Development of the Pharyngeal Arches Flashcards
What gives rise to the oral plate?
stomadeum- ends at the pharynx. Surrounded by the 1st pharyngeal arch and is surrounded by ectoderm. (ectoderm also present anterior of the tonsillar fossa)
What are the arches made of externally, at the core and internally?
ectoderm=external
mesenchyme=core
endoderm=internal
What do each of the arches consist of?
- aortic arch
- cranial nerve
- mesenchyme
What are each of the arches separated by?
- pharyngeal cleft on the outside
- pharyngeal pouch on the inside
(together they make the pharyngeal membrane)
Blood and nerve supply of the first pharyngeal arch?
blood- 1st aortic arch
nerve- mandibular and maxillary of trigeminal (CNV)
Blood and nerve supply of the 2nd pharyngeal arch?
blood- 2nd aortic arch
nerve- facial (CNVII)
Blood and nerve supply of the 3rd pharyngeal arch?
blood- 3rd aortic arch
nerve- glossoopharyngeal (CNIX)
Blood and nerve supply of the 4th pharyngeal arch?
blood- 4th aortic arch
nerve- vagus (CNX)
What do the neural crest cells make?
- bones of the face and skull
- hyoid cartilage from 2nd arch
- cartilage, bone, dentin, tendon, dermis, sensory neurons and glandular stroma
What are the 3 segments of the early brain?
forebrain, midbrain and hindbrain surrounded by somatomeres.
What is the role of HOX genes?
aid in cephalocaudal development and helps the neural crest cells migrate from different regions of the brain to the pharyngeal arches.
**HOX genes are NOT expressed anterior to rhombomere 3
What is the stomadeum bounded by?
posteriorly-buccopharyngeal membrane aka oral plate
- surrounded by the 1st arch and ectoderm
What is found anterior of the tonsillar fossa?
ECTODERM
What are the 4 prominences that the 1st arch develops into?
- 2 maxillary prominences
- 2 mandibular prominences
What does the 1st pharyngeal cleft develop into?
external auditory meatus
What gives rise to the external ear?
1st and 2nd pharyngeal arches
What is the cervical sinus?
the 2nd arch grows downward and covers the 3rd 4th and 6th arches forming the cervical sinus
What is the fate of the ectoderm of the 1st arch?
- skin over maxilla, mandible, around the ear and external auditory meatus.
- salivary glands
- enamel around the teeth
- epithelium of buccal cavity
- epithelium of anterior portion of the tongue
Fate of ectoderm of the 2nd arch?
- skin around ear and part of external auditory meatus
- epithelium behind the ear
Fate of ectoderm of the 3rd and 4th arches?
epithelium around the ear
What does the 1st pharyngeal pouch give rise to?
middle ear cavity and auditory tube (tympanic membrane, tympanic cavity, mastoid antrum, eustacian tube)
What does the 2nd pharyngeal pouch give rise to?
endoderm and mesoderm give rise to lymphatic tissue (tonsils) and palatine tonsillar fossa
What does the 3rd pharyngeal pouch give rise to?
- Endoderm gives rise to the thymus which migrates downward into the superior mediastinum (week 4-7)
- Inferior parathyroids (week 5)
What does the 4th pharyngeal pouch give rise to?
- superior parathyroids at week 5-7
- ultimobranchial body
What does the thyroid develop from?
Endoderm. Develops as a diverticulum of the foramen secum that is located between the 1st and 3rd arch or between the tuberculum impar and the hypobranchial eminence.
Where does the diverticulum migrate to in the development of the thyroid? And where is the diverticulum from?
Endoderm of the pharynx forms the diverticulum that moves downward in front of the pharynx and as this happens there is a thyroglossal duct that appears and can persist into adulthood on occasion.
What is the thyroglossal duct?
A narrow duct that allows the pharynx to stay in contact with the thyroid.
Where do the parafollicular cells develop from?
From the 4th and 5th pouch (ultimobranchial body)
What is the pharynx?
first part of the foregut and is surrounded by the pharyngeal arches
What is the face development as of week 5?
- Frontonasal prominence (5 frontal prominences)
- 2 nasal placodes
What are the nasal placodes?
placodes are ectoderm that are induced by the ventral forebrain to invaginate and they for nasal pits by day 34.
What 2 new prominences appear at the same time that invagination of nasal placodes is occurring?
