lecture recording on 11 March 2025 at 15.31.16 PM

Overview of the Respiratory System

• The respiratory system functions under autonomic control.

• Normal quiet breathing vs. forced breathing.

• Importance of bronchodilation and bronchoconstriction in respiratory function.

  • Sympathetic nervous system facilitates bronchodilation (opens airways).

  • Parasympathetic nervous system leads to bronchoconstriction.

Anatomy of the Lungs

• The lungs are covered by two pleura layers:

  • Visceral pleura: Covers the lungs (like shrink wrap).

  • Parietal pleura: Lines the thoracic wall.

• Pleural cavity: The potential space between the pleura filled with fluid, providing lubrication and preventing friction.

• Pressure in the pleural cavity is crucial to lung function and prevents collapse; excess fluid can lead to pain and difficulty breathing.

Pulmonary Ventilation

• Definition: Process of air movement into and out of lungs.

• Respiratory pressures: Defined relative to atmospheric pressure:

  • Intrapulmonary pressure: Pressure inside the lungs.

  • Intrapleural pressure: Pressure in the pleural cavity.

• Pressure differentials drive air movement during breathing:

  • Intrapulmonary pressure fluctuates with breathing, always equalizing with atmospheric pressure during inhalation/exhalation.

  • Intrapleural pressure is always negative relative to both intrapulmonary and atmospheric pressure to keep lungs inflated.

Mechanics of Breathing

• Quiet breathing mainly utilizes:

  • Diaphragm (flattens during contraction to increase thoracic volume).

  • External intercostals (lift rib cage).

• Expiration is generally a passive process (relaxation of muscles without active contraction).

• Boyle's Law: Inverse relationship between volume and pressure:

  • Increase volume = decrease pressure ( \text{(Air flows in)} )

  • Decrease volume = increase pressure ( \text{(Air flows out)} )

Gas Exchange and Transport

• Key processes involved in oxygen and carbon dioxide transport:

  • Oxygen transport: Mainly bound to hemoglobin in red blood cells.

  • Carbon dioxide transport: 70% as bicarbonate, 23% bound to hemoglobin, and a small percentage dissolved in plasma.

• Influences on gas exchange:

  • High levels of CO2 and low pH stimulate increased breathing rate (hypercapnia).

  • Temperature and pH affect oxygen unloading in tissues (Bohr effect).

Regulation of Respiration

• Controlled by the medulla and pons (brain stem):

  • Dorsal respiratory group (DRG): Primarily responsible for rhythm of breathing.

  • Ventral respiratory group (VRG): Active in forced breathing scenarios.

• Chemoreceptors monitor blood pH and CO2 concentrations and adjust breathing accordingly.

  • Peripheral receptors in carotid and aortic bodies respond to changes in blood chemistry (O2 and CO2 levels).

Abnormal Breathing Patterns

• Sleep Apnea: Temporary cessation of breathing during sleep; can arise from obstructions or neurological issues.

• Hyperventilation: Decreased levels of CO2 due to excessive breathing; may lead to faintness.

• **Conditions affecting ventilation:

  • Restrictive disorders (e.g., fibrosis) reduce lung expansion.

  • Obstructive disorders (e.g., asthma) hinder airflow due to blockages.

Important Definitions

• Tidal volume: Volume of air exchanged during quiet breathing (about 500 mL).

• Vital capacity: Maximum volume of air exchanged during breathing.

• Residual volume: Volume of air left in lungs after maximal exhalation.

• Total lung capacity: Sum of all different lung volumes.

• Dead space: Air in the respiratory system that doesn't participate in gas exchange (anatomical and alveolar).

Summary Points

• Intrapulmonary pressure fluctuations drive air in/out of the lungs based on volume changes.

• Proper lung function relies heavily on maintaining negative intrapleural pressure.

• Respiratory rate and depth are regulated primarily by CO2 levels and pH changes in blood.

• Understanding these mechanisms is crucial for diagnosing and treating respiratory conditions.