Session 3 Embryology Flashcards
What develops from the cardiogenic field?
In what process is the field created?
Initially, where is it in the embryo?
The heart, blood vessels and blood cells
gastrulation
Cranial end (before folding)
When forms in the cardiogenic field in the 3rd week of development?
two endocardial tubes
Describe the folding in the embryo
lateral folding- fuses the two endocardial tubes into the primitive heart tube
cephalocaudal folding- moves the tube into the thoracic region
What does looping achieve?
What prompts it to occur?
Which sinus does looping create?
Looping of the heart tube places both the inflow and outflow at the cranial end of the heart as seen in the adult heart
(inflow is behind (dorsal) to outflow)
The tube is getting bigger and must rearrange to fit the pericardial sac
the transverse sinus
By what day in development is the primitive heart tube beating?
Day 22
Which primitive structure drains blood returning from the embryo into the primitive atrium?
sinus venosus
What does the right atrium form from?
How does it form?
- primitive atrium (heart tube) MAJOR
- sinus venosus
(R atrium enlarges to include the R sinus horn)
How does the sinus venosus develop?
Initially two inflow horns
Venous return shifts to the right horn and left recedes
(R horn included in R atrium)
How does the L atrium develop?
What is it formed from?
Which sinus does it create?
Pulmonary veins begin to develop and the enlarging left ventricle absorbs them
- pulmonary veins MAJOR
- small part of the primitive atrium
oblique sinus
Why are the R and L atrium structurally different?
R - trabecular appearance bc it derives from neural tube
L- smooth walls due to development from the pulmonary veins
Where is the oblique sinus?
Posterior of the heart between the pulmonary veins
Name the three shunts in foetal circulation
Explain what they do
- Formaen ovale
shunts blood from right atrium to L - Ductus arteriosus
shunts blood from pulmonary trunk to aorta - Ductus venosus
shunts a portion of blood from the umbilical vein to the IVC
How do the foetal shunts close?
Foramen ovale closes when respiration begins and a huge venous return causes R atrium pressures to rise
Ductus arteriosus wall muscle is very sensitive to changes in pO2; it contracts and closes
Ductus venosus becomes flaccid and closed as there’s no blood entering from the umbilical vein anymore
Describe the primitive arterial system which the great vessels develop from?
The aortic arches
- symmetrical bilateral system of arched vessels
Which arches of the primitive structure are important?
4th branch
6th branch
What does the 4th branch of the aortic arches develop into?
L side- aorta
R side- subclavian vein
What does the 6th branch of the aortic arches develop into?
Hint; what is the 6th arch known as?
Pulmonary arch
L- L pulmonary artery and ductus arteriosus
R- R pulmonary artery
Which nerve descends with the 6th aortic arch? (Left branch)
What is it hooked around?
the left recurrent laryngeal nerve
the ductus arteriosus
What happens in septation?
The heart tube is divided into 4 chambers and the outflow tract divided into the aorta and pulmonary trunk
Septi grow towards the endocardial cushions in the heart tube. Where are they located?
Where does the cushion tissue come from?
At the junction between atrium and ventricles
Endocardial cushion tissue migrates in (not from primitive heart) thus this process can go wrong
Which septum forms the foramen ovale in the atria?
What feature of the septum allows this?
Which atrium is it closest to?
septum secundum
crescent shaped
right atrium
How does atrial septation occur?
- Septum primum grows downwards towards the endocardial cushions
- Ostium secundum appears in the septum before ostium primum disappears to allow continuous blood flow
- Septum secundum forms the foramen ovale due to crescent shape
The foramen ovale becomes the ____ ____ after birth?
How does the shunt close?
Fossa ovalis
After birth, pressure in the left atrium exceeds that of the right atrium. The septum primum is pushed against secundum, stopping blood flow between. They eventually become fused by fibrous tissue
Describe the ostium secundum in hypoplastic left heart syndrome
What does this syndrome mean?
It’s too small
The left side of the heart doesn’t develop properly
