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.