development of tongue, thyroid gland and respiratory system (special embryology)

Derivatives of Floor of Pharynx(Page 71)

Dr. Sherif Fahmy

Forebrain bulge

Pericardial bulge

Stomodeum

Bucco-pharyngeal membrane

Pharynx

Floor of pharynx

Dr. Sherif Fahmy

Dr. Sherif FahmyLaryngeo-trachial groove

Site of developing tongue, epiglottis and thyroid gland in the floor of pharynx

Dr. Sherif Fahmy

Development of Tongue(Page 71)

Sulcus terminalis

Foramen cecum

Lingual tonsil

Anterior 2/3

Posterior 1/3

Epiglottis

Dr. Sherif Fahmy

Development of Tongue• Tongue is developed at the floor of pharynx.• Mucosa of tongue is developed from

endodermal cells at floor of pharynx opposite 1st, 2nd and 3rd pharyngeal arches.

• Most of muscles of tongue are developed from mesoderm of occipital myotomes, some are devolped from mesoderm in situ.

Dr. Sherif Fahmy

A- Mucosa of Tongue• Anterior 2/3 is developed from floor of

pharynx opposite 1st pharyngeal arch from: two lingual swellings and tuberculum impar.

• Posterior 1/3 is developed from cranial ½ of hypobranchial eminence which is developed in floor of pharynx opposite 3rd pharyngeal arch.

• Sulcus terminalis separates between anterior 2/3 and posterior 1/3.

• Linguo-gingival groove partially separates between tongue and both alveolar margin and floor of oral cavity.

Dr. Sherif Fahmy

Forebrain bulge

Pericardial bulge

Stomodeum

Bucco-pharyngeal membrane

Pharynx

Floor of pharynx

Dr. Sherif Fahmy

Dr. Sherif Fahmy

2 lingual swellings

Tuberculum impar

Foramen ceacum

Copula

Hypobranchial eminence

1st

2nd

3rd

4th

Dr. Sherif Fahmy

Lingual swellings

Tuberculum impar

Foramen caecum

Hypobranchial eminence

Lingual swelling

Anterior 2/3 of tongue

Hypobranchial eminence

Posterior 1/3 of tongue

Foramen caecum

Epiglottis

Tuberculum impar

Dr. Sherif Fahmy

Dr. Sherif Fahmy

2 lingual swellings

1st arch

B- Muscles of Tongue• Lingual muscles are developed from occipital

myotomes (2nd, 3rd and 4th myotomes).• These myotomes migrate ventrally superficial

to external and internal carotid arteries.• Hypoglossal nerve follows occipital

myotomes to enter developing mucosa of tongue.

Dr. Sherif Fahmy

Bucco-pharyngeal membrane

Cloacal membrane

Cardiogenic area

Notochord

Paraxial mesoderm (somites)

Dr. Sherif Fahmy

Somites

A- Muscles of tongue

Nerve Supply of Tongue• Anterior 2/3 of mucosa: is supplied by lingual

nerve for general sensations and chorda tympani for taste.

• Posterior 1/3 of mucosa: is supplied by glossopharyngeal nerve for general sensation and taste.

• Muscles of tongue are supplied by hypoglossal nerve.

Dr. Sherif Fahmy

Anomalies of Tongue• 1- Aglossia: Complete absence of tongue.• 2- Microglossia: Small sized tongue.• 3- Macroglossia: Large sized tongue.• 4- Bifid tongue: due to failure of fusion between 2

lingual swellings.• 5- Tongue tie: short frenulum due to defective

formation of linguo-gingival groove. .

Dr. Sherif Fahmy

Bifid tongue

Tie tongue

Development of Thyroid Gland

(Page 73)

• It begins as thyroid primordium which is endodermal proliferation between tuberculum impare and hypobranchial eminence.

• Invagination of the primordium will form a bilobed diverticulum.

• Elongation of thyroid diverticulum to form thyro-glossal duct. It elongates downwards infront hyoid and thyroid cartilage. It reaches its final site by the 7th week.

