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Flashcards in CV development Deck (11):

Early circulation

-Inflow of the heart is the sinus venosus, which becomes the sinus venarum (on the right side) in the adult heart
-3 inflow sources: embryo, yolk sac, and placenta
-Placenta is only source of oxygenated blood, which is brought to fetus by umbilical vein



-3rd week-6th week: converts early linear heart tube into a structure similar to mature heart
-The atrial chamber is brought superior and posterior to the ventricular chamber


Atrial maturation

-The single atrial chamber is connected to the ventricular chamber thru the AV canal
-Endocardial cushions grow within the AV canal and will become the tricuspid and mitral valves (canal is divided into right and left side
-The sinus venosus on the left side will become the coronary sinus


Atrial septation and foramen ovale 1

-Atrial septum is formed from 2 things: septum primum, which extends from the roof of the atria, and septum secundum, which forms from the floor of the atria
-Neither of these growths completely fuse with the opposite side, meaning there are 2 holes (one in each growth) but these holes are off-set
-The gap is foramen ovale


Atrial septation and foramen ovale 2

-Septum secundum is thicker and rigid, and septum primum is really just a flap lying over the gap in septum secundum
-Thus, septum primum serves as a one-way valve over foramen ovale for blood to flow from RA to LA, but prevents flow in the reverse direction


Ventricular maturation

-The inter ventricular septum (IVS) forms btwn the left and right AV canals
-Complete separation of the ventricles relies on fusion of the septum with the endocardial cushion, and the tissue that grows down from the outflow tract septum


Outflow tract septation

-Two opposing ridges (cushions) form longitudinally on the inner surface of the outflow tract
-They grow towards each other and ultimately fuse to form a septum separating the R and L outflow tracts
-The two outflow tracts assume a spiral orientation around each other
-The bottoms of the outflow tract septum continues to grow downwards and fuses w/ the muscular IVS to fully divide the RV from LV


Aortic arch arteries (pharyngeal arch derivatives)

-Left and right 3rd arches become common carotid arteries
-Left 4th arch becomes arch of the aorta
-Right 4th arch becomes the brachiocephalic artery
-Left 6th arch becomes the left PA and ductus arteriosus
-Right 6th arch forms the R PA (distal portion regresses)


Position of recurrent laryngeal nerves

-Since the distal portion of the left 6th arch becomes ductus arteriosus but the distal R 6th arch regresses, the recurrent laryngeal nerves (from the 6th arch) will be in different places on the two sides
-On the R side the nerve is near under the subcalvian because the distal portion is gone, allowing the nerve to migrate superiorly
-But on the left side the distal portion becomes the ductus arteriosus, thus the nerve is trapped under the aorta and cannot move superiorly


Fetal shunts

-Ducutus venosus: oxygenated blood from umbilical vein bypasses fetal liver via ductus venosus to reach the IVC
-Becomes ligamentum venosum
-Foramen ovale: opening in the atrial septum to let oxygenated blood from IVC to reach the LA so it can bypass the lungs and go straight to systemic circulation
-Foramen ovale becomes fossa ovalis
-Ductus arteriosus: shunts blood from main PA to desc Ao so the blood mostly bypasses the lungs
-Becomes ligamentum arteriosum
-Umbilical vein becomes ligamentum teres


Changes at birth

-Before birth the pressure in RA is higher than pressure in LA so blood can stream thru foramen ovale
-Resistance in the lungs before birth is very high, meaning most blood favors bypassing the lungs, either thru foramen ovale or thru ductus arteriosus
-At birth when the infant breathes the lungs expand and the resistance in the lungs decreases, leading to a great increase in pulmonary blood flow
-This process leads to a rise in LA pressure (LAP now greater than RAP), forcing septum primum to close over septum secundum and closing foramen ovale
-Ductus arterioles now is not needed, and closes due to increase in pO2 and decrease in PGE1