Respiratory System

• Functions of the Respiratory System

  • Gas Exchange
  • Communication
  • Olfaction
  • Acid base balance
  • Blood pressure regulation
  • Blood & lymph flow
  • Blood filtration
  • Expulsion of abdominal contents
• Principal organs of the Respiratory System

  • nose
  • pharynx
  • larynx
  • trachea
  • bronchi
  • lungs
• Divisions of the Respiratory System

  • Conducting division
  • Respiratory division
• Conducting division

  • Includes those passages that serve only for airflow
  • No gas exchange
  • Nostrils through major bronchioles
• Respiratory division


  • Alveoli & other gas exchange regions
• Regions of the Upper Respiratory Tract

  • nose
  • mouth
  • sinuses
  • pharynx
  • larynx
• Regions of the Lower Respiratory Tract

  • trachea
  • lungs
• Nose

  • Warms, cleanses, humidifies inhaled air
  • Detects odor
  • Resonating chamber that amplifies voice
• Nose


  • Extends from nostrils (external nares) to posterior nasal apertures (internal nares)
  • Vestibule
  • Nasal conchae (turbinates)
  • Olfactory epithelium
  • Respiratory epithelium
  • Nasolacrimal ducts
• Regions of the Pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Nasopharynx


  • Internal nares to soft palate (prevents food from entering nasal cavity during swallowing) & uvula
  • Continuous with auditory (Eustachian) tubes
  • Contains the pharyngeal tonsil (adenoids)
  • Lined with respiratory epithelium
• Oropharynx


  • Space between soft palate + uvula & epiglottis
  • Contains palatine tonsils
  • Lined with stratified squamous epithelium
  • Portion of the digestive tract that receives food directly from the oral cavity
• Laryngopharynx


  • Epiglottis to cricoid cartilage
  • Ends with split between esophagus & trachea
  • Lined with stratified squamous epithelium
• Larynx

  • Cartilaginous chamber about 1.5 inches long
  • Functions: airway protection & sound production
• Larynx


  • Epiglottis
  • Thyroid cartilage
  • Cricoid cartilage
  • Arythenoid cartilages
  • Corniculate cartilage
  • Cuneiform cartilage
  • Vestibular folds (false vocal cords/folds)
  • Vocal cords (true vocal cords/folds)
  • Glottis
• Trachea


  • A rigid tube about 4.5 inches & 1 inch in diameter (largest in diameter compared to bronchus)
  • Anterior to esophagus
  • Supported by rings of hyaline cartilage
  • Trachealis muscle
• Tracheal Wall Layers

  • Inner lining is ciliated pseudostratified columnar epithelium
  • Middle tracheal layer is CT that contains lymphatic nodules, mucous + serous glands, tracheal cartilages
  • Adventitia: outermost layer of trachea
• Right & left main (primary) bronchi

  • Trachea forks at level of sternal angle
  • Carina: internal medial ridge in the lowermost tracheal cartilage
• Lung Anatomy

  • Base
  • Apex
  • Costal surface
  • Mediastinal surface
  • Hilum
• Differences between Right & Left Lungs

  • Right lung is shorter, more vertical, has 3 lobes
  • Left lung is taller, narrower, has 2 lobes
• Structures air passes through during inhalation

  • Terminal bronchiole
  • Respiratory bronchiole
  • Alveolar ducts
  • Alveolus
• Components of the Bronchial Tree

  • Main bronchi
  • Lobar (secondary) bronchi
  • Segmental (tertiary) bronchi
  • Bronchioles
  • Terminal bronchioles
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveolar sacs
• Bronchi

  • Lined with ciliated pseudostratified columnar epithelium
  • Cells grow shorter & epithelium thins distally
  • Lamina propria has an abundance of mucous glands & lymphocyte nodules (MALT)
  • Large amount of elastic CT
• Bronchioles

  • Ciliated cuboidal epithelium
  • Well-developed layer of smooth muscle
  • No mucous glands or goblet cells
  • Cilia that move mucus away & out
• Respiratory bronchioles


  • Beginning of the respiratory division
  • Divide into alveolar ducts with alveoli (air sacs) budding from the walls
  • Ends in alveolar sacs: cluster of alveoli arrayed around a central space
• Cells of the Alveolus

  • Squamous (type I) alveolar cells
  • Great (type II) alveolar cells
  • Alveolar macrophages (dust cells)
• Respiratory membrane

  Thin barrier between the alveolar air & blood, consisting of squamous alveolar cells, endothelial cells of blood capillary, and their shared basement membrane
• The Pleurae

  • Visceral pleura: serous membrane that covers lung surface
  • Parietal pleura: adheres to mediastinum, inner surface of the rib cage, and superior surface of the diaphragm
  • Pleural cavity: potential space between pleurae
• Functions of pleurae & pleural fluid

  • Reduce friction
  • Maintain intrapleural pressure, lower than atmospheric pressure
  • Compartmentalization
• Types of Pulmonary Ventilation

  • Quiet respiration
  • Forced respiration
• Quiet respiration

  Effortless, automatic, occurs when the diaphragm and external intercostal muscles relax
• Forced respiration

  Unusually deep breathing, such as during exercise or blowing up a balloon, uses accessory muscles
• Respiratory muscles


  • Diaphragm
  • Internal & external intercostal muscles
• Diaphragm

  • Prime mover of respiration, accounts for ⅔ airflow
  • Contraction flattens diaphragm → lungs expand & thoracic cavity volume increases → air is sucked into lungs
  • Relaxation allows diaphragm to bulge upward again → compresses lungs & thoracic cavity volume decreases → air is pushed out of the lungs
• External intercostals

  Primarily contribute to enlargement & contraction of thoracic cage
• Internal intercostals

  Play biggest role in forced respiration
• Accessory muscles


  Lumbar, abdominal, pelvic muscles
• Increased abdominal pressure


  1. Pushes viscera up against diaphragm

  2. Increases thoracic pressure
• Flow of air in & out lung

  Depends on a pressure difference (gradient) between air in lungs & outside body
• Respiratory muscles


  • Change lung volumes
  • Create differences in pressure relative to the atmosphere