Respiratory_System

Respiratory System Overview

  • The respiratory system comprises the upper and lower respiratory tracts.

    • Upper Respiratory Tract: Nose, nasal cavity, paranasal sinuses, nasopharynx.

    • Lower Respiratory Tract: Trachea, bronchial tree, lungs.

  • The respiratory system is divided into:

    • Conducting Zone: Includes nose, pharynx, larynx, trachea, bronchi, and up to terminal bronchioles.

    • Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Respiratory Mucosa

  • The respiratory mucosa is primarily lined with:

    • Pseudostratified Columnar Ciliated Epithelium: Cilia move mucus upward toward the pharynx for removal.

Nose

  • Nasal Septum: Divides the internal nostrils into two cavities.

  • Mucous Membrane: Lines the nose.

  • Hard Palate: Composed of maxillae and palatine bones, separations between oral and nasal cavities.

  • Sinuses Draining into Nose: Frontal, maxillary, sphenoidal, and ethmoidal sinuses.

  • Functions:

    • Warms and moistens inhaled air.

    • Contains sense organs for smell.

Pharynx

  • Serves both respiratory and digestive systems.

    • Passageway for Food and Liquids: Shared pathway for air and food.

    • Air Distribution: Passageway for air.

  • Length: Approximately 12.5 cm (5 inches).

  • Divisions:

    • Nasopharynx

    • Oropharynx

    • Laryngopharynx

  • Openings: Nasal cavities, mouth, esophagus, larynx, and auditory tubes connect to pharynx.

  • Tonsils:

    • Pharyngeal tonsils (in nasopharynx).

    • Palatine tonsils (in oropharynx).

Larynx

  • Structure:

    • Framework of cartilage, including:

      • Largest: Thyroid cartilage (Adam's apple).

      • Epiglottis: Covers the opening into the larynx.

      • Unpaired Cartilages: Thyroid, Cricoid, Epiglottis.

      • Paired Cartilages: Arytenoids, Corniculate, Cuneiform.

  • Vocal Mechanism:

    • True Vocal Cords and Vestibular Folds stretch across the larynx.

  • Functions:

    • Air passageway to and from lungs, and voice production.

Trachea

  • Structure:

    • A tube approximately 4.5 inches long, extending from larynx to thoracic cavity, held open by C-shaped rings of cartilage.

  • Function: Air passageway to and from lungs.

Bronchi, Bronchioles, and Alveoli

  • Structure:

    • Trachea bifurcates into right and left bronchi at T5 (Thoracic Vertebra 5).

    • Right Bronchus: Wider and shorter, allowing foreign bodies to pass more easily from trachea.

    • Continuous branching leads to smaller bronchioles ending in alveolar sacs comprised of alveoli.

  • Functions:

    • Bronchi and Bronchioles: Air distribution and passageway to and from alveoli.

    • Alveoli: Primary site for gas exchange between air and blood.

Alveolar Cells

  • Type I Alveolar Cells: Make up the majority of alveolar wall.

  • Type II Alveolar Cells: Produce surfactant to reduce surface tension in alveoli.

Lungs and Pleura

  • Structure:

    • Lungs fill the chest cavity, with the apex (upper part) beneath the collarbone and the base resting on the diaphragm.

    • Lobes:

      • Right Lung: 3 lobes.

      • Left Lung: 2 lobes.

  • Pleura: Smooth membrane lining the chest cavity and covering the lungs, reducing friction during breathing.

  • Function: Essential for breathing (pulmonary ventilation).

Breathing Mechanics

  • When the diaphragm contracts, thoracic cavity size increases, causing a pressure drop that allows air to flow into lungs.

Gas Exchange

  • External Respiration:

    • Carbon dioxide exits lung capillaries into alveolar air, expelled from the body.

    • Oxygen enters lung capillaries from alveoli.

  • Internal Respiration:

    • Oxygen diffuses from tissue capillaries into tissue cells.

    • Carbon dioxide moves from tissue cells into tissue capillaries.

Respiratory Rhythm and Control

  • Medulla Oblongata: Controls basic respiratory rhythm.

  • Pons: Regulates breathing rate along with the medulla.

  • Chemoreceptors: Detect changes in CO₂, O₂, and pH, adjusting breathing as necessary.

  • Mechanoreceptors: Prevent overinflation of the lungs and respond to physical irritants.

  • Higher Centers for Respiratory Influence: Found in the cerebrum and hypothalamus.