Pulmonary Function Tests and Gas Exchange Quiz

Respiratory System

• Alveolar sacs contain clusters of alveoli (~300 million) which make up most of lung volume and are the sites of actual gas exchange.

Respiratory Zone Structures

• Alveoli are responsible for gas exchange
• Alveolar ducts connect to respiratory bronchioles
• Respiratory bronchioles lead to terminal bronchioles

Respiratory Membrane

• Consists of a single layer of squamous epithelium and scattered cuboidal alveolar cells that secrete surfactant and antimicrobial proteins
• Acts as a blood-air barrier, allowing gas exchange by simple diffusion

Lungs and Pleurae

• Lungs flank the mediastinum in the thoracic cavity
• Root: site of vascular and bronchial attachment to the mediastinum
• Costal surface: surfaces in close contact with ribs
• Apex: superior tip, deep to the clavicle
• Base: inferior surface that rests on the diaphragm

Pulmonary Ventilation

• Inspiration: active process that occurs during vigorous exercise or in people with COPD
• Expiration: passive process that occurs when inspiratory muscles relax, thoracic cavity volume decreases, and lungs recoil
• Intrapulmonary pressure (Ppul) increases, causing air to flow out of the lungs

Gas Exchange

• Occurs between lungs and blood, as well as between blood and tissues
• External respiration: diffusion of gases between blood and lungs
• Internal respiration: diffusion of gases between blood and tissues

Pulmonary Function Tests

• Forced vital capacity (FVC): amount of gas forcibly expelled after taking a deep breath
• Forced expiratory volume (FEV): amount of gas expelled during a specific time interval of FVC
• Patients with obstructive disease exhale less than 80% in 1st second, while those with restrictive disease exhale 80% or more, even with reduced FVC

Alveolar Ventilation

• Minute ventilation: total amount of gas that flows into or out of the respiratory tract in 1 minute
• Alveolar ventilation rate (AVR): flow of gases into and out of alveoli during a particular time
• Better indicator of effective ventilation as it accounts for the anatomical dead space

Gas Exchange Laws

• Dalton's Law: each gas will dissolve in the liquid in proportion to its partial pressure
• Henry's Law: amount of each gas that dissolves depends on solubility, temperature, and other factors

External Respiration

• Involves the exchange of O2 and CO2 across respiratory membranes
• Influenced by pressure gradients and gas solubilities
• Thickness and surface area of respiratory membrane affect the rate of gas exchange

Oxygen Transport

• Association of oxygen and hemoglobin: each Hgb can transport four oxygen molecules
• Oxyhemoglobin (HgbO2): hemoglobin-O2 combination
• Deoxyhemoglobin (HHb): hemoglobin that has released O2

Oxygen Binding and Release

• Loading and unloading of O2 is facilitated by a change in shape of Hgb
• Factors that influence hemoglobin saturation: PO2, temperature, blood pH, PCO2, and concentration of BPG