Session 11: Embryology II - Development of the Midline Structures Flashcards
Where can the pituitary be found?
Within the bone of the sphenoid, within the hypophyseal fossa of the sella turcica.
What does the pituitary gland consist of?
Two lobes- posterior and anterior.
Tissue type of anterior lobe.
Endocrine (ectoderm)
Tissue type of posterior lobe.
Neuroendocrine (neuroectoderm)
Explain the embryonic development of the posterior pituitary.
Begins as a downward outgrowth of the forebrain called the infundibulum which is made of neuroectoderm. This will grow down towards the pharynx.
The infundibulum also gives rise to the pituitary stalk.
Explain the embryonic development of anterior pituitary.
Region of the stomatodeum there is an invagination of ectoderm called the Rathke’s pouch. This will grow up towards the developing forebrain and as the sphenoid bone ossifies the Rathke’s pouch will be pinched off and the ectoderm will join with the infundibulum.
Explain the development of the tongue.
Develops from all the pharyngeal arches (however arch 6 is not that important)
Two lateral swelling develop from the 1st arch
Three median lingual swellings develop from the 1st-4th arch.
The lateral lingual swellings will grow over the median swelling from the 1st arch (Tuberculum impar).
The median swelling from the 3rd arch grows over the 2nd.
The tongue is then lifted and freed from the floor by apoptosis leaving only a small midline portion of tissue called the lingual frenulum.
Where does the thyroid gland originally start to develop?
In the floor of the pharynx between the tuberculum impar and the cupola.
Explain the descent of the thyroid into its adult position.
It descends down the neck from its point of origin which is makred as the foramen cecum.
The gland will bifurcate to become a bi-lobed diverticulum.
It descends down the neck via the thyroglossal duct which will then regress and fuse to leave the thyroid gland separate from the tongue.
It is however still found in the pretracheal fascia.
What is a pyramidal lobe of the thyroid gland?
If the thyroglossal duct’s distal part fails to fuse there will still be a pyramidal shape of thyroid tissue left.
This is not clinically important.
Give other thyroid abnormalities related to its development.
Thyroglossal cysts and fistulae.
Ectopic thyroid tissue.
How does cleft lip and palate come by?
Failure of the frontonasal prominence to fuse with the maxillary prominence and also failure of the palatal shelves to fuse.
What is Treacher Collins syndrome.
A first arch syndrome that result from failure of colonisation of the 1st arch with the neural crest cells.
Autosomal dominant condition that is characterised by hypoplasia of mandible and facial bones.
What is Di-George syndrome.
Congenital thymic aplasia and the absence of parathyroid glands.
Deletion on chromosome 22
Disruption of 3rd and 4th pharyngeal pouches and abnormal development of neural crest.
What is CHARGE syndrome?
CHD7 heterozygous mutation
Coloboma
Heart defects
choanal Atresia
growth & developmental Retardation
Genital hypoplasia
Ear defects
