embryology 3: development of midline structures Flashcards
where does the pituitary gland sit?
in the pituitary fossa of the sella turcica (deepest part of sphenoid bone - middle cranial fossa)
what is the pituitary gland?
a functional connection with the cerebellum and forebrain
what are the anatomical relations of the pituitary gland?
inferior to hypothalamus
hypophysis (hypothesis) + hypophysis cerebri (pituitary) - joined together by pituitary stalk
what is the posterior lobe of pituitary gland composed of?
neuroectoderm (collection of neurons)
neurohypophysis - modified neural tissue
where does the posterior lobe of the pituitary gland originate from?
infundibulum of the forebrain (downward outgrowth of diencephalon which grows toward the roof of the pharynx - CAUDALly)
where does the pituitary stalk originate from?
posterior lobe
what does the anterior lobe of the pituitary gland form from?
outpocketing of ectoderm of the stomatoderm called RATHKE’s POUCH
(stomatoderm forms body organs, and the pituitary gland is a glandular tissue)
where does the evagination of Rathke’s pouch for anterior pituitary come from?
roof of oropharynx primordial and grows DORSALly towards the developing brain
what happens to Rathke’s pouch?
pinches off from the ectoderm (outpocketing from stomatoderm) and becomes separated
what functionally links the anterior lobe of the hypothalamus and posterior pituitary lobe?
hypophyseal portal system
no need to enter systemic circulation
summary of origin of anterior and posterior lobes of the pituitary gland
anterior: endocrine organ (stomatoderm), Rathke’s pouch (outpocketing of ectoderm), grows up dorsally from roof of oropharynx
posterior: neuroectoderm (neural tissue), from infundibulum of forebrain, grows caudally towards roof of oropharynx
both linked by hypophyseal portal system
what happens after the anterior and posterior lobes grows towards each other?
they sit in the developing sphenoid bone as it ossifies to form the sella turcica (pituitary fossa)
where does the tongue receive contributions from?
all 5 arches
where does the tongue lie?
partly in the oral cavity and partly in the (oro)pharynx
what is the tongue comprised of?
extrinsic and intrinsic muscles
highly mobile, attached to floor of mouth via lingual frenulum
how is the tongue divided functionally?
anterior 2/3 and posterior 1/3
separated by sulcus terminalis with foramen cecum forming apex
when does the primordial of the tongue appear?
at the same time as the palate begins to form (palatal shelves of maxillary prominence)
what forms the pharyngeal floor?
from the fusion of ventral parts of the pharyngeal arches and pouches (endoderm)
what happens as the pharynx floor develops?
the tongue primordia receives a component from each of the pharyngeal arches where they meet in the midline
what is the tongue formed from?
2 lateral swellings (Ph A 1)
3 median swellings (PhA 1-4)
how can the median swellings of the tongue be further subdivided?
Median Ph 1 = tuberculum impar
median Ph 2,3,4 = cupola (slight Ph 4)
median Ph 4 = epiglottal swelling
what happens to pharyngeal arch 1 in the development of the tongue?
the lateral lingual swellings (Ph A 1) overgrows the tuberculum impar (Ph A 1 median)
what happens to cupola in the development of the tongue?
median Ph A 3 of cupola overgrows Ph A 2
how does the development of the tongue allows high mobility?
further extensive degeneration (via apoptosis) of the tongue primordial, freeing it from the floor of the oral cavity, with lingual frenulum being remnant
what is meant by children who are ‘tongue-tied’?
have a small lingual frenulum
majority of tongue still attached to the floor of the mouth
what does Ph A 4 form?
cupola component = posteiror tongue
epiglottal swelling = epiglottis
innervation of Ph A 4?
Ph A 4 = CN X
Ph A 4 tongue = superior laryngeal branch of vagus
innervation of Ph A 1?
CN V
lingual nerve
(mandibular branch of trigeminal = CN V3)
what is the mucosa of the anterior 2/3rd of the tongue derived from? therefore innervation?
Ph A 1 + 3 (3 overgrows 2 in cupola)
lingual (CN V3) and CN IX (glossopharyngeal)
what are the innervations of the 4 parhyngeal arches of the tongue?
1 = V 2 = VII 3 = IX 4 = X
what is the mucosa of the posterior 1/3rd of the tongue derived from?
Ph A 3 (+4)
general + special sensory innervation = CN IX + X
(vagus innervates palatoglossus - extrinsic muscle of the tongue)
where do taste buds develop?
in pupillae (nipple like structures on upper tongue)
where do pupillae of the tongue develop from? innervation?
Ph A 2
CN VII - chorda tympani (taste buds - special sensory)
where does the chorda tympani pass?
from Ph A 2 to Ph A 1, therefore crosses Ph pouch 1 (middle ear and eustachian tube) - therefore chorda tympani passes between malleus and incus
how do intrinsic + extrinsic muscles of the tongue develop?
as myogenic precursors (muscle cells) from occipital somites (paraxial mesoderm) that migrate into the developing tongue
innervation of the muscles of the tongue? (motor)
hypoglossal nerve (CN XII) (apart from palatoglossus - by CN X)
where does the primordial of the thyroid gland appear?
thyroid diverticulum appears in in the floor of the pharynx between tuberculum impar and cupola (both median lingual swellings) - foramen cecum
(epithelial outgrowth giving rise to thyroid)
what happens to the thyroid after thyroid diverticulum has appeared?
descents:
it migrates to its position in the anterior neck to pharyngeal gut (posterior), hyoid bone (superior) and laryngeal cartilages (superior)
describe the descent of the thyroid gland
from foramen cecum (middle of sulcus terminalis)
proliferates + bifurcates
descends as BI-lobed diverticulum (connected by isthmus)
what happens to the thyroid gland as it descends?
remains connected to the tongue by thyroglossal duct (patient connection between the tongue and the thyroid gland) - connects foramen cecum to thyroid gland
what happens to the foramen cecum?
seals off and becomes a small indentation on dorsum of tongue
what is the remnant of the thyroglossal duct?
pyramidal lobe
when and where do thyroglossal cysts appear?
incomplete obliteration of the thyroglossal duct
commonly base of tongue, just inferior to hyoid
what can thyroglossal duct give off?
ectopic thyroid tissue anywhere along the path of thyroglossal duct
function of follicular cells of the thyroid gland and where are they derived from?
produce T3 + T4
from thyroid diverticulum (Ph A 2)
what is the thyroid diverticulum?
cells which grew on the pharynx
which descends through foramen cecum
where do the parafollicular cells of the thyroid gland derive from and what is their function?
produce calcitonin (PTH to regulate Ca2+)
derive from ultimobranchial body of Ph 4 pouch
(Ph 3 pouch for inferior parathyroid with thymus)
what are the 2 sets of teeth humans have?
deciduous (baby) teeth
permanent teeth
when do deciduous teeth appear? how many are there?
start to erupt about 6 months, fallout in childhood, replaced by permanent teeth
20 in total, does NOT have pre-molars
when do permanent teeth appear? how many are there in total?
about 12 years, MOST permanent teeth erupted, EXCEPT 3rd MOLARS (wisdom teeth)
by about 21 years, ALL permanent teeth erupted (total 32)
