Pharyngeal arches and clefts Flashcards
Pharyngeal arches and clefts
week 4 and 5
Cephalic precocity
anterior end develops before posterior end (head before tail)
Development of somites
cranial to caudal (aged)
Relationship between head and lateral folds
forms of 3D embryo
Where ectoderm and endoderm meet is called what?
Oral plate
Stomodeum
invagination of ectoderm
External body form principles
- rupture oral plate to become mouth orifice
- opening into foregut
Oral plate rupture
opening of mouth
Failure of this oral plate (membrane) to rupture before birth, block the flow into the mouth, need to surgically break the ________
membrane
arches, clefts, and pharyngeal pouches
- development of the head, neck, and face
- 3rd-4th week of gestation
- heart is also forming
growth of CT and direction by ________ _______ ______ in the cranial region results in the formation of arches __________ by clefts and pharyngeal pouches
neural crest cells; separated
Internally, lateral wall of the pharynx
Pharyngeal pouches
Arch
tissue hump
Cleft
“crack”
Pharyngeal (Brachial) cleft
external ectoderm
Pharyngeal (Brachial) arch
mesoderm
Pharyngeal (Brachial) pouch
internal endoderm
How many arches?
6
How many clefts?
4
How many pouches?
4
Which arch deteriorates?
5th
External ectoderm
keratinized epidermis that covers the face and throat, and oral epithelium and sensory neurons of the epibranchial ganglia
Internal endoderm
covers the inside of each pharyngeal arch
Depressions of this layer form the pharyngeal pouches, which are rich in ______ fibers
internal endoderm; actin
Endoderm and ectoderm layers physically touch to form a closed pharyngeal membrane, and portions of this layer contact with ectoderm to form what?
pharyngeal membrane
Middle mesoderm
is the core of the pharyngeal arches and develops into the skeletal musculature of the head and neck
Endothelial cells for vascular structures are derived from this germ layer
middle mesoderm
Neural crest
strip of tissue that runs down the back of the embryo and gives rise to a large number of different organs
Neural crest cells
surround the mesoderm core and contributes to the formation of smooth muscle structures, bones, cartilages, tendons, and nerves
Pharyngeal arches produce ________ cartilage, bone, nerves, muscles, glands, and connective tissue of the face and neck
specific
Pharyngeal clefts (ectoderm)
Initially 4 clefts
1st cleft
- remains in the adult as the external auditory meatus
2nd, 3rd, and 4th cleft
temporary, cervical sinuses then taken over by enlarging 2nd pharyngeal arch
Pharyngeal arches
mesoderm and neural crest cells
Each arch is associated with a specific _____ ____ structure
head; neck
Which pharyngeal arch regresses soon after forming?
5
Which pharyngeal arches are usually the focus?
1, 2, 3, 4
Each arch components
- innervated by an arch associated cranial nerve
- artery
- muscle compartment
- skeletal/cartilaginous component
In some animals, the arches rupture to form _____
gills
Water comes in through mouth and pushed out through gills
respiration
Humans also have gill ____ but we have modifications that prevent “break through”
slits
At 5 weeks
- 1, 2, 3, pharyngeal pouches are formed
- 1-4 arches
- clefts
1-4 arches
- cartilage becomes bone via endochondral ossification
- connective tissue
- neural crest cells dorsal to neural tube migrate down to form cranial nerves
- somitomeres (mesoderm near neural tube migrates to arch) to form muscle and cartilage
- blood supply via aortic arches
Additional hemangioblasts that did not become vessels can give rise to __________ or hematopoietic stem cells that will give rise to all blood cells
angioblasts
_______ commences in the extraembryonic mesoderm of the connecting stalk, umbilical vesicle and chorion
vasculogenesis
Primitive heart function
- as the blood and blood vessels begin to form, there is a concomitant establishment of the cardiogenic area
- a pair of longitudinal tubes with endothelium called the endocardial heart tubes are formed during this time
- they eventually fuse to form the primordial heart tube
- it merges with embryonic and extraembryonic blood vessels to establish the primordial cardiovascular system
In most cases, heartbeats commence at the end of week ____, making the heart the first functional organ of the embryo. However, this heartbeat is not readily appreciated until the 5th week of gestation
3
Arch 1
Mandibular arch
Arch 1 “Mandibular Arch”
- all 3 germ layers involved
- at week 5, Bifurcates to form:
A.) Maxillary process
B.) Mandibular process “arch”
Maxillary process
- Bone: upper jaw (maxilla), soft and hard palate, zygomatic, squamosal temporal, vomer
- epidermis of upper lip (philtrum) and cheek
- enamel of upper teeth
- Parotid salivary gland (Stenson’s ducts)
- “Mumps”
Ectoderm invaginates to form _______ salivary gland on sides of face
parotid
Buds form the echo and teeth form the ____
meso
Mandibular process
- Bone: mandible
- Meckel’s cartilage
- incus, malleus of middle ear
- forms epidermis of upper auricle of ear and lower lip and jaw
- enamel forms from ectoderm and early formation dentine from mesh
- submandibular and sublingual glands
- portions of tongue (muscle and frenulum)
Pouch 1
- Eustachian tube and part of tympanic cavity
- internal membrane of eardrum
- middle ear area
- Innervated by Trigeminal nerve
Cleft I
external auditory meatus
Cleft II-IV
obliterated
Epithelium covers
- vestibule of mouth
- palate of mouth
- body of tongue
Arch II
Hyoid arch
Arch II “Hyoid Arch”
- Bone: stapes
- Part of hyoid (lesser horns)
- Styloid process (temporal)
- sides and front of upper neck area
- epithelium of root of tongue
- circulation of pharynx
- dorsal 1/2 of auricle (ear)
Pouch II
- palatine tonsils
- innervated by Facial nerve
Arch III
- Bone: part of hyoid bones (inferior part and greater Cornu/body)
- common carotids and part of internal carotid artery
Pouch III
- thymus
- parathyroid (inferior portion)
- innervated by Glossopharyngeal nerve
Arch IV
forms certain muscle and cartilage of larynx and lower pharynx
Pouch IV
- ultimobranchial bodies (fuse with thyroid as Parafollicular cells that produce Calcitonin “C” cells)
- Parathyroid (superior portion
- innervated by Vagus nerve
Arch 5
disappears
