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Respiratory System, Fluids, and Electrolytes Lecture Review

Respiratory System: Functions, Anatomy, and Pulmonary Ventilation

Introduction to Respiratory System & Key Connections

  • The respiratory system, fluids and electrolytes, and acid-base imbalances are interconnected. Understanding them together reveals their critical importance.

  • Cardiovascular System: Transports oxygen (O2) and carbon dioxide (CO2) via blood, with gas exchange occurring between alveoli and blood vessels.

  • Nervous System: Controls pulmonary ventilation.

  • Muscular System: Specific muscles (e.g., diaphragm, intercostals) cause volume changes for inhalation and exhalation.

Functions of the Respiratory System

  • Gas Exchange: Primarily involved in taking oxygen (O2) into the blood and delivering it to cells for cellular respiration (ATP production), and expelling carbon dioxide (CO2), a waste product. Carbon dioxide buildup has detrimental effects on the body.

  • Air Passageway: Provides a route for air, especially through the conducting zone.

  • Odor Detection: The nasal cavity contains olfactory epithelium for detecting odors.

  • Vocalization: The larynx is responsible for sound production.

  • Air Conditioning: The nasal cavity conditions inhaled air by warming, cleansing, and humidifying it. Cold air can stimulate bronchoconstriction.

  • Defense Mechanisms: Part of the first line of immune defense:

    • Lysozymes: Enzymes that destroy bacteria.

    • Defensins: Antimicrobial peptides.

    • Immunoglobulin A (IgA): An antibody that protects mucous membranes.

Respiratory Epithelium & Mucosa

  • Mucosa/Mucous Membrane: The respiratory lining typically consists of epithelium, a basement membrane, lamina propria, and sometimes submucosa and cartilage.

    • Epithelium Changes by Location:

      • Pseudostratified Ciliated Columnar Epithelium: Found from the nasal cavity down to the lobar bronchi (e.g., trachea). Contains goblet cells and cilia.

      • Stratified Squamous Epithelium: Found in certain areas of the pharynx.

      • Simple Squamous Epithelium: Found in the alveoli, where it is thinnest.

  • Functions of Pseudostratified Ciliated Columnar Epithelium:

    • Goblet Cells: Secrete mucin, which mixes with water to form mucus. Mucus increases viscosity, trapping pollen, allergens, microorganisms, dust, and debris.

    • Cilia: Beat rhythmically to move trapped particles and mucus (mucus escalator), usually moving it toward the esophagus to be swallowed and destroyed by stomach acid. Can also exit via the nose or mouth.

    • Mucus Production: Normally produces 1 to 7 tablespoons daily; production increases significantly during illness or allergic reactions to expel irritants.

  • Importance of Thin Alveolar Epithelium: Simple squamous epithelium in the alveoli is crucial for efficient gas exchange, as a thick tissue layer or mucus barrier would impede the process.

  • Air Warming: Superficial blood vessels beneath the epithelium warm the mucus, which in turn warms the incoming air.

  • Air Humidification: Mucus provides moisture to humidify the air.

  • Turbinate Bones (Conchae): Bony structures in the nasal cavity that swirl incoming air, increasing its contact with the mucosal lining for more effective cleansing, warming, and humidification.

Airflow Pathway & Structure-Function

  • Nasal Cavity: Air conditioning (warming, cleansing, humidifying), odor detection.

  • Pharynx: Air, food, and liquid passage (also contains palatine and lingual tonsils).

  • Larynx: Sound production, prevents ingested materials from entering the respiratory tract, increases intra-abdominal pressure (Valsalva maneuver), produces sneezing and coughing reflexes.

    • Epiglottis: Made of elastic cartilage (bends easily), covers the laryngeal opening during swallowing.

    • Vestibular Folds (False Vocal Cords): Superior to true vocal cords, primarily for protection.

    • True Vocal Cords: Inferior, produce sound through vibration as air passes over them during exhalation. Contain elastic tissue.

    • Rima Glottidis: The space between the vocal folds.

    • Voice Characteristics:

      • Pitch: Determined by the tension of the vocal cords (increased tension = higher pitch; regulated by intrinsic laryngeal muscles).

      • Range (Bass to Soprano): Influenced by the length and thickness of vocal folds and the space within the larynx.

        • Puberty in Males: Testosterone elongates and thins the thyroid cartilage and vocal cords, leading to a deeper voice. Laryngeal drop also contributes to deeper voices.

      • Loudness: Determined by the amount of air forced over the vocal folds (more air = louder sound).

    • Laryngitis: Inflammation of the vocal cords, often due to overuse (e.g., yelling) or infection. Causes hoarseness or loss of voice due to impaired vibration. Infections can spread to the epiglottis, causing epiglottitis, which can be lethal.

  • Trachea: Air passage, supported by C-shaped cartilage rings.

  • Bronchi (Main, Lobar/Secondary, Segmental/Tertiary): Air passage, cartilage rings decrease in prominence as they branch.

  • Bronchioles (Terminal, Respiratory): Air passage, lose cartilage entirely, gaining more smooth muscle. This smooth muscle allows for bronchoconstriction (narrowing) and bronchodilation (widening), regulating airflow. Terminal bronchioles mark the end of the conducting zone.

  • Respiratory Bronchioles: Start of the respiratory zone, facilitate gas exchange.

  • Alveolar Ducts: Give rise to alveoli (approx. 2 million per lung).

  • Alveoli: Primary site of gas exchange (300-400 million per lung), covered extensively by pulmonary capillaries. Lined with simple squamous epithelium.

Accessory Structures & Related Conditions

  • Sinuses: Air-filled cavities continuous with the nasal cavity via ducts. Upper respiratory infections can travel to sinuses, causing sinus infections due to inflammation and trapped mucus, which creates a breeding ground for bacteria.

  • Lungs: House the bronchial tree and alveoli. Rich in elastic tissue, allowing them to expand during inhalation and recoil to their original shape during exhalation, which is essential for ventilation.

Alveoli and Surfactant: Ensuring Gas Exchange

  • Respiratory Membrane: The extremely thin barrier where gas exchange occurs, composed of the alveolar epithelium and the capillary epithelium (both simple squamous).

  • Surface Tension in Alveoli: The natural water layer inside alveoli creates attractive forces through hydrogen bonds, causing the alveoli to tend to collapse inwards.

  • Surfactant: A lipid-based substance (similar to phospholipids) produced by specific alveolar cells. It acts as a