Intro to respiratory system

Proximity to Vessels in the Respiratory System

  • Importance of proximity to blood vessels for gas exchange.

  • Larger surface area provided by alveoli facilitates efficient gas exchange.

Communication and Sensory Functions

  • Role of communication in the respiratory system.

  • Olfaction (Smell)

    • Definition: The act of perceiving odors or scents through airborne molecules entering the nasal cavity.

    • Air must be brought into the nose for the sense of smell to function effectively.

Acid-Base Balance

  • Relationship between breathing and the regulation of blood pH through CO₂ elimination.

    • Elevated CO₂ levels in the blood correlate with decreased pH (increased acidity of blood).

    • Connection to bicarbonate and other ions.

Blood Pressure Regulation

  • BP Regulation

    • Involves the conversion of angiotensin I to angiotensin II, part of the Renin-Angiotensin-Aldosterone system (RAAS).

    • Key Enzyme: Angiotensin Converting Enzyme (ACE) released from lung tissue manages this conversion.

Respiratory Function and Blood/Lymph Flow

  • Breathing affects the flow of blood and lymph through pressure changes in the thoracic cavity.

    • Inhalation: Decrease in thoracic cavity pressure assists venous return of blood from the abdominal cavity.

    • Lymphatic System: Also affected by breathing; transports excess fluid back to the bloodstream.

    • This process is termed Respiratory Pump.

Structures of the Respiratory System

  • List of major respiratory structures:

    • Nose

    • Pharynx

    • Larynx

    • Trachea

    • Bronchial Tree

    • Bronchi

    • Bronchioles

    • Alveoli

    • Lungs

    • Pleura

    • (Notable omissions: Nasal Cavity and Oral Cavity)

  • Physiology: Air is brought in through nose/mouth, travels down the trachea into the lungs, and exchanges gases in the alveoli with adjacent vessels.

Pulmonary Ventilation

  • Definition: The process of moving air in and out of the lungs.

  • Mechanism: Involves movement of rib cage and thoracic cavity volume change through respiratory muscles.

    • Inspiration and Expiration:

    • Inspiration:

      • Diaphragm main muscle responsible for inhalation.

      • Effect of Diaphragm: Contracts, flattens, and increases thoracic cavity volume, lowering intrathoracic pressure to allow air inflow.

      • External intercostals also assist; they raise ribs and increase thoracic dimensions.

    • Forced Expiration:

      • Generally passive but requires muscular effort during exercise.

      • Primarily abdominal muscle contractions force air out by raising abdominal pressure, helping to push diaphragm up.

      • Internal intercostals help draw ribs downward.

  • Nervous System Input: Breathing muscles are skeletal, requiring neural activation from the brain and spinal cord.

    • Autonomous Breathing: Breathe reflexively without conscious thought; disruption can lead to conditions like Ondine's curse, where sleep leads to asphyxiation due to lack of breathing.

Brainstem Centers for Respiratory Control

  • Main Centers:

    • Ventral Respiratory Group (VRG): Located in the medulla; primary respiratory rhythm generator; activates inspiratory and expiratory muscles.

    • Dorsal Respiratory Group (DRG): Modulates rhythm affected by inputs to the VRG.

    • Pontine Respiratory Group (PRG): Located in the pons; influences transitions between inhalation and exhalation based on higher brain center communications.

Hierarchical Arrangement of Brain Centers

  • Neurological Hierarchy:

    • VRG (medulla) controls muscle activation.

    • DRG receives sensory feedback and modulates VRG output.

    • PRG influences breathing patterns; receives info from higher brain centers (e.g., limbic system impacts on emotion).

Inputs to Respiratory Centers

  • Central Chemoreceptors: Sensitive to changes in pH within cerebrospinal fluid; activation increases ventilation when CO₂ levels rise (lowering pH).

  • Peripheral Chemoreceptors: Located in the carotid and aortic bodies; monitor O₂, CO₂, pH, lactate, and potassium levels, responding primarily when O₂ drops significantly.

    • Receptors include:

    • Carotid body triggers increase in ventilation.

    • Potassium and lactate rising during muscle activity stimulate breathing.

  • Stretch Receptors: Located in lung tissues; activated upon inflation and inhibit further inhalation.

  • Dust and Particle Response: Presence of irritants triggers cough or sneeze reflexes to expel substances.

Mechanics of Breathing: Pressures, Resistance, and Flow

  • Pressure Types:

    • Atmospheric Pressure: Standard at sea level (760 mmHg).

    • Intrapulmonary Pressure: Pressure within the alveoli; decreases during inspiration, increases during expiration.

    • Intrapleural Pressure: Pressure between pleura layers, typically negative relative to atmospheric pressure, crucial for lung inflation.

  • Mechanism: Air flow occurs from high to low pressure, with resistance contingent upon airway diameter.

  • Inspiration Process:

    • Diaphragm contraction lowers thoracic pressure (negative pressure) allowing air to flow into lungs.

  • Expiration Process:

    • Relaxation of diaphragm increases thoracic pressure; air flows out as pressure rises above atmospheric.

  • Ongoing Rhythm: Regular activation and cessation of VRG neurons control tidal volume and pacing of breath.

Conclusion

  • Respiratory function involves intricate control through brainstem coordination, muscle action, and feedback mechanisms concerning various pressures and pleural dynamics.