accessory cartilages.
• This gets incorporated into expanding ramus and forms coronoid process.

Development of Mental Region:

• Ossification of 1 or 2 small cartilages occurs on either side of symphysis.
• It forms the mental region.