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
What is the septum secondum? What forms as soon as it is complete, and what is this new structure’s purpose?
Septum secondum is the second septal structure that forms adjacently and to the R of the septum primum
The septum secondum does not fuse with the endocardial cushions like the septum primum does, and the gap it leaves is called the foramen ovale. The channel between the foramen ovale and ostium secondum creates the R-L shunt.
What is the fossa ovalis?
It is the adult remnant of a thin fibrous sheath that covered the foramen ovale
What are the 2 portions of the ventricular septum?
- The muscular component: grows upwards from the apex and forms most of the septum. It leaves a hole known as the primary interventricular foramen
- The membranous component is growing downwards from the fused endocardial cushions and ‘fills the gap’ by closing the primary interventricular foramen
What is the membranous portion of the ventricular septum derived from and what does that structure do?
Derived from the spiral septum: this grows to separate the truncus arteriosus into the outflow vessels: aorta and pulmonary trunk (semilunar valves develop shortly after)
What is especially important in the development of fetal lungs?
Important they do not receive a lot of blood so they’re not damaged
Explain the fetal circulation
The fetus receives oxygenated blood from the placenta through the ductus venosus (bypasses the liver) into the inferior vena cava via the umbilical vein.
Blood reaches the R atria where it is shunted into the L atria via the foramen ovale.
The blood is then pumped around the body via the aorta. The ductus arteriosus allows the blood to pass from the pulmonary trunk to the aorta and bypass the baby’s fluid-filled non-functional lungs
How does circulation change (and the function of the 3 shunts) as soon as the fetus is born?
When the fetus takes its first breath, this massively decreases pressure in the lungs - resulting in more blood entering the lungs and more blood returning to the L atrium. Once the L atrial pressure > R atrial pressure the foramen ovale is closed and the ductus arteriosus contracts. Once placental support has been removed the ductus venous also closes.
What is the adult fate of the following…
a) foramen ovale
b) ductus arteriosus
c) ductus venosus
d) umbilical vein
a) fossa ovalis
b) ligamentum arteriosum
c) ligamentum venosum
d) ligamentum teres (hepatitis)
What separates the primitive ventricle from the bulbus cordis?
The bulbloventricular sulcus
What does the bulbus cordis form?
The R ventricle and aids the formation of the outflow tracts for both ventricles (connected to the truncus arteriosus)
When is the epicardium formed?
Week 4, formed by the visceral pericardium
What forms the SA and AV node?
In the wall of the sinus venosus (R atria) a group of myocardial cells organize and synchronize their electrical discharge
AV node: myocardial cells specialize in the atrioventricular septum
Where and when does the development of the heart start?
In the ‘heart field’ areas of the mesoderm during week 3 (horseshoe-shaped)
