Respiratory System

• General functions of the respiratory system

  • Air passageway
  • Site for O2 & CO2 exchange
  • O2 - alveoli to blood
  • CO2 - blood to alveoli
  • Detects odors (olfactory receptors in superior nasal cavity)
  • Sound production
• Sound production

  1. Air moves across vocal cords of larynx

  2. Vocal cords vibrate, making sound
• Structural organization of the respiratory system

  • Upper respiratory tract: Nose, nasal cavity, pharynx
  • Lower respiratory tract: Larynx, trachea, bronchi, bronchioles, alveolar ducts, alveoli
• Functional organization of the respiratory system

  • Respiratory Zone: Site of gas exchange, has respiratory bronchioles, alveolar ducts, & alveoli
  • Conduction Zone: Everything else (nose to terminal bronchioles)
• General anatomy of the respiratory system

  • Upper respiratory tract: Nose, nasal cavity, pharynx
  • Lower respiratory tract: Larynx, trachea, bronchus, bronchiole, terminal bronchiole, respiratory bronchiole, alveolar duct, alveoli
• Functions of the conducting zone

  • Transport air to respiratory zone
  • Voice production in larynx as air passes cords
  • Warms, humidifies, filters, cleans air
  • Mucus secreted to trap small particles
  • Mucociliary escalator & clearance
• Progressively thinner epithelium of respiratory mucosa

  • Pseudostratified ciliated columnar - lines nasal cavity, paranasal sinuses, nasopharynx, trachea, inferior portion of larynx, main bronchi, lobar bronchi
  • Simple ciliated columnar - lines segmental bronchi, smaller bronchi, large bronchioles
  • Simple ciliated cuboidal - lines terminal & respiratory bronchioles (progressive loss of cilia = observed)
  • Simple squamous - forms alveolar ducts & alveoli
• Respiratory mucosa has no cilia, is linear, flat, and thin for easy exchange
• Mucous secretions of respiratory mucosa

  • Produced from secretions of goblet cells of epithelial lining
  • Mucous & serous glands of the lamina propria
  • Contains mucin protein
  • Increases mucus viscosity therefore traps dust, dirt, pollen, etc.
  • Contains defenses against microbes: Lysozyme (antibacterial enzyme), Defensins (antibacterial proteins), IgA (antibody)
  • Sputum when coughed up with saliva & trapped substances
• Respiratory system muscles


  • Diaphragm
  • Internal intercostal muscles
  • External intercostal muscles
• Respiration


  Obtain O2 for use by body's cells & eliminate CO2 that body produces
• Processes of respiration


  • Internal Respiration
  • External Respiration
• Functions of the nose

  • Provide airway for respiration
  • Moisten & warm entering air
  • Filter air & clean of foreign matter
  • Glands secrete mucus containing lysozyme & defensins to help destroy bacteria
  • Ciliated mucosal cells remove contaminated mucus
  • Resonating chamber for speech
  • Houses olfactory receptors
• Regions of the pharynx


  • Nasopharynx: closes during swallowing to prevent food from entering nasal cavity
  • Oropharynx: common passage for food & air
  • Laryngopharynx: (hypopharynx) point where pharynx divides anteriorly into larynx & posteriorly to esophagus
• The nasopharynx prevents food from entering the nasal cavity
• Paranasal sinuses are lined by pseudostratified ciliated columnar epithelium, and mucus is swept into the pharynx and swallowed
• Functions of the larynx

  • Provide patent airway
  • Act as switching mechanism to route air & food to proper channels
  • Function in voice production
• Vocal production

  • Speech - intermittent release of expired air while opening & closing glottis
  • Pitch - determined by length + tension of vocal cords
  • Loudness - depends on force which air rushes across vocal cords
  • Sound - "shaped" into language by action of pharynx, tongue, soft palate, lips
• Layers of the trachea

  • Mucosa - goblet cells & ciliated epithelium
  • Submucosa - connective tissue
  • Adventitia - outermost, made of C-shaped rings of hyaline cartilage
• Rings of cartilage prevent the trachea from collapsing
• Differences between trachea/larger bronchi and bronchioles

