B4.046 Prework 2: Chamber Partitioning and Blood Vessel Formation Flashcards
weeks 4-7
atrial and ventricular septation occurs
how is early septation initiated
endocardial cushion formation myocardium deposits a unique ECM between the endocardium and itself endocardial cells in certain regions undergo an epithelial to mesenchymal transformation mesenchymal cells (migrating endocardial cushion cells) aid in formation of the AV canal
when does partitioning of the AV canal occur?
day 23-35; weeks 4-5
in what 2 regions do endocardium derived cushion tissue form?
AV region and outflow tract region
outflow tract region also populated by neural crest cells
what forms from the fusion of opposing cushion tissues?
2 AV canals
outlets of both ventricles (aorta and pulmonary trunk)
membranous portion of IV septum
what happens in the first phase of atrial septation at day 28?
septum primum grows down from common atrium roof towards the endocardial cushions in the AV canal
foramen primum is the hole between the R and L atrium at this point
what happens in the second phase of atrial septation in the 5th week?
programmed cell death creates new openings in the septum primum near the superior edge
this new hole is the foramen secundum
endocardial cushions grow along septum primum and close foramen primum
what happens in the third phase of atrial septation, also in the 5th week?
septum secundum forms to the right of the septum primum
septum secundum grows down and fuses with an intermediate septum by the end of the 6th week, but a foramen ovale persists throughout embryonic development
what is the function of the foramen ovale in the septum secundum and the foramen secundum in the septum primum?
allows blood to flow from RA to LA, but not L to R
acts as a one way inter-atrial valve, allowing oxygenated venous blood from placenta to bypass the fetal lungs and be pumped to rest of the embryo
what happens in the final stage of atrial septation by the 6th week?
septum primum meets and fuses with septum intermedium
foramen secundum is obliterated and R and L atria are now separated
blood flows through foramen ovale when its valve is open, but not when it is closed
when does the muscular IV septum form?
during the 5th week
medial walls of the expanding ventricles becomes apposed
describe the formation of the membranous portion of the IV septum on day 37
outgrowth of endocardial cushions toward muscular IV septum closes IV foramen
neural crest cell derivatives contribute to membranous part of IV septum
outflow tract septation also contributes to membranous IV septum
when do the AV valves form?
5th to 8th weeks
how do the AV valves form
dependent on AV cushions and ventricular myocardium
valves are connective tissue covered by endocardium
valves connected to thick trabeculae in the ventricle wall via chordae tendinae; start to function
describe the septation of the outflow tract during the 5th week
opposing ridges form from the walls of the truncus arteriosus and bulbus cordis
ridges form a spiral within the outflow while growing towards aortic sac
ridges (conotruncal swellings) form aorticopulmonary septum in week 8
neural crest cells contribute to ridges
defects due to abnormal partitioning of the outflow tract
transposition of great arteries
persistent truncus arteriosus (single outflow)
pulmonary stenosis
what forms the aortic and pulm valves?
outflow cushion and neural crest cells
where do SA pacemaker cells reside initially/ where do they end up?
initially at caudal end of left heart tube
as sinus venosus becomes incorporated into RA, pacemaker cells come to reside near the junction of the superior vena cava and RA forming the SA node
where are the AV node and bundle of His cells derived from?
- cells in the left wall of the sinus venosus
2. cells from the AV canal
where does the AV node end up?
base of interatrial septum in the right atrium, near the opening of the coronary sinus
first major blood vessels
dorsal aortae
cardinal veins
coronary artery formation
arise from epicardium following epithelial to mesenchymal transformation
neural crest cells contribute to smooth muscle cells along proximal segments of coronary arteries
coronary arteries grow to invade the aorta to establish blood flow to the heart muscle
vitelline veins
drain blood from yolk sac
functional in early development
become portal venous system
umbilical vein
carries blood from placenta to embryo
cardinal veins
drain the body of the embryo
form superior vena cava
vitelline arteries
supply yolk sac
eventually fuse and form vessels to gut
umbilical arteries
course to placenta
right horn of the sinus venosus
becomes incorporated into the right atrium
left horn of the sinus venosus
becomes the coronary sinus
major venous drainage for blood that has perfused the myocardium
