Embryology of the Heart and Great Vessels Flashcards
When does the heart develop?
Starts in the 3rd week
Role of the primary heart field?
Progenitor heart cells migrate from the epiblast, adjacent to the cranial end of the primitive streak, to the splanchnic layer of lateral plate mesoderm where there is a horshou-shaped cluster of cells called the PRIMARY HEART FIELD - myoblast cells form the atria, left ventricle and part of the right ventricle.
How does the heart reach its final position?
Via:
Lateral folding - brings edges of horseshoe into midline so heart tube forms in the midline
Cranio-caudal folding - heart gradually moves down into thoracic regions as embryo grows around it
Regions of the heart tube?
Heart tube develops 5 dilatations, which develop into adult heart structure; from caudal to cranial:
Sinus venosus - in-flow (venous) end with right and left horns; involved with right atrium (smooth part) and coronary sinus formation
Atrium - involved with formation of trabeculated (muscular) parts of both atria
Ventricle - involved with formation of trabeculated part of left ventricle
Bulbus cordis - outflow part of both ventricles; involved with formation of trabeculated part of right ventricle
Truncis arteriosus - forms the aorta and pulmonary trunk
When does the heart begin to loop and fold?
Day 23
Events in looping and folding?
In-flow and out-flow ends must move dorsally and cranially
Ventricle (future left ventricle) is displaced left until it lies to the left of the inter-ventricular groove
Bulbus cordis (right ventricle) moves inferiorly and ventrally to the right - communicates with the truncus arteriosus
Extensive saculations projecting laterally will ultimately become the right and left
How does the heart divide into chambers?
A four chambered heart is formed from looped and folded heart tube by development of 3 septa:
Partition atria, ventricles and the truncus arteriosus
Describe partitioning of atria and ventricles
Atrio-ventricular groove appears as deep invaginations:
Canal becomes divided by two partitions growing from walls of two chambers towards the junction
Endocardial cushion extend from opposite sides of the junction and fuse to divide the atrium and ventricle
From interventricular ridge, a muscular septum extends towards base of heart; inter-atrial septum rapidly grows towards the endocardial cushions, shrinking the foramen (primum) between the atria
Before the primum disappears, a new opening (foramen secundum) appears, high on inter-atrial septum - shunts blood from right to left atrium
Another inter-atrial septum (secundum) extends over foramen secundum to form the foramen ovale, with the septum primum acting as a membranous valve (only allowing blood from right to left atrium)
Partitioning of truncus arteriosus?
Splits right and left ventricle completely
Bifurcation of the truncus arteriosus:
4th aortic arch forms aorta
6th forms PT
A pair of ridges SPIRAL down truncus arteriosus to produce a single spiral septum
Blood flow is new 4 chambered heart?
Right ventricle to pulmonary artery :
Major part goes through truncus arteriosus, from pulmonary artery, into descending aorta
Due to collapsed lungs, there is resistance to blood flow through pulmonary arteries so only small blood flow there and back to left atrium
Oxygenated blood from placenta enters IVC but tends to stream across right atrium into left atrium (via foramen ovale)
Mixture of venous and oxygenated blood is pumped into aorta
How does blood flow through heart change after birth?
Within a few seconds, supply from placenta is gone and lungs become inflated (so resistance to pulmonary blood flow is gone and blood can flow through pulmonary arteries)
When the pressure in left atrium exceeds that in right atrium, the valvula is pressed over foramen ovale and partitioning of heart is complete
Blood flow to sinus venosus?
Vitelline vein
Umbilical vein
Common cardinal vein
Development of the sinus venosus?
As development continues, systemic venous return is diverted to the right horn (which becomes bigger) and the left horn becomes smaller, as it loses its venous return
All that remains of the left atrium are the oblique vein of left atrium and the coronary sinus (communicates into RA and loses its connection to the systemic circulation)
Remodelling the atria?
Uniting the SVC and IVC is smooth wall (arose from sinus venosus); muscular part came from the primitive atrium
From the left atrium, pulmonary veins sprout
Development of aortic arches?
6 pairs, associated with the pharyngeal arches:
1 and 2 are mostly obliterated
5 disappears very quickly, if it was ever there at all
3 - gives rise to the common carotid arteries and the 1st part of the internal carotid artery
4 - gives rise to the right subclavian vein and part of the aortic arch
6 - sprouts branches that form the pulmonary arteries and the ductus arteriosus on th left
