In-Depth Notes on the Respiratory System

Respiratory System Overview

• Location:

  • Lungs are situated in the thoracic cavity.
  • Each lung is encased in a double-layered serous membrane known as pleura.
  • Components of pleura:
  • Visceral pleura: covers the lungs.
  • Parietal pleura: lines the thoracic cavity.
  • Pleural fluid: present between the layers to reduce friction.

• Function:

  • Gas exchange between air and blood:
  • Oxygen (O2) is absorbed from air into the blood.
  • Carbon dioxide (CO2) is expelled from blood into the air.

Types of Respiration

1. Ventilation: Process of moving air in and out of the lungs.
2. External respiration: Gas exchange between lung air and blood.
3. Gas transport in blood: Distribution of gases in the bloodstream.
4. Internal respiration: Gas exchange from blood to body's cells.

Alveolar Structure

• Major site for gas exchange (O2 and CO2) occurs here.
• Composed of simple squamous epithelium which facilitates rapid diffusion.
• Functions of the respiratory system:
  • Filters, warms, and humidifies incoming air through mucous membranes lined with pseudostratified ciliated epithelium.
  • Contains numerous mucus cells for trapping particles.

Key Respiratory Structures

• Nose/Nostrils

• Nasal Cavity:

  • Divided by the nasal septum.
  • Contains nasal conchae and meatuses to facilitate airflow.
  • Paranasal sinuses open into the nasal cavity.

• Pharynx (Throat): Divided into three parts:

  1. Nasopharynx:
  • Lined with ciliated epithelium.
  • Air passage connected to nasal cavity.
  1. Oropharynx:
  • Features stratified squamous epithelium.
  • Located posterior to the soft palate.
  1. Laryngopharynx:
  • Features stratified squamous epithelium, serving as a passage to the esophagus.

Larynx and Vocal Cords

• Epiglottis: Flap that prevents food from entering the trachea.
• Larynx: Holds the vocal cords.
  • Factors affecting sound:
  • Pitch: Determined by the length of vocal cords.
  • Loudness: Determined by the force of air.
  • Speech: Produced by actions of the tongue, lips, nasal cavity, and sinuses.

Conducting Zone Structures

• Trachea (Windpipe): Begins air passage to bronchi.
• Bronchial Tree: Includes:
  • Primary bronchi (2).
  • Secondary bronchi: Leads to lung lobes.
  • Bronchioles: Smaller branches leading to alveoli.
  • Alveoli: Tiny air sacs where gas exchange occurs.
  • Each alveolus is surrounded by capillaries for gas exchange.

Breathing Mechanism

Inhalation (Inspiration)

• Diaphragm contracts, moving downwards.
• External intercostal muscles contract, raising the rib cage.
• Surfactants in alveoli reduce surface tension.

Exhalation (Expiration)

• Driven by elastic recoil of the lungs.
• Diaphragm relaxes and moves upwards.
• Internal intercostal muscles and abdominal muscles may assist in forced exhalation.

Lung Volumes and Capacities

1. Tidal Volume (TV): Amount of air exchanged in normal respiration.
2. Expiratory Reserve Volume (ERV): Air exhaled after normal cycle.
3. Residual Volume (RV): Air remaining post-exhalation.
4. Inspiratory Reserve Volume (IRV): Air inhaled beyond tidal volume.
5. Vital Capacity (VC): Maximum air volume exhalable.
   • VC = ERV + TV + IRV
6. Total Lung Capacity (TLC): Total air volume in lungs.
   • TLC = VC + RV

Gas Exchange Process

• Takes place between alveolar air and blood.
• Henry’s Law: Amount of gas in solution is proportional to the partial pressure.
  1. Oxygen (O2) diffuses into capillaries.
  2. Carbon dioxide (CO2) diffuses into alveolus from blood.

Hemoglobin and Oxygen Transport

• Hemoglobin (Hb) is responsible for most oxygen transport.
  • Influenced by:
  • Partial pressure of O2 (PO2): Directly proportional to Hb saturation.
  • pH levels: Increased pH raises Hb affinity for O2.
  • Temperature: Higher temperature decreases Hb affinity for O2.

Carbon Dioxide Transport

• Mostly transported as carbonic acid formed by Carbonic anhydrase:
  • CO2 + H2O
    ightleftharpoons H^+ + HCO_3^-
• About 70% as bicarbonate, 23% bound to Hb, and 7% dissolved in plasma.

Common Respiratory Disorders

1. COPD (Chronic Obstructive Pulmonary Disease):

   • Difficulty in airflow; associated with tar and cilia paralysis due to smoking.

2. Lung Cancer:

   • Triggered by carcinogens in tobacco smoke; very aggressive.

3. Respiratory Distress Syndrome:

   • Common in premature infants due to surfactant deficiency.

4. Bronchitis:

   • Inflammation of bronchial tubes; can be acute or chronic.

5. Pneumonia:

   • Infectious inflammation leading to fluid-filled alveoli.

6. Asthma:

   • Airway hypersensitivity; treated with bronchodilators and anti-inflammatories.