First Aid for the USMLE Step 2 CK,9th Edition PDF
First aid for the step 2 ck 9th edition pdf is must have book for your USMLE step 2 ck preparation .I don’t want give deep description about this book because you already know about this book.below I just described fetal circulation as a bounus.
Deoxygenated blood leaves the fetus via the umbilical arteries. The umbili-
cal arteries travel through the umbilical cord toward the placenta. Oxygen-
ated blood (approximately 80% saturated with 0 ) returns from the placenta
toward the fetus via the umbilical vein (Figure l-6) . Blood from the umbilical
vein bypasses the liver by flowing through the ductus venosus and empties
into the inferior vena cava (IVC). The IVC brings blood into the right atrium.
Since this blood is already oxygenated, the pulmonary circulation is unneces-
sary and can be bypassed. In the fetus, pressures in the right heart are greater
than those in the left heart due to high resistance in the pulmonary circula-
tion. The pressure gradient drives right-to-left shunts, allowing the bypass of
the pulmonary circulation. Blood in the RA has two methods of bypassing the
1. Flowing through the foramen ovale to the LA, continuing to the LV,
aorta, and eventually supplying the head.
2. Continuing into the RV, out the pulmonary trunk, and then through the
ductus arteriosus to the aorta, primarily supplying the trunk and lower
The aorta sends blood to fetal tissues. Deoxygenated blood leaves the iliac
arteries via the umbilical arteries to return to the placenta.
After birth, as the neonate begins to breathe, the pulmonary arterial resistance
decreases. For the first time, pressures in the left heart exceed pressures in
the right heart.
First Aid for the USMLE Step 2 CK, 9th Edition
The increase in left atrial pressure forces the septum primum
against the septum secundum, closing the foramen ovale. Closure of the duc-
tus arteriosus is mediated by falling levels of prostaglandins subsequent to
increased 02 content in the circulation.
First Aid for the USMLE Step 2 CK, 9th Edition PDF