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Respiratory System Notes

Respiratory System

Overview

  • Functions of the respiratory system.
  • Distinction between the upper and lower respiratory tracts.
  • Difference between conducting and respiratory functions.

Anatomy of the Respiratory Tract

Upper Respiratory Tract

  • Sphenoidal sinus
  • Frontal sinus
  • Nasal cavity: moistens and warms air, provides an airway, filters air, contains olfactory receptors; size variation due to cartilages.
  • Pharynx: Passageway for air and food.
    • Regions:
      • Nasopharynx: Passageway for air only, lined with pseudostratified ciliated columnar epithelium (respiratory mucosa).
      • Oropharynx: Passageway for both air and food, lined with stratified squamous epithelium.
      • Laryngopharynx
    • Structures:
      • Nasal conchae (superior, middle, and inferior)
      • Nasal meatuses (superior, middle, and inferior)
      • Nasal vestibule
      • Nostril
      • Hard palate
      • Soft palate
      • Tongue
      • Hyoid bone
      • Cribriform plate of ethmoid bone
      • Sphenoidal sinus
      • Posterior nasal aperture
      • Pharyngeal tonsil
      • Opening of pharyngotympanic tube
      • Uvula
      • Palatine tonsil
      • Lingual tonsil
      • Esophagus
  • Larynx: conducts air, prevents food entry, produces sound, involved in Valsalva maneuver and reflexes.
    • Epiglottis
    • Thyroid cartilage
    • Vocal fold (vocal cords): Create sound when air is expelled across adducted folds.
    • Cricoid cartilage

Lower Respiratory Tract

  • Trachea
    • Cartilage rings: Significance of cartilage rings in the trachea.
    • Layers:
      • Mucous membrane: Pseudostratified ciliated columnar epithelium.
      • Submucosa: Seromucous glands.
      • Adventitia: Hyaline cartilage.
      • Trachealis muscle.
  • Bronchi
    • Right main (primary) bronchus.
    • Left main (primary) bronchus.
    • Bronchial tree:
      • Primary (main) bronchus
      • Secondary (lobar) bronchus
      • Tertiary (segmental) bronchus
      • Bronchiole
      • Terminal bronchiole
      • Respiratory bronchiole
      • Alveolar duct
      • Alveolar sac
      • Alveolus
  • Lungs
    • Right lung: three lobes (superior, middle, inferior), horizontal fissure, oblique fissure.
    • Left lung: two lobes (superior, inferior), oblique fissure.
    • Apex of lung.
    • Base of lung.
    • Root of lung.
  • Pleura
    • Parietal pleura.
    • Visceral pleura.
    • Pleural cavity: Pressure gradient created by cohesiveness of pleurae with chest wall.
    • Mediastinum:
  • Diaphragm

Respiratory Zone

  • Respiratory bronchioles.
  • Alveolar ducts.
  • Alveolar sacs.
  • Alveoli (singular: alveolus).
  • Structures: smooth muscle, elastic fibers, capillaries.

Respiratory Membrane

  • Where respiratory gases cross.
  • Components:
    • Alveolar epithelium (squamous epithelial cell).
    • Fused basement membranes.
    • Capillary endothelium.
  • Alveolar pores.
  • Macrophage.
  • Surfactant-secreting cell.

Respiration Processes

Four processes in respiration:

  • Pulmonary ventilation: Air movement in and out of lungs.
    • Inspiration (inhalation).
    • Expiration (exhalation).
  • External respiration: Gas exchange between blood and air at lung alveoli.
  • Transport of respiratory gases: Blood transports gases from lungs to body cells.
  • Internal respiration: Gas exchange between capillaries and body tissues.
  • Oxygen used in mitochondria for ATP synthesis.

Ventilation

Muscles Involved

  • Inhalation: Diaphragm and external intercostals contract; an active process. Ribs are elevated and sternum flares.
  • Exhalation: Diaphragm and external intercostals relax; chiefly a passive process. Ribs and sternum are depressed.

Volume and Pressure Changes

  • Inhalation: Intrapulmonary volume increases, pressure decreases; pressure is less than atmospheric pressure; air enters the lungs until intrapulmonary pressure equals atmospheric pressure.
  • Exhalation: Intrapulmonary volume decreases, pressure increases; pressure is greater than atmospheric pressure; air exits the lungs.

Respiratory Volumes and Capacities

  • Tidal Volume (TV): Normal breathing, approximately 500mL.
  • Inspiratory Reserve Volume: Amount of air forcibly taken in above TV.
  • Expiratory Reserve Volume: Amount of air forcibly exhaled.
  • Vital Capacity (VC): Amount of exchangeable air, approximately 4800 mL.
  • Forced inhalation and exhalation require different muscles.

Gas Exchange

External Respiration (Pulmonary Gas Exchange)

  • Gas exchange between alveoli and blood.
  • Gases follow concentration gradients.
  • O2 enters blood (oxygen loading).
  • CO2 exits blood (carbon dioxide unloading).

Gas Transport in Blood

  • Oxygen binds to hemoglobin forming oxyhemoglobin.
  • Carbon dioxide is transported as a bicarbonate ion (HCO_3).
  • Forms carbonic acid, which dissociates into CO2 and H2O.
  • CO_2 diffuses from blood into alveoli.

Internal Respiration (Systemic Capillary Gas Exchange)

  • Gas exchange between blood and tissue cells.
  • Gases follow concentration gradients.
  • O_2 exits blood (oxygen unloading).
  • CO_2 enters blood (carbon dioxide loading).

Gas Transport in Blood

  • O_2 is released from hemoglobin (Hb).
  • Diffuses out of blood into tissue cells.
  • CO2 binds with H2O to form carbonic acid.
  • Carbonic acid releases bicarbonate ions.

Control of Respiration

  • Breathing control centers in pons and medulla are stimulated by:
    • CO_2 and H^+ increase in tissue.
    • Nerve impulse from O2 sensor indicating O2 decrease.
  • Efferent nerve impulses from medulla trigger contraction of inspiratory muscles (phrenic nerves, intercostal nerves).
    • Intercostal muscles.
    • Diaphragm.

Clinical Conditions

  • Atelectasis: Collapsed lung caused by air entry into the pleural space.
  • Pneumothorax: Air in the intrapleural space disrupts fluid bond between pleurae.

Review Questions

  • When you EXHALE, air flows through respiratory structures in which sequence? (alveolus, bronchiole, bronchus, trachea, larynx, pharynx, nasal cavity).
  • When you inhale, the diaphragm: Contracts and moves inferiorly.
  • During external respiration, oxygen binds to hemoglobin to form oxyhemoglobin.
  • Which statement about the laryngopharynx, nasopharynx, and oropharynx is TRUE? The oropharynx lies in between the nasopharynx and laryngophanyx.
  • What structures does oxygen travel through to reach the lungs? Nose.