Integrative Physiology - Respiratory System

Components of the Respiratory System

  • Major Sections
    • Ventilation: The process of breathing, involving the flow of air into and out of the lungs.
    • Lung Volumes and Capacities: Measurements used to assess lung function and health.
    • Exchange of Oxygen and Carbon Dioxide: The process of gas exchange in the lungs and tissues.
    • Transport of Oxygen and Carbon Dioxide: The movement of gases through the blood.
    • Control of Ventilation: Regulation of breathing patterns and respiratory rates.
    • Exercise and the Respiratory System: How the respiratory system adapts during physical activity.

Ventilation

  • Guiding Principles
    • The primary function of the lungs is to facilitate the transport of air through the process described as "bulk flow".
    • Pressure Gradiation: Air flows from areas of higher pressure to lower pressure. This is primarily created by a muscular pump that changes lung volume.
    • Resistance to Flow: Influenced by the diameter of the airways and differences between gases, with air being compressible whereas blood is not.

Phases of Respiration

  1. Ventilation: Movement of air in and out of the lungs.
  2. Pulmonary Gas Exchange: Gases are exchanged in the alveoli of the lungs, converting deoxygenated blood to oxygenated blood.
  3. Transport of Gases Through Blood: Hemoglobin in red blood cells transports gases between lungs and tissues.
  4. Systemic Gas Exchange: Exchange of gases between blood and tissues in body systems.
  5. Cellular Respiration: Cells utilize oxygen for metabolism and produce carbon dioxide as a waste product.

Respiratory Epithelium

  • Nature and Function:
    • The respiratory tract is lined with respiratory epithelium that serves to trap dust and debris.
    • Cilia: Short, hair-like projections that help move mucus out of the respiratory tract.
    • Mucus: Traps particles and acts as a lubricant in the airways.
    • Mucociliary Escalator: The coordinated movement of cilia transporting mucus upward to eliminate trapped materials.

Anatomy of the Respiratory System

  • Air Flow Path:
    • Nose: Air enters through the nostrils and is filtered by nasal conchae.
    • Pharynx: A shared pathway for air and food.
    • Larynx: Routes air into the trachea and contains vocal cords.
    • Trachea: Conducts air into the primary bronchi leading to the lungs.

Zones of the Respiratory System

  • Conducting Zone: Prepares and filters air (includes trachea, bronchi, and bronchioles).
  • Respiratory Zone: Where gas exchange occurs, primarily in the alveoli.

Lung Anatomy

  • Lungs:
    • Shape: Paired, cone-shaped organs located in the thoracic cavity, covered by a pleura (double-layered membrane).
    • Alveoli: Small air sacs at the end of bronchioles where gas exchange occurs. Consists of:
    • Type I Alveolar Cells: Main site for gas exchange.
    • Type II Alveolar Cells: Secrete surfactant to reduce surface tension in the alveoli.
    • Blood Supply: Lungs receive a significant blood flow, with low blood pressure (around 25/8 mmHg) allowing for optimal gas exchange.

Lung Volumes and Capacities

  • Measuring Techniques:
    • Measured using a spirogram, lung volumes and capacities are helpful in assessing lung function.
  • Types of Lung Volumes:
    • Tidal Volume (TV): The amount of air exchanged during a normal breath (about 500 mL).
    • Inspiratory Reserve Volume (IRV): Maximum volume of air that can be inhaled in addition to tidal volume (around 3100 mL).
    • Expiratory Reserve Volume (ERV): Maximum volume of air that can be exhaled beyond tidal volume (around 1200 mL).
    • Residual Volume (RV): Air remaining in the lungs after maximal exhalation (around 1200 mL).
  • Lung Capacities:
    • Vital Capacity (VC): Maximum amount of air that can be exhaled after maximal inhalation (TV + IRV + ERV; approximately 4800 mL).
    • Total Lung Capacity (TLC): The total volume of air that the lungs can hold (typically around 6000 mL).

Pulmonary Gas Exchange

  • Mechanism: Gaseous exchange occurs through passive diffusion and is described by:
    • Fick’s Law of diffusion.
  • Dalton’s Law: Each gas in a gas mixture exerts its own pressure, known as the partial pressure.
  • Henry’s Law: The quantity of gas that dissolves in a liquid is proportional to the partial pressure of the gas and its solubility in the liquid (e.g., carbon dioxide is 20x more soluble than oxygen).

Transport of Gases

  • Oxygen Transport:
    • 1.5% dissolved in plasma, 98.5% carried by hemoglobin in red blood cells.
  • Carbon Dioxide Transport:
    • 7% dissolved in plasma.
    • 23% as carbamino compounds (bound to hemoglobin).
    • 70% as bicarbonate ions in plasma.

Control of Ventilation

  • Respiratory Centers: Cluster of neurons in the medulla and pons regulating breathing.
  • Components:
    • Medullary Respiratory Center: Includes the Pre-Bötzinger complex, regulating rhythmic breathing.
    • Pontine Respiratory Center: Coordinates smooth breathing transitions.
  • Regulatory Influences: Breathing is influenced by:
    • Cortical influences (conscious control).
    • Modifications from chemoreceptors monitoring blood gas levels.
    • Feedback from proprioceptors and the inflation reflex.

Exercise and the Respiratory System

  • The respiratory system undergoes significant changes in response to physical activity:
    • Increased blood flow to the lungs and improved alveolar ventilation to enhance oxygen diffusion capacity, which can increase up to threefold during intense exercise.

Summary

  • The respiratory system is crucial for gas exchange, gas transport, and regulation of pH in the body via breathing control. Understanding the structures and processes involved in respiration is essential for comprehending overall physiology and the impact of exercise on respiratory efficiency.