Respiration and Respiratory Diaphragm

October 20, 2012 | By | Reply More

Respiration and Respiratory Diaphragm


  • Serous fluid adhesion between visceral and parietal pleura links volume of lungs with movements of diaphragm and thoracic wall and facilitates respiration
  1. Inspiration increases volume of thoracic cavity and lungs to create a negative intrathoracic pressurethat draws air into lungs
    1. Quiet inspiration
      • Involves contraction of diaphragm, pulling it downward to increase vertical dimensionof thorax
        The diaphragm is the primary muscle of inspiration.
    2. Forced inspiration
      • (1) External intercostal muscles contract, elevating ribs and carrying sternum upward and forward, and increase anteroposterior and lateral diameters of thorax
      • (2) Recruits accessory muscles of respirationto assist elevating ribs, further increasing depth of inspiration
        Patient with dyspnea may lean on upper extremities to allow accessory muscles to aid in respiration.


  2. Expiration decreases volume of thorax and lungs to create a positive intrathoracic pressurethat forces air from lungs
    1. Quiet expiration is passive process largely caused by elastic recoil of lungs and relaxation of diaphragm
    2. Forced expiration is active process involving contraction of anterior abdominal wall muscles, which depress ribs and sternum and increase intraabdominal pressure, and internal intercostal muscles
  3. Accessory muscles of respiration
    • Include head and neck muscles and upper limb muscles attached to rib cage or sternum


Respiratory Diaphragm


Category: Physiology

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