The Respiratory system Pulmonary ventilation – Chp 16 Respiration

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Factors affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Factors affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Overview Respiration = gas exchange -- Occurs at the levels of the lungs and tissues (external respiration) and cell (internal or cellular respiration). External respiration: - Pulmonary ventilation: movement of air in and out of the lungs -Gas exchange in the alveoli -Gas transport in the blood -Gas exchanges between blood and tissues

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Factors affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Airways

Upper airways: - nose to pharynx Lower airways: - Conducting airway: larynx  bronchioles - Respiratory airway: alveoli Due to the wall structure of the airway: one cell layer (SSE) allows for gas exchange

Conducting airways Presence of cartilage in the wall, from larynx to small bronchi prevents airway collapse. Goblet cells secreted mucus. Ciliated cells help move the mucus out of the airway. Presence of smooth muscle fibers in the bronchioles (but no cartilage) Volume of the conducting airway: 150 ml

Respiratory airway: Alveoli Alveolar wall is formed by simple squamous epithelium = type I cells (SSE)  gas exchange Respiratory membrane: membrane separating alveolus from blood capillary. Large surface area from the numerous alveoli  better gas exchange Presence of elastic fibers between alveoli

Blood supply to the lungs

Alveolar structure Type I cells  gas exchange Type II cells  secrete surfactant (lipoproteins)  decrease surface tension  allowing for easier alveoli inflation Surfactants start to be secreted by the 7 th month of pregnancy  risk of lung disease in premature babies Presence of macrophages in alveoli

Structure of the thoracic cavity

The pleura Formed by 2 layers: the parietal and visceral pleura Roles: - prevents friction of the lungs against the rib cage (due to the thin layer of liquid present in the pleural space) - maintains lung expansion: due to the negative pressure within the pleural space What is negative pressure? What is its importance?

Pleura and negative pressure Pneumothorax: lung collapse due to air entering in the pleural cavity (not to be confused with atelectasy  alveoli collapse)

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Factors affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Mechanics of breathing Boyle’s law: The pressure of a gas in a closed container is inversely proportional to the volume of the container. Air flow in the lungs is driven by the differences in pressure between the atmosphere and the alveoli P.atm is constant  changes in P.alv drive ventilation

Inspiration and expiration Inspiration: chest wall expands due to muscle contraction (diaphragm and/or other muscles)  Pressure in alveoli ↓  air moves toward alveoli Expiration: passive process  muscle relax  chest wall return to resting state  alveoli become compressed  ↑ alveolar pressure  move moves out

Ventilation

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Factors affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Factors affecting pulmonary ventilation 1- Lung compliance: ease with which lungs can be stretched - Compliance is a measure of the elasticity of lung tissue and the alveolar surface tension 2- Airway resistance: to changes in airway radius (↓radius  ↑resistance ) Pathology lung disease resulting in stiffness of tissue no or ↓ surfactant Asthma Airway obstruction COPD

Outline Overview of the respiratory system Anatomy Forces for pulmonary ventilation Forces affecting pulmonary ventilation Clinical significance of respiratory volumes and air flows

Lung volumes

Pulmonary function tests Can help distinguish between obstructive pulmonary disease and restrictive pulmonary disease -Obstructive disease: obstruction in bronchi-bronchioles severely restricts the speed and amount of air movement - Damage to lung tissue prevents full lung expansion and recoil

Anatomical dead space Anatomical dead space: space within the conductive airway, about 150 ml. What will happen to a person who has a tidal volume of 150 ml due to lung disease? What can be done to help the person?