- medial nasal prominences
- lateral nasal prominences
What is the bucconasal groove?
A groove that separates the maxillary prominence from the medial nasal prominence as they both grow medial to eventually fuse.
What is the naso-optic groove?
Groove that separates the maxillary prominence from the lateral nasal prominence.
*What forms the upper lip?
Fusion of the medial nasal prominences at the midline and the fusion of the maxillary prominences with the medial nasal prominences at the midline.
*What does the medial nasal prominence form?
Filtrum and the crest and tip of the nose
*What does the maxillary prominence form?
any part of the lip outside of the filtrum
*What happens if maxillary prominence does not fuse with the medial nasal prominence?
Get cleft lip or cleft jaw
What is the nasolacrimal groove?
groove that separates the maxillary prominence from the lateral nasal prominence and the lower part forms the lacrimal duct and the upper part forms the lacrimal sac.
What forms the lower lip and jaw?
fusion of the mandibular prominences at the midline
What forms the cheeks and maxillae?
the maxillary prominences
**What forms the nose?
bridge- frontal prominence
crest and tip- medial nasal prominences
alae- lateral nasal prominences
What makes up the intermaxillary segment?
2 nasomedial prominences
What does the intermaxillary segment give rise to?
- 4 incisors
- jaw
- primary palate
- labial component: filtrum of upper lip
- *is the pink part on the slide
What is the order of palate fusing?
Primary palate first fuses to the palatine shelves and then afterwards the palatine shelves (from maxillary processes) both fuse together in the midline. Important because you can have a cleft palate without a cleft lip or vice versa because they don’t fuse at the same time
What makes up the first and second palate?
Primary palate- intermaxillary segment (medial nasal prominence)
Secondary palate- maxillary outgrowths called palatine shelves
How does the tongue and palate development correlate?
Initially the palatine shelves grow down toward the base of the tongue. The tongue starts to grow down too and the palatine shelves grow toward each other and fuse in the midline above the tongue. As the palatine shelves fuse, the nasal septum grows down and fuses with the primary and secondary palate.
What is the incisive foramen?
the point where the palatine shelves and the intermaxillary segment fuse
Where does the tongue develop?
From the diverticulum of foramen cecum, where the stomadeum and the pharynx meet
What are the 1st arch contributions of tongue development?
lingual swellings which give rise to the mucosa of the anterior 2/3 of the tongue
What are the 2nd arch contributions to the tongue?
Not much, hypobranchial eminence
What are the 3rd arch contributions to the tongue?
hypobranchial eminence, mucosa of the posterior 1/3 of the tongue
What are the 4th arch contributions to the tongue?
hypobranchial eminence, mucosa of the most posterior part of the tongue and the epiglottis
What gives rise to the tongue muscles?
occipital somites (innervated by hypoglossal)
what is the oronasal membrane?
separates the oral cavity from the nasal cavity. eventually breaks down with formation of the secondary palate.
What are the 2 components of the pituitary gland?
- rathke’s pouch: oral ectoderm
- infundibulum: diverticulum of ectoderm from forebrain (neural ectoderm)
What does rathke’s pouch develop into?
pars glomerulosa, pars fasiculata, pars tuberalis
What does the infundibulum develop into?
infundibular stalk and the pars nervosa
What does the primordial stem cell give rise to?
somatotropes, lactotropes, gonadotropes, corticotropes, and thyrotropes
What hormones are produced from the infundibulum?
oxytocin and ADH
What hormones are produced from rathke’s pouch?
basophils-LH, FSH, ACTH, TSH
acidophils- prolactin and GH
What do the adrenal glands develop from?
coelemic epithelial cells from intermediate mesoderm and neural crest cells from the sympathetic chain
What do the coelemic epithelial cells and neural crest cells become?
coelemic epithelial- adrenal cortex
neural crest- adrenal medulla
What genes are important for adrenal development?
SF1 and DAX
What gives rise to the adult adrenal?
the definitive zone (different from fetal zone)
What inhibits ACTH in early development?
high levels of cortisol secretion resulting in less androgen secretion and therefore plays a role in female development
What is the role of the placenta in hormone production?
- converts DHEA to estrogen promoting beginning of parturition
What is the role of cortisol in fetal development?
high levels of cortisol favor development and maturation of fetal organs (thats why mothers who do drugs actually have babies with more developed organs–drugs=stress=cortisol!)