  • Trachea & larger bronchi: Fairly rigid, non muscular tubes, rings of cartilage prevent collapse

  Bronchioles: No cartilage, walls have smooth muscle innervated by ANS, sensitive to certain hormones & local chemicals
• Components of the respiratory zone

  • Respiratory bronchioles subdivide to alveolar ducts -> to alveolar sacs

  ~300 million alveoli, accounts for most of lungs volume, provides increased surface area for gas exchange
• Composition of the respiratory membrane

  • Air-blood barrier composed of: Alveolar & capillary walls, Fused basal laminas

  Alveolar walls: Single layer of type 1 alveolar epithelial cells, permit gas exchange by simple diffusion

  Type 1 cells secrete angiotensin converting enzyme (ACE)

  Type 2 alveolar epithelial cells secrete pulmonary surfactant, reabsorb Na+ & H2O to prevent fluid buildup
• Alveoli are surrounded by fine elastic fibers & capillaries, have open pores that connect adjacent alveoli (collateral ventilation) and allow air pressure throughout lung to be equalized, and house macrophages that keep alveolar surfaces sterile
• Contents of the thoracic cavity

  • Heart, trachea, esophagus, thymus within mediastinum

  Lungs fill rest of cavity
• Components of the outer chest wall (thorax)

  • 12 pairs of ribs that join sternum anteriorly + thoracic vertebrae posteriorly
• Components of the pleural sac

  • Parietal pleura lines thoracic wall

  Visceral pleura covers lungs (protects)
• The visceral pleura covers the lungs
• Each lung is divided into several lobes, and the tissue contains highly branched airways, alveoli, pulmonary blood vessels, and large quantities of elastic connective tissue
• Diaphragm


  Dome-shaped sheet of skeletal muscle that separates the thoracic cavity from the abdominal cavity
• Blood supply to the lungs

  • Pulmonary arteries - supply systemic venous blood to be oxygenated

  Pulmonary veins - carry oxygenated blood from respiratory zones to heart
• Phases of breathing (pulmonary ventilation)

  • Inspiration - air to lungs

  Expiration - gas leaves lungs
• Pressure considerations in respiratory mechanics

  • Atmospheric (barometric) pressure (ATMp)

  Intra-alveolar pressure (intrapulmonary pressure; IPp)

  Intrapleural pressure (thoracic pressure)
• IPp + intrapleural pressure fluctuate with phases of breathing, IPp always eventually equalizes with ATMp, and intrapleural pressure is always less than IPp and ATMp
• Two forces promote lung collapse: Elasticity of lungs causes them to assume smallest possible size, and surface tension of alveolar fluid draws alveoli to smallest possible size
• Boyle's Law


  Pressure exerted by a gas varies inversely with volume (P1V1 = P2V2)
• Normal atmospheric pressure = 760 mmHg, low pressure causes air to go in to equalize, high pressure causes air to leave
• Respiratory muscles


  • Diaphragm (major inspiratory muscle)

  External intercostal muscles (major expiratory muscles)

  Internal intercostal muscles (major expiratory muscles)

  Abdominal muscles (accessory muscles of expiration)

  Accessory muscles of inspiration (contract only during forceful inspiration)

  Muscles of active expiration (contract only during active expiration)

  Major muscles of inspiration (contract every inspiration; relaxation causes passive expiration)
• Respiratory muscle activity during inspiration


  Contraction of diaphragm > thoracic cavity enlarges > intrapleural pressure decreases > lungs draw into the area of lower pressure > lungs expand…intra-alveolar pressure decreases below atmospheric pressure > inspiration
• Respiratory muscle activity during expiration

  Relaxation of diaphragm & muscles of chest wall > intrapleural pressure increases > intra-alveolar pressure increases…greater than atmospheric pressure > expiration

  Forced expiration occurs by contraction of expiratory muscles: Abdominal wall muscles, Internal intercostal muscles