Respiratory System Overview

Respiratory System Overview • Function: Facilitates O₂ intake and CO₂ removal. • Components: Nose, pharynx, larynx, trachea, bronchi, bronchioles, lungs, and respiratory muscles. • Main Role: Gas exchange between body and environment. Upper Respiratory Tract Nose & Nasal Cavity • Filters, warms, and humidifies air. • Lined with ciliated epithelium + goblet cells (mucus production). • Nasal hairs + mucus trap dust/pathogens. • Paranasal sinuses: Lighten skull, aid speech. • Olfactory function for smell. Pharynx • Common passage for air and food. • 3 parts: Nasopharynx, Oropharynx, Laryngopharynx. • Functions: Warm/humidify air, speech resonance, protection via tonsils. Larynx • Connects pharynx to trachea. • Contains vocal cords for voice production. • Epiglottis prevents food from entering airway. • Helps in cough reflex, humidification. Lower Respiratory Tract Trachea • ~10–11 cm long, with C-shaped cartilage rings. • Splits into right & left bronchi at the carina. • Mucociliary escalator moves debris upward for removal. Bronchi & Bronchioles • Bronchi → Bronchioles → Terminal → Respiratory bronchioles → Alveoli. • Right bronchus: Shorter, wider, more vertical (more prone to aspiration). • Controls airflow speed/volume via smooth muscles. • Defense: Goblet cells, cilia, macrophages. Alveoli (Gas Exchange Units) • ~300 million alveoli in lungs. • Type I pneumocytes: Gas exchange. • Type II pneumocytes: Produce surfactant (↓ surface tension, prevents collapse). • Surrounded by dense capillary network. Lungs & Pleura • Right lung: 3 lobes; Left lung: 2 lobes. • Pleura: Double membrane (visceral + parietal) with pleural fluid to reduce friction. Respiration Components 1. Pulmonary Ventilation: Air in/out of lungs. 2. Gas Diffusion: Between alveoli & capillaries. 3. Gas Transport: O₂ & CO₂ in blood. 4. Respiration Regulation: Neural control of breathing. Breathing Mechanics • Inspiration: Diaphragm contracts (down), ribs elevate. • Expiration: Mostly passive; active during exertion. • Involved muscles: o Inspiration: Diaphragm, external intercostals, scaleni. o Expiration: Internal intercostals, abdominal muscles. Respiratory Pressures • Pleural Pressure: Always negative (keeps lungs inflated). • Alveolar Pressure: • o At rest: 0 cm H₂O o Inspiration: -1 cm H₂O o Expiration: +1 cm H₂O Transpulmonary Pressure = Alveolar – Pleural pressure (keeps lungs open). Lung Compliance & Surfactant • Compliance: Lung stretch per pressure unit (normal: 200 ml/cm H₂O). • Surfactant (Type II cells): Reduces surface tension, prevents alveolar collapse. Gas Exchange & Dead Space • Minute volume = Tidal Volume (500 ml) × RR (12) = ~6 L/min. • Alveolar ventilation = RR × (VT - Dead Space) = ~4.2 L/min • Dead Space: o Anatomical: Conducting airways (150 ml) o Alveolar: Non-functional alveoli o Physiological = Anatomical + Alveolar Diffusion Principles • Gases move from high to low partial pressure. • O₂ diffuses from alveoli → blood. • CO₂ diffuses from blood → alveoli. • Diffusion depends on: Thickness, surface area, pressure difference. Respiratory Membrane • Thin barrier for gas exchange. • Layers: Surfactant → alveolar cells → basement membrane → interstitium → capillary endothelium. • Diffusing Capacity: o O₂: ~21 ml/min/mmHg (increases during exercise) o CO₂: ~20x more diffusive than O₂ Transport of Respiratory Gases Oxygen (O₂) • 3% dissolved in plasma. • 97% bound to hemoglobin (Hb) as oxyhemoglobin. • 1g Hb carries 1.34 ml O₂. • O₂-Hb dissociation curve: Sigmoid shape. o P50 = PO₂ at 50% saturation (~26 mmHg). o Right shift = more O₂ released (↑ CO₂, ↑ H⁺, ↑ temp, ↓ pH). o Left shift = more O₂ bound (↓ CO₂, ↓ H⁺, ↓ temp, ↑ pH). Carbon Dioxide (CO₂) • Transported in 3 forms: o 7% dissolved o 63% as bicarbonate (HCO₃⁻): Formed in RBCs, catalyzed by carbonic anhydrase o 30% as carbamino compounds (bound to Hb & proteins) Chloride Shift (Hamburger Phenomenon) • Bicarbonate exits RBC, chloride enters to maintain charge balance. Key Gas Values • Alveolar PO₂ = 104 mmHg, Venous PO₂ = 40 mmHg • Arterial PO₂ after shunt = 95 mmHg • Tissue PO₂ = ~40 mmHg → intracellular ~23 mmHg • Venous PCO₂ = 45 mmHg, Alveolar PCO₂ = 40 mmHg