- I. RESPIRATORY
- A. Why a respiratory
- Respiratory function: Gas transport for
- Non-Respiratory function: Filtering and
- B. Gas transport: Oxygen in and
Carbon Dioxide out
- Ventilation: (atmosphere <-> respiratory
- Lung diffusion: (respiratory zone <->
- Circulation: (blood flow carries
erthyrocyte/plasma <-> tissue)
- Tissue diffusion: (erythrocyte/plasma
<-> tissue cells)
- Internal respiration: (cellular metabolism
using O2 & producing CO2)
- II. VENTILATION: Structure and
- A. Gas
- Upper respiratory tract: Gas humidification,
filtration, and warming
- Conducting airways: Gas distribution to
- Trachea: Cartilage rings
- Bronchi: Cartilage plates
- Bronchioles: No cartilage -> depend upon
- Total cross-sectional area of conducting
airways INCREASES as we move from
the trachea to the respiratory zone.
- VELOCITY (cm/sec) =
FLOW (cm3/sec) / CROSS-SECTION
AREA(cm2). Therefore in the periphery of the lung near the
respiratory zone gas velocity drops to zero and there is no
CONVECTIVE movement of gas. Movement of gas in the respiratory
zone is by DIFFUSION alone.
- Terminal bronchioles of conducting airways
have ciliated and goblet cells to help clear particulate
- Respiratory bronchioles mark the beginning of
the respiratory zone and have alveoli in their walls.
- B. Negative Pressure
- Pump Structure:
- Rib cage and spine
- Intercostal muscles
- Respiratory control is a complex, integrated
phenomenon with voluntary and involuntary controls.
- III. DIFFUSION: Structure and
- A. Diffusion: Basic
- Gas diffusion is Passive from high
partial pressure to low partial pressure.
- Alveolar O2 > Pulmonary
capillary O2: O2 diffuses to
- Pulmonary capillary CO2 >
Alveolar CO2: CO2 diffuses to alveolar
- B. The respiratory zone:
- Respiratory bronchioles, alveolar ducts and
- The zone is designed to maximize efficient gas
exchange by diffusion:
- Large surface area: 70 m2 (300
- Large volume of gas to maintain diffusion
pressure gradient (150ml in conduction zone vs 4,000 ml in
- Very thin membrane (0.5 micron)
- Alveolar blood-gas barrier:
- Respiratory epithelium
- Interstitial space
- Capillary endothelium
- C. Pulmonary blood flow:
- All of cardiac output (+/-5%) passes through
the respiratory zone.
- . Pulmonary arteries carry blood from the
right heart (de-oxygenated).
- Pulmonary arteries distribute blood to the
pulmonary capillary system to maximize erythrocyte exposure to
alveolar gas tensions.
- The churning/pumping action of the heart aids
in gas diffusion in the respiratory zone.
- The bronchial vessels arise from the aorta and
carry nutrient blood to the airways.
- Thus the lung is efficiently designed to
conduct and distribute gas to a very large, thin diffusion
membrane with good blood supply.
- IV. NON-RESPIRATORY FUNCTION OF THE
- A. Basic concepts:
- The lung performs other functions than gas
- Maintenance and defense
- Chemical processing
- Maintenance and defense:
- Protein and connective tissue
- Surfactant synthesis
- Mucociliary clearance
- Immune function
- The lung is ideally designed to filter the
bloodstream of particulate matter (clots, bacteria, etc.) before
passing that blood on to the body.