early embryology and branchial arch Flashcards
prenatal development
embryonic development
1) proliferation and migration
- fertilization
- cleavage
- blastocyte
- implantation
- bilaminar disc
- trilaminar disc
2) morphogenesis and differentiation
- overlapping events
fetal development
- after 3 months
crown rump length
over time, size of the embryo increases
fertilization and cleavage
1) after fertilization, proliferative phase
- rapid division that leads to formation of morula
day 4-6
1) morula on day 4
2) blastocyst on day 5-6
- trophoblast (around the blastocyst)
- embryoblast (concentrated on one side)
- fluid-filled space
blastocyst formation
1) embryoblast
- forms embryo proper
2) trophoblast
- only for implantation and placenta
3) blastocoele (primary yolk sac)
after blastocyst
1) implantation
- day 6-7
2) formation of the bilaminar disc
- day 8-14
- epiblast (columnar cells)
- hypoblast (simple cuboidal)
- amniotic cavity and secondary yolk sac present
prochordal plate
1) where epiblast and hypoblast meet, and epithelium becomes taller
2) establishment of the axis of the embryo
- will be formation of the head at the plate
3) week 1-2
3rd week
1) gastrulation
2) bilaminar disc to trilaminar disc
-cells of epiblast migrate inward, forming indentation
- push inward to make endoderm and ectoderm
- mesoderm forms in between
three germ layers give rise to
1) ectoderm
- outer layer of skin, hair, lining nose and mouth
2) endoderm
- digestive tract, respiratory tract, liver, pancreas
3) mesoderm
- muscle and skeleton
formation of the three-layer embryo
1) morula day 4
2) early blastocyst day 6
- hollow ball, fluid filled
3) late blastocyst day 10
- two layers of cells that become embryo proper
4) gastrula day 16
- three primary germ layers
gastrulation
1) primitive streak develops along midline
- primitive groove, node, pit
2) rostral end of the streak finishes in the primitive node (ridges) or pit
3) notochord (mesoderm) extends from the pit to the prochordal plate
4) as a result of the cell migrations, the notochord/mesoderm separates the ectoderm from the endoderm
- except in the prochordal and cecal plates (they will JOIN)
5) cells that accumulate anterior to the prochordal plate give rise to the cardiac plate
formation of the notochord
1) week 3-4
2) transient embryonic structure formed from mesoderm
3) influences embryo folding
4) SHH proteins diffuse into notochord and help cells orient in 3d space
5) notochord extends from primitive pit to the prochordal plate and starts the process of neurulation
next 3-4 weeks of development
1) neural tube formation
2) cephalic formation
3) neural crest cell formation
neural tube formation
1) neurulation
2) thickening of the ectodermal layer at the rostral end of the embryo
- neural plate or the neuroectoderm
3) margins = neural folds
4) neural folds delineate a deepening midline depression (neural groove)
5) fusing of the folds (Neural tube) occurs centrally then proceeds cranially and caudally
- forms anterior and posterior neuropores, closes 4th week
paraxial mesoderm
somites and somatomeres
intermediate mesoderm
urogenital system
lateral mesoderm
CT associated with muscle and viscera, CV system, blood, etc
anencephaly
Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development.
It is a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close
spina bifida
Spina bifida is a birth defect in which there is incomplete closing of the spine and the membranes around the spinal cord during early development in pregnancy.
