Respiratory Physiology Key Terms

The Respiratory System

• Introduction:

  • Major functions:
  • Ventilation (Breathing): Mechanical process moving air into/out of lungs.
  • Gas Exchange: Between blood/lungs (external respiration) and blood/tissues (internal respiration).
  • Oxygen Utilization: Cells use oxygen to generate ATP via cellular respiration.

• Gas Exchange Mechanism:

  • Lungs: Gas exchange occurs by diffusion:
  • Oxygen (O2): Higher concentration in lungs leading to diffusion into the blood.
  • Carbon Dioxide (CO2): Higher concentration in blood leads to diffusion out.

• Anatomical Divisions:

  • Conduction Zone: Delivers air to respiratory zone.
  • Respiratory Zone: Site for gas exchange.

Structure of the Respiratory System

• Alveoli:

  • Air sacs in lungs (~300 million) providing large surface area (~760 sq ft).
  • Facilitates diffusion due to thin walls (one cell layer thick, high tensile strength).

• Types of Alveolar Cells:

  • Type I Cells: Occupy ~95-97% of alveolar surface area for gas exchange.
  • Type II Cells: Secrete pulmonary surfactant, reabsorb sodium and water, help prevent fluid buildup.

• Airway Pathway:

  1. Nasal cavity
  2. Pharynx
  3. Larynx (through glottis and vocal cords)
  4. Trachea
  5. Primary bronchi (right and left)
  6. Secondary bronchi
  7. Tertiary bronchi
  8. Terminal bronchioles
  9. Respiratory zone (respiratory bronchioles → terminal alveolar sacs)

• Conducting Zone Functions:

  • Transports air to respiratory zone.
  • Produces sound (voice) in larynx as air passes over vocal folds.
  • Conditions inhaled air (warms, humidifies, filters).
  • Mucociliary Clearance: Mucus traps particles; cilia move mucus to pharynx for clearance.

Thoracic Cavity

• Contains:
  • Heart, trachea, esophagus, thymus in mediastinum.
  • Lungs fill remaining cavity.
  • Pleura:
  • Parietal Pleura: Lines thoracic wall.
  • Visceral Pleura: Covers lungs.
• Diaphragm: Dome-shaped skeletal muscle, separates thoracic & abdominal cavities.

Physical Aspects of Ventilation

• Ventilation Overview:

  1. Air moves from high to low pressure; pressure differences driven by lung volume changes.
  2. Key Properties:
  • Compliance (ease of lung expansion), elasticity (recoil capability), surface tension (fluid resistance in alveoli).

• Pressure Definitions:

  • Atmospheric pressure: Outside air pressure.
  • Intrapulmonary pressure: Air pressure within lungs.
  • Intrapleural pressure: Pressure within pleural space.

• Breathing Mechanics:

  • Inspiration:
  • Intrapulmonary pressure falls to lower than atmospheric pressure (e.g., -1 cmH2O).
  • Lungs expand, drawing air in.
  • Expiration:
  • Intrapulmonary pressure rises above atmospheric pressure (e.g., +1 cmH2O).
  • Lungs compress, pushing air out.

Mechanics of Breathing

• Muscles of Breathing:

  • Inspiratory Muscles:
  • Diaphragm: principal muscle, contracts during inhalation, relaxes during exhalation.
  • External intercostals: raise rib cage during inhalation.
  • Accessory muscles (scalenes, pectoralis minor, sternocleidomastoid) assist during forced inspiration.
  • Expiratory Muscles:
  • Internal intercostals and abdominal muscles assist during forced expiration.

• Overview of Mechanics:

  1. Inspiration:
  • Thoracic cavity volume increases.
  • Intrapulmonary pressure drops → air intake.
  1. Expiration:
  • Thoracic cavity volume decreases.
  • Intrapulmonary pressure rises → air expulsion.

Pulmonary Function Tests

• Spirometry: Measures air volume/frequency during breathing:
  • Lung Volumes:
  • Tidal Volume (TV): air exchanged in normal breathing.
  • Expiratory Reserve Volume (ERV): air exhaled after TV.
  • Inspiratory Reserve Volume (IRV): air inhaled after TV.
  • Residual Volume (RV): air remaining post-max expiration.
  • Lung Capacities:
  • Vital Capacity (VC): max exhaled after the max inhalation.
  • Total Lung Capacity (TLC): total gas in lungs post-max inhale.
  • Functional Residual Capacity (FRC): gas remaining in lungs after quiet exhalation.

Gas Exchange in the Lungs

• Gas Exchange Overview:

  • Conducted via diffusion in alveoli.
  • Key Principles:
  • Dalton’s Law (total pressure = sum of partial pressures).
  • Partial pressure calculations adjust for water vapor pressure in lung air.
  • Oxygen partial pressure calculated through % of O2 in air multiplied by total atmospheric pressure.

• Effects of High Altitude:

  • Reduced ambient oxygen alters gas exchange, resulting in adaptations (e.g., increased red blood cell production).

Acid-Base Balance of the Blood

• Homeostasis Overview:
  • Maintained primarily by lungs and kidneys.
  • Buffers in blood: Bicarbonate plays critical role in balancing pH.
  • Acidosis and Alkalosis:
  • Imbalance results from respiratory issues (hypoventilation → acidosis, hyperventilation → alkalosis) or metabolic disorders (excess acids or bicarbonate production).

Regulation of Breathing

• Involuntary Regulation:
  • Controlled by respiratory centers in medulla and pons.
  • Chemoreceptors: Monitor CO2 and O2 levels, influencing breathing rate and depth.

Pulmonary Disorders

• Common Disorders:
  • Asthma: Caused by inflammation/narrowing of airways.
  • COPD: Characterized by chronic obstruction, often due to smoking.
  • Emphysema: Destruction of alveoli reducing a surface area for gas exchange.
  • Pulmonary Fibrosis: Accumulation of fibrous tissue leading to reduced lung function.
• Acute Mountain Sickness: Results from rapid ascent to high altitudes, leading to headaches, tightness in chest, etc.