CVS Embryology and Embryology recap Flashcards
When is the embryonic age?
Time since fertilisation
When is the gestational age?
Time since last menstruation - fertilisation + 2 weeks
When is germinal stage?
Fertilisation oil end of 2nd week
When is embryonic period?
2nd week to end of 8th week
When is foetal period?
Start of 9th week to 38 weeks
When does a morula form? What is it?
Group of around 16 cells 3-4 days
When does a blastocyst form? What is it?
Around day 4-5 forms an inner and outer cell mass
—> blastocyst
Blastocyst contains: Embryoblast, and primitive endoderm, outer layer of cells call trophoblasts.
What day does implantation occur? What do you need to lose before implantation can occur?
Day 6
Zona pellucida - leads to ‘hatching’
Where does fertilisation normally occur?
Ampulla
What does the embryoblast and trophoblast become?
Embryo blast - early embryo
Trophoblast - yolk sac and placenta
What is histiopathic nutrition? When does it occur?
Histiopathic nutrition is not from maternal blood, it is from uterine glands/tissues etc up until 12th week in embyro
What is haemotrophic nutrition? When does this occur?
From maternal blood this occurs after week 12
Where does placenta normally lie?
Upper posterior wall of uterus
What is placenta previa?
Placenta blocking exit of baby
What happens in week 2 gestation?
“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
What is gastrulation?
Forming of the 3 germ layers
What happens in week 3 gestation? What is the role of gastrulation?
Week of threes
Gastrulation - endo meso ectoderm
Gastrulation ensures precursor cells are in the right place to allow for growth of those tissues
Between which weeks is the period of greatest change? What does this mean for congenital abnormalities?
3-8 organogenesis
Means great risk for teratogenesis
Which germ layer forms the heart?
Mesoderm
Which week does the embryo fold? What does this do for the heart?
4
Puts it in the right place
What is the cardiogenic field and what does it differentiate into?
It is the area of embryo that forms:
Heart
Blood
Vessels
What are three causes of congenital cardiac abnormalities?
- Genetic
- De novo
- Teratogenic agents e.g. alcohol
Why are congenital cardiac conditions so common? (Think about role of heart in utero then after birth)
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
What is the primitive heart tube essentially? What does it not have (2)?
A modified blood vessel
Has no chambers no valves
Why does CVS develop so early in embryogenesis?
Growing embryo needs blood
What is the order of structures from top to bottom in the primitive heart? What do they become?
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
What are neural crest cells and what are they sensitive to?
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.
What happens during cardiac looping and why?
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
What is the LA made from?
The primitive atrium, but mostly the primitive pulm veins (smooth part)
What is the RA made from?
From most of primitive atrium and also part of the sinus venosus
What are the three shunts in foetal life? Why do they need one around the liver?
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
Which vessel has the highest PO2 in foetus?
IVC
How does the foramen ovale shut at birth?
Increased LA pressure
Closes physiologically and then chemically –> fibrotic
How does the ductus arteriosus shut at birth?
Muscular contraction with first breath
What causes ductus venosus to shut?
Placenta removal
How many initial aortic arches are there in primitive vessels?
6
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?
4 - prox part of subclavian and Aorta
6 ‘AKA pulm arch’- R and L pulm arteries and ductus arteriosus
What causes the left recurrent laryngeal nerve to hook round aortic arch?
The heart descends inferiorly during development and this causes it to hook round
What happens if the PDA doesn’t close? When is this more common?
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
What are the roles of the endocardial cushions?
Scaffold to divide heart into L and R and atria and ventricles
What are the 5 stages of foramen ovale formation?
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
What could happen if the osteum primum and secundum do line up at birth?
They could cause communication between RA and LA, shunt from L->R ASD.
What pathology is a risk with ASD?
TIA/Stroke due to emboli from DVT
Where else would you need endocardial cushions?
Truncus arteriosus when forming the PA and Aorta - need to divide the one tube into two.
How do pulm trunk and aorta develop around each other?
Spiral
What are truncal ridges and bulbar ridges?
Endocardial cushions that together make spiral septum