cephalic folding head
1) head fold is critical to the formation of the primitive oral cavity (stomatodeum) and foregut
2) formation of the buccopharyngeal membrane
3) stomatoderum
- delimited by frontal prominence and cardiac bulge
4) buccopharyngeal membrane
- bilaminar structure with ectoderm and endoderm
- separated stomatodeum from the foregut
- soon breaks down so the stomatodeum communicates directly with the foregut
cephalic folding differentiation of layers
1) ectoderm encapsulates the embryo and forms the surface epithelium
2) paraxial mesoderm remains adjacent to the neural tube and notochord
3) lateral plate mesoderm cavitates to form a cavity (coelom) that lines the body wall and gut
4) endoderm forms the gut
neural crest cell migration
1) cells can migrate and differentiate extensively within the developing embryo
2) ectomesenchyme (CT that originate from neural crest cells/ectoderm) x mesenchyme (CT in embryo derived from mesoderm)
3) except enamel, all tissues that compose the teeth depend on the neural crest cells
neural crest cells and head formation
1) anterior portion of this neural tube expands greatly as the forebrain, midbrain, and hindbrain form
2) part associated with the hindbrain develops 8 rhombomeres
3) lateral to the neural tube is the paraxial mesoderm
- rostrally to form somatomeres
- caudally to form somites
- first of them is “occipital somites”
migration of neural crest cells
1) migration of neural crest cells (from rhombomeres) make embryonic CT (mesenchyme) needed for craniofacial development (ectomesenchyme in the head, reflecting its origin from the neuroectoderm)
*midbrain and rhombomeres 1 and 2 contribute to the face and branchial arch 1
2) pre-determined migration paths (homeobox genes)
- 180 bp element (homeobox)
3) Hox genes are a group of related patterning genes that determine the basic structure and orientation of an organism
branchial arch formation
1) major transcription factors (Msx, Dlx, Barx) orchestrate migration and pattern formation
- at about day 35
2) SHH affect neural crest proliferation, differentiation, and survival
3) branchial arches form in pharyngeal wall as a result of the proliferating lateral plate mesoderm and by migrating neural crest cells
branchial arches
1) 6 pairs of branchial arches (I-VI)
- V and VI are transient
2) externally
- branchial grooves (Ectoderm)
3) internally
- pharyngeal pouches (endoderm)
anatomy of branchial arches
1) cartilage
2) aortic arch
3) cranial nerve
4) muscle
branchial arch I
1) CN V (trigeminal nerve)
- mandibular and maxillary division
2) mandible and maxilla
3) meckel’s cartilage: sphenomandibular ligament
4) muscles of mastication
5) formation of external auditory meatus
branchial arch II
1) CN VII or facial nerve
2) reichert’s cartilage: styloid process of temporal bone and stylohyoid ligament, lesser horns of the hyoid bone
3) muscles of facial expression
branchial arch III
1) CN IX (glossopharyngeal nerve)
2) greater horns of the hyoid bone
3) stylopharyngeus muscle
branchial arch IV
1) CN X (vagus)
2) cartilages of the larynx
pouch 1
1) auditory tube
- tympanic membrane / cavity
- mastoid antrum
- eustachian tube
pouch 2
1) palatine tonsil
pouch 3
1) inferior parathyroid (II) and thymus gland
pouch 4
1) superior parathyroid (IV) and thymus (vestigial) glands
2) postbranchial body
- source of parafollicular or C cells of thyroid gland
formation of the tongue
1) ectomesenchyme of branchial arch enlarges (tuberculum impar)
2) enlargement of on both sides of tuberculum impar (lateral lingual swellings)
3) will merge to form the anterior 2/3 of the tongue
- innervated by CN V
4) posterior 1/3 develops from ectomesenchyme of II, III, and IV
- from hypobranchial eminence
- III and IV outgrow II
- innervated by CN IX
5) epiglottis forms from branchial arch IV
- innervated by CN X
—-
1) muscle arises from the post-occipital somites
- segments of the mesoderm - extending caudally
- innervated by CN XII
pierre robin syndrome
baby has an underdeveloped jaw, a cleft palate and a tongue that’s placed further back toward the throat. This condition often leads to eating problems and breathing difficulties
- genes defective for neural crest migration
treacher collins syndrome
Treacher Collins syndrome (TCS) is a genetic disorder characterized by deformities of the ears, eyes, cheekbones, and chin
- neural crest cells do not migrate properly
