Embryology

Question 1

What surrounds the blastomeres after first mitotic divide?

Answer 1

Zona pellucida

Question 2

When does the first mitotic divide occur?

Answer 2

30 hours after fertisilation

Question 3

What is created in day 3?

Answer 3

Morula - totipotent cells

Question 4

What happens to the morula?

Answer 4

Compaction occurs to create blastocyst (formation of first cavity)

Question 5

What are the four components of the blastocyst?

Answer 5

Zona pellucida
Outer cell mass - trophoblast
Inner cell mass - embryoblast
Blastocyst cavity

Question 6

What occurs after the formation of the blastocyst?

Answer 6

Hatching from zona pellucida

Question 7

After implantation begin, what occurs?

Answer 7

Formation of bilaminar disc

Question 8

What does the embryoblast form?

Answer 8

Epiblast and hypoblast

Question 9

What does the trophoblst form?

Answer 9

Cytotrophoblast and syncytiotrophoblast

Question 10

Name the components present after the formation of the bilaminar disc

Answer 10

Epiblast, hypoblast - forming bilaminar disc
Cytotrophoblast, synctiotrophoblast
Amniotic cavity
Blastocyst cavity

Question 11

What occurs after the formation of the bilaminar disc?

Answer 11

Formation of primitive yolk sac by hypoblast development

Question 12

What happens to the primitive yolk sac that is connected to the cytotrophoblast?

Answer 12

It is pushed away from the cytotrophoblast

Extraembryonic mesoderm fills its place

Question 13

What occurs after primitive yolk sac is pushed away from cytotrophoblast?

Answer 13

Uteroplacental circulation begins

Question 14

How does uteroplacental circulation occur?

Answer 14

Invasion of maternal sinusoid to syncytiotrophoblast

Question 15

What occurs after uteroplacental circulation?

Answer 15

Formation of secondary yolk sac

Question 16

How does the secondary yolk sac form?

Answer 16

Pinches off from primitive yolk sac

Question 17

In terms of embryology, what is the present at the end of week 2?

Answer 17

Bilaminar disc composed of epiblast and hypoblast
Amniotic cavity of epiblast cells
Primary yolk sac of hypoblast cells
Secondary yolk sac of hypoblast cells
Chorionic cavity
Connecting stalk

Question 18

Where is the ideal location of implantation?

Answer 18

Posterior uterine wall

Question 19

What is the different between topipotent and pluripotent cells? When does the change occur?

Answer 19

Totipotent - capacity to become anything
Pluripotent - capacity to become one of many cell types
Change occurs during compaction

Question 20

What occurs during gastrulation?

Answer 20

Process of establishing the 3 germ layers (trilaminar disc)

Sets axes

Question 21

From where does the primitive streak develop?

Answer 21

Develops from caudal end of epiblast layer

Question 22

Describe the formation of the primitive streak, node and pit

Answer 22

The primitive streak is a narrow groove with bulging edges

The primitive node is at the end with the pit lying between it and the streak

Question 23

What occurs after the formation of the primitive streak, node and pit?

Answer 23

Migration and invagination of epiblast layer, spreading laterally and cephalad between epiblast and hypoblast
Displacement of the hypoblast layer with creation of third layer
Trilaminar disc is formed

Question 24

What are the 3 layers of the trimlaminar disc?

Answer 24

Ectoderm
Mesoderm
Endoderm

Question 25

Describe the formation of the notochord

Answer 25

Prenotochordal cells of the spiblast migrate through the cranial part of the primitive pit to form solid rod of cells

Question 26

Why is the notochord important?

Answer 26

Defines midline Axial skeleton forms around it Drives neurulation

Question 27

Why is the primitive node important?

Answer 27

Emits molecular signals which ensure correct dorso-ventral and left-right orientation

Question 28

What is ultimately derived from the ectoderm?

Answer 28

Organs and structures with contact to the outside world (nervous, epidermis)

Question 29

What is ultimately derived from the mesoderm?

Answer 29

Supporting tissues (muscles, cartilage, bone & vascular system)

Question 30

What is ultimately derived from the endoderm?

Answer 30

Internal structures (GI, respiratory & urinary tract)

Question 31

How is left and right asymmetry formed?

Answer 31

Action of cilated cells at node results in leftward flow of signalling molecules - side specific signalling cascades initiated

Question 32

What occurs during the fourth week?

Answer 32

Neurulation Mesoderm differentiation Folding

Question 33

What is neurulation?

Answer 33

Notochord driven induction of ectoderm to form nervous system

Question 34

How does neurulation occur?

Answer 34

Notochord signals for overlying ectoderm to thicken to form neural plate Edges elevate out of plane of disc and then curl towards each other to form neural tube

Question 35

What is the first step in mesoderm diffrentiation?

Answer 35

Mesoderm organises into paraxial mesoderm, lateral mesoderm (somatic mesoderm, splanchnic mesoderm) and intermediate mesoderm

Question 36

What does the paraxial mesoderm form?

Answer 36

Somites which develop craniocaudal - 31 pairs

Question 37

Describe organised degeneration of the somite

Answer 37

Degeneration of the ventral wall of somite forms sclerotome Further organisation occurs to form combined dermomyotome Myotome proliferates and migrates and dermatome disperses

Question 38

What do the dermatome, myotome and sclerotome give rise to?

Answer 38

Dermatome - Skin section (dermis) Myotome - Muscle section (muscle) Sclerotome - Hard tissue (bone)

Question 39

What do somites ultimately give rise to?

Answer 39

Repeating structures e.g. vertebrae, ribs, intercostal muscles, spinal cord segments Also guides innervation

Question 40

What does the paraxial mesoderm ultimately give rise to?

Answer 40

Axial skeleton, dermis, muscles

Question 41

What does the intermediate mesoderm ultimately give rise to?

Answer 41

Urogenital system

Question 42

What does the lateral mesoderm ultimately give rise to?

Answer 42

Somatic - connective tissues of limbs | Splanchnic - Smooth masculature, connective tissue and vascularture of gut

Question 43

How does the embryo fold?

Answer 43

Driven by lateral plate mesoderm pulling downwards and encompassing all the primitive yolk sac creating the embryo suspended within aminotic sac