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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