early embryology and branchial arch

Question 1

prenatal development

Answer 1

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

Question 2

crown rump length

Answer 2

over time, size of the embryo increases

Question 3

fertilization and cleavage

Answer 3

1) after fertilization, proliferative phase
- rapid division that leads to formation of morula

Question 4

day 4-6

Answer 4

1) morula on day 4
2) blastocyst on day 5-6
- trophoblast (around the blastocyst)
- embryoblast (concentrated on one side)
- fluid-filled space

Question 5

blastocyst formation

Answer 5

1) embryoblast
- forms embryo proper
2) trophoblast
- only for implantation and placenta
3) blastocoele (primary yolk sac)

Question 6

after blastocyst

Answer 6

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

Question 7

prochordal plate

Answer 7

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

Question 8

3rd week

Answer 8

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

Question 9

three germ layers give rise to

Answer 9

1) ectoderm
- outer layer of skin, hair, lining nose and mouth
2) endoderm
- digestive tract, respiratory tract, liver, pancreas
3) mesoderm
- muscle and skeleton

Question 10

formation of the three-layer embryo

Answer 10

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

Question 11

gastrulation

Answer 11

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

Question 12

formation of the notochord

Answer 12

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

Question 13

next 3-4 weeks of development

Answer 13

1) neural tube formation
2) cephalic formation
3) neural crest cell formation

Question 14

neural tube formation

Answer 14

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

Question 15

paraxial mesoderm

Answer 15

somites and somatomeres

Question 16

intermediate mesoderm

Answer 16

urogenital system

Question 17

lateral mesoderm

Answer 17

CT associated with muscle and viscera, CV system, blood, etc

Question 18

anencephaly

Answer 18

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

Question 19

spina bifida

Answer 19

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.

Question 20

cephalic folding head

Answer 20

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

Question 21

cephalic folding differentiation of layers

Answer 21

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

Question 22

neural crest cell migration

Answer 22

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

Question 23

neural crest cells and head formation

Answer 23

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”

Question 24

migration of neural crest cells

Answer 24

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

Question 25

branchial arch formation

Answer 25

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

Question 26

branchial arches

Answer 26

1) 6 pairs of branchial arches (I-VI)
- V and VI are transient
2) externally
- branchial grooves (Ectoderm)
3) internally
- pharyngeal pouches (endoderm)

Question 27

anatomy of branchial arches

Answer 27

1) cartilage
2) aortic arch
3) cranial nerve
4) muscle

Question 28

branchial arch I

Answer 28

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

Question 29

branchial arch II

Answer 29

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

Question 30

branchial arch III

Answer 30

1) CN IX (glossopharyngeal nerve)
2) greater horns of the hyoid bone
3) stylopharyngeus muscle

Question 31

branchial arch IV

Answer 31

1) CN X (vagus)
2) cartilages of the larynx

Question 32

pouch 1

Answer 32

1) auditory tube
- tympanic membrane / cavity
- mastoid antrum
- eustachian tube

Question 33

pouch 2

Answer 33

1) palatine tonsil

Question 34

pouch 3

Answer 34

1) inferior parathyroid (II) and thymus gland

Question 35

pouch 4

Answer 35

1) superior parathyroid (IV) and thymus (vestigial) glands
2) postbranchial body
- source of parafollicular or C cells of thyroid gland

Question 36

formation of the tongue

Answer 36

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

Question 37

pierre robin syndrome

Answer 37

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

Question 38

treacher collins syndrome

Answer 38

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