Embryology Flashcards
What starts the beginning of the heart tube? What does it grow in conjunction with?
Blood islands induced by the underlying endoderm that secretes VEGF; grows in conjunction with the pericardial cavity
How do the heart tubes receive bloodflow?
At each heart tube’s inferior end it connects to a vitelline vein (comes from the yolk sac) and blood exits superiorly through the dorsal aorta
What is the bloodflow to the singular primitive heart tube?
The dorsal aortas fuse into the aortic sac (superiorly) which drains the heart (outflow) and the L and R vitelline vein fuse into the sinus venosus (inferiorly) which supplies the heart (inflow)
How is the singular primitive heart tube formed?
Through lateral folding of the embryo
What are the 2 layers of the heart tube?
- endothelial lining; endocardium
2. cardiac myoblasts; myocardium
List the 4 segments (between the aortic sac and sinus venosus) of the primitive heart tube from cranial –> caudal
- truncus arteriosus
- bulbus cordis
- primitive ventricle
- primitive atrium
After looping, how does the atrium communicate with the ventricle?
The atrioventricular canal, the atrioventricular sulcus can be seen (surface groove encircling the heart separating the primitive atria from the primitive ventricles)
What’s the transverse pericardial sinus?
formed by looping of the primitive heart tube, it’s the space behind the outflow and in front of the inflow (can stick a finger through)
Where does the sinus venosus collect blood from?
The placenta, yolk sac and the body
Explain the transition that the L and R sinus horns undergo
At first, the L and R sinus horns are equal in size
BUT as venous return shifts to the R, the L sinus horn recedes (and forms the coronary sinus) and the enlargening Right atria absorbs the R sinus horn
Where do the right atria develop from? Where does it receive drainage from?
Most of the primitive atrium, (and absorbs the R horn of the sinus venosus) which forms its smooth wall portion. It receives drainage from the vena cava (superior and inferior) and the coronary sinus.
Where does the left atrium develop from?
A small portion of the primitive atrium and absorbs proximal parts of pulmonary veins
Explain why atria have differing textures
Rough: remainder from the primordial atrium
Smooth: where primordial veins have been sucked in
Why is inflow dorsal to outflow? Which ventricle (R or L) is closest to the inflow/outflow tract?
Because during looping the atrium is dorsal to the bulbous cordis.
The primordium of the R ventricle is closest to outflow tract
The primordium of the L ventricle is closest to inflow tract
What is the auricle?
The remainder of the rough portion (primitive part) of the L atrium
What forms the smooth portion of the L atria?
All 4 branches of the pulmonary veins have been sucked into the L atrium
What is the oblique pericardial sinus and when does it form?
As the L atrium expands and absorbs the pulmonary veins the oblique pericardial sinus is formed. It is the “cull-de-sac” formed by the palm of your hand when you hold a heart
How do the aortic arches begin and which number is missing from the arched vessels?
The aortic arches sprout from the aortic sac and form a bilaterally symmetrical system of arched vessels, the aortic arch 5 has no derivatives in humans.
What does the 4th, 6th and 3rd aortic arch form?
4th aortic arch:
R: proximal R subclavian artery
L: aortic arch
6th aortic arch: Recurrent laryngeal nerve
R: R pulmonary artery
L: L pulmonary artery and ductus arteriosus
3rd: internal carotid arteries
What is the ductus arteriosus?
A blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta to bypass the developing lungs
What is the first step in septation between the atria and ventricles?
The endocardial cushions, they grow towards each other (anterior and posterior) to divide the heart into R and L channels (R and L atrioventricular canals)
What does the division of the common atrium form?
2 septa with 3 holes
What is ostium primum and septum primum?
Septum primum: is the first septal structure appearing between the R and L atria, grows from the roof of the common atrium towards the endocardial cushions
Ostium primum: gap underneath the growing septum primum
What is ostium secondum? What closes shortly after this develops?
Hole in the septum primum, the ostium primum closes shortly thereafter