What are the structures and functions of the conducting and respiratory zones of the lungs?
Conducting zone: Nose to terminal bronchioles; warms, humidifies, and filters air.
Respiratory zone: Respiratory bronchioles to alveoli; site of gas exchange.
What structures are involved in gas exchange and how does it occur?
Structures: Alveoli, alveolar sacs, and capillaries.
Mechanism: Diffusion of gases across the alveolar-capillary membrane driven by partial pressure gradients.
How is each lung compartmentalized by pleural membranes?
Visceral pleura: Covers lungs directly.
Parietal pleura: Lines thoracic cavity.
Pleural space: Between membranes; filled with fluid to reduce friction and maintain negative pressure.
What pressure changes occur during inspiration, and how does Boyle’s law explain them?
Intrapulmonary pressure drops, drawing air in.
Boyle’s law: Pressure and volume are inversely related (↑volume = ↓pressure).
How do lung compliance and elasticity affect breathing?
Compliance: Ease of lung expansion.
Elasticity: Ability to recoil. High compliance = easier inspiration; high elasticity = more effective expiration.
What is pulmonary surfactant and why is it important?
Surfactant: Lipoprotein that reduces surface tension in alveoli, preventing collapse (especially important in newborns).
What muscles are used during quiet inspiration and expiration?
Inspiration: Diaphragm and external intercostals contract.
Quiet expiration: Passive recoil of lungs and diaphragm relaxation.
How are forced inspiration and expiration produced?
Forced inspiration uses: Sternocleidomastoid (neck), scalenes (neck), pectoralis minor (chest), serratus anterior (side ribs), external intercostals (between ribs), diaphragm.
How it works: These muscles pull the ribs up and out and push the sternum forward, making the chest bigger so more air can come in.
Forced Expiration uses: Internal intercostals (between ribs) and abdominal muscles (abs).
How it works: These muscles pull the ribs down and push the diaphragm up, making the chest smaller so air is pushed out quickly.
Define tidal volume and vital capacity.
Tidal volume (TV): Air moved per breath (~500 mL).
Vital capacity (VC): Max air exhaled after max inhalation.
How is total minute volume calculated and how does exercise affect it?
Minute volume = TV (tidal volume) × respiratory rate.
Increases with exercise due to increased rate and depth.
How are VC (vital capacity) and FEV (Forced Expiratory Volume) affected by asthma and pulmonary fibrosis?
Asthma: ↓FEV (obstructive).
Pulmonary fibrosis: ↓VC (restrictive).
How is PO₂ (partial pressure of oxygen) of air calculated and how is it affected by altitude, diving, and humidity?
PO₂ = %O₂ × (atmospheric pressure – water vapor pressure) ↓ with altitude, ↑ with diving, ↓ with high humidity.
How is blood PO₂ measured and what is its clinical significance?
Measured via arterial blood gas (ABG).
Reflects lung oxygenation efficiency.
Why is systemic arterial PO₂ lower than alveolar PO₂?
Ventilation-perfusion mismatch and physiological shunting.
How is breathing regulated by the CNS?
Controlled by medulla (rhythm) and pons (modulation).
How does ventilation respond to changes in arterial PCO₂?
Negative feedback: ↑PCO₂ → ↑ventilation to blow off CO₂.
How does oxyhemoglobin saturation change with arterial PO₂?
Sigmoidal curve: Steep rise at low PO₂, plateau at high PO₂.
What affects the oxyhemoglobin dissociation curve?
pH, temperature, CO₂ levels, 2,3-BPG.
Right shift = easier oxygen release
How do pH and temperature affect oxygen transport?
↓pH and ↑temperature = ↓affinity for O₂ (Bohr effect).
Occurs during exercise or acidosis.
How is CO₂ transported in blood and in what proportions?
Dissolved (10%), carbaminohemoglobin (20%), bicarbonate (70%).
What is the chloride shift and where does it occur?
Tissues: Cl⁻ enters RBCs as HCO₃⁻ exits.
What is the reverse chloride shift and where does it occur?
Lungs: HCO₃⁻ re-enters RBCs, Cl⁻ exits.
How are carbonic acid and bicarbonate formed?
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. Buffer system regulating pH.
Define acidosis and alkalosis. What are the two components of acid-base balance?
Acidosis: pH < 7.35 Alkalosis: pH > 7.45 Components: Respiratory and metabolic.
What are the roles of lungs and kidneys in acid-base balance?
Lungs: Regulate CO₂ (fast).
Kidneys: Regulate H⁺ and HCO₃⁻ (slow).
What do bicarbonate and carbonic acid do in blood?
Act as a buffer system to resist pH changes.
How do hyperventilation and hypoventilation affect pH?
Hyperventilation: ↓CO₂ → respiratory alkalosis.
Hypoventilation: ↑CO₂ → respiratory acidosis.
Why does a person with ketoacidosis hyperventilate?
To compensate for metabolic acidosis by reducing CO₂ and raising blood pH (e.g., Kussmaul breathing).