Card Embryo Flashcards
When does the heart begin to develop?
18-19 days after conception
What does the heart develop from?
The embryologic mesoderm
What is the Carnegie Stage System?
Carnegie stages are a system used by embryologists to describe the maturity of an embryo across species
What Carnegie Stage does cardiac development occur?
Between Carnegie Stage 8 and 23 (human days post-conception 17-19 and 56-60)
What is the cardiogenic plate?
Develops from the mesodermal germ layer at the cranial pole of the embryo and develops into the myocardium and endocardium
What is the cardiogenic cord?
Develops from the cardiogenic plate; the 2 cardiogenic cords develop into an internal lumen (endocardial tube)
What is the endocardial tube?
Forms from the cardiogenic cords; they fuse to form the primitive heart tube
When does the primitive heart tube demonstrate regionalization?
DPC 22-23 (dates post conception)
Describe the primitive heart tube from venous to arterial pole
Sinus venosus (posterior RA, sinus node, coronary sinus) –> Primitive atrium (anterior RA and LA and auricles) –> Primitive ventricle (LV) –> Bulbus Cordis (RV) –> Truncus Arteriosus (ascending aorta and pulmonary trunk)
What is heart folding?
Morphogenesis of the primitive heart tube on DPC 23-28 resulting in the S-shaped, asymmetric heart
What happens if heart folding is disrupted?
May lead to abnormal atrial situs, dextrocardia, and ventricular inversion
Where does the primitive sinus venosus develop during heart folding?
Develops cranially and posteriorly/superiorly
Where does the primitive atria develop during heart folding?
Develops dorsally and caudally
Where does the primitive ventricle develop during heart folding?
Develops ventrally and cranially
What does the intervening transitional zones between the primitive atria and ventricle become during heart folding?
Cardiac septa, valves, conduction system, and fibrinous skeleton of the heart
What do the endocardial cushions become?
The AV valves, septation of the heart chambers, and outflow tracts
What does the ventricular inflow septum arise from?
The primary ring
What does the ventricular inflow septum develop into?
Superior and inferior atrioventricular cushions
What happens if there is disruption of the ventricular inflow septum formation?
Tricuspid valve abnormalities or atresia
What does the ventricular outflow septum arise from?
The transitional zone on the arterial pole of the folded heart
What happens if there is disruption of the ventricular outflow septum formation?
A spectrum of outflow tract malformations and subaortic VSDs
What makes up the interatrial septum?
Septum primum, septum secundum, and AV canal septum
Describe the formation of the interatrial septum
At ~ DPC 28, the septum primum grows from the atrial roof down towards the AV endocardial cushions (does not touch so you get an ostium primum/foramen primum) –> The septum secundum then forms as an infolding of the atrial roof on the RA border of the septum primum –> as it grows, it closes the ostium primum and fuses with the septum primum by second month of gestation except for at the ostium secundum (anterior and superior border)
What is the fossa ovalis?
Closure of the foramen ovale (fusion of the septum primum and secundum); remnant of the foramen ovale
What does the leading edge of the septum secundum become?
The superior limbic band (seen in the RA)
What does the atrioventricular endocardial cushion develop into?
The AV valves, interatrial septum and interventricular septum
What is an ostium primum ASD?
Failure of the septum secundum to fuse with the endocardial cushion
What is a partial versus transitional vs complete AV canal defects?
Partial = isolated primum defect; Transitional = concurrent inlet VSD below the AV plane with a primum defect that is restrictive; Complete = transitional AV canal defect that is non-restrictive
What is commonly seen with transitional and complete AV canal defects?
They present with abnormalities of both AV valves + a common annulus, bridging leaflets, and a “cleft” left AV valve
What determines cardiac situs?
The position of the morphologic RA, NOT where the heart sits in the chest or where the apex is located
What are morphologic features of the RA?
Pectinate muscles outside of the appendage + larger, broader atrial appendage + eustachian valve + limbus of the fossa ovalis + IVC and coronary sinus drainage (except in certain heterotaxy syndromes)
Levocardia vs Dextrocardia vs Mesocardia
Based on where the apex is directed (levo = apex directed to the left, dextro = apex to the right, meso = midline)
Levoposition vs Dextroposition vs Mesoposition
Based on the heart’s position within the chest (levo = normal anatomy, dextro = heart in the right chest, meso = heart in the middle of the chest)
