Lecture 6- Embryology Flashcards
What is aetiology?
The cause of a disease or condition
Main event in third week of development?
Gastrulation
Main event in fourth week of development?
Folding
What i the cardiogenic field?
Group of cells that will develop into whole cardiovascular system
What is the effect of lateral and cephalocaudal folding?
Lateral creates the heart tube
Cephalocaudal brings the tube into the thoracic region
When does heart begin to beat?
Day 25 of gestation
What is the problem with vital organs eg the heart developing early?
Woman may not be aware that she is pregnant
What must happen to the primitive heart tube?
It must be remodelled in order to supply both the pulmonary and systemic circulations
Primitive heart tube structures?
Sinus venosus- atrium- ventricle- bulbous cordis- truancy’s arteriosus- aortic roots
What drives looping of the primitive heart tube?
Constraints on size caused by the pericardial sac
How does looping result in the formation of the transverse pericardial sinus?
Looping causes atria to be pushed up above and behind the ventricles. The gap between the aorta and superior vena cava forms the transverse pericardial sinus
How does the sinus venosus develop?
Initially left and right sinus horns equal in size. Venous return shifts to the right and so the left sinus horn recedes. Right atrium enlarges and absorbed right sinus horn which becomes part of right atrial wall
How does right atrium develop?
Develops from primitive atrium and uses sinus venosus to make part of its wall. Receives systemic venous drainage and venous drainage from heart through coronary sinus.
How does left atrium develop?
Primitive atrium contributes a small amount. A pulmonary vein is sprouted and is absorbed to help form left atrial wall. Eventually end up with entrances for four pulmonary veins.
What is the oblique sinus and its relevance to development?
The cul de sac of the pericardial sac found at the cranial end of the heart. The cul de sac is created through the left atrium absorbing the pulmonary veins which creates the “dead end” at the top of the pericardial sac and this can be felt by putting your hand underneath the heart
Why re shunts required in the foetus?
Lungs aren’t used so blood needs to be moved directly from right atrium to left atrium.
Shunts also need to be reversible at birth
What are the three foetal shunts?
Ductus venosus
Ductus arteriosus
Fossa ovale
What happens with the circulatory shunts?
Ductus venosus brings blood from placenta to inferior vena cava.
Blood enters right atrium.
Some blood goes from right atrium to right ventricle and from there to the pulmonary trunk and to the aorta through the ductus arteriosus bypassing the lungs. This happens as its important that the right ventricle is used to prevent it from wasting.
Most of blood goes straight from right atrium to the left atrium through the fossa ovale.
What does the fossa ovale become?
Fossa ovalis
What causes the shunts to close?
Fossa ovale- on breathing pressure is increased in left atrium which closes the shunt.
Ductus arteriosus- increase in oxygen is sensed and DA contracts and regents blood going through it
Ductus venosus- placental support is removed so ductus venosus closes as no more blood is passing through it
What is patent ductus arteriosus?
Congenital heart defect where ductus arteriosus doesnt close properly. This means that the aorta and pulmonary artery remain connected and blood will shunt from the left to the right side of the heart.
This is most commonly seen in prematurity
Which aortic arch derivatives are particularly important?
4th arch
RHS- proximal part of R subclavian A
LHS- arch of aorta
6th arch “pulmonary arch”
RHS- R pulmonary artery
LHS- left pulmonary artery and ductus arteriosus
