Human Structure and Function Week 4

Functions of the Respiratory System

• Respiration includes ventilation (air movement), external respiration (gas exchange in lungs), transport of respiratory gases, and internal respiration (gas exchange between blood and tissues).
• Plays a role in blood pH regulation.
• Facilitates voice production.
• Responsible for the sense of smell (olfaction).
• Provides protection against pathogens and foreign particles.

Divisions of the Respiratory System

• Structural Classification:
  • Upper respiratory tract: nose, nasal cavity, pharynx.
  • Lower respiratory tract: larynx, bronchi, bronchioles, alveoli.
• Functional Classification:
  • Conducting zone: passage for air movement.
  • Respiratory zone: site of gas exchange within the lungs.

Anatomy of the Nose

• External Nose and Nasal Cavity:

  • Nasal cavity extends from nostrils (nares) to choanae.
  • Vestibule: entryway lined by stratified squamous epithelium with glands and hair follicles.
  • Hard palate forms the floor of the nasal cavity.
  • Nasal septum divides cavity into left and right portions.

• Nasal Conchae:

  • Bony "ridges" (superior, middle, inferior) create superior, middle, and inferior meatus.
  • Lined by pseudostratified ciliated columnar epithelium for function.

• Functions of Nasal Cavity:

  • Air passage and cleaning via mucous and cilia.
  • Humidifies and warms air with moisture and blood.
  • Supports olfaction and contributes to voice resonance.

Pharynx Structure

• Regions of the Pharynx:
  • Nasopharynx: posterior to nasal cavity, has Eustachian tube openings, and pharyngeal tonsils.
  • Oropharynx: posterior to oral cavity, contains palatine and lingual tonsils.
  • Laryngopharynx: posterior to the epiglottis.

Larynx

• Known as the voice box, composed of 9 cartilages (6 paired and 3 unpaired).
• Functions: facilitates air passage, directs food away from respiratory tract, enables sound production, traps debris to protect lungs.

Trachea and Bronchial Tree

• Descends from larynx, supported by 15-20 C-shaped cartilage rings.
• Tracheal lumen lined with pseudostratified ciliated columnar epithelium with goblet cells.
• As bronchi divide, smooth muscle increases while cartilage decreases. Epithelium changes from pseudostratified to simple ciliated types.

Alveoli and Lungs

• Cone-shaped lungs: left lung has 2 lobes (with cardiac notch), right lung has 3 lobes.
• Lobes separated by fissures; hilum serves as entry for blood vessels, lymphatics, and bronchi.

Gas Exchange Mechanism

• Involves respiratory membrane between alveoli and capillaries.
• Factors affecting gas exchange: membrane thickness, surface area, diffusion coefficient, and partial pressure differences.

Gas Transport

• Oxygen Transport: Mostly via red blood cells (98.5% bound to hemoglobin); additional 1.5% dissolved in plasma.
• Carbon Dioxide Transport: 70% as bicarbonate (HCO3-), 23% bound to hemoglobin, 7% dissolved in plasma.

Ventilation Mechanics

• Pulmonary Ventilation: Air movement driven by diaphragm, rib cage, sternum, and intercostal muscles.
• Inspiration increases lung volume; expiration decreases it.
• Boyle's Law states that volume is inversely proportional to pressure.

Alveolar Pressure Dynamics

• Barometric pressure (PB) typically equals 760 mm Hg.
• Intra-alveolar pressure (Palv) varies during breathing:
  • During inspiration, PB > Palv (air flows into lungs).
  • During expiration, Palv > PB (air flows out).

Respiratory Volumes and Capacities

• Pulmonary Volumes:

  • Tidal volume: air volume with each breath.
  • Inspiratory and expiratory reserve volumes for additional air capacity.
  • Residual volume is air remaining post-forced expiration.

• Pulmonary Capacities:

  • Sum of two or more volumes: inspiratory capacity, functional residual capacity, vital capacity, total lung capacity.

Measurements of Lung Function

• Utilized to diagnose lung diseases; includes static and dynamic measurements.
• Dynamic Lung Function Parameters:
  • Forced vital capacity (FVC): maximal air expelled after deep inhalation.
  • Forced expiratory volume in 1 second (FEV1 sec): air expelled in first second.
  • FEV1%: FEV1 expressed as a percentage of FVC.

Additional Breathing Definitions

• Respiratory Rate (RR): Number of breaths per minute.
• Minute Ventilation: Total air moved per minute (TV x RR).
• Anatomic Dead Space: Volume of air not participating in gas exchange.
• Alveolar Ventilation: Effective air volume available for gas exchange per minute.