Respiratory System Overview

The respiratory system is essential for gas exchange between the atmosphere, blood, and cells. It is organized into distinct zones and processes that ensure efficient oxygen delivery and carbon dioxide removal.

• Respiration: Exchange of gases between atmosphere, blood, and cells.

• Three main processes:

  • Ventilation: Movement of air in and out of the lungs.

  • External Respiration: Gas exchange between the lungs and blood.

  • Internal Respiration: Gas exchange between blood and tissues.

• Zones of the Respiratory System:

  • Conducting Zone: Directs air to the lungs; includes structures from the nose to the bronchioles, where air is filtered, warmed, and moistened.

  • Respiratory Zone: Sites of gas exchange; includes respiratory bronchioles, alveolar ducts, and alveoli.

Conducting Zone

Nose & Pharynx

The nose and pharynx serve as the initial passageways for air, conditioning it before it reaches the lower respiratory tract.

• Nose:

  • External Portion: Visible, made of cartilage and skin, lined with mucous membranes.

  • Nostrils (External Nares): Openings for air entry.

  • Internal Portion: Extends from the nasal vestibule to the pharynx, lined with olfactory epithelium.

  • Functions: Warms, moistens, and filters incoming air; houses olfactory receptors.

• Pharynx:

  • Common chamber for respiratory and digestive tracts.

  • Three regions:

    • Nasopharynx: Respiration only.

    • Oropharynx and Laryngopharynx: Respiration and digestion.

  • Epiglottis: Closes the tracheal opening during swallowing to prevent food from entering the respiratory tract.

Larynx

The larynx, or "voice box," connects the laryngopharynx to the trachea and plays a vital role in protecting the airway and producing sound.

• Contains: Epiglottis and multiple regions of cartilage

  • Thyroid cartilage: Adam's apple

  • Cricoid cartilage

  • Three paired cartilages: Arytenoid, corniculate, cuneiform

• Vocal Folds:

  • Vestibular folds (false vocal cords): Do not produce sound; help close the glottis during swallowing.

  • Vocal folds (true vocal cords): Produce sound via skeletal muscle adductors or elastic ligaments; sound is modulated by movement and tension.

Trachea

The trachea, or windpipe, is a hollow tube that connects the larynx to the bronchi and is located anterior to the esophagus.

• Wall contains 16–20 C-shaped "rings" of hyaline cartilage:

  • Rigid and flexible: Maintain airway patency.

  • Open region (no cartilage): Faces the esophagus, allowing for expansion during swallowing.

• Layers of the Trachea:

  • Mucosa: Pseudostratified ciliated columnar epithelium; traps and moves debris out of the trachea.

  • Submucosa: Contains seromucous glands that produce mucus.

  • Hyaline cartilage: Provides structural support.

Bronchial Tree

The bronchial tree begins at the trachea and branches extensively within the lungs, conducting air to the respiratory zone.

• Trachea divides into right and left primary bronchi at the carina.

• Primary bronchi: Each supplies one lung; right is wider and more vertical (higher risk of foreign object lodging).

• Secondary bronchi: Right lung has three, left has two (accommodating the heart).

• Tertiary bronchi: Each lung has about 10; left may have fewer.

• Tissue changes along the bronchial tree:

  • Cartilage: Decreases from C-shaped rings to irregular plates.

  • Smooth muscle: Increases, allowing control over airflow.

  • Epithelium: Transitions from ciliated pseudostratified to simple cuboidal as bronchi become smaller.

Respiratory Zone

The respiratory zone is where gas exchange occurs in the lungs, consisting of structures like respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

• Bronchopulmonary segments: Largest subdivisions of lung lobes; each contains several lobules with its own blood and lymphatic vessels.

• Respiratory bronchioles: Branch into alveolar ducts, which end in alveolar sacs (clusters of alveoli).

• Alveoli: Main site of gas exchange.

  • Type I alveolar cells: Numerous, squamous cells; allow rapid gas diffusion.

  • Type II alveolar cells: Fewer, secrete surfactant (reduces surface tension, prevents alveolar collapse).

  • Alveolar macrophages: Immune defense; remove debris and pathogens.

Example: Bronchopulmonary segments allow for surgical removal of diseased lung tissue without affecting other parts of the lung.