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Respiratory System Overview

  • Definition: Gas exchange between the atmosphere, blood, and body cells

Three Key Processes of Respiration

  1. Ventilation - Air exchange between the atmosphere and alveoli

  2. External Respiration - Gas exchange between alveoli and pulmonary capillaries (O2 in, CO2 out)

  3. Internal Respiration - Gas exchange between blood and tissue cells (O2 out, CO2 in)

Functions of the Respiratory System

  • Gas exchange

  • Regulate blood pH

  • Smell (receptors)

  • Air filtration

Structures of the Respiratory System

Divisions

  • Upper Respiratory System: Nose, nasal cavity, pharynx

  • Lower Respiratory System: Larynx, trachea, bronchi, lungs

Zones

  • Conducting Zone: Nose → terminal bronchioles

  • Respiratory Zone: Respiratory bronchioles → alveolar sacs

Key Structures

Nose

  • Nostrils: Lead to nasal cavity

  • Nasal cavity:

    • Olfactory mucosa: Smell receptors

    • Respiratory mucosa: Filters and humidifies air

    • Sinuses: Paranasal sinuses

    • Lacrimal and Paranasal ducts: Drain into nasal cavity

Pharynx (Throat)

  • Regions:

    • Nasopharynx: Uvula, tonsils, Eustachian tubes

    • Oropharynx: Palatine and lingual tonsils

    • Laryngopharynx: Leads to larynx

Larynx (Voice Box)

  • Composed of 9 cartilages, including:

    • Thyroid cartilage (Adam’s apple)

    • Epiglottis (prevents choking)

    • Cricoid cartilage

    • Vocal folds (voice production)

Trachea (Windpipe)

  • C-shaped cartilage: Prevents collapsing

  • Trachealis: Smooth muscle for diameter changes

  • Carina: Sensitive area for cough reflex

Bronchi and Bronchioles

  • Main Bronchi: Right is shorter, wider, and more vertical

  • Branching:

    • Trachea → Main bronchi → Lobar bronchi → Segmental bronchi → Bronchioles → Terminal bronchioles

Lungs

  • Lung Layers:

    • Parietal pleura (outer)

    • Visceral pleura (inner)

    • Pleural cavity: Contains pleural fluid

    • Hilum: Where vessels and bronchi enter/exit

  • Right Lung: 3 lobes

  • Left Lung: 2 lobes (due to heart's position)

Pleural Cavities

  • Pneumothorax: Air in pleural cavity (lung collapse)

  • Hemothorax: Blood in pleural cavity

Alveoli

  • Alveolar cells:

    • Type I: Structural cells

    • Type II: Secrete surfactant

  • Macrophages: Remove debris

  • Pores of Kohn: Connect alveoli

  • Respiratory membrane: Gas exchange area

Pulmonary Ventilation (Breathing)

  • Definition: Air movement between atmosphere and alveoli due to pressure changes

Boyle's Law

  • Pressure (P) is inversely proportional to volume (V)

Inhalation & Exhalation Muscles

  • Inhalation: Diaphragm, external intercostal muscles

  • Exhalation: Passive, but can use accessory muscles

Pressure Changes

  • Inhalation: Chest cavity expands, pressure decreases

  • Exhalation: Chest cavity contracts, pressure increases

Factors Affecting Pulmonary Ventilation

  1. Surface Tension: Alveolar fluid creates inward force

  2. Compliance: Ability of lungs to stretch (affected by elasticity)

  3. Airway Resistance: Depends on airway diameter

Lung Volumes and Capacities

  • Tidal Volume (TV): Normal breath volume

  • Inspiratory Reserve Volume (IRV): Air taken in after normal inhalation

  • Expiratory Reserve Volume (ERV): Air pushed out after normal exhalation

  • Residual Volume (RV): Air left after exhalation

  • Minute Ventilation (MV): Rate x Tidal Volume

  • Alveolar Ventilation: Air reaching respiratory zone

  • Vital Capacity (VC): TV + IRV + ERV

Gas Exchange and Transport

Dalton’s Law

  • Each gas exerts its own pressure

Henry’s Law

  • Higher pressure and solubility = more gas dissolved in liquid

Oxygen Transport:

  • 98.5% O2 carried by hemoglobin (Hb)

Carbon Dioxide Transport:

  • 23% as carbaminohemoglobin

  • 70% as bicarbonate ions (HCO3)

Factors Affecting Hemoglobin's Affinity for Oxygen

  1. pH: Low pH (acidic) → Hb releases more O2 (Bohr effect)

  2. CO2 Pressure: High CO2 → O2 dissociation

  3. Temperature: Higher temp → more O2 released

  4. 2,3-BPG: Decreases Hb's affinity for O2

  5. Fetal Hb: Higher O2 affinity

Control of Respiration

  • Medullary Center: Basic rhythm of breathing

    • Dorsal Respiratory Group (DRG): Quiet inhale

    • Ventral Respiratory Group (VRG): Forceful breathing

  • Pontine Center: Modifies breathing patterns

  • Chemoreceptors:

    • Central: Medulla oblongata (detect CO2)

    • Peripheral: Aortic/carotid bodies (detect O2)

Disorders

  • Asthma: Airway inflammation and obstruction

  • COPD: Chronic bronchitis, emphysema

  • Lung Cancer

  • Pneumonia: Infection of alveoli

  • Tuberculosis (TB)

  • Pulmonary Edema

  • Cystic Fibrosis