Respiratory System: Anatomy, Histology, and Pulmonary Volumes

Respiratory System Anatomy

Major Structures of the Respiratory System

The respiratory system is responsible for gas exchange and consists of several anatomical structures that facilitate the movement of air and the exchange of oxygen and carbon dioxide. Understanding the location and function of each structure is essential for identifying them on models or diagrams.

• Nostril: The external openings of the nose, allowing air entry into the nasal cavity.

• Nasal cavity: The space inside the nose lined with mucosa; warms, moistens, and filters incoming air.

• Superior, middle, and inferior nasal conchae: Curved bony projections inside the nasal cavity that increase surface area for air filtration.

• Superior, middle, and inferior nasal meatuses: Passages beneath each concha that direct airflow and drain sinuses.

• Soft palate: The posterior muscular portion of the palate, separating the nasopharynx from the oropharynx.

• Hard palate: The anterior bony portion of the palate, forming the roof of the mouth.

• Uvula: The small, fleshy extension at the back of the soft palate; helps prevent food from entering the nasopharynx.

• Pharynx: The muscular tube connecting the nasal cavity to the larynx and esophagus; divided into:

  • Nasopharynx: Uppermost part, behind the nasal cavity.

  • Oropharynx: Middle part, behind the oral cavity.

  • Laryngopharynx: Lowest part, leading to the larynx and esophagus.

• Larynx: The "voice box"; contains vocal cords and is involved in sound production and airway protection.

  • Epiglottis: Flap of cartilage that covers the larynx during swallowing.

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

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

• Trachea: The "windpipe"; a tube reinforced with cartilage rings, conducting air to the bronchi.

• Primary Left and Right Bronchi: The first branches of the trachea, leading to each lung.

• Hilum: The region of the lung where bronchi, blood vessels, and nerves enter and exit.

• Bronchioles: Smaller branches of the bronchi, leading to alveolar sacs.

• Alveolar sacs / Alveoli: Clusters of tiny air sacs where gas exchange occurs.

• Lungs: The main organs of respiration; each lung has specific features:

  • Apex: The pointed upper portion.

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

  • Base: The broad lower portion resting on the diaphragm.

  • Diaphragm: The muscular sheet separating thoracic and abdominal cavities; main muscle of respiration.

  • Lobes: The right lung has three lobes (superior, middle, inferior); the left lung has two lobes (superior, inferior).

Example: On a model, the left lung's cardiac notch is visible, and the right lung is larger with three lobes.

Respiratory Histology

Microscopic Structure of the Trachea and Lung

Respiratory tissues can be distinguished by their cellular composition and structural features. Recognizing these differences is important for identifying tissues on slides.

• Trachea: Lined with pseudostratified ciliated columnar epithelium; contains goblet cells and prominent hyaline cartilage rings.

• Lung tissue: Contains simple squamous epithelium in alveoli for gas exchange; lacks cartilage; alveolar sacs are visible as open spaces.

• Cell types: Trachea has ciliated cells and goblet cells; alveoli have type I (simple squamous) and type II (cuboidal, surfactant-producing) cells.

• Cartilage presence: Cartilage is present in the trachea and bronchi, absent in bronchioles and alveoli.

Example: On a slide, the trachea shows thick cartilage rings and ciliated epithelium, while lung tissue shows thin-walled alveoli.

Pulmonary Volumes and Spirometry

Key Pulmonary Volumes

Pulmonary volumes are measurements of air movement during breathing. These values are important for assessing lung function.

• TV (Tidal Volume): The amount of air inhaled or exhaled during normal breathing.

• ERV (Expiratory Reserve Volume): The additional air that can be exhaled after a normal exhalation.

• IRV (Inspiratory Reserve Volume): The additional air that can be inhaled after a normal inhalation.

• RV (Residual Volume): The air remaining in the lungs after maximal exhalation.

Vital Capacity (VC): The total amount of air that can be exhaled after maximal inhalation. It is calculated as:

$VC = TV + IRV + ERV$

Formula for IRV: If given TV, ERV, and VC, IRV can be calculated as:

$IRV = VC - (TV + ERV)$

Example: If VC = 4000 mL, TV = 500 mL, ERV = 1000 mL, then:

$IRV = 4000 - (500 + 1000) = 2500 \text{ mL}$

Spirometer

A spirometer is a device used to measure pulmonary volumes and capacities. It records the amount and rate of air inhaled and exhaled, helping diagnose respiratory conditions.

• Measures: Tidal volume, vital capacity, and other lung volumes.

• Applications: Used in clinical and laboratory settings to assess lung function.

Example: A spirometer can detect reduced vital capacity in patients with restrictive lung disease.

Respiratory System Lobes

Lung Lobes and Their Positions

The lungs are divided into lobes, each with distinct anatomical positions.

Lung	Lobe Name	Position
Right	Superior	Uppermost
Right	Middle	Between superior and inferior
Right	Inferior	Lowest
Left	Superior	Uppermost
Left	Inferior	Lowest

Additional info: The left lung is smaller due to the cardiac notch, accommodating the heart.