Fetus depends on placenta to meet O2 needs while organs continue formation
Oxygenated blood flows from the placenta
To the fetus via the umbilical vein
After reaching fetus the blood flows through the inferior vena cava
The circulatory system of the mother is not directly connected to that of the fetus, so the placenta functions as the respiratory center for the fetus
as well as a site of filtration for plasma nutrients and wastes. Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen.
The uterine arteries carry oxygenated blood to the placenta, and permeates the sponge like material there.
Anatomy and Physiology Fetal Circulation
2 umbilical arteries: return non-oxygenated blood, fecal waste, CO2 to placenta
1umbilical vein : brings oxygenated blood and nutrients to the fetus
Facilitates gas and nutrient exchange between maternal and fetal blood.The blood itself does not mix.
How does the blood move??
Umbilical VEIN carries oxygenated blood and nutrients from the placenta to the fetus
Where does the vein enter??
At the navel and ascends into the liver
How is the blood dispersed??
½ of the blood enters the liver while the other half comes into the ductus Venosus and then into the inferior vena cava
Blood is shunted from right atrium to left atrium, skipping the lungs.
More than one-third of blood takes this route.
Is a valve with two flaps that prevent back-flow.
Blood continues to travel from the inferior vena cava to the ductus Venosus
Ductus Venosus : shunts a significant majority (80%) of the blood flow of the umbilical vein directly to the inferior vena cava.
Ductus Venosus it allows oxygenated blood from the placenta to bypass the liver and puts blood into the hepatic veins.
Small amount of blood routed to growing liver
Increased blood flow leads to large liver in newborns
What happens to the blood after it reaches the right atrium??
Blood flows right into the left atrium through the foramen ovale.
Alamak,What is that? It’s Small opening in the septum of the heart
Small opening in the septum of the heart
Completely by passes the non-functioning lungs
Here again it mixes with a smaller amount of deoxygenated blood from the pulmonary veins.
Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale , but enters the right ventricle and is pumped into the pulmonary artery .
In the fetus, there is a special connection between the pu l monary artery and the aorta , called the ductus arteriosus , which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid)
After it proceeds to the left ventricle where it is pumped to the heart and brain
Blood continues journey to the left ventricle blood is then pumped into the aorta
Blood is circulated to the upper extremities
Blood then returns to the right atrium
What about the rest of the blood??
The blood still in the right atrium goes into the right ventricle then to the pulmonary artery.
Once there most of the blood by passes the lungs and heads to the aorta through the ductus arteriosus.
About 15% of the blood flows through lungs to the right atrium by way of the pulmonary veins
Small amount goes to the maturing lungs
Rest of blood is shunted away from lungs by ductous ateriosus back to aorta
What is happening further down??
Common iliac arteries branch into the external and internal iliacs.
The blood in the internal iliacs come into the umbilical arteries and flow back to the placenta to gather oxygen and to get rid of the waste products
Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, the maternal circulation
Low pressure system
Lungs are closed
Most oxygenated blood flows between the atria of the heart through the foramen ovale
This oxygen rich blood flows to the brain through the ductus arteriosus
What happens after birth?
Once the baby is born and the lung, renal, digestive and liver functions are working the fetal circulation undergoes some changes since they are no longer needed
Conversion of Fetal to Infant Circulation
Clamping the cord shuts down low-pressure system
Increased atmospheric pressure(increased systemic vascular resistance) causes lungs to inflate with oxygen
Lungs now become a low-pressure system
Pressure from increased blood flow
What happens to these special structures after birth?
Umbilical arteries atrophy
Umbilical vein becomes part of the fibrous support ligament for the liver
The foramen ovale, ductus arteriosus, ductus venosus atrophy and become fibrous ligaments
Overview of Conversion
Umbilical cord is clamped
Closure of ductus venosus
Blood is transported to liver and portal system
Fetal vs. Infant Circulation
Low pressure system
Right to left shunting
Increased pulmonary resistance
Decreased systemic resistance
High pressure system
Left to right blood flow
Decreased pulmonary resistance
Increased systemic resistance
Overall anatomic changes are not complete for weeks