Gastrulation and Germ Layers

Question 1

When is something most likely to go wrong in human development?

Answer 1

First 7 weeks

Question 2

What is the Zona Pellucida?

Answer 2

a thick layer of glycoproteins surrounding the oocyte.

Helps with sperm recognition.

Question 3

What are granulosa cells? What types are there?

Answer 3

They are responsible for follicle development
Cumulus oophorous: anchor oocyte to follicle wall.
Mural granulosa cells: line wall of follicle
Corona Radiata: firmly anchored to ZP

Question 4

What is the Acrosome reaction?

Answer 4

sperm head releases enzymes to pass CR and ZP

Need to go ‘across’ 2 layers

Question 5

What is Zona reaction?

Answer 5

changes in ZP making it impermeable to other sperm cells. Prevents dispermy
(Creates a ‘zone’)

Question 6

What marks the beginning of human development?

Answer 6

pronuclei fusing to create a zygote

Question 7

When does cleavage begin? What happens?

Answer 7

30 hrs after fertilization

Zygote cleaves –> blastomere (2 cells w 2 polar bodies)

Question 8

When/ why does compaction begin (#of cells)?

Answer 8

9 cell stage. Because ZP is restricting further growth

Question 9

What is a morula?

Answer 9

when compaction stops ~32 cells
(mulberry)
Day 3

Question 10

How does a blastocycst cavity form? What makes up new blastocyst?

Answer 10

After morula enters uterus, it absorbs fluid and creates blastocyst cavity
Early Blastocyst: has embryo and its membranes
- trophoblast (surrounds blast. cavity)
- embryoblast (inner cell mass)

Question 11

When does the ZP degenerate? What happens?

Answer 11

After ~4-5 days, the blastocyst ‘hatches’

It forms later blastocyst

Question 12

Where does fertilization occur?

Answer 12

Ampulla (distal 2/3 of uterine tube)

Question 13

What is spontaneous abortion?

Answer 13

when zygotes, morulae, and blastocysts abort
~45% of fertilized ovums (before you know you know you’re preggo)
Causes: Chromosomal anomalies (segregation, duplication, deletions, dispermy)
-Low progesterone & estrogen from corpus luteum

Question 14

When does implantation occur?

Answer 14

day 6-8

Question 15

What happens to the trophoblast before it can implant?

Answer 15

Differentiate to cytotrophoblast and syncytiotrophoblast

Question 16

What are syncytiotrophoblasts and what do they do?

Answer 16

differentiated trophoblast. Multiple nuclei. Invade endometrium with enzymes.
Allows blastocyst to ‘burrow’ into endometrium

Question 17

What does the embryoblast become? and when?

Answer 17

epiblast and hypo blast

day 7

Question 18

What does the hypoblast do? Where is it?

Answer 18

Forms exocoelomic membrane (future yolk sac).

It is continuous inner lining wih the exocoelomic membrane. Lies just behind epiblast.

Question 19

What does the epiblast form?

Answer 19

It forms the amniotic cavity by making a separation in the epiblast.
The amnion encloses the embryo and house amniotic fluid.

Question 20

What makes up the bilaminar disk?

Answer 20

Hypoblast & Epiblast

Question 21

What is the primary umilical vessel? When does it form?

Answer 21

When the (newly formed) extraembryonic mesoderm begins to compress, the hypoblast + lining of exocoelomic membrane form the primary umbilical vessical.
Day 10-12

Question 22

What is the secondary umbilical vessel? When does it form?

Answer 22

Extraembryonic coelom pinches of remnant (primary vessicle), leaving behind 2ndary umbilical vessicle.
- Originate from hypoblast
- Site of primordial germ cells
Day 13

Question 23

What does the extraembryonic somatic mesoderm line?

Answer 23

trophoblast and amnion

Question 24

What does the extraembryonic splanchnic mesoderm line?

Answer 24

umbilical vessical

Question 25

What is the chorionic sac?

Answer 25

fetal component of placenta

extraembrionic somatic mesoderm + syncytiotrophoblast

Question 26

What is an ectopic pregnancy? Where do they typically happen?

Answer 26

Implantation of blastocyst outside the uterine cavity
2% of all pregs
95% of them happen in oviduct (proximal uterine tube)

Question 27

When does gastrulation begin? What starts gastrulation?

Answer 27

week 3
forming of primitive streak
over by week 4

Question 28

What is gastrulation

Answer 28

Epiblast migrate –> Ectoderm + Mesoderm + Endoderm

It defines all the body axes

Question 29

What do epiblasts migrate through to form germ layers?

Answer 29

The primative streak. They move Cephally and Laterally

Question 30

What is Sacrococcygeal Teratoma? Why does it form?

Answer 30

Germ cell tumor derived from primitive streak.
When gastrulation exceeds 4 weeks.
1:35,000 live births (80%female)

Question 31

How does the notochordal process form?

Answer 31

1. cranial extension from primitive node
2. begins hollow tube (early notochordal process)
3. Grows in mesoderm until reaching prechordal plate
4. Complete by day 20

Question 32

What is the notochord?

Answer 32

Mesodermally derived rod
From oropharyngeal membrane to primitive node
Signaller for early embryo
Future nucleus pulposus

Question 33

What is the caudal eminence?

Answer 33

Temporary Tail (tail bud) made from mesodermal cells
Gives rise to caudal structures of body
Contribute cells to caudal end of neural tube and  NCCs

Question 34

Ectoderm Derivatives

Answer 34

• Epidermis (skin hair nails etc.), nervous system,

Question 35

Mesoderm Derivatives?

Answer 35

Muscle, bone, blood, heart

Question 36

Endoderm Derivatives

Answer 36

Lungs, GI tract, bladder, liver, pancreas

Question 37

What layer does epithelia come from?

Answer 37

ALL LAYERS

Question 38

What are the extraembryonic membranes?

Answer 38

2ndary umbilical vessical, amnion, and chorion