The Respiratory System

Overview

The respiratory system is responsible for the exchange of gases between the body and the environment, supplying oxygen to the blood and removing carbon dioxide. This system consists of a series of organs and structures that facilitate breathing, gas exchange, and protection of the respiratory tract.

Major Organs of the Respiratory System

Identification and Structure

• Nose: The primary entrance for outside air into the respiratory system; filters, warms, and moistens air.

• Nasal cavity: Hollow space behind the nose; lined with mucous membrane and cilia.

• Pharynx: Muscular tube (throat) that serves as a passageway for air and food.

• Larynx: Voice box; contains vocal cords and is involved in sound production.

• Trachea: Windpipe; a tube supported by C-shaped hyaline cartilage rings.

• Primary bronchi (right and left): Branches from the trachea into each lung.

• Lungs: Main organs of respiration; contain bronchi, bronchioles, and alveoli for gas exchange.

Example: Air enters through the nose, passes through the pharynx and larynx, travels down the trachea, and enters the lungs via the primary bronchi.

Structures of the Nose

Anatomical Features

• Nasal cavity: Main chamber for air passage.

• Meatuses (superior, middle, inferior): Grooves beneath each nasal concha that increase surface area.

• Nasal conchae (superior, middle, inferior): Curved bones that help filter, warm, and moisten air.

• External nares: Nostrils; external openings of the nose.

• Hard palate: Bony structure forming the floor of the nasal cavity and roof of the mouth.

Structures of the Pharynx

Regions and Functions

• Nasopharynx: Upper part, behind the nasal cavity; passageway for air only.

• Oropharynx: Middle part, behind the oral cavity; passageway for air and food.

• Laryngopharynx: Lower part; leads to the larynx and esophagus.

• Soft palate: Muscular posterior portion of the palate.

• Uvula: Small projection from the soft palate; helps prevent food from entering the nasopharynx.

Structures of the Larynx

Cartilages and Folds

• Hyoid bone: U-shaped bone supporting the tongue and larynx.

• Arytenoid cartilage: Paired cartilages involved in vocal cord movement.

• Thyroid cartilage: Largest cartilage; forms the Adam's apple.

• Tracheal cartilages: C-shaped rings supporting the trachea.

• Cricoid cartilage: Ring-shaped cartilage below the thyroid cartilage.

• Epiglottis: Flap that covers the trachea during swallowing to prevent food entry.

• Vocal fold: True vocal cords; produce sound.

Key Question: The epiglottis prevents food from entering the trachea during swallowing.

Key Question: The tracheal rings are C-shaped to allow the esophagus (behind the trachea) to expand during swallowing.

Structures of the Bronchial Tree

Branching Pathways

• Trachea: Main airway.

• Tracheal cartilage: Supports the trachea.

• Carina: Ridge at the base of the trachea where it splits into bronchi.

• Primary (main) bronchi: First branches into each lung.

• Secondary (lobar) bronchi: Branches to each lung lobe.

• Tertiary (segmental) bronchi: Further subdivisions supplying bronchopulmonary segments.

• Bronchioles: Smallest airways leading to alveoli.

Structures of the Lung

Lobes and Features

• Apex: Top of the lung.

• Base: Bottom of the lung.

• Lobes: Right lung has superior, middle, and inferior lobes; left lung has superior and inferior lobes.

• Cardiac notch: Indentation in the left lung for the heart.

• Hilum: Entry/exit site for bronchi, blood vessels, lymphatics, and nerves.

The lungs are located in the thoracic cavity. The parietal pleura lines the thoracic cavity wall, the visceral pleura covers the lung surface, and the pleural cavity is the space between them containing pleural fluid.

Microscopic Structure of the Trachea

Histological Features

• Pseudostratified ciliated columnar epithelium: Lines the trachea; contains cilia and goblet cells.

• Goblet cells: Produce mucus to trap particles.

• Cilia: Move mucus and trapped particles upward toward the pharynx.

• Hyaline cartilage: Provides structural support to the trachea.

Microscopic Structures of the Lungs

Alveolar Pathways

• Terminal bronchioles subdivide into respiratory bronchioles, which further subdivide into alveolar ducts, leading to alveolar sacs composed of clusters of alveoli.

• Alveoli: Tiny air sacs where gas exchange occurs; lined by simple squamous epithelium.

Ventilation and Respiration

Key Definitions

• Pulmonary ventilation: Movement of air into and out of the lungs (breathing).

• External respiration: Exchange of gases between alveoli and blood in pulmonary capillaries.

• Internal respiration: Exchange of gases between blood in systemic capillaries and body tissues.

Lung Volumes and Capacities

Spirometry and Spirograms

• Spirometer: Device used to measure lung volumes and capacities.

• Spirogram: Graphical recording of lung volumes during breathing.

• Vital Capacity (VC): The maximum amount of air exhaled after a maximal inhalation; calculated as the sum of tidal volume (TV), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV):

Normal VC ranges from 3100 to 4800 mL, depending on age, sex, and body size. VC is measured by inhaling deeply and exhaling forcefully into a spirometer.

Predicted Vital Capacities

The following tables provide predicted vital capacities for females and males based on age and height. These values are used to compare measured VC to expected norms for clinical assessment.

Additional info: These tables are used to assess respiratory health and diagnose restrictive or obstructive lung diseases by comparing measured values to predicted norms.