Difference Between Upper and Lower Respiratory Tract

Main Difference – Upper vs Lower Respiratory Tract

Respiratory system in animals consists of organs and structures that are adapted for gas exchange. Lungs are the major organs involved in the gas exchange in higher animals. The respiratory tract can be divided into two sections based on the position and function. They are the upper respiratory tract and the lower respiratory tract. The upper respiratory tract is composed of nose, sinus, pharynx, and larynx while the lower respiratory tract is composed of trachea, bronchi, bronchioles, and alveoli. The main difference between upper and lower respiratory tract is that upper respiratory tract is mainly involved in the conduction of air to the bottom parts whereas lower respiratory tract is mainly involved in the gas exchange.

Key Areas Covered

1. What is Upper Respiratory Tract
– Definition, Structure, Function
2. What is Lower Respiratory Tract
– Definition, Structure, Function
3. What are the Similarities Between Upper and Lower Respiratory Tract
– Outline of Common Features
4. What is the Difference Between Upper and Lower Respiratory Tract
– Comparison of Key Differences

Key Terms: Gas Exchange, Infections, Lower Respiratory Tract, Lungs, Upper Respiratory Tract

What is Upper Respiratory Tract

Upper respiratory tract refers to the uppermost section of the respiratory tract, which is mainly involved in the conduction of air. It includes the nose, sinus, pharynx, and larynx. During breathing, the air first enters into the nose through the nostrils. Dust and the other foreign particles are filtered out from the air by the nasal hair (vibrissae). The upper respiratory tract is lined by the pseudostratified epithelium. It is a ciliated epithelium and consists of goblet cells that secrete mucus. Mucus also traps small particles such as dust, pollen, smoke, and pathogens. The action of cilia helps to eliminate those particles out of the respiratory passageway. Thus, in addition to conduction of air to the bottom parts of the respiratory system, the upper respiratory tract cleans the air. The anatomy of the upper respiratory system is shown in figure 1.

Main Difference - Upper vs Lower Respiratory Tract

Figure 1: Upper Respiratory System

The other functions of the upper respiratory tract involve humidification and warming the air. The upper respiratory system is also involved in some non-respiratory functions such as sensation of smell and production of the voice. The smell is sensed by the epithelium of the nose. The larynx or the voice box is responsible for the production of voice.

What is Lower Respiratory Tract

Lower respiratory tract refers to the lowermost section of the respiratory tract, which is mainly involved in the gas exchange. It includes structures such as trachea, bronchi, bronchioles, and alveoli. Bronchi arise from the trachea by dividing the trachea into two as right primary bronchus and left primary bronchus. Primary bronchi further divide into secondary and tertiary bronchi. Bronchi form bronchioles. The three types of bronchioles are lobular bronchioles, terminal bronchioles, and respiratory bronchioles. Trachea, bronchi and bronchioles are made up of pseudostratified epithelium. The components of upper and lower respiratory tract are shown in figure 2.

Difference Between Upper and Lower Respiratory Tract

Figure 2: Upper and Lower Respiratory Tract

The alveoli and the respiratory bronchioles are lined by the simple squamous epithelium. Both alveoli and respiratory bronchioles are involved in the gas exchange. They receive deoxygenated blood through the pulmonary artery from the right ventricle of the heart. The oxygenated blood from the alveoli and respiratory bronchioles reaches the left atrium of the heart through the pulmonary veins.

Similarities Between Upper and Lower Respiratory Tract

Upper and lower respiratory tracts are the two sections of the respiratory system of animals.
Both upper and lower respiratory tract consist of tubules that conduct air.
Most of the structures in the upper and lower respiratory tract are lined by the pseudostratified epithelium.
Most epithelia of the upper and lower respiratory tract produce mucus.
Some of the structures in the upper and lower respiratory tract are composed of fibrocartilaginous rings.

Definition

Upper Respiratory Tract: Upper respiratory tract is the uppermost section of the respiratory tract, which is mainly involved in the conduction of air.

Lower Respiratory Tract: Lower respiratory tract is the lowermost section of the respiratory tract, which is mainly involved in the gas exchange.

Position in the Respiratory Tract

Upper Respiratory Tract: Upper respiratory tract consists of the upper parts of the respiratory tract above the lung.

Lower Respiratory Tract: Lower respiratory tract consists of the lower parts of the respiratory tract that occur inside the lung.

Components

Upper Respiratory Tract: Upper respiratory tract is composed of nose, sinus, throat, larynx, and trachea.

Lower Respiratory Tract: Lower respiratory tract is composed of bronchi, bronchioles, and alveoli.

Type of Epithelium

Upper Respiratory Tract: Upper respiratory tract is lined by the pseudostratified epithelium.

Lower Respiratory Tract: Alveoli and bronchioles of the lower respiratory tract are lined by the simple squamous epithelium.

Function

Upper Respiratory Tract: The main function of the upper respiratory tract is to conduct air to the bottom part of the respiratory tract.

Lower Respiratory Tract: The main function of the lower respiratory tract include the conduction of air and gas exchange.

Infections

Upper Respiratory Tract: Flu, common cold, laryngitis, sinusitis, and tonsillitis are infections of the upper respiratory tract.

Lower Respiratory Tract: Pneumonia, tuberculosis, bronchitis, and bronchiolitis are infections of the lower respiratory tract.

Conclusion

Upper and lower respiratory tract are the two sections of the respiratory system of animals. The upper respiratory tract includes the respiratory passageway from the nose to the lungs. The lower respiratory tract includes the respiratory passageway and respiratory membranes inside the lungs. Therefore, the upper respiratory tract is mainly involved in the conduction of air to the bottom part of the respiratory tract while the lower respiratory tract is involved in the conduction of air as well as the gas exchange. The main difference between upper and lower respiratory tract is the function of each section in the respiratory system.

Reference:

1. “Anatomy and function of the respiratory system – Penn State Hershey Medical Center.” Penn State Hershey Health Information Library, Available here.

Image Courtesy:

1. “Blausen 0872 UpperRespiratorySystem” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia
2. “Illu conducting passages” By Lord Akryl – (Public Domain) via Commons Wikimedia