• Thyroid follicles are developed from endodermal cells while ultimobranchial body gives parafollicular cells to thyroid gland. Capsule and fiberous septa are formed from mesoderm. Dr. Sherif

Fahmy

Dr. Sherif Fahmy

2 lingual swellings

Tuberculum impar

Thyroid primordium

Copula

Hypobranchial eminence

1st

2nd

3rd

4th

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Foramen cecum

Thyroid diverticulum

Developing anterior 2/3 of tongue

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Thyroglossal duct

Thyroid gland

Developing anterior 2/3 of tongue

Developing hyoid bone

Posterior 1/3 of tongue

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Foramen cecum

Degenerating thyro-glossal duct

Hyoid bone

Thyroid cartilage

Levator glandulae thyroidaePyramidal lobe Lobe of

thyroid gland

Fate of thyroglossal duct

Dr. Sherif Fahmy

Fate of Thyro-glossal Duct• Upper end of the duct remains as foramen cecum

at apex of sulcus terminalis on dorsum of tongue.• The duct degenerates from foramen cecum and

hyoid bone.• The duct from the hyoid to divisions of the duct

form levator glandulae thyroidae and may be pyramidal lobe.

• Divisions of the duct will form lobes of thyroid gland with isthmus inbetween.

• Ultimobranchial body forms parafollicular cells of the gland.

Congenital Anomalies • Thyroid agenesis: Failure of its formation.• Lingual thyroid: Failure of thyroid descend.• Aberrant thyroid (Retrosternal goiter): over-

descend of thyroid gland in the thorax.• Thyroglossal cyst: It is persistence of a part of

the thyroglossal duct.• Thyroglossal fistula: Thyroglossal duct opens

to skin.

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Dr. Sherif Fahmy

Development of Respiratory System

(page 75)

• Respiratory diverticulum: It begins by formation of endodermal laryngo-tracheal groove at floor of pharynx caudal to hypobranchial eminence.

• Laryngotracheal tube is separated from foregut by formation of tracheo-esophageal septum. This tube elongates till the thorax.

• Upper part of the tube forms the mucous membrane of larynx while lower part form mucus membrane of trachea and bronchi.

• The lower end of the tube will divides to form 2 bronchial buds.

• Surrounding mesoderm will form muscles and cartilages of larynx and trachea.

Dr. Sherif Fahmy

Formation of Larynx• Cartilages: Epiglottis from caudal ½ of

hypobranchial eminence. Thyroid cartilage from 4th arch, rest of laryngeal cartilages from 6th arch.

• Muscles: cricothyroid from 4th arch, rest of muscles from 6th arch.

• Mucous membrane: Supraglottic from 4th arch, infraglottic from 6th arch.

Formation of Lungs• Each bronchial bud divides into 3 branches, but on left side

one of the branches disappears. Right lung has 3 lobes, left lung has 2 lobes.

• Each branch of the bronchial bud divides repeatedly to form bronchioles and lastly alveoli (17 generations of divisions before birth and 6 after birth).

• Blood vessels fiberous tissue of the lungs are formed from surrounding mesoderm.

• Lung invades pleura from medial aspect, so pleura surrounds lung by 2 layers.

• Expansion of lung occurs after birth when the baby takes his first inspiration.

Dr. Sherif Fahmy

2 lingual swellings

Tuberculum impar

Foramen ceacum

Copula

Hypobranchial eminence

Laryngeo-trachial groove

Dr. Sherif Fahmy

Pharynx

Respiratory diverticulum

Laryngeo-tracheal tube

esophagus

Dr. Sherif Fahmy

Laryngo-tracheal duct

Foregut Tracheo-esophageal ridges

Bronchial buds

Dr. Sherif Fahmy

Congenital Anomalies• 1- Respiratory distress syndrom: Due

to absence of surfactant.• 2- Ectopic lung lobe: lung lobe that

arises from trachea or esophagus.• 3- Congenital lung cysts: Dilatation of

terminal bronchi.• 4- Esophageal atresia: with or without

tracheo-esophageal fistula

Dr. Sherif Fahmy