embryology Flashcards
how are the definitive endoderm and mesoderm formed?
Invagination of the epiblast cells through the primitive streak
what are the 3 main groups of the mesoderm?
Paraxial, Intermediate and Lateral plate
when do the pharyngeal arched develop?
Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29
(no arch 5 in mammals)
what are the components of the pharyngeal apparatus?
Core pharyngeal arch (Mesenchymal tissue)
External pharyngeal cleft (Ectoderm)
Internal pharyngeal pouch (Endoderm
what does each pahryngeal arch consist of?
- core of mesenchyme (derived from paraxial and lateral plate mesoderm)
- neural crest cells
- cranial nerve component
- artery (aortic arch arteries)
what does the 1st pharyngeal arch from?
maxillary process
- maxilla and zygomatic bone
& mandibular process
- Forms Meckel’s cartilage
- incus and Malleus (ear ossicles)
- Mandible
- Squamous portion of temporal bone
what does the 2nd cranial arch form?
reichet’s cartilage
skeletal derivatives-
- Stapes
- Styloid process of temporal bone
- Stylohyoid ligament
- Lesser horn of Hyoid
- upper part of Hyoid body
what does the 3rd pharyngeal arch form?
greater horn & lower part of hyoid bone
what do the 4th-6th pharyngeal arches form?
laryngeal cartilages
what nerve is the 1st pharyngeal arch related to?
CN V2 and CN V3
what nerve is the 2nd pharyngeal arch related to?
CN VII (facial)
what nerve is the 3rd pharyngeal arch related to?
CN IX (glossopharyngeal)
what nerve are the 4th-6th pharyngeal arches related to?
CN X (vagus)
arch 4 - superior laryngeal branch
arch 6 - recurrent laryngeal branch
what muscular derivatives are formed by each of the pharyngeal arches?
the muscles supplied by their associated nerves
where are cervical cysts and fistulas usually found?
along the anterior border or the sternocleidomastoid
what does the 1st pharyngeal pouch form?
Tympanic membrane
Middle ear
Eustachian tube
what does the 2nd pharyngeal pouch form?
palatine tonsil
what does the 3rd pharyngeal pouch form?
inferior parathyroid gland
thymus
what does the 4th pharyngeal pouch form?
superior thyroid gland
ultimobranchial body
describe the nasolacrimal groove
Lies between the maxillary prominence and the lateral nasal prominence
Solid epithelial cord in floor of groove
Cord detaches from the ectoderm
Canalization forms the nasolacrimal duct
what are the embryological origins of the upper and lower lip?
Upper lip
2 medial nasal prominences
2 maxillary prominences
Lower lip
Mandibular prominences
what are the embryological origins of the nose?
Frontonasal prominence = Bridge and nasal septum
Medial nasal prominences = Crest and tip
Lateral nasal prominences = Alae (sides)
how does the primary palate develop?
fusion of medial nasal prominences to give intermaxillary segment:
Labial portion -> Philtrum of upper lip
Upper jaw component -> Carries 4 incisors
Palatal component -> form primary palate
describe development of the nasal cavities
Nasal pits deepen and penetrate into the underlying mesenchyme with forward growth of frontonasal prominence
As the intermaxillary segment forms it is connected by a nasal fin.
Nasal fin vacuolizes and thins, this opens the developing nasal sac.
Nasal cavities communicate with oral cavity via Primitive choanae behind primary palate
Definitive choanae open at junction of nasal cavity with pharynx due to formation of secondary palate
describe the formation of the secondary palate
Right and left palatal shelves develop parallel to the tongue.
Fused in the central region initially then expands anteriorly and posteriorly.
Mandibular development facilitates clearance of the tongue
what can happen if there is an error in fusion of the secondary palate?
cleft palate
