Which vessels form the short common cardinal veins?
The bilateral anterior and posterior cardinal veins unite to form the short common cardinal veins.
When and how is the left brachiocephalic vein formed, and what is the significance of this vessel?
When - during shunting of venous blood toward the right sinus horn
How - formed by an anastomosis between the left and right anterior cardinal veins
Significance - most venous blood from the left side of the head and left upper limb is channeled to the right side.
What forms the Superior vena cava?
The union of the right anterior and common cardinal veins forms the SVC.
What happens to the posterior cardinal veins?
The posterior cardinal veins are obliterated, EXCEPT for the proximal portion of the right posterior cardinal vein which becomes the azygos vein.
Where is the aortic sac located in the heart tube and what does it generate?
The aortic sac (not labeled) is located at the cranial end of the heart tube and it is continuous with the truncus arteriosus (black segment). It generates the left and right dorsal aortae (also not labeled).
What structures arises from the aortic sac and where do they travel?
Pairs of aortic arches arise from the aortic sac, travel through the mesenchyme of paired pharyngeal arches and terminate in the dorsal aortae.
Describe the pairs of aortic arches.
The aortic sac originally generates six pairs of aortic arches numbered I, II, III, IV, and VI, because the 5th pair forms incompletely and regresses.
What does the truncus arteriosus separate into and what is responsible for this separation?
What does the aortic sac form?
The truncus arteriosus is separated by the aorticopulmonary septum into the aorta and pulmonary trunk.
The aortic sac forms the ascending aorta and proximal portion of the arch of the aorta that generates the brachiocephalic artery.
What happens to the aortic arches?
arches I & II vanish
arches III form the right and left common carotid arteries
left arch IV completes the arch of the aorta and forms the left subclavian artery
right arch IV forms the right subclavian artery.
What happens to the right and left dorsal aortas?
The left dorsal aorta forms the descending aorta which continues as the singel midline aorta.
The right dorsal aorta disappears beyond the right subclavian artery.
What result if the right dorsal aorta fails to disappear?
A double arch of the aorta wraps around the trachea and esophagus, sometimes compressing these structures and requiring surgical division of the vascular ring if dyspnea or dyscphagia occur.
What is coarctation of the aorta? Define the types.
Coarctation of the aorta is an abnormal narrowing (stenosis) that reduces the size of the descending aortic lumen thereby obstructing blood flow to the inferior part of the body.
There are two types, pre-ductal and post-ductal (referring to the location of the stenosis before or after the ductus arteriosus respectively).
In the post-ductal coarctation, the ductus arteriosus is obliterated forming the ligamentum arteriosum and good collateral circulation usually develops between the proximal and distal parts of the aorta via the intercostal and internal thoracic arteries, thus survival is feasible.
In the pre-ductal coarctation, the ductus arteriosus remains patent (open).
What is neonatal surgery required to correct pre-ductal coarctation of the aorta, and why can post-ductal coarctation of the aorta be asymptomatic in newborns?
Neonatal surgery is required to correct pre-ductal surgery because if not then the ductus arteriosus will stay open and will allow blood from the right ventricle to bypass the lungs resulting in deoygenated blood entering the systemic circulation.
Post-ductal coarctation can be asymptomatic because first, the ductus arteriosus closes, and second, because collateral circulation provided by the internal thoracic and intercostal arteries allows blood flow to the lower part of the body.
With postductal coarctation, which arteries typically create a compensatory collateral circulation and why can notable pulsations occur in the intercostal spaces?
The intercostal and internal thoracic arteries provide collateral circulation, and these arteries may become so large that they cause notable pulsation in the intercostal spaces.
Which arch forms the right and left pulmonary arteries that extend from the pulmonary trunk?
Which arch forms the ductus arteriosus and what does this structure do?
Aortic arch VI (pulmonary arch) forms the right and left pulmonary arteries and on the left side it forms the ductus arteriosus that joins the left pulmonary artery with the arch of the aorta.
Why can a patent ductus arteriosus in premature infants result in the cascade of pulmonary hypertension, left ventricular hypertrophy, and left atrial distension? Why is the condition fatal?
Why does PDA (patent ductus arteriosus) cause a continuous murmur heard parasternally at the left 2nd ICS?
If the ductus arteriosus is patent, then blood from the aorta is leaking into the pulmonary trunk and mixing with the normal blood flow from the right ventricle into this trunk. This mixing creates turbulence which results in a coninuous murmer heard parasternally at the left 2nd ICS.
Where does most of the blood from the umbilical vein go?
Most of the blood from the umbilical vein is oxygenated from the placenta, enters the ductus venosus in order tobypass the liver, and empties into the IVC.
In the fetus, where does blood from the IVC go?
In the fetus, where does blood from the SVC go?
Blood from the IVC goes through the foraman ovale into the left atrium and passes into the left ventricle for pumping into the aorta.
Blood from the SVC goes through the right atrium into the right ventricle for pumping into the pulmonary trunk.
What is the function of the common iliac arteries?
The common iliac arteries deliver deoxygenated blood from the fetus to the umbilical arteries for return to the placenta.
What happens to the umbilical arteries and veins shortly after birth?
A few minutes after birth, vasoconstriction closes the umbilical arteries then shortly after the arteries close the umbilical veins and the ductus venosus close.
When and how does the foramen ovale close?
Between the 8th and 12th month postnatally, the increased left atrial pressure presses the septum primum-derived valve of the foramen ovale against the septum secundum, which eventually fuses.
Why does left atrial pressure increase and right atrial pressure decrease when a newborn begins to breath?
Because when the baby begins to breath, the lungs inflate and decreases the pressure in the thoracic cavity, allowing blood to flow through the pulmonary circulation.
Why would crying creat cyanotic periods in neonates but not normal 8-12 month old infants?
When the baby cries, it takes deep breaths and the main bronchi, specifically the left main bronchi becomes distended, compressing the pulmonary veins which reduces the amount of oxygenated blood going to the left atrium.