Flashcards in Cardiovascular Development Deck (69)
How are the endocardial tubes formed and what are their splits?
In the splanchnic mesoderm in the cardiogenic plate, two longitudinal angioblastic cell clusters form ventrolateral to the neural plate. They will canalize to become the two endocardial tubes
1. Lateral endocardial tube
2. Dorsal aorta
How is the dorsal aorta made? (outflow tract)
This outflow tract is connected to the dorsal aorta endocardial tube before folding begins
What do the endocardial tubes become as a result of folding?
Lateral: two tubes fuse ventrally (lateral folding) to form primitive heart tube in thoracic region (cephalic folding)
Dorsal aorta: Head folding forms the first aortic arch
How is the inflow tract of the heart made? What vessels contribute?
Sinus venosus - receives blood from three pairs of vessels:
1. Common cardinal
What is the precursor to the pulmonary artery / aorta?
What is the precursor to the right ventricle?
What is the precursor to the left ventricle?
What two layers does the splanchnic mesoderm differentiate into after the heart tubes are formed?
1. Myoepicardial mantle -> becomes myocardium
2. Cardiac jelly
What is cardiac jelly?
An acellular matrix composed of GAGs and matrix proteins, separates myocardium from heart tube
What are the functions of the cardiac jelly?
1. Serves as a substrate for cell migration in cardiac septation and valve formation
2. Accumulates to form endocardial cushions at AV junction and in outflow tract
3. Stimulates endothelial cells to come to this cushion matrix, and become mesenchyme which will form fibrous mitral and tricuspid valves.
What forms the endocardium and the serous epicardium?
Endocardium - endothelial heart tube
Epicardium - dorsal mesocardium which surrounds the heart tube as it bulges into the pericardial cavity
How does the heart tube become suspended in the pericardial cavity?
It is pinched off from dorsal mesocardium, a derivative of foregut splanchnic mesoderm. The heart tube will be left hanging cranially be the dorsal aorta and caudally by the vitelloumbilical veins when the dorsal mesocardium ruptures
What forms the transverse pericardial sinus?
It's formed by the space behind the heart tube and the wall of the visceral pericardium, as the dorsal mesocardium ruptures and leaves room.
What happens during cardiac looping of the heart tube? What is this the first of?
Future right ventricle, bulbus cordis, pushes out to the right, forming the bulboventricular loop. Primitive atrium moves cranially to become cranial and dorsal to both ventricles. Both ventricles will move caudally.
This is the first asymmetrical structure to appear in the body, probably due to asymmetrical distribution of actin bundles + cardiac jelly
What constrains the cardiac tube at the sinus venosus?
The septum transversum
Where does nodal tissue for the conduction system develop? Where are its two spots?
Develops in sinus venosus
SA node - entry of SVC
AV node - right A-V orifice
The bundle of His appears in the ventricular septae at this point
What are the paired dorsal aorta and where do they unite?
The truncus arteriosis opens into the aortic sac, from which the aortic arches give rise to paired dorsal aorta. They will be formed in paraxial mesoderm, but ultimately unite behind the heart to the level of LV4 (where the common iliac is)
What does vitelline circulation do and what does it correspond to in the adult?
Arteries arise from dorsal aorta and bring blood to yolk sac and future gut (in the midgut).
Correspond to celiac, superior, and inferior mesenteric arteries.
Blood returns to the heart via the vitelline veins, which will form the portal and hepatic veins of the portal system!
What does umbilical circulation correspond to?
Arteries arise from dorsal aorta and conduct 50% of cardiac output to the placenta. Oxygenated blood returns to heart via the umbilical vein
What is the general circulation of the embryo?
Blood distributed by dorsal intersegmental branches of dorsal aorta to neural tube + somites. Lateral segmental arteries to developing kidneys + gonads.
Blood returns to heart via anterior + posterior cardinal veins, which becomes the common cardinal vein to empty into the sinus venosus
How does the sinus venosus shift?
Overtime, it moves to the right more and is called the sinoatrial orifice (SA), until it communicates only with the right atrium.
What happens to the left horn of the sinus venosus?
It gets smaller, while the right one enlarges. In time, the left horn (receiving blood from common cardinal, vitelline, and umbilical veins) will become the coronary sinus, and they will all dump into the right atrium.
What is the sinus venarum?
The smooth-walled portion of the right atrium to the left of crista terminalis, which is formed by the incorporated sinus venosus
What does the right venous valve of the SA orifice make?
The crista terminalis (division between smooth and muscular), valve of IVC, and valve of coronary sinus
What does the original embryonic right atrium become?
The pectinate auricular appendage, to the right of crista terminalis. Contains the pectinate muscles
What does the primitive pulmonary vein become? What does the embryonic left atrium become?
Pulmonary vein - becomes smooth-walled part of definitive atrium
Embryonic left atrium - auricular appendage which is rough
What happens to the single A-V canal?
The endocardial cushions made form cardiac jelly form on the dorsal and ventral walls, approaching one another, and fuse to make the single canal into a left and right A-V canal
What is the function of adherons produced by myocardial cells? Where does this happen?
They accumulate in endocardial cushion tissue and induce the overlying endothelium to become mesenchymal cells which will form the mitral and tricuspid valves
This EMT occurs in bulbus cordis (primitive right ventricle), but not primitive atrium / ventricle
What originally divides the primitive atrium in two?
The formation of the interatrial septum, which is forming due to the endocardial cushions which are moving dorsally towards the atrium (behind the ventricles)