Phys-fetal circulation Flashcards
Name the four anatomical shunts
- Placental circulation (lungs, GI tract, kidneys)
- Ductus arteriosus (bypasses lungs, connects pulmonary a. to descending aorta)
- Ductus venosus (bypasses liver, connects umbilical v. to IVC)
- Foramen ovale (bypasses RV and lungs, connects RA to LA)
Placental has exchange is inefficient due to ___
Large diffusion distances
PO2 for fetal umbilical v. blood is ___
~30 mmHg
*maternal is ~100mmHg
How does the fetus compensate for the extremely low PO2?
- Hemoglobin is ~50% more concentrated in the fetus (this increases oxygen content)
- Fetal hemoglobin has a higher affinity for O2 (more O2 is carried per gram of hemoglobin)
- Unloading of O2 is easier due to metabolites (Bohr effect)
- Increase in placental cross sectional area, thinning of villar membranes (this enhances oxygen flux)
At PO2, fetal hemoglobin is ___ saturated compared to ___ in adults
80%
50%
What things are exchanged through passive diffusion in the placenta?
Fatty acids
Small ions such as Na, K, Cl
Waste products
What things are exchanged through facilitated diffusion in the placenta?
Glucose (GLUT 1 and 3)
-not insulin dependent
What things are exchanged through active transport in the placenta?
Amino acids
Ascorbic acid
Ca
Phosphate
Fetus –> Newborn –> Adult
Change from circulation in ___ to ___
Parallel to series
True or false:
The left ventricle alone supplies systemic circulation in the fetus
False
Both the left and right
Left ventricular output is ___ of the CVO while the right is ___
1/3: (67% of this goes to the head, coronary arteries, upper limb, torso, 33% goes to lower body)
2/3: (10% goes to pulmonary circ, 90% crosses the ductus arteriosus to the descending aorta and goes to the abdomen Minaj organs, lower limbs, and placenta)
True or false:
The right ventricular output is more highly oxygenated
False
The left is
___ contain oxygenated blood leaving the placenta
Umbilical v.
Highest oxygen sat in the fetus
80% in the umbilical v.
Pressure in the ___ atrium is greater than the ___ because ___
Right
Left
Flow moves from right to left
Larger stream (60%) from the ____ goes to the (RV/LV) and is (more/less) oxygenated. The smaller stream (40%) from the ____ goes to the (RV/LV) and is (more/less) oxygenated.
IVC-RV-less
Umbilical v.-LV-more
Sources of RV blood
64% from IVC (lower body and placenta)
32% from SVC (upper torso and head)
4% from coronary sinus
Sources of LV blood
79% from IVC (lower body and placenta)
21% from lungs
The ___ contains the highest O2 sat in arterial circulation
LV at 62%
Mean pressure in the pulmonary artery is ___ than that of the aorta because ___
Greater
Flow across the ductus arteriosus is from pulmonary a. to aorta (right to left)
The starling mechanism is not well developed in the fetus, so increasing preload causes ___ while increasing afterload causes ___
Little increase in SV
Big decrease in SV
Two main circulatory events occur at birth:
Parallel to series arrangement is facilitated by:
- Pulmonary vasodilation leading to increased pulmonary blood flow
- Cessation of flow in the umbilical arteries and vein
In the fetus, pulmonary vascular resistance is ___ due to ___
High due to
Hypoxic vasoconstriction and physical compression of the collapsed lungs
At birth, pulmonary vascular resistance ___ and this leads to ___
Falls
-increase in pulmonary blood flow, increase in left atrial pressure so foramen ovale closes
