6.3 Mechanism of Breathing · Part 3

is – mL. • Expiratory Reserve volume (ERV) Additional volume of air a person can forcefully exhale by forceful expiration is called Expiratory Reserve Volume. The normal value is – mL. • Residual Volume (RV) The volume of air remaining in the lungs after a forceful expiration. It is approximately – mL. Respiratory Capacities: • Vital capacity (VC) the maximum volume of air that can be moved out during a single breath following a maximal inspiration. A person first inspires maximally then expires maximally. VC = ERV+TV+IRV • Inspiratory capacity (IC) The total volume of air a person can inhale after normal expiration. It includes tidal volume and inspiratory reserve volume. IC = TV+IRV • Expiratory capacity (EC) The total volume of air a person can exhale after normal inspiration. It includes XI Std Biology-Zoology Chapter- tidal volume and expiratory reserve volume. EC=TV+ERV • Total Lung Capacity (TLC) The total volume of air which the lungs can accommodate after forced inspiration is called Total Lung Capacity. This ­includes the vital capacity and the residual volume. It is approximately 6000mL. TLC=VC+RV • Minute Respiratory Volume The amount of air that moves into the respiratory passage per minute is called minute respiratory volume. Normal TV = 500mL; Normal respiratory rate = times/minute Therefore, minute respiratory ­ volume = Litres/minute (for a ­normal healthy man). Figure . Lung Volumes and Capacity Healthy lungs contain large amounts of elastic connective tissue around the alveoli, containing elastin, which makes the lung tissue elastic. People with emphysema and bronchitis have difficulty in exhaling because the enzyme elastase destroys the elastin around the alveoli and reduces the elasticity of the lungs. Minimal volume ( -120mL) Volume (mL) Resting tidal volume ( V T = mL) Expiratory reserve volume (ERV) Inspiratory reserve volume (IRV) Residual volume Inspiratory capacity Vital capacity Functional residual capacity Why do some people snore? – Breathing with a hoarse sound during sleep is caused by the vibration of the soft palate. Snoring is caused by a partially closed upper air way (nose and throat) which becomes too