embry 4 again Flashcards
what is pharyngeal arch?
a core of mesenchyme covered externally by ectoderm and internally by endoderm
what happens during the fourth week?
During the fourth week, most of the mesenchyme is derived from neural crest cells that migrate into the pharyngeal arches
- migration of neural crest cells into the arches and their differentiation into mesenchyme produces the maxillary and mandibular prominences
a pharyngeal arch contains
○ A pharyngeal arch artery that arises from the truncus arteriosus of the primordial heart and passes around the primordial pharynx to enter the dorsal aorta
○ 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.
what is the main formative elements of the face, nasal cavities, mouth, larynx, pharynx, and neck?
the pharyngeal arches
During the fifth week, the second pharyngeal arch enlarges and overgrows the third and fourth arches, forming
cervical sinus
when does the second to fourth pharyngeal grooves and the cervical sinus disappear
, giving the neck a smooth contour
by the end of the 7th week
what widens cranially where it joins the stomodeum, and narrows caudally where it joins the esophagus
primordial pharynx
the primordial pharynx is derived from what?
the foregut
what is the pharyngeal pouches
The pharyngeal endoderm lines the internal aspects of the pharyngeal arches and passes into diverticula (outpouchings)
how many pairs of pharyngeal pouches are there?
four pairs of pharyngeal pouches; the fifth pair is rudimentary or absent
how is the pharyngeal membrane formed
endoderm of the pouches contacts the ectoderm of the pharyngeal grooves and together
what does the pharyngeal membrane separate?
separates the pharyngeal pouches from the pharyngeal grooves
when does the pharyngeal arches begin to develop?
early in the fourth week
when the pharyngeal arches begin to develop, what cells migrate into the ventral parts of the future head and neck regions?
neural crest cells
what are the first pair of pharyngeal arches turn into
the jaws
the first pharyngeal arch separates into 2 prominences, what are the prominences?
maxillary prominence and the mandibular prominence
what does the maxillary prominence give rise to?
maxilla, zygomatic bone, and a portion of the vomer
what does the mandibular prominence forms?
mandible and the squamous temporal bone
what does the second and third pharyngeal arches form?
the hyoid bone
what does the first and second pharyngeal cartilages give rise to?
the ossicles of the middle ear and the styloid process of the temporal bone
what give rise to the laryngeal cartilage?
fourth and sixth pharyngeal arches
what give rise to the epiglottis?
3rd and 4th pharyngeal arches
what does the fifth pharyngeal arch form?
it is rudimentary - nothing is derived from it, and it disappears
the first pharyngeal pouch expands into a ?
tubotympanic recess
The expanded distal part of this recess contacts the first pharyngeal groove -> contributes to the formation of the ?
tympanic membrane (eardrum)
the cavity of the tubotympanic recess becomes the ?
tympanic cavity and mastoid antrum
The connection of the tubotympanic recess with the pharynx elongates and forms the ?
pharyngotympanic tube (auditory tube, Eustachian tube)
the second pharyngeal pouch eventually gives rise to parts of the ?
palatine tonsils
by the sixth week, the third pouch develops:
○ Into parathyroid glands – dorsal part (inferior pair)
○ Into a thymus – ventral part
the fourth pouch also develops into ?
parathyroids - the superior pair
what is the first endocrine gland to develop in the embryo?
thyroid gland
For a short time, the thyroid gland is connected to the tongue by a narrow tube, what is it called?
thyroglossal duct
the thyroid gland begins to form 24 days after fertilization from a median endodermal thickening in the floor of the primordial pharynx, this thickening forms a small outpouching called
thyroid primordium
