Respiration II PT 1

• Lung Function is the topic
• Department of Biology, BIO 269

Lecture Goals

• Understand the anatomy/function of the conductive zone
• Understand the anatomy/function of the respiratory zone
• Identify the cell types found specifically in the alveoli and their particular roles
• Describe the layers gases diffuse through during pulmonary gas exchange
• Relate diffusion distance to the speed of gas exchange
• Understand the pleural layers around the lungs
• Understand intrapulmonary and intrapleural pressure
• Relate ventilation to changes in intrapulmonary volume and pressure

Conducting Zone

• It is the passageway for air in and out of the:
  • Larynx, the voice box
  • Trachea, also known as the windpipe
  • Bronchi – primary, secondary, tertiary
  • Bronchioles which are <1mm in diameter
  • Terminal Bronchioles, those are <0.5mm in diameter
• This area is surrounded by smooth muscle

Conducting Zone Functions

• Warms and humidifies incoming air, making it less irritating
• Cleanses air of debris and pathogens
• Phonation or speaking, vocal cords within the larynx make this possible
• Regulation of air flow by dilation and constriction

Respiratory Zone

• It comprises the site of gas exchange within the:
  • Respiratory zone
  • Respiratory Bronchioles
  • Alveolar Ducts
  • Alveoli

Alveoli Cells

• Alveoli are part of the respiratory zone
• Type I alveolar cells:
  • Compose alveolar epithelial walls
• Type II alveolar cells:
  • Secrete surfactant that contains antimicrobial proteins therefore help with protein and surfactant
• Macrophages:
  • Consume bacteria, dust and debris to clean up messes

Respiratory Zone - Diffusion Distance

• Pulmonary gas exchange occurs through diffusion across the 3 layers of respiratory membrane
  • Capillary endothelium/wall
  • Alveolar epithelium/wall (type I alveolar cells)
  • Fused basement membrane
• The thickness of the respiratory membrane determines the diffusion distance
• Diffusion distance establishes how far gases must travel to reach blood or aveoli

Diffusion Distance Importance

• Shorter diffusion distance results in faster diffusion
• Therefore, shorter is better

Lungs

• Lungs are located within the thoracic cavity
• The thoracic cavity includes:
  • Head
  • Diaphragm
  • Sternum
  • Ribs
  • Intercostal muscles
• Pleurae are double-layered serous (watery) membranes
• The structure is composed of:
  • Parietal lining, closest to the thoracic wall
  • Visceral lining around lungs
• Pleurae produce pleural fluid that fills the pleural cavity between them

Intrapulmonary Pressure

• Pulmonary and Pleural areas have Cavities
• Intrapulmonary pressure is pressure in alveoli
  • Also called the alveolar pressure
  • Pressure rises and falls with breathing
  • Always equalizes with atmospheric pressure eventually

Intrapleural Pressure

• Pulmonary and Pleural areas have Cavities
• Intrapleural pressure is pressure in the pleural cavity
  • Always 4mmHg less than intrapulmonary pressure, if equal, the lungs would collapse
• Several causes of intrapleural pressure:
  • Tendency of lung recoil
  • Surface tension of alveolar fluid
  • Opposed by chest wall elasticity

Ventilation

• Ventilation is the exchange of air between atmosphere and alveoli
• It depends on volume changes in the thoracic cavity
• Volume changes cause pressure changes and result in the flow of gases to equalize pressures

Ventilation Process

• During inspiration:
  • There is an increase in intrapulmonary volume
  • Which decreases intrapulmonary pressure
  • Gas flows into the lungs
• During expiration:
  • There is a decrease in intrapulmonary volume
  • Which increases intrapulmonary pressure
  • Gas flows out of the lungs
• Gas always flows from high to low pressure
• Atmospheric Pressure = 760 mm Hg