Which of the following part of the respiratory system is the site for external respiration?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

The alveoli are the primary structures of the respiratory zone, where gas exchange occurs.
External respiration is the exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries.
The walls of the alveoli are extremely thin (simple squamous epithelium) and are in close contact with capillaries, forming the respiratory membrane.
This structure provides a large surface area (about 70 square meters in an adult) and a short diffusion distance, facilitating rapid gas exchange.

Option A: The trachea, or windpipe, is the main airway to the lungs. It is part of the conducting zone, responsible for air transport, not gas exchange.
Option B: The bronchi are the two main branches of the trachea that lead into the lungs. Like the trachea, they are part of the conducting zone and function to conduct air.
Option C: Bronchioles are smaller airways that branch off the bronchi. Most bronchioles, specifically terminal bronchioles, are the final part of the conducting zone. While respiratory bronchioles begin the respiratory zone, the vast majority of gas exchange occurs in the alveoli.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy and Physiology of the Respiratory System: Site of External Respiration as background academic context rather than a clinical decision trigger.
Understanding the site of gas exchange is crucial for nurses, as many respiratory diseases directly affect the alveoli.
Conditions like pneumonia (inflammation and fluid in alveoli), ARDS (Acute Respiratory Distress Syndrome), and emphysema (destruction of alveolar walls) impair external respiration, leading to hypoxemia (low blood oxygen).
Nursing interventions such as administering oxygen therapy, encouraging deep breathing and coughing, and positioning the patient (e.g., Fowler's position) are aimed at improving alveolar ventilation and gas exchange.

How to Approach the Question

First, identify the key term in the question: 'external respiration'. Recall or look up its definition, which is gas exchange between the lungs and blood.
Next, mentally divide the respiratory system into its two functional zones: the conducting zone and the respiratory zone.
Recall the function of each zone. The conducting zone (trachea, bronchi, most bronchioles) transports air, while the respiratory zone is for gas exchange.
Evaluate each option based on its location and function. Trachea, bronchi, and bronchioles are primarily for conduction.
Identify the alveolus as the main structure of the respiratory zone, specifically designed with thin walls and a rich capillary supply for efficient gas exchange. This makes it the correct answer.

Concept Tested & Keywords

Concept Tested: Anatomy and Physiology of the Respiratory System: Site of External Respiration
Stem keywords: respiratory system, site, external respiration
Lead-in keywords: Which
Negative lead-in flag: false

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