lesson 107, trachea and bronchiial patterns

Systems 1: Cardiovascular & Respiratory (CVR)

Lesson Overview

• Lesson #107: The Trachea, Bronchial Tree, and Associated Structures

• Instructor: Dr. Mahesh Shriram Deokar

Learning Outcomes

By the end of this lesson, students will be able to:

• Identify the anatomical features of the trachea and bronchial branching pattern.

• Understand integrated medical imaging of the trachea and bronchi.

Outline of Lesson Content

• Location of the trachea and its association with the larynx

• The trachea in the visceral space of the neck / Cervical space

• The thoracic inlet

• Tracheal bifurcation and bronchial tree

• Lung lobes in relation to the bronchial tree

• Microscopic structure of the trachea

• Blood and nerve supply to the trachea

• Endoscopy and radiography of the trachea

The Trachea

• A tubular organ that extends from the cricoid cartilage of the larynx to the tracheal bifurcation (at 4th or 5th thoracic vertebra).

• Composed of approximately 35 'C' shaped cartilages in dogs (hyaline in nature).

  • Free ends of the cartilages are located dorsally.

• Cervical and thoracic parts:

  • Cervical part: Located in the visceral space of the neck.

  • Thoracic part: Enclosed within the mediastinum.

Cervical Space

Boundaries of the Cervical Space

• Dorsal: Cervical vertebrae and muscles.

• Lateral: Muscles between the forelimb and neck/head (e.g., brachiocephalicus, omotransversarius, omohyoideus in horses).

• Ventral: Strap muscles (sternothyroideus, sternohyoideus, sternocephalicus).

Organs in the Cervical Space

• Larynx and trachea

• Esophagus

• Thyroid gland

• Thymus gland (bovine)

• Carotid sheath

• Lymph nodes

• External jugular vein

Trachea and Esophagus Relations

Sections and Views

• Transverse sections of the cervical vertebrae outline relations between the trachea and esophagus.

• Cranial, mid, and caudal views through various cervical vertebrae (C2-C6) to illustrate positions.

Thoracic Inlet

• Composition:

  • 1st ribs, 7th cervical and 1st thoracic vertebrae, manubrium of the sternum.

• Located below the trachea and esophagus, surrounded by blood vessels and nerves.

Tracheal Cartilages

• Tracheal rings: C-shaped hyaline cartilage that is incomplete and varies by species.

  • Free ends are directed dorsally and connected by smooth muscle (trachealis muscle).

• Variations in shape and size depending on species; diameter changes throughout the length, typically narrowest at the thoracic inlet.

Bronchial Tree

• Structure: Branching from tracheal bifurcation to alveoli, the functional respiratory unit.

• Formed by principal bronchi which further divide into secondary, tertiary, and ultimately bronchioles.

Conducting Airways

• Responsible for carrying air without gaseous exchange:

  • Primary bronchi

  • Secondary (lobar) bronchi

  • Tertiary (segmental) bronchi

  • Bronchioles and terminal bronchioles

Respiratory Airways

• Responsible for gaseous exchange with defined structures:

  • Respiratory bronchioles (have alveoli)

  • Alveolar ducts and pulmonary alveoli

Microscopic Structure of the Trachea

Histological Features

• Lined by ciliated pseudostratified columnar epithelium with goblet cells for mucous secretion.

• Layers include:

  • Subepithelial layer of elastic fibers for support and recoil

  • Mixed tubuloacinar glands and smooth muscle for fluid secretion

  • C-shaped hyaline cartilage support

  • Adventitia, a thin layer of fibrovascular connective tissue

Blood Supply

Cranial and Caudal Blood Supply

• Arterial: Cranial and caudal thyroid arteries

• Venous: Cranial and caudal thyroid veins

Nerve Supply

• Parasympathetic:

  • Recurrent laryngeal nerves (from vagus nerve)

• Sympathetic:

  • Branches from the middle cervical ganglion

Tracheal Examination and Disorders

• Endoscopy used for tracheal examination in animals.

• Tracheal collapse: occurs due to weakening of tracheal rings; can be treated with stenting or surgical methods.

Lesson Summary

• The trachea consists of cervical and thoracic sections featuring C-shaped cartilages and branching into the bronchial tree.

• The bronchi correspond to lobes of the lung, with the trachea lined by respiratory epithelium and supported by various arteries and nerves.

• Endoscopic techniques are common for tracheal assessments, especially for addressing conditions like tracheal collapse.

Next Steps & Questions

• For questions, post in discussion forums or book office hours.

• Prepare for laboratory sessions.