CVS Embryology and Embryology recap

Question 1

When is the embryonic age?

Answer 1

Time since fertilisation

Question 2

When is the gestational age?

Answer 2

Time since last menstruation - fertilisation + 2 weeks

Question 3

When is germinal stage?

Answer 3

Fertilisation oil end of 2nd week

Question 4

When is embryonic period?

Answer 4

2nd week to end of 8th week

Question 5

When is foetal period?

Answer 5

Start of 9th week to 38 weeks

Question 6

When does a morula form? What is it?

Answer 6

Group of around 16 cells 3-4 days

Question 7

When does a blastocyst form? What is it?

Answer 7

Around day 4-5 forms an inner and outer cell mass
—> blastocyst

Blastocyst contains: Embryoblast, and primitive endoderm, outer layer of cells call trophoblasts.

Question 8

What day does implantation occur? What do you need to lose before implantation can occur?

Answer 8

Day 6

Zona pellucida - leads to ‘hatching’

Question 9

Where does fertilisation normally occur?

Answer 9

Ampulla

Question 10

What does the embryoblast and trophoblast become?

Answer 10

Embryo blast - early embryo

Trophoblast - yolk sac and placenta

Question 11

What is histiopathic nutrition? When does it occur?

Answer 11

Histiopathic nutrition is not from maternal blood, it is from uterine glands/tissues etc up until 12th week in embyro

Question 12

What is haemotrophic nutrition? When does this occur?

Answer 12

From maternal blood this occurs after week 12

Question 13

Where does placenta normally lie?

Answer 13

Upper posterior wall of uterus

Question 14

What is placenta previa?

Answer 14

Placenta blocking exit of baby

Question 15

What happens in week 2 gestation?

Answer 15

“Week of twos”

trophoblasts splits into two layers

1) Hypoblast –> embryonic yolk sac, chorionic cavity
2) Epiblast (will later become 3 germ layers endo, meso, ectoderm)

Together the hypoblast and epiblast are the bilaminar embryonic disc

Question 16

What is gastrulation?

Answer 16

Forming of the 3 germ layers

Question 17

What happens in week 3 gestation? What is the role of gastrulation?

Answer 17

Week of threes
Gastrulation - endo meso ectoderm

Gastrulation ensures precursor cells are in the right place to allow for growth of those tissues

Question 18

Between which weeks is the period of greatest change? What does this mean for congenital abnormalities?

Answer 18

3-8 organogenesis

Means great risk for teratogenesis

Question 19

Which germ layer forms the heart?

Answer 19

Mesoderm

Question 20

Which week does the embryo fold? What does this do for the heart?

Answer 20

4

Puts it in the right place

Question 21

What is the cardiogenic field and what does it differentiate into?

Answer 21

It is the area of embryo that forms:
Heart
Blood
Vessels

Question 22

What are three causes of congenital cardiac abnormalities?

Answer 22

• Genetic
• De novo
• Teratogenic agents e.g. alcohol

Question 23

Why are congenital cardiac conditions so common? (Think about role of heart in utero then after birth)

Answer 23

Because of the complexity of the heart and the fact it needs to work in utero and then switch to work with inflated lungs - lots of coordination of different structures that change at birth

Question 24

What is the primitive heart tube essentially? What does it not have (2)?

Answer 24

A modified blood vessel

Has no chambers no valves

Question 25

Why does CVS develop so early in embryogenesis?

Answer 25

Growing embryo needs blood

Question 26

What is the order of structures from top to bottom in the primitive heart? What do they become?

Answer 26

1) Aortic roots (2) 2) Truncus arteriosus -> Ao and pulm trunk 3) Bulbous cordis -> caudal end is smooth outflow tracts of LV and RV, cranial end (conus cords) gives rise to Ao and Pulm trunk with truncus arteriosus 4) Primative ventricle -> R+L ventricle 5) Primative atria -> R+L atria 6) Sinus venosus (4) -> Becomes the RA, coronary sinus and SAN

Question 27

What are neural crest cells and what are they sensitive to?

Answer 27

Form the CNS and sensitive to alcohol in particular. Foetal alcohol syndrome Neural crest cells also have important role in cardiac septation (Endocardial cushions) - hence septal abnormalities in foetal alcohol syndrome.

Question 28

What happens during cardiac looping and why?

Answer 28

``` Runs out of space for linear dimension Folding of primitive heart tube Structures now in right place Folding is predictable and regular Ventricles enlarge most, then atria Now occupies all of pericardial sac ```

Question 29

What is the LA made from?

Answer 29

The primitive atrium, but mostly the primitive pulm veins (smooth part)

Question 30

What is the RA made from?

Answer 30

From most of primitive atrium and also part of the sinus venosus

Question 31

What are the three shunts in foetal life? Why do they need one around the liver?

Answer 31

Foramen ovale - allows R->L shunt to bypass lungs Ductus arteriosus - allows blood from RV (as some still goes to RV to allow it to develop muscle) to go out to PA-->Ao--> body Ductus venous - as liver v metabolically active in utero so need to bypass so it doesn't use up all O2

Question 32

Which vessel has the highest PO2 in foetus?

Answer 32

IVC

Question 33

How does the foramen ovale shut at birth?

Answer 33

Increased LA pressure | Closes physiologically and then chemically --> fibrotic

Question 34

How does the ductus arteriosus shut at birth?

Answer 34

Muscular contraction with first breath

Question 35

What causes ductus venosus to shut?

Answer 35

Placenta removal

Question 36

How many initial aortic arches are there in primitive vessels?

Answer 36

6

Question 37

Which arch does the prox part of subclavian artery and Ao come from? Which arch does the R pulm artery and L pulm artery and ductus arteriosus come from?

Answer 37

4 - prox part of subclavian and Aorta 6 'AKA pulm arch'- R and L pulm arteries and ductus arteriosus

Question 38

What causes the left recurrent laryngeal nerve to hook round aortic arch?

Answer 38

The heart descends inferiorly during development and this causes it to hook round

Question 39

What happens if the PDA doesn't close? When is this more common?

Answer 39

``` More common in premature babies Doesn't close leads to: Pulm HTN Congestive HF Arrhythmias ``` As blood will go from Ao to pulm A due to pressure

Question 40

What are the roles of the endocardial cushions?

Answer 40

Scaffold to divide heart into L and R and atria and ventricles

Question 41

What are the 5 stages of foramen ovale formation?

Answer 41

1) Endocardial cushions from neural crest cells 2) Wedge of tissue forms downwards to form 2 atria 3) Form crescent (septum primum) --> free flowing 'osteum primum' 4) Osmium secundum made in septum primum by apoptosis - need septum secundum to make flow one way 5) Septum secundum forms with hole --> misaligned holes mean only one way flow of blood

Question 42

What could happen if the osteum primum and secundum do line up at birth?

Answer 42

They could cause communication between RA and LA, shunt from L->R ASD.

Question 43

What pathology is a risk with ASD?

Answer 43

TIA/Stroke due to emboli from DVT

Question 44

Where else would you need endocardial cushions?

Answer 44

Truncus arteriosus when forming the PA and Aorta - need to divide the one tube into two.

Question 45

How do pulm trunk and aorta develop around each other?

Answer 45

Spiral

Question 46

What are truncal ridges and bulbar ridges?

Answer 46

Endocardial cushions that together make spiral septum