Oxygenated blood from the placenta reaches the fetal heart in utero via?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2021

Obstetrics & Gynaecology

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2021

Explanation

The umbilical vein is the sole vessel responsible for transporting oxygen-rich and nutrient-rich blood from the placenta to the fetus.
This blood enters the fetus at the umbilicus and travels towards the liver.
A significant portion of this blood bypasses the liver through a shunt called the ductus venosus, entering the inferior vena cava to reach the right atrium of the heart.
This is a key difference from postnatal circulation, where veins (except the pulmonary vein) carry deoxygenated blood.

Option A: The two umbilical arteries carry deoxygenated, waste-laden blood away from the fetus back to the placenta for re-oxygenation and waste removal.
Option C: The ductus venosus is a shunt located within the fetal body. It connects the umbilical vein to the inferior vena cava, allowing a portion of the oxygenated blood to bypass the liver.
Option D: The ductus arteriosus is a shunt that connects the pulmonary artery to the aorta. Its primary function is to allow blood from the right ventricle to bypass the non-functional fetal lungs.

Clinical Relevance

Nursing practice connection: Knowing Fetal Circulation helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
At birth, nurses must assess the umbilical cord for the presence of two arteries and one vein (AVA). The absence of one umbilical artery (a two-vessel cord) can be associated with congenital anomalies, particularly of the kidneys and heart, and may warrant further investigation.
What if? If the ductus arteriosus fails to close after birth, the condition is known as Patent Ductus Arteriosus (PDA). This results in a left-to-right shunt, where oxygenated blood from the high-pressure aorta flows into the lower-pressure pulmonary artery. This increases pulmonary blood flow and can lead to pulmonary hypertension and heart failure if not corrected.

How to Approach the Question

First, identify the key components of the question: 'oxygenated blood', 'from placenta', and 'reaches the fetal heart'.
Recall the basic principles of fetal circulation, which differ significantly from postnatal circulation.
Differentiate between the vessels in the umbilical cord. Remember the mnemonic 'AVA': two Arteries, one Vein. Also remember the functional reversal: the vein carries oxygenated blood, and the arteries carry deoxygenated blood.
Distinguish between the primary transport vessel (umbilical vein) and the internal shunts (ductus venosus, ductus arteriosus, foramen ovale) that redirect blood flow within the fetus.
Evaluate each option based on its specific function in the circulatory pathway.
Eliminate incorrect options: Umbilical arteries carry blood away from the fetus. The ductus arteriosus and ductus venosus are shunts within the fetus, not the primary vessel from the placenta.

Concept Tested & Keywords

QbmFQ49nh6N3kJmbRn6afU

E6 Pathology- ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE 10TH Ed p. 1027-1029

E6 Obstetrics Williams p. 22-41

E6 Anatomy Grays 43e Vol 1 Part 2 p. 54-56