Embryology of the heart and great vessels Flashcards
From which germ layer does the heart develop?
The visceral mesoderm
Where does the heart begin its initial development?
- quite cranially
- forms from a region of myoblasts and blood islands in the visceral mesoderm
How does the heart reach its final position?
Lateral and craniocaudal folding
Lateral folding:
- like a horse shoe closing
- creates a central vessel
Craniocaudal folding:
- Moves heart caudally
List the dilatations (regions) of the heart tube (Caudal –> cranial)
Sinus venosus (right and left horns) --> Atrium --> Ventricle --> Bulbus cordis --> Truncus arteriosus
Describe the direction of blood flow in the primitive heart
Blood enters at the sinus venosus
Blood leaves via the truncus arteriosus
What region of the adult heart do the sinus venosus develop into?
- Smooth part of the right atrium
- Coronary sinuses
What region of the adult heart does the atrium develop into?
- Trabeculated part of both atria
What region of the adult heart does the ventricle develop into?
- Trabeculated part of Left ventricle
What region of the adult heart does the bulbus cordis develop into?
- Trabeculated part of right ventricle
- Outflow part of both ventricles
What region of the adult heart does the truncus arteriosus develop into?
- Aorta
- Pulmonary Trunk
By what day does the heart begin to loop and fold?
Day 23
Describe the movements of the artium, ventricle, and bulbus cordis during looping and folding
Atrium –> dorsal and cranial
Ventricle –> displaced left
Bulbus cordis –> inferiorly, ventrally to the right
Describe the relative timing of heart septa development
All 3 heart septa develop simultaneously
Describe the formation of the atrioventricular septum
Atrioventricular groove already constricts the gap
–>
Endocardial cushions extend from both side of the groove to close the gap
Describe the formation of the interatrial septum
Interatrial septum (septum primum) grows towards the endocardial cushions
–>
foramen primum forms (last gap in septum)
–>
foramen secundum opens
–>
foramen primum closes
–>
septum secundum develops partially covering the foramen secundum
–>
Gap left is the foramen ovale
Describe the formation of the interventricular septum
Muscular septum begins to separate the 2 ventricles
–>
leaves interventricular foramen
–>
ridges from the truncus arteriosus’ bifurcation spiral down, fusing as they go
–>
fills in interventricular foramen
What does the foramen secundum allow?
Shunting of blood from the right to left atria
Describe the foramen ovales
As the septum secundum develops partially covering the foramen secundum the gap left is the foramen ovale
- Acts as a valve only allowing blood to go right atrium –> left
Describe the spiral septum down the truncus arteriosus
Ridges from the truncus arteriosus’ bifurcation spiral down, fusing as they go
Makes a 180 degree spiral
This is why the pulmonary artery and aorta and intertwined in the adult heart
What are the aortic arches associated with?
pharyngeal arches
List the 5 aortic arches and what they develop into
1 –> disappear
2 –> disappear
5 –> rudimentary/absent
3 –> common carotid arteries, internal carotid artery
4 –> right subclavian artery, part or aortic arch
6 –> pulmonary arteries, ductus arteriosus
Describe the ductus arteriosus and its function
- Connects the pulmonary trunk to the proximal descending aorta
- It allows most of the blood from the right ventricle to bypass the fetus’s fluid-filled non-functioning lungs
Describe the development of the 4th aortic arches
The right arch
–>
right subclavian artery
The left arch
–>
part or aortic arch
Describe the development of the sinus venosus
The right and left sinus horns merge with the RIGHT atrium
Right sinus horn
–>
Inferior and Superior vena cava
Left sinus horn
–>
Coronary sinus
(From the left sinus horn the right umbilical, left vitelline and left common cardinal veins are obliterated)
Describe the remodelling of the atria
Right atrium:
- The sinus venosus merges with the right atrium
- forming the smooth part of the artium
Left atrium:
- The proximal part of the pulmonary veins merge with the walls of the left atrium
- forming the smooth part of the artium, with 4 openings in it
Name and give the functions of the 3 venous systems in an embryo
Vitelline veins:
- drain yolk sac
Umbilical veins:
- carry oxygenated blood from the placenta
Cardinal veins:
- systemic venous system
What do the vitelline veins develop into?
- Portal venous system draining gut
- Hepatic sinusoids and veins
- Hepatic portion of IVC
What do the umbilical veins develop into?
- Right degenerates
- Left remains as the definitive umbilical vein
Describe the ductus venosus
What happens to it after birth?
A vein that goes directly through the developing liver
It closes up
Give the 2 types of systemic veins
What do they drain?
Anterior cardinal veins:
- head and neck
Posterior cardinal veins:
- drain trunk
List veins that join with the anterior and posterior cardinal veins:
Anterior cardinal veins:
- jugular system
- left brachiocephalic vein
- superior vena cana
Posterior cardinal veins:
- inferior vena cava
- azygos and hemiazygos systems
- gonadal
- renal veins
- iliac veins
Compare foetal and neonatal circulation
- No ductus arteriosus
- Oxygenated blood on the left, deoxygenated blood on the right
- Ductus venosus closes up
- Umbilical vein closes up
- Foramen ovale closes up
