Overview of the Respiratory System

Apr 30, 2025

Lecture Notes: The Respiratory System and Gas Exchange

Key Functions of the Lungs

  • Main Function: Gas exchange, involving the intake of oxygen and expulsion of carbon dioxide.
  • Inhalation: Diaphragm and chest muscles contract, creating a vacuum to draw air in.
  • Exhalation: Muscles relax, allowing lungs to return to normal size and expel air.

Air Pathway in the Respiratory System

Nasal Cavity and Sinuses

  • Mucus: Secreted by nasal cavity cells, contains enzymes called lysozymes to kill bacteria.
  • Nasal Hairs: Trap dust, pollen, and bacteria, forming clumps known as boogers.
  • Paranasal Sinuses: Frontal, ethmoid, sphenoid, and maxillary sinuses warm and moisten air and amplify voice.

Throat and Voice Box

  • Pharynx: Connects nasal and oral cavities.
    • Nasopharynx: Connects to nasal cavity.
    • Oropharynx: Connects to oral cavity.
  • Uvula and Soft Palate: Prevent food from entering nasopharynx during swallowing.
  • Laryngopharynx: Continuous with the larynx or voice box.

Airway Protection

  • Epiglottis: Flap that seals airway during swallowing to direct food into the esophagus.
  • Cough Reflex: Expels non-air particles from the larynx.

Lower Respiratory Tract

Trachea and Bronchi

  • Trachea: Windpipe, splits into two main bronchi at the carina.
  • Bronchi: Two main branches, right and left.
    • Right Lung: Three lobes (upper, middle, lower).
    • Left Lung: Two lobes (upper and lower).
    • Right Mainstem Bronchus: Wider and more vertical, prone to obstruction.

Smaller Airways

  • Bronchioles: Smaller branches of bronchi without cartilage, lead to conducting bronchioles and eventually respiratory bronchioles.
  • Conducting Bronchioles: Conduct air, lined with ciliated cells and goblet cells.
  • Terminal Bronchioles: Lead to respiratory bronchioles.

Alveoli and Gas Exchange

  • Alveoli: Tiny air sacs where gas exchange occurs, around 500 million per lung.
  • Type I Pneumocytes: Thin epithelial cells in alveoli for gas exchange.
  • Type II Pneumocytes: Secrete surfactant to reduce surface tension in alveoli; can transform into Type I to repair damage.
  • Alveolar Macrophages: Remove particles from alveoli, use mucociliary escalator.

Blood-Gas Barrier

  • Structure: Consists of alveolar wall, basement membrane, and capillary wall.
  • Function: Facilitates diffusion of carbon dioxide out and oxygen in.
  • Blood Flow: Deoxygenated blood from pulmonary arteries, oxygenated blood to pulmonary veins and body tissues.

Summary

  • The respiratory system ensures oxygen reaches the body's tissues and carbon dioxide is expelled.
  • Air travels through the pharynx, larynx, trachea, bronchi, and into the alveoli where gas exchange occurs.
  • Carbon dioxide follows the reverse path to be exhaled.

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These notes provide a comprehensive overview of the respiratory system's structure and function, focusing on the pathway of air and the process of gas exchange.

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