SMS 1053Dr. Mohanad R. Alwan

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Anatomy and Physiology

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

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The Placenta

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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 PhysiologyFetal Circulation

Umbilical cord 2 umbilical arteries: return non-oxygenated

blood, fecal waste, CO2 to placenta 1umbilical vein: brings oxygenated blood and

nutrients to the fetus

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Facilitates gas and nutrient exchange between maternal and fetal blood.The blood itself does not mix.

Fetal Circulation

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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

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Foramen Ovale

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.

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Fetal Circulation

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

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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

Foramen ovale 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.

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F.C

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 pulmonary 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)

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Ductus Arteriousus

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Fetal Circulation

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

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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

Pulmonary arteries Small amount goes to the maturing lungs

Rest of blood is shunted away from lungs by ductous ateriosus back to aorta

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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

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Fetal 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

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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

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Conversion of Fetal to Infant Circulation

At birth 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

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Conversion (cont)

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

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Overview of Conversion

Umbilical cord is clamped Loose placenta Closure of ductus venosus Blood is transported to liver and portal

system

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Fetal vs. Infant Circulation

Fetal Low pressure system Right to left shunting Lungs non-functional Increased pulmonary

resistance Decreased systemic

resistance

Infant High pressure system Left to right blood flow Lungs functional Decreased pulmonary

resistance Increased systemic

resistance

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Overall anatomic changes are not complete for weeks

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