Oxygen and carbon dioxide are exchanged in the placenta through the process of?& x20; - AIIMS Nagpur NO - 2018

AIIMS Nagpur NO - 2018

Obstetrics & Gynaecology

Easy

Appeared in: AIIMS Nagpur NO - 2018

Explanation

The exchange of respiratory gases (O₂ and CO₂) in the placenta is governed by simple diffusion.
This is a passive process driven by the partial pressure gradient of the gases between maternal and fetal blood.
Oxygen moves from the mother's blood, which has a higher partial pressure of oxygen (PO₂), to the fetal blood, which has a lower PO₂.
Conversely, carbon dioxide moves from the fetal blood (higher PCO₂) to the maternal blood (lower PCO₂).
This process does not require cellular energy (ATP) or carrier molecules.

Option A: Facilitated transport requires a carrier protein to move substances across the membrane. While it is a crucial process in the placenta, it is not the mechanism for gas exchange. Gases are small, lipid-soluble molecules that can pass directly through the cell membrane.
Option C: Active transport requires energy (ATP) to move substances against their concentration gradient. Gas exchange is a passive process that follows the pressure gradient, so it does not require energy.
Option D: Pinocytosis is a process for transporting large molecules and fluids by engulfing them in vesicles. It is an inefficient method for the rapid exchange of small molecules like oxygen and carbon dioxide.

Visual 1: Diagram: A cross-section of a placental villus showing the maternal and fetal blood spaces. Arrows should clearly indicate the movement of O₂, CO₂, glucose, amino acids, and IgG, with each arrow labeled with its corresponding transport mechanism (Diffusion, Facilitated Transport, Active Transport, Pinocytosis).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placental Transport Mechanisms as background academic context rather than a clinical decision trigger.
Understanding that gas exchange is diffusion-dependent is critical for nurses, as any condition that reduces the pressure gradient or placental surface area can lead to fetal hypoxia.
Maternal conditions like smoking (which increases carboxyhemoglobin), severe anemia, or high-altitude living can decrease the oxygen available in maternal blood, thereby reducing the diffusion gradient and compromising fetal oxygenation.
Nurses monitor fetal heart rate and activity as indirect measures of adequate oxygenation, which relies on efficient placental diffusion.

How to Approach the Question

First, identify the key terms in the question: 'Oxygen and carbon dioxide', 'placenta', and 'exchanged'. This points to the topic of gas exchange in the maternal-fetal unit.
Recall the basic principles of transport across biological membranes. Differentiate between passive processes (no energy required) and active processes (energy required).
Consider the nature of the substances being transported. Gases like O₂ and CO₂ are small, lipid-soluble molecules.
Evaluate the options: Active transport and pinocytosis require energy. Facilitated transport requires a carrier. Simple diffusion is the passive movement of substances down a gradient.
Conclude that the movement of small gas molecules across a membrane, driven by differences in partial pressure, is the definition of simple diffusion.

Concept Tested & Keywords

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