Physiology of the Respiratory System

Created March 1, 2024 by Dongho Kim

Respiration

Respiration has 3 phases:

1. Pulmonary ventilation - movement of air into and out of the lungs

2. External respiration - exchange of gases b/n lungs and blood

3. Internal respiration - exchange of gases b/n blood and tissues

Pulmonary ventilation consists of

1. Inspiration - inhalation, movement of air into lungs

2. Expiration - exhalation, emptying air from lungs into atmosphere

Pulmonary Ventilation

For pulmonary ventilation to occur, the pressure in the thoracic cavity must be different from atmospheric pressure

· Inspiration is an active process, it requires the contraction of several muscles to change volumes and pressures

· Expiration is passive, muscles relax, thoracic wall and lungs recoil, air moves out

A Spirometer measures respiratory volumes

· Tidal Volume* is the amount of air inhaled or exhaled during normal resting breathing

· Inspiratory Reserve Volume (IRV) is the amount of air forcibly inspired above normal inhalation

· Expiratory Reserve Volume (ERV)* is the amount of air forcibly expired after a normal exhalation

· Vital Capacity* is the maximum amount of air exhaled from lungs after maximum inhalation

* can be measured directly with spirometer

IRV can be calculated from the VC, TV, and ERV:

VC = IRV + ERV + TV à IRV = VC – ERV – TV

· The Residual Volume is the amount of air that cannot be forcefully exhaled from the lungs

· Total Lung Capacity is ~ 6,000 ml; TLC = VC + RV

· Minimal Volume is the amount of residual air that stays in the lungs even after collapse

· Respiratory Rate is the number of breaths taken per minute

· Minute Volume amount of air exchanged b/n lungs and environment in 1 minute: MV = TV x RR