Respiratory System

Respiratory System Overview

Functions of the Respiratory System

• Air Passageway: Facilitates airflow in and out of the body.

• Gas Exchange: Exchange of oxygen (O2) and carbon dioxide (CO2) between the lungs and bloodstream.

• pH Control: Helps maintain the acid-base balance in the body.

• Voice Production: Allows for the production of sound and speech.

• Olfactory Receptors: Houses receptors for the sense of smell.

Structural and Functional Organization of the Respiratory System

Structural Division

• Upper Respiratory Tract:

  • Nose

  • Nasal cavity

  • Pharynx

  • Larynx

• Lower Respiratory Tract:

  • Trachea

  • Bronchus

  • Bronchiole

  • Terminal bronchiole

Functional Organization

• Conducting Zone:

  • Structures that transport air; includes trachea, bronchi, and bronchioles.

• Respiratory Zone:

  • Site of gas exchange; includes respiratory bronchioles, alveolar ducts, and alveoli.

Respiratory Mucosa

• Components:

  • Rich in goblet cells and glands that produce mucus.

  • Epithelium varies:

    • Pseudostratified Ciliated Columnar Epithelium: Lines nasal cavity to lower larynx and bronchi.

    • Simple Ciliated Columnar Epithelium: Lining of smaller bronchi.

    • Simple Cuboidal Epithelium: Lining of terminal and respiratory bronchioles.

    • Simple Squamous Epithelium: Found in alveolar ducts and alveoli.

• Function: Mucus traps dust and pathogens; cilia help in moving mucus out.

Exceptions

• Nonkeratinized Stratified Squamous Epithelium: Found in parts of the respiratory tract subject to abrasion (e.g., oropharynx, vocal cords).

Nasal Cavity and Paranasal Sinuses

• Nasal Cavity Features:

  • Vestibule: Area posterior to the nostrils.

  • Turbinates (Conchae): Structures that help in air filtration.

  • Choanae: Opening leading to nasopharynx.

• Function: Moistens, warms, cleanses, and filters inspired air.

Paranasal Sinuses

• Types:

  • Frontal sinus, Ethmoidal sinuses, Sphenoidal sinus, Maxillary sinus.

• Function: Provide resonance to the voice; inflammation leads to sinusitis.

Pharynx

• Regions:

  • Nasopharynx: Contains pharyngeal tonsils, auditory tube openings.

  • Oropharynx: Contains palatine and lingual tonsils.

  • Laryngopharynx: Leads to esophagus and larynx.

Larynx (Voice Box)

• Components: Nine cartilages, including epiglottis, thyroid, and cricoid cartilages.

• Vocal Folds:

  • True Vocal Folds: Elastic ligaments that vibrate with airflow for sound production.

  • False Vocal Folds: Help in closing the larynx for increased pressure during actions like lifting.

Trachea (Windpipe)

• Structure: Connects larynx to bronchi, approximately 5 inches long.

• Layers:

  • Mucosa: Pseudostratified columnar epithelium with goblet cells.

  • Submucosa: Contains glands.

  • Cartilage: C-shaped rings provide support.

  • Smooth Muscle: Trachealis muscle permits constriction.

• Carina: Where trachea divides into the right and left bronchi.

Bronchial Tree

• Components:

  • Main bronchi (primary), Lobar bronchi (secondary), Segmental bronchi (tertiary).

  • Bronchioles and terminal bronchioles.

• Changes:

  • Epithelial changes from ciliated columnar to cuboidal.

  • Decrease in cartilage and increase in smooth muscle leads to bronchoconstriction and bronchodilation.

Airflow Regulation

• Mechanisms:

  • Contraction of smooth muscle regulates airflow (bronchoconstriction vs. bronchodilation).

Lungs

• Structure: Spongy, cone-shaped organs with abundant elastic fibers.

• Pleura: Visceral and parietal pleura with pleural cavity fluid to reduce friction.

Alveolar Structure and Gas Exchange

• Types of Cells:

  • Type I (for gas exchange), Type II (produce surfactant to reduce surface tension), alveolar macrophages (dust cells).

• Surfactant: Prevents alveolar collapse and maintains surface tension.

Respiratory Membrane

• Components: Alveolar sac wall and pulmonary capillary wall, facilitating efficient gas exchange.

• Surface Area: Equivalent to a racquetball court (807 sq ft).

Steps of Respiration

1. Pulmonary Ventilation: Inhaling (inspiration) and exhaling (expiration).

2. Pulmonary Respiration: Gas exchange between alveoli and blood.

3. Gas Transport: Movement of gases in the blood.

4. Tissue Respiration: Gas exchange at the tissue level.

Control of Breathing

• Ventilation Control: Involves sensory receptors (chemoreceptors), motor neurons (phrenic and intercostal nerves), and brainstem respiratory centers.

• Respiratory Rate: Influenced by CO2 levels, pH, temperature, and other physiological changes.

Lung Volumes and Capacities

• Volume Definitions: Tidal Volume (TV), Inspiratory Reserve Volume (IRV), Expiratory Reserve Volume (ERV), Residual Volume (RV).

• Capacities: Total Lung Capacity, Functional Residual Capacity, Inspiratory Capacity, Vital Capacity.

Gas Exchange Mechanisms

• Diffusion Processes: Governed by Dalton’s Law (gas partial pressures) and Henry’s Law (gas solubility in liquids).

• Oxygen Transport: Most O2 binds to hemoglobin; CO2 primarily transported as bicarbonate.

• Regulation Factors: O2 binds more readily with factors like increased acid, temperature, and PCO2, typically seen in metabolically active tissues.