Embryology

Question 1

Overall 3 stages of human development before birth 🤰🏽

+ weeks of each stage

Answer 1

1 - Pre-embryonic (1-2)
2- Embryonic (2-8)
3- Fetal (>8)

Question 2

3 events during the pre-embryonic period

Answer 2

1 - Cleavage
2 - Compaction
3- Beginning of implantation

Question 3

Where is the oocyte fertilised?

Answer 3

Ampulla

Question 4

Function of Zona Pellucida

Answer 4

Prevent polyspermy 🙅🏽‍♀️

Glycoprotein shell

Question 5

Describe cleavage

Answer 5

The first cell division

Results in 2 blastomere of equal size 🟡🟡

Question 6

Describe the morula

Answer 6

A ball of 16 TOTIPOTENT cells

Question 7

Define totipotent

Answer 7

The ability of the cell to become ANY cell type

Question 8

Clinical use of morula prior to implantation during IVF

Answer 8

PGD (Pre-implantation Genetic Diagnosis) 🩺

Question 9

Define pluripotent

Answer 9

The capacity of a single cell to become MANY cells

Question 10

When does cleavage occur?

Answer 10

30 minutes after fertilisation

Question 11

Time period when ‘compaction’ occurs

Answer 11

Week 1

Question 12

Describe compaction

Answer 12

1) Formation of the blastocyst cavity

2) Differentiation of cells to:
- inner cell mass (embryoblast)
- Outer cell mass (trophoblast)

Question 13

When can the blastocyst interact with the uterine surface

Answer 13

After hatching from the zona pellucida

Question 14

Describe the Week 2 of the pre-embryonic stage

Answer 14

1) Differentiation of
- inner cell mass
- outer cell mass

2) Implantation is completed
3) Utero-placental blood supply is established

Question 15

What does the outer cell mass differentiate into

Answer 15

• Cytotrophoblast

AND

• Syncytiotrophoblast

Question 16

What does the inner cell mass differentiate to?

Answer 16

• Epiblast

AND

• Hypoblast

Question 17

Describe bilaminar disc

Answer 17

• Made of the epiblast and hypoblast

- Separates the amniotic cavity and blastocyst cavity

Question 18

2 distinct features of the syncytiotrophoblast

Answer 18

• Multinucleated

- No clear cell boundaries

Question 19

Pre-embryonic structure that develops to the umbilical cord

Answer 19

The Connecting stalk

Question 20

What pole is the yolk sac formed 🍳

Answer 20

Abrembrionic pole

Question 21

What pushes the yolk sac from the cytotrophoblast

Answer 21

The Extraembryonic Mesoderm

Question 22

Describe how uteroplacental circulation is established

Answer 22

• Syncytiotrophoblast embeds embryo maternal uterine
• Syncytiotrophoblast invades the endothelium of maternal sinusoids
• Maternal sinusoids become continuous with syncytial lacunae

Question 23

Why can ‘spotting’ cause inaccuracy in determining expected delivery date

Answer 23

⬆️ bleeding due to blood flowing from sinusoids to lacunae

Can be confused as normal menstrual bleeding

Question 24

What merges to form the chorionic cavity 🤔

Answer 24

The spaces in the extraembryonic mesoderm

Question 25

Describe an ectopic pregnancy

Answer 25

Implantation of embryo at any other site than the uterine body

Question 26

Describe placenta praevia | + major complication & treatment

Answer 26

Implantation in the lower uterine segment Can cause haemorrhage in pregnancy C-section

Question 27

What are the 3 titles given to the ‘conceptus’ in order of formation

Answer 27

Zygote ➡️ Morulla ➡️ Blastocyst

Question 28

Which developmental stage is the most sesnsitive to teratotogenesis (And why)

Answer 28

Fetal stage because the organ systems are developing at this stage *The CNS is susceptible to teratogenesis in the fetal stage as well because it continues to develop*

Question 29

Outline the 4 processes occurring during the embryonic stage

Answer 29

1 - Gastrulation 2 - Neurulation 3 - Segmentation 4 - Folding

Question 30

What is gastrulation

Answer 30

The process that establishes the 3 germ layers | Bilaminar to Trilaminar

Question 31

What are the 3️⃣ germ layers derived from gastrulation

Answer 31

- Ectoderm - Mesoderm - Endoderm

Question 32

What structures are formed at the beginning of gastrulation

Answer 32

- Primitive streak | - Primitive node

Question 33

What is a potential explanation for the formation of conjoined twins

Answer 33

The formation of 2 primitive streak

Question 34

What causes the formation of the endoderm and mesoderm

Answer 34

Migration and invagination of epiblast cells underneath the primitive streak

Question 35

All 3 layers of the trilamiar disc are derived from the ...

