Trach Anatomy and Physiology

 

A knowledge of the anatomy and physiology of the respiratory system is necessary to the health care provider who is involved in the care of the tracheostomized patient.

The Upper Airway

The nose plays a very important role in the upper airway. As air enters the nostrils large particles of dust and dirt are filtered. The mucus membranes of the nasopharynx further filter this air, warm or cool the inspired air, and humidify it.

The column of inspired air travels down through the oral pharynx to the laryngopharynx. Here it passes through the larynx where the vocal cords are located. The larynx is located at the top of the trachea. When a person breathes in, the vocal cords open, allowing air to pass freely into the trachea.

The larynx is composed of nine cartilage structures: three large single cartilages and three paired cartilages. The three large single cartilages are the epiglottis, the thyroid, and the cricoid. The three paired cartilages are the smaller arytenoids, cuneiforms, and the corniculates. The cricoid cartilage is the only circumferential cartilage of the trachea, and is an important landmark used during tracheostomy.

The trachea is a tubular structure 10-14 cm in length in an adult. It extends from the larynx through the neck to the thorax, where it terminates at the carina, dividing into the right and left main stem bronchi.

The trachea joins with the larynx at the level of the 6th cervical vertebra,- it bifurcates at the carina at about the level of the 5th thoracic vertebra. Within the thorax the trachea lies in the mediastinum, its lower position being directly behind the heart and its large vessels.

It is constructed of 15 to 20 C-shaped cartilaginous rings separated by fibrous muscular tissue which form the supporting framework. Each cartilage is incomplete dorsally where it is adjacent to the esophagus. A fibro-elastic membrane containing smooth transverse fibers of muscle extends across the open portion of the trachea where the cartilages are incomplete dorsally. The anterior cartilage provides the rigidity necessary to maintain patency of the tube.

The tracheal structure consist of four layers: mucosa, submucosa, cartilage, and adventitia. The inner layer, the mucosa, has ciliated pseudo-stratified columnar epithelium with goblet cells. Mucus excreted from the goblet cells helps trap inhaled particles of dust and the cilia sweep it upward into the laryngopharynx where it can be swallowed or coughed out.

The submucosa is loose connective tissue containing glands that secrete mucus.

The trachea ends by dividing into the right and left main stem bronchi which extend to the lungs. Each bronchus enters its own respective lung through the hilus (an opening through which nerves, vessels, etc. enter or exit an organ). The right main stem bronchus is shorter, wider, and more vertical than the left. Consequently, this

bronchus is more easily intubated, suctioned, and foreign bodies more frequently end up in the right bronchus.

The Lower Airway

As soon as the bronchi enter each lung they branch to form smaller or secondary bronchi, one for each lobe of the lung (three lobes on the right and two on the left). The secondary bronchi continue to branch to form still smaller tubes or bronchioles.

Structurally, the bronchi are very similar to the trachea. Their walls have cartilaginous rings and are lined with ciliated mucus membrane. However, as they become smaller and smaller, less and less cartilage is present in their walls, and more and more smooth muscle appears.

 

The lungs are truly the organs of respiration where exchange of gases between blood and air takes place.


 

The lungs are made up of light spongy tissue. Within this spongy tissue lie the secondary bronchi and bronchioles, which conduct air to and from the respiratory units (alveoli) of the lung.

Fissures divide each lobe of the lung. The right lung has three lobes and the left lung has two. Each lobe is further divided into lobules. Lobules are irregular in size and shape, but each is supplied with air by a bronchiole. As the bronchioles enter the lobules they divide repeatedly to form very small airways called terminal bronchioles and then the smallest airways, the respiratory bronchioles. These smallest of airways finally reach the functional unit of the lung, the alveoli. It is here within the alveoli that the exchange of oxygen and carbon dioxide takes place.