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Fetal Circulation

By AdminPosted On 05-Oct-2016

1. Fetal Circulation : Hypogastric arteries

Fetal blood is returned to the umbilical arteries and the placenta through the

a) Hypogastric arteries
b) Ductus venosus
c) Portal vein
d) Inferior vena cava
e) Foramen ovale

Correct Answer: a) Hypogastric arteries. Oxygenated Blood from the placenta is carried to the fetus by the umbilical vein. Deoxygenated Blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta. In the fetus, the internal iliac artery is twice as large as the external iliac, and is the direct continuation of the common iliac. It ascends along the side of the bladder, and runs upward on the back of the anterior wall of the abdomen to the umbilicus, converging toward its fellow of the opposite side. Having passed through the umbilical opening, the two arteries, now termed umbilical, enter the umbilical cord, where they are coiled around the umbilical vein, and ultimately ramify in the placenta. At birth, when the placental circulation ceases, the pelvic portion only of the umbilical artery remains patent gives rise to the superior vesical artery (or arteries) of the adult; the remainder of the vessel is converted into a solid fibrous cord, the medial umbilical ligament (otherwise known as the obliterated hypogastric artery) which extends from the pelvis to the umbilicus.

2. Which of the following statements is true of the fetal circulation?

a) 100% of the cardiac output goes to the lungs via the pulmonary artery. b) The arterial duct (ductus arteriosus) helps send oxygenated blood to the brain. c) Blood shunts across the duct ‘left to right’ (from the aorta to the pulmonary artery). d) The foramen ovale typically closes by 36 weeks' gestation. e) The umbilical vein carries well-oxygenated blood.Correct Answer: e) The umbilical vein carries oxygenated blood from the placenta to the IVC via the ductus venosus. Less than 10% of the cardiac output goes to the fetal lung. Relatively deoxygenated blood is pumped from the right ventricle, up the pulmonary artery and across the duct where it joins the aorta after the carotid vessels, diverting this blood away from the brain. In the fetus the pulmonary vascular resistance is high and the systemic vascular resistance is low, so blood shunts right to left. The foramen ovale sends well-oxygenated blood across to the left atrium and only closes after birth.

3. After birth, all of the following fetal vessels constrict EXCEPT:

a) Ductus arteriosus.
b) Umbilical arteries.
c) Ductus venosus.
d) Hepatic portal vein.
e) Umbilical vein.

Correct Answer: d) Hepatic portal vein. At birth, placental blood flow ceases and lung respiration begins. The sudden drop in right atrial pressure pushes the septum primum against the septum secundum, closing the foramen ovale. The ductus arteriosus begins to close almost immediately, and may be kept open by the administration of prostaglandins. Other embryonic circulatory vessels are slowly obliterated and remain in the adult only as fibrous remnants. Fetal Structure >>> Adult Remnant 1) Foramen ovale >>> Fossa ovalis of the heart 2) Ductus arteriosus >>> Ligamentum arteriosum 3) Left umbilical vein - a. Extra-hepatic >>> Ligamentum teres b. Intra-hepatic (ductus venosus) >>> Ligamentum venosum 4) Left and right umbilical arteries a. Proximal portions >>> Umbilical br.of int iliac art b. Distal portions >>> Medial umbilical ligaments

4. Fetal Circulation : Oxygenated Blood

In the fetus, the most well oxygenated blood is allowed into the systemic circulation by the:

a) Ductus arteriosus.
b) Foramen ovale.
c) Rt. Ventricle.
d) Ligamentum teres.
e) Ligamentum venosum

Correct Answer: Left Ventricle via > Eustachian valve > b) Foramen ovale > left atrium > aorta. Fetal cardiovascular system is designed in such a way that the most highly oxygenated blood is delivered to the myocardium and brain. In the fetus, deoxygenated blood arrives at the placenta via the umbilical arteries and is returned to the fetus in the umbilical vein. The partial pressure of oxygen in the umbilical vein is around 4.7 kPa and fetal blood is 80–90% saturated. Between 50–60% of this placental venous flow bypasses the hepatic circulation via the ductus venosus (DV) to enter the inferior vena cava (IVC). In the IVC, the better oxygenated blood flow from the DV tends to stream separately from the extremely desaturated systemic venous blood, which is returning from the lower portions of the body with an Formula of around 25–40%. At the junction of the IVC and the right atrium (RA) is a tissue flap known as the Eustachian valve. This flap tends to direct the more highly oxygenated blood, streaming along the dorsal aspect of the IVC, across the foramen ovale (FO) and into the left atrium (LA). In the LA, the oxygen saturation of fetal blood is 65%.1 This better oxygenated blood enters the left ventricle (LV) and is ejected into the ascending aorta. The majority of the LV blood is delivered to the brain and coronary circulation thus ensuring that blood with the highest possible oxygen concentration is delivered to these vital structures.

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Dr. Niraj Mahajan

MD- Gynecologist, Laparoscopic Surgeon, Uro-gynecologist , Infertility specialist & Cosmetic Gynecologist.

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