Step by step fetal circulation flow chart

Following are the important features of fetal circulation:

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What are the steps of fetal circulation?
What are the 14 steps of circulation?
How does blood flow through the heart and lungs in fetal circulation?
Which of the following is the correct pathway of blood from the mother to her fetus?

1. Placenta plays the role of lungs; lungs are not functional:

Like pulmonary veins, left umbilical vein carries highly oxygenated blood from placenta to heart.
Like pulmonary artery, right and left umbilical arteries braing deoxygenated blood to placenta.

2. Mixing potentially occurs at 4 sites:

Left umbilical vein (Oxygen saturation ~80%) – Portal vein (Much bypassed by ductus venosus to Inferior Venacava)
Left umbilical vein – Inferior venacava – Portal vein (Oxygen saturation of IVC blood is ~65%)
Superior venacava – Right atrium (Much bypassed by Foramen ovale)
Pulmonary veins – Left atrium (Much bypassed by Foramen ovale and ductus arteriosus)

Oxygen saturation of blood in various vessels:

Umbilical vein: 80%
Abdominal IVC and portal vein: 28%
Thoracic IVC: 67%
Superior venacava: 25%
Pulmonary veins: 42%
Pulmonary trunk: 52%
Umbilical arteries: 56%

Overview of Fetal Circulation:

Blood is oxygenated in the placenta.
Highly oxygenated and nutrient-enriched blood returns to the fetus from the placenta via the left umbilical vein.
Some blood enters liver sinusoids; most of the blood bypasses the sinusoids by passing through the ductus venosus and enters the inferior vena cava (IVC)
From the IVC, blood enters the right atrium, where most of the blood bypasses the right ventricle through the foramen ovale to enter the left atrium.
From the left atrium, blood enters the left ventricle and is delivered to fetal tissues via the aorta.
Poorly oxygenated and nutrient-poor fetal blood is sent back to the placenta via right and left umbilical arteries.
Some blood in the right atrium enters the right ventricle; blood in the right ventricle enters the pulmonary trunk, but most of the blood bypasses the lungs through the ductus arteriosus.

Fetal Combined Cardiac Output (CCO) Distribution:

The 3 shunts of Fetal Circulation:

Location	Shunt	Between	Function	Closure	Remnant
Pre-cardiac (Venous)	Ductus Venosus	Left umbilical vein (Remember: Left is left and right regresses) and Inferior Venacava (IVC)	Bypasses portal circulation Left umbilical vein carries highly oxygenated blood (80%). Prevents mixing with desaturated blood in portal circulation. Has sphincter mechanism: Closes and prevents overloading of heart during uterine contraction.	Functional: With umbilical cord clamping, venous return in the IVC decreases and reduction of flow through ductus venosus allows passive collapse. occurs during the 1st minutes after birth and is not complete. An appreciable amount of the portal venous blood is shunted through this channel during the 1st hours and perhaps days of life. Anatomical: Proliferation of the obliterating tissue in specially structured border strips by 15th to 20th days.	Ligamentum venosum
Cardiac	Foramen Ovale	Left atrium and Right atrium	Blood from IVC directly flows to Left atrium due to the valves in IVC i.e. Right atrium only acts as a conducting pathway No mixing of deoxygenated blood from Superior Venacava (SVC) Bypasses pulmonary circuit	Functional: With the 1st breath – septum primum is pressed agains septum secundum Decreased right atrial pressure – interruption of placental blood flow Increased left atrial pressure – Closure of ductus arteriosus (increased blood in pulmonary circulation) Anatomical: Fusion of 2 apposed septa in about 1 year	Fossa ovale
Post-cardiac (Arterial)	Ductus Arteriosus	Pulmonary artery and Aorta	Blood enters Right ventricle through the Right atrium from: Superior Venacava Inferior Venacava (some amount of blood is prevented from passing through foramen ovale by crista dividens, i.e. lower edge of septum secundum) Pulmonary circuit is bypassed due to high resistance in pulmonary vessels – blood flows from pulmonary artery to aorta via ductus arteriosus.	Functional: Within 48 hrs if birth by muscular contraction Increase in oxygen tension inhibits ductal smooth muscle voltage-dependent potassium channels, which results in an influx of calcium and ductal constriction. PGE2 and PGI2 levels fall because of metabolism in the now functioning lungs and elimination of the placental source. Anatomical: By intimal proliferation; takes 1-3 months.	Ligamentum arteriosus

Fate of Umbilical Vessels:

1. Umbilical arteries:

Functional closure: Immediately after birth due to thermal and mechanical stimuli and increased oxygen tension leading to constriction.

Anatomical closure: By fibrosis; takes 2-3 months

Remnants:

Distal part: Medial umbilical ligaments
Proximal part: Superior vesical arteries

2. Umbilical vein:

Obliterates shortly after birth like ductus venosus.

Remnant: Ligamentum teres hepatis

What are the steps of fetal circulation?

Inside the fetal heart.

Blood enters the right atrium. ... .

Blood then passes into the left ventricle. ... .

From the aorta, blood is sent to the heart muscle itself and to the brain and arms. ... .

This less oxygenated blood is pumped from the right ventricle into the pulmonary artery..

What are the 14 steps of circulation?

In summary from the video, in 14 steps, blood flows through the heart in the following order: 1) body –> 2) inferior/superior vena cava –> 3) right atrium –> 4) tricuspid valve –> 5) right ventricle –> 6) pulmonary arteries –> 7) lungs –> 8) pulmonary veins –> 9) left atrium –> 10) mitral or bicuspid valve –> 11) left ...

How does blood flow through the heart and lungs in fetal circulation?

It flows down into the right ventricle, where it normally would be sent to the lungs to be oxygenated. Instead, it bypasses the lungs and flows through the ductus arteriosus into the descending aorta, which connects to the umbilical arteries. From there, blood flows back into the placenta.

Which of the following is the correct pathway of blood from the mother to her fetus?

The umbilical vein carries oxygenated, nutrient-rich blood from the placenta to the fetus, and the umbilical arteries carry deoxygenated, nutrient-depleted blood from the fetus to the placenta (Figure 2.2).