The Respiratory System and Tracheostomy | Anatomy 3D

by Robert Tallitsch, PhD | February 1, 2022

Short video featuring real 3D anatomy over the respiratory system and tracheostomy patient case example!

Written by: Robert Tallitsch, PhD

The respiratory system consists of the nose, nasal cavities, paranasal sinuses, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles, all of which lead to the alveoli within the lungs, which is the site where gas exchange occurs. This Brain Builder will focus on the respiratory structures that are found within the thoracic cavity.

Trachea

Structures within the respiratory system that are not involved in the process of gas exchange are termed conducting pathways. These structures serve to warm, moisten, and clean the air passing through them. The trachea descends within the superior mediastinum of the thoracic cavity, and terminates in the posterior mediastinum. At its most inferior point the trachea divides into the right and left bronchi, which enter the lungs at the hilum.

Surface Anatomy of the Lungs

Each lung is pyramidal in shape, with an apex, mediastinal surface, costal surface, and diaphragmatic surface. The apex of each lung projects into the most superior segment of the thoracic cavity at the base of the neck. The mediastinal surface faces the mediastinum of the thoracic cavity. The costal surface is adjacent to the inner surface of the rib cage, and the diaphragmatic surface comes into contact with the superior surface of the diaphragm.

The root of the lung is composed of those mediastinal structures that enter and/or leave the lung via the hilum. The most prominent of these would be the bronchi, pulmonary arteries, and pulmonary veins.

Each lung possesses an oblique fissure, and the right lung possesses an additional fissure termed the horizontal fissure. The two fissures of the right lung divide the lung into three lobes: upper, middle, and lower. The single fissure of the left lung divides that lung into upper and lower lobes.

Internal Anatomy of the Lungs

The conducting and respiratory pathways within the lung branch repeatedly, forming the bronchial tree. With each division the diameter of the conducting and respiratory pathways decreases, and the surface area increases.

The conducting pathways within each lung, which do not participate in gas exchange with the blood, are composed of the primary bronchi, segmental bronchi, bronchioles, and terminal bronchioles. In the right lung the primary bronchus divides into the upper lobar bronchus and the intermediate bronchus. The intermediate bronchus further subdivides into the middle and lower lobar bronchi. In the left lung the main bronchus subdivides into upper and lower bronchi. 

The respiratory pathways are the thinnest and most delicate branches of the respiratory tree. Their walls are incomplete, and these structures participate in gas exchange with the blood via the rich capillary network surrounding them. The respiratory pathways are composed of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. 

Microscopic Structure of the Alveoli

The alveoli of the lungs are small sacs of simple squamous epithelial cells. Three types of alveolar cells are found within the alveolar walls. Type I alveolar cells are thin squamous cells, and are the site of gas diffusion. Type II alveolar cells are larger than Type I cells and produce surfactant, which plays an important role in reducing surface tension and keeping the alveoli open. Large alveolar macrophages phagocytize foreign particles that have eluded other defense mechanisms of the respiratory system.

Tracheostomy: What is it, how is it done, and why is it done?

A tracheostomy is a surgical procedure that creates an opening in the anterior trachea in order to facilitate respiration. Often a tracheostomy is required in an emergency to allow breathing when one’s airway is obstructed or damaged in an accident. More commonly a tracheostomy may be performed in order to assist mechanical ventilation or to wean an individual from a ventilator.

Most tracheostomies are performed using a local anesthetic. The patient’s neck is slightly extended so that the trachea is easily palpated. A horizontal incision is made immediately inferior to the thyroid cartilage of the trachea. The thyroid gland is gently moved inferiorly and the larynx is stabilized. A tracheostomy tube is then inserted into the lumen of the trachea, and the tube is secured in place by two or more sutures.

A tracheostomy is typically performed in order to prevent or alleviate respiratory failure. Some common causes of respiratory failure could involve one or more of the following:

• Coma following a severe head injury or stroke
• A condition that damages the lungs, such as pneumonia or cystic fibrosis
• Any condition that causes paralysis of one or more of the respiratory muscles or a condition that damages the nervous system, such as Guillain-Barré syndrome

Anatomy Terms to Know:

Apex - The portion of the lung that projects into the uppermost, or most superior portion of the thoracic cavity at the base of the neck.

Mediastinal Surface - Surface of the lung that faces the mediastinum of the thoracic cavity.

Diaphragmic Surface -  Surface of the lung that comes into contact with the diaphragm.

Root - The root of the lung is composed of mediastinal structures that enter and/or leave the lung via the hilum.

Costal Surface - Surface of the lung that is adjacent to the inner surface of the rib cage.

Type I alveolar cells - Epithelial cells of the alveolus that are thin squamous cells, and are the site of gas diffusion.

Type II alveolar cells -  Epithelial cells of the alveolus that are larger than Type I cells and produce surfactant.

Large alveolar macrophages - Epithelial cells of the alveolus that phagocytize foreign particles.

Tracheostomy - A surgical procedure that creates an opening in the anterior trachea in order to facilitate respiration.

Alveolus - The small sac-like structures within the lung where gas exchange with the blood occurs.

Questions:

1. What is one surface-anatomy difference between the right and left lungs?
   A: The right lung has three lobes and the left lung only has two lobes.
   
   
2. What general type of medical condition typically initiates the performance of a tracheostomy by a physician?
   A: Respiratory failure
   
   
3. What is surfactant, and what type of cells secrete it?
   A: Surfactant is secreted by a Type II alveolar cell, and serves to reduce surface tension and keep the alveoli of the lungs open.
   
   
4. What is the anatomical term for the group of structures that do not participate in gas exchange?
   A: Conducting pathways
   
   
5. What are the various structures of the lung that do not participate in gas exchange?
   A: Primary bronchi, segmental bronchi, bronchioles, and terminal bronchioles
   
   
6. What is the name of the fissure that is found in both the right and left lungs? 
   A: Oblique fissure
   
   
7. What are the names of the anatomical structures of the lungs that do participate in gas exchange with the blood?
   A: The respiratory pathways are composed of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. 
   
   
8. The conducting pathways of the respiratory system change the air within them in what three ways? 
   A: The conducting pathways of the respiratory system warm, moisten, and clean the air.
   
   
9. Where do the right and left bronchi enter the lung at?
   A: Hilum of the lung
   
   
10. What structure is the incision for a tracheostomy directly inferior to?
    A: Thyroid cartilage
    
     

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