3.3 - Lecture - Embryology

Question 1

Oropharyngeal membrane

Answer 1

• located at cranial/cephalic end of developing embyro
• temporary boundary between the oral cavity + foregut
• fusion of endoderm + ectoderm (no mesoderm here)
• breaks down on day 26

Question 2

Cloacal membrane

Answer 2

• separates the upper part of the anal canal from the extrenal environment
• caudal end of developing embryo
• fusion of endoderm + ectoderm (no mesoderm here)
• breaks down at day 43

Question 3

Prechordal plate

Answer 3

• collection of mesoderm cells
• located between oropharyngeal membrane and cranial end of the notochord
• cells are important for forebrain induction
• possibly contribute to connective tissue of head and neck region

Question 4

Surface Ectoderm

Answer 4

• derived from epithelium lining of the amniotic cavity

- gives rise to: the epidermis, hair, nails, sweat glands, adenohypophysis

Question 5

Neuroectoderm

Answer 5

• arises from neural plate

- gives rise to: all neurons of brain + spinal chord, retina, pineal gland, neurohypophysis

Question 6

mesoderm

Answer 6

germ layer that gives rise to:

• paraxial mesoderm
• intermediate mesoderm
• lateral mesoderm
• intraembryonic body cavity

these regions then form: muscle, connective tissue, dermis, cartilage, bone, endothelium, kidney, adrenal cortex

Question 7

Endoderm

Answer 7

• germ layer forms the epithelial lining of the yolk sac –> gives rise to epithelial lining of GI tract, trachea, bronchi, lungs, paraenchymal cells of liver, gallbladder, pancreas

Question 8

Notochord

Answer 8

• “axial mesoderm”
• solid cord of cells forming a midline
• underlies the developing neural tube
• serves as basis for the axial skeleton
• important for inducing the neural plate and the scelerotome portion of the somite that will form the vertebral column

Question 9

Neural Crest Cells

Answer 9

• derived from neuroepithelium
• found at the “crest” of the neural folds during neural tube development
• pluripotent cells that migrate throughout the body in the mesoderm layer of the developing embryo
• sometimes called “fourth” germ layer

Question 10

Somite

Answer 10

• cells formed in segmental pairs along the neural tube
• derived from paraxial mesoderm
• form the bone of axial skeleton, muscles of the back + body wall, dermis (layer of skin) of the back

Question 11

Foregut

Answer 11

• arises from endoderm lining the yolk sac during body folding
• part of the gut tube
• beginning caudal to the pharynx and extending to the liver bud

Question 12

Midgut

Answer 12

• arises from endoderm lining the yolk sac during body folding
• part of gut tube
• extending from distal to the liver bud to the proximal 2/3s of the transverse colon

Question 13

Hindgut

Answer 13

• arises from endoderm lining the yolk sac during body folding
• part of gut tube
• extending from the distal 1/3 of the transverse colon to the upper portion of the anal canal

Question 14

10 Important Events In development of the neural tube

Answer 14

1) Ectoderm overlying the notochord thickens to form the neural plate
2) Neural plate thickens further and the cranial end expands (where brain will form)
3) Neural plate develops an axial neural groove with neural folds on either side of it
4) lateral edges of the neural folds each from a ridge-like neural crest (where the neuroectoderm merges with somatic ectoderm)
5) neural groove depends –> brings the edges of neural folds close enough for them to fuse
6) fusion of the neural folds results in formation of the hollow neural tube
7) 2 neural crests detach from the neural tube & migrate into the mesoderm layer as neural crest cells
8) somatic ectoderm fuses at the surface as the neural tube sinks into the mesoderm layer
9) cranially the neural tube enlarges and changes shape to form the primitive brain
10) caudally the wall of the neural tube thickens to form the primitive spinal chord

Question 15

Neurulation

Answer 15

• process by which the neural tube forms

- begins ~ day 18

Question 16

paraxial mesoderm forms?

Answer 16

• the somites (pairs of block-like segments) (42-44 pairs initially –> regress to ~ 37 pairs)
• (somitomeres in the head an neck region - contribute to the mesenchyme there)

Question 17

intermediate mesoderm forms?

Answer 17

urogenital system

Question 18

lateral plate mesoderm forms?

Answer 18

• coelom, and gives rise to connective tissue + muscle of the viscera, serous membranes
• eventually develops clefts and splits the solid mesoderm into splanchnic mesoderm layer + somatic mesoderm layer

Question 19

Splanchnic Mesoderm Layer

Answer 19

• associated with the endoderm

- gives rise to mesothelial covering of the organs and the muscle, connective tissue and vasculature of the organ

Question 20

Somatic Mesoderm

Answer 20

• associated with the ectoderm

- gives rise to the inner lining of the body wall and parts of limbs

Question 21

Morphogenesis

Answer 21

• development of shape or form

- can apply to whole body or even just an organ or part of one

Question 22

Organogenesis

Answer 22

• formation of an organ or related organs
• includes –> differentiation of the organ’s cells + tissues, development of the pattern of their arrangements, development of function

Question 23

what does it mean to say body folding rearranges the flat disc of the embryo into a “tube within a tube”

Answer 23

• outer tube of ectoderm forming the skin with an internal tube of endoderm forming the gut
• space between the two tubes is primarily mesoderm

Question 24

3 Differentiations of somites

Answer 24

1) Scelerotome
2) Myotome
3) Dermatome

Question 25

Scelerotome will give rise to

Answer 25

most of the axial skeleton (vertebrae, ribs, occipital bone of the skull)

Question 26

Myotome will give rise to

Answer 26

voluntary muscle of the body

Question 27

Dermatome will give rise to

Answer 27

dermis of some of the body