Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

there is a negative intrapleural pressure pulling at the lung walls.

pressure in the lungs is higher than the atmospheric pressure.

there is a negative pressure in the lungs.

there is a positive intrapleural pressure.

Respiratory Volumes

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NCERT Class 11 · Breathing and Exchange of Gases · 4 NEET questions

Most students confuse 'Capacity' with 'Volume'. A volume is a single measurement; a capacity is the sum of two or more volumes. If you cannot distinguish these, you are losing 4 marks on a basic definition question.

The idea

Respiratory volumes are the specific quantities of air moved during respiration. Tidal Volume (TV) is 500 mL per breath. Inspiratory Reserve Volume (IRV) is 2500-3000 mL, while Expiratory Reserve Volume (ERV) is 1000-1100 mL. Residual Volume (RV), the air remaining after forced expiration, is 1100-1200 mL. These values are non-overlapping and additive.

Why it matters

These measurements are essential for clinical assessment of pulmonary function and diagnosing respiratory disorders.

NEET lens

NEET focuses on the numerical values and the definition of RV. Expect a 'Match the Following' or a calculation-based question involving Vital Capacity (VC). Memorize the exact mL ranges provided in the NCERT table. Do not confuse IRV/ERV with Inspiratory/Expiratory Capacity.

Clinical significance

Residual Volume is critical; it prevents lung collapse by keeping alveoli inflated. In conditions like Emphysema, the destruction of alveolar walls increases RV, leading to air trapping. This reduces the efficiency of gas exchange, causing chronic hypoxia.

Introduction

Respiratory volumes are measures of the amount of air moved during breathing. Key volumes: tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume — which together make up total lung capacity.

Core concept

Four primary lung volumes: (1) Tidal Volume (TV): air inhaled/exhaled in each normal breath. ~500 mL. (2) Inspiratory Reserve Volume (IRV): extra air that can be forcefully inhaled after normal inspiration. ~2500-3000 mL. (3) Expiratory Reserve Volume (ERV): extra air that can be forcefully exhaled after normal expiration. ~1100 mL. (4) Residual Volume (RV): air remaining in lungs after maximum expiration. ~1100-1200 mL. Cannot be exhaled — keeps alveoli from collapsing.

Go deeper

Why residual volume exists: alveoli cannot completely collapse (surfactant prevents) and the chest wall has inherent outward recoil. If lungs collapsed fully each breath, reopening would require enormous effort. RV ensures gas exchange continues even between breaths.

From Class 10

Each breath moves a specific volume of air. Different volumes can be measured under different breathing conditions. These are called respiratory volumes or lung volumes.