Respiratory System Overview

Respiratory System Overview

• The respiratory system is divided anatomically into upper and lower respiratory tracts.
• Functionally, it's divided into conducting and respiratory parts.

Respiratory System Divisions

• Conducting portion:
  • Nasal cavity
  • Nasopharynx
  • Larynx
  • Trachea
  • Primary bronchi
  • Secondary bronchi
  • Bronchioles
  • Terminal bronchioles
• Respiratory portion (where gas exchange occurs):
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveoli

Lungs

• Cone-shaped, triangular organs.
• Apex: Narrow superior tip.
• Base: Inferior surface resting on the diaphragm.
• Hilum: Site of entry for pulmonary and systemic blood vessels.
• Left lung: Two lobes (upper and lower) separated by the oblique fissure.
• Right lung: Three lobes (upper, middle, and lower) separated by oblique and horizontal fissures.

Larynx

• Connected to the trachea.
• Supported by cartilages (thyroid, cricoid, arytenoids).
• Larger cartilages are hyaline, smaller are elastic.
• Contains vocal folds (true and false).

Trachea

• Flexible tube extending from the larynx to the mediastinum.
• Divides into two main bronchi at the level of T4.
• Composed of C-shaped cartilages.
• Lined with respiratory epithelium.

Lung Histology

• Components of the intrapulmonary (secondary) bronchi wall:

  • Mucosa
    • Respiratory epithelium (with fewer goblet cells)
    • Rich in elastic fibers
  • No submucosa
  • Complete smooth muscle layer (surrounding the mucosa)
  • Adventitia (containing elastic fibers and incomplete hyaline cartilage).

• Bronchioles:

  • Smaller airways (<1 mm) branching from bronchi.
  • Mucosa with simple columnar ciliated epithelium (Clara cells present).
  • Decreasing epithelial cell height and cilia towards terminal bronchioles.
  • Connective tissue.
  • Smooth muscle layer surrounding the lumen.
  • Loose connective tissue (adventitia).

• Alveolar ducts:

  • Free terminations of respiratory bronchioles.
  • Alveolar walls are interrupted by openings of alveoli.

• Alveolar sacs:

  • Common spaces formed by adjacent alveoli.

• Alveoli:

  • Structural and functional units of the lungs.
  • Separated by interalveolar septa and connected by alveolar pores (of Kohn).
  • Lined by two cell types: Type I and Type II pneumocytes.

• Type I pneumocytes:

  • Flat, squamous cells.
  • Covering the majority of alveolar surface (~95%).
  • Function in gas exchange.

• Type II pneumocytes:

  • Cuboidal cells with central nuclei.
  • Produce surfactant (reducing surface tension).
  • About 5% of the alveolar surface.

Recommended References

• Junqueira's Basic Histology: Text and Atlas, Thirteenth Edition 2013
• The histology tutor online resource

This quiz covers the anatomy and function of the respiratory system, detailing its upper and lower tracts. Learn about the divisions of the respiratory system, including the conducting and respiratory portions, as well as the structure of the lungs and larynx. Test your knowledge on how these components facilitate gas exchange.