Answer 35

Epiblast

Question 36

What is derived from the ectoderm

Answer 36

- Nervous system | - Skin

Question 37

What is derived from the mesoderm

Answer 37

- Muscle - Cardiovascular system - Bone

Question 38

What is derived from the endoderm

Answer 38

1) Lining of - GI tract - Respiratory tract 2) Parenchyma of glands

Question 39

Define gestational age

Answer 39

Time since last menstruation

Question 40

Define embryonic age

Answer 40

Gestational age + 2 weeks

Question 41

How is left-right asymmetry established

Answer 41

Signalling molecules at the primitive node initiated side specific cascades that signal “left” and “right” sidedness

Question 42

Describe ‘situs inversus’

Answer 42

Complete mirror image of viscera (organs) Generally causes no problems unless a person presents with both normal and mirror image viscera orientation

Question 43

How does situs inversus affect cilia

Answer 43

Immotile/abnormal cilia

Question 44

What is a potential explanation for situ inversus

Answer 44

Immotile cilia during gastrulation Causing the misdirection of side-specific signalling molecules

Question 45

Describe neurulation

Answer 45

Formation of the early nervous system

Question 46

Describe the notochord | Composition, location and function

Answer 46

- Solid tube of cells - In the Mesdoderm - Convesion of the overlying ectoderm into neuroectoderm

Question 47

What structure overlies the notochord following neurulation

Answer 47

The neural tube

Question 48

Name the 4 parts of the mesoderm

Answer 48

Paraxial Intermediate Somatic Splanchnic

Question 49

What is occurs the intraembryonic coelom in later development

Answer 49

Organs form within this space

Question 50

What forms from the intermediate mesoderm

Answer 50

The Genito-Urinary Tract

Question 51

What forms from the paraxial mesoderm

Answer 51

Somites which then turns into: - Muscles - Bones

Question 52

What arises from the Splanchnic mesoderm

Answer 52

The Viscera of the body (I.e. the organs)

Question 53

What develops from the somatic mesoderm

Answer 53

Connective tissue

Question 54

How many somites are there in total following segmentation

Answer 54

31

Question 55

Why can somites be used to determine developmental stage

Answer 55

Because they appear in an ordered and predictable fashion

Question 56

What forms from the dermatome

Answer 56

Skin

Question 57

What forms from myotome

Answer 57

Muscle

Question 58

What forms from sclerotome

Answer 58

Bones

Question 59

What are the 2 implications of segmentation

Answer 59

1) Gives rise to repeating structures (e.g. ribs, vertebrae) | 2) Guides innervation

Question 60

Describe the 2 stages of embryonic folding and the resulting external structure

Answer 60

1 - Cephalocaudal folding The head and tail fold towards the centre 2 - Lateral folding The edges fold into the centre Causing ectoderm to completely cover the surface with a small segment of endoderm showing through

Question 61

When is the conceptus more vulnerable to teratogenesis and why

Answer 61

Embryonic Organs develop during this time

Question 62

How does the relationship between the amniotic sac and the embryo change after folding

Answer 62

- Folding pulls the amniotic membrane around the disc | - Suspending the embryo within the amniotic sac

Question 63

Describe how folding affects the early: - Gut - Heart ❤️ - Diaphragm

Answer 63

- Creates the primordium of the gut - Puts the positioning of the heart in the correct place - Puts the primordium of the diaphragm in the correct place

Question 64

At which developmental stage does implantation normally occur

Answer 64

Blastocyst

Question 65

What is the function of the hypoblast layer

Answer 65

It lines the blastocyst cavity forming the yolk sac

Question 66

What is the forms from the notochord in later life

Answer 66

The nucleus purposes of intervertebral discs

Question 67

Why does the buccopharngeal and cloacal membrane have no mesoderm

Answer 67

It gives rise to the future mouth and anus respectively

Question 68

What does the primitive streak contain and how can these lead to fetal tumours

Answer 68

- They contain stem cells | - Persistence of the primitive streak can lead to differentiation of the cells to many different cell types

Question 69

Define a zygote

Answer 69

A single diploid cell formed following the fusion of a sperm and an oocyte