Embryology 4 - The Oropharyngeal Apparatus (Week 9) Flashcards
a core of mesenchyme (embryonic connective tissue) covered externally by ectoderm and internally by endoderm
pharyngeal arch
Note: pharyngeal arches are the main formative elements of the face, nasal cavities, mouth, larynx, pharynx, and neck
Migration of ___________ into the arches and their differentiation into mesenchyme produces the maxillary and mandibular prominences
neural crest cells
What does a pharyngeal arch contain?
- an artery that arises from the truncus arteriosus (aortic trunk) of the primordial heart
- a cartilaginous rod that forms the skeleton of the arch
- a muscular component that differentiates into muscles in the head and neck
- sensory and motor nerves that supply the mucosa and muscles derived from the arch (derived from neuroectoderm of the primordial brain)
During the 5th week, the second pharyngeal arch gets bigger and overgrows the third and fourth arches, forming an ectodermal depression on the outside of the developing pharynx called what?
cervical sinus
True or False: By the end of the 5th week, all of the arches disappear, creating a smoother appearance
False
By the end of the 7th week
At the pharyngeal grooves, there are only two layers. What are they?
ectoderm and endoderm
(NO mesoderm)
Pharyngeal grooves are on the _________ (inside/outside) of the developing pharynx and pharyngeal pouches are on the __________ (inside/outside)
outside,
inside
How many pharyngeal pouches are there?
4
The _____________ separates the pharyngeal pouches from the pharyngeal grooves
pharyngeal membrane
Recall: only has 2 layers (ectoderm and endoderm, NO mesoderm)
When do pharyngeal arches begin to develop?
early in 4th week
The first pair of pharyngeal arches = the primordium of what?
the jaws
The first pharyngeal arch (mandibular arch) separates into two prominences. What are they?
1) maxillary prominence
2) mandibular prominence
Note: even though the first pharyngeal arch is also known as the “mandibular arch”, it doesn’t just give rise to the mandible
gives rise to the maxilla, zygomatic bone, and a portion of the vomer
maxillary prominence
gives rise to the mandible and squamous temporal bone
mandibular prominence
The second and third pharyngeal arches give rise to the _________ (which bone/cartilage derivative?)
hyoid bone
second arch = upper part of hyoid bone, stapes, and styloid process
third arch = lower part of hyoid bone
The fourth and sixth pharyngeal arches give rise to the ________________ (which bone/cartilage derivative?)
laryngeal cartilage (thyroid cartilage, cricoid cartilage)
The third and fourth pharyngeal arches give rise to _____________ (which bone/cartilage derivative?)
the epiglottis
The first and second pharyngeal arches give rise to ________________(which bone/cartilage derivative?)
the ossicles of the middle ear and the styloid process of the temporal bone
first arch = malleus, incus
second arch = stapes
True or False: The fifth pharyngeal arch also gives rise to the thyroid cartilage
False.
The fifth pharyngeal arch is rudimentary, as nothing is derived from it and it disappears
The first pharyngeal arch gives rise to _______________ (which muscular derivative(s)?)
- muscles of mastication*
- muscles of middle ear
The second pharyngeal arch gives rise to __________________(which muscular derivative(s)?)
- stapedius
- stylohyoid
- posterior belly of digastric muscles
- auricular
- muscles of facial expression*
The third pharyngeal arch gives rise to ___________________ (which muscular derivative(s)?)
- stylopharyngeus
The fourth pharyngeal arch gives rise to ______________(which muscular derivative?)
- cricothyroid
- levator veli palatini
- constrictors of the pharynx
The sixth pharyngeal arch gives rise to _________________(which muscular derivative(s)?)
- intrinsic muscles of the larynx
True or False: The fifth pharyngeal arch has no muscle derivatives
True
What are the associated cranial nerves for each of the following pharyngeal arches?
First =
Second =
Third =
Fourth & Sixth =
First = trigeminal nerve (except V1)
Second = facial nerve
Third = glossopharyngeal nerve
Fourth & Sixth = vagus nerve
The first pharyngeal pouch expands into a tubotympanic recess, whereby the distal part of this recess contacts the first pharyngeal groove. This contributes to the formation of what?
the tympanic membrane (eardrum)
Note: this forms between the first and second arches
The cavity of the tubotympanic recess becomes the ________________ where the bones of the middle ear are found and the _______________
tympanic cavity,
mastoid antrum
The connection of the tubotympanic recess with the pharynx elongates and forms the ____________________
pharyngotympanic tube (aka the Eustachian tube, aka the auditory tube)
The second pharyngeal pouch gives rise to __________
parts of the palatine tonsils
The dorsal part of the third pouch develops into _____________
the inferior parathyroid glands
The ventral part of the third pouch develops into _______________
the thymus
Note: defects with third pouch related to DiGeorge Syndrome
The fourth pouch develops into _______________
the superior parathyroids
True or False: There are no fifth or sixth pouches
True
What is the first endocrine gland to develop in the embryo?
the thyroid gland
Note: it forms from a median endodermal thickening in the floor of the primordial pharynx beginning ~ day 24
Note: the thyroid gland does NOT develop from the pharyngeal arches but it develops at the same time and in the same area
For a short time, the thyroid gland is connected to the tongue via what?
thyroglossal duct
Note: by week 7 this degenerates and the thyroid gland is located in its final site
