Quiz 3 - Cardiac Embryology (ONLY TESTED SECTIONS) Flashcards
where does the heart form?
-visceral layer of the lateral plate mesoderm at the cranial end of the embryo (the “cardiogenic region”)
angiogenic cell clusters
- coalesce to form two tubes
1. endocardial tubes (lateral)
2. dorsal aortae (medial)
*the endocranial tubes and dorsal aortae maintain a connection cranially
during folding, what happens in regard to the endocardial tubes?
- yolk sac is incorporated into the embryo, allowing the endocardial tubes to come together in the ventral midline of the embryo, where they fuse into a single primary heart tube, except at their caudal end.
- meanwhile, dorsal aortae have remained in their original position (dorsal and towards the medial aspect of the embryo)
the developing heart is initially ____ to the septum transversum (diaphragm)
caudal
longitudinal folding of the embryo does what in regard to the endocardial tubes?
- forces them into the thoracic region of the embryo
- also causes the developing heart to come to lie cranial to the septum transversum
after longitudinal folding, the heart is initially located ____ to the pericardial cavity
-dorsal
series of constrictions and expansions in the heart tube (21 days)
- starting at the caudal (venous/inflow) end these are the:
- sinus venosus
- primitive atrium
- atrioventricular sulcus
- primitive ventricle
- interventricular sulcus
- bulbus cordis
why is the heart tube forced to bend and twist on itself as it grows?
-because the cranial and caudal ends of the heart tube are anchored in the pericardial cavity
what does the forced patterned folding of the heart form?
-the cardiac loop, which in normal folding of the heart tube results in the ventricles coming to lie inferior and anterior to the atria
transverse cardiac sinus
- formed during cardiac looping
- represents the space between the inflow and outflow tracts of the primitive heart tube
- in an adult, there remains a passage between the venous (inflow) and arterial (outflow) tracts of the heart (e.g. between the aorta & pulmonary trunk [anterior] and the SVC [posterior]) called the TRANSVERSE PERICARDIAL SINUS.
**if you clamp this during cardiac surgery it will clamp off all arterial flow out of the heart
primary heart tube after looping
-after cardiac looping, there is still a single primitive atrium and a single primitive ventricle connected by a narrow AV canal.
separation of the heart into left and right circulations
4 stages which occur nearly simultaneously
- division and shifting of AV canal
- partitioning of the primitive atrium
- partitioning of the primitive ventricle
- division of the outflow tract (conus cordis and truncus arteriosus)
separation of the heart into left and right circulations
1. shifting of AV canal
- neural crest cells migrate into the developing heart and cause swelling of the endocardial mesenchyme (swollen areas = endocardial cushions)
- superior and inferior endocardial cushions eventually fuse and separate the AV canal into L and R canals
- abnormalities of endocardial cushions contribute to many cardiac malformations
separation of the heart into left and right circulations
2. partitioning of the primitive atrium
- first, a C-shaped piece of tissue called the septum primum grows from the dorsal wall of the primitive atrium towards the endocardial cushions. the opening formed by the free edge of the septum primum is the ostium primum.
- as the septum primum is fusing with the endocardial cushions (and closing the ostium primum), cell death occurs in the superior part of the septum producing an opening called the ostium secundum
- thus, even tho a septum forms, blood can still pass b/w the two atria
- meanwhile, another septum begins to form immediately to the right of the septum primum, the septum secundum
unlike the septum primum, the septum secundum…
- never forms a complete partition in the atrial cavity
- the opening that remains is called the foramen ovale
- blood flows b/w atria via foramen ovale and ostium secundum
separation of the heart into left and right circulations
3. partitioning of ventricles
- the interventricular septum has both a muscular and a membranous portion
- muscular component: made up of muscular tissue that grows from the floor of the ventricles towards the endocardial cushions
- membranous component: formed by further growth of the endocardial cushions and downgrowth from the aorticopulmonary septum.
separation of the heart into left and right circulations
4. division of the outflow tract
- major outflow tracts of the ventricles are divided by R and L truncoconal ridges that grow from the walls of the conus cordis and truncus arteriosus. They meet in the midline and fuse with endocardial cushions and muscular interventricular septum, forming the aorticopulmonary (spiral) septum
- the septum develops as a spiral, so this is why the pulmonary trunk and aorta twist around each other in the adult heart
fetal lungs are ____ until birth
- fluid-filled (non-functional)
- no reason to circulate blood thru them, so R-L shunts reroute fetal blood from pulmonary to systemic circulations
- fetal pulmonary circulation pressure = systemic circulation pressure
fetal pulmonary and systemic circulations linked by 3 shunts
- foramen ovale: shunts blood from R to L atrium
- ductus arteriosus: shunts blood from pulmonary artery to descending aorta
- ductus venosus: shunts oxygenated blood from umbilical vein directly to the IVC, bypassing the liver
which shunt helps blood flow bypass liver in fetus?
ductus venosus
arterial and venous blood are ______ in fetal circulation
mixed
adult circulation
- lo pressure pulmonary
- hi pressure systemic
**no mixing of blood
what happens when the infant takes its first breath?
-the lungs expand, the pulmonary vessels open, and the resistance of pulmonary vasculature drops (increasing pulmonary blood flow)
opening of pulmonary circulation causes what changes to the septum primum?
- increased intra-atrial pressure forces the septum primum against the septum secundum, functionally closing the foramen ovale
- fusion of the septum primum and secundum (formation of fossa ovalis) occurs later
