What is Respiratory Epithelium?

Respiratory Epithelium: Structure, Function & Role in Airway Defence

Respiratory epithelium is one of the main points of contact between the immune system and the external environment. It is present as the respiratory mucosa, which lines the majority of the respiratory system and protects and lubricates the airways.

Understanding Respiratory Epithelium

The respiratory epithelium, or airway epithelium, is a ciliated pseudostratified columnar epithelium. As people breathe, their respiratory systems continuously filter air from the outside world. To preserve homeostasis and avoid inflammation, airways must continue to be able to remove debris, allergens, and pathogens while breathing.

Effective gas exchange, absorption of oxygen from the surroundings, and removal of carbon dioxide from the body all depend critically on the integrity and functionality of epithelium.

What is the main function of the respiratory epithelium?

Just like the skin protects our body from irritants and external pathogens, the respiratory epithelium works to protect against and efficiently remove irritants and pathogens from the lungs and airways.

The respiratory epithelium has three main cell types, each of which is essential for controlling human breathing. The body is more vulnerable to infections, pathogens, inflammation, and haemostasis disruption if any of these barrier components are not operating correctly.

These are some of the key functions of the respiratory epithelium:

• Humidification and Warming : Serous and mucous secretions are necessary for humidification. Air is warmed and humidified primarily in the nasal cavity and upper airways by a rich vascular network in the submucosa. The alveoli are the sites of gas exchange, where their thin walls and vast capillary network allow for the efficient diffusion of oxygen and carbon dioxide.
• Filtration : Mucus secreted by goblet cells traps inhaled particles and pathogens. The coordinated beating of cilia then propels this mucus layer upward toward the pharynx, where it is swallowed or coughed out, effectively removing the trapped material from the airways.
• Oxidant Defence and Injury Response : The respiratory epithelium’s cells are constantly fighting against infections and particles while also healing from damage. Basal cells are attached to the basement membrane via hemidesmosomes. These cells act as stem cells, capable of dividing and differentiating into the ciliated and goblet cells necessary to maintain and repair the epithelial lining. Ciliated and goblet cells can adhere to the basal lamina through basal cells. Additionally, they react to damage and participate in transepithelial water flow and oxidant defence of the airway epithelium.
• Gas Exchange : Carbon dioxide and oxygen exchange happen in hundreds of microscopic alveolar sacs. Air that is inhaled diffuses into the pulmonary capillaries through the alveoli. Simultaneously, while exhalation takes place, carbon dioxide from deoxygenated blood diffuses into capillaries, then into alveoli, and finally out of airways.

Why is Respiratory Epithelium Clinically Important?

Respiratory epithelium has clinical significance, as it plays a crucial role in acting as a barrier to pathogens and outer particles. However, it also works by using the mucociliary elevator to stop tissue damage and infection.

What are the types of epithelium?

A single layer of cells makes up an epithelium. They are usually sites of filtration, secretion, and absorption. The thinness of the epithelial barrier facilitates these processes. Different types of epithelium are classified depending on the number of cell layers and the shape of the cells. The standard classification of epithelium, are as follows:

• Simple Epithelium (one layer) : Simple Squamous (alveoli, capillaries), Simple Cuboidal (kidney tubules, glands), Simple Columnar (intestines, stomach).
• Stratified Epithelium (multiple layers) : Stratified Squamous (skin, mouth, esophagus), Stratified Cuboidal (ducts of sweat glands), Stratified Columnar (conjunctiva, some gland ducts).
• Pseudostratified Columnar : A type of simple epithelium where all cells touch the basement membrane but nuclei are at different heights (found in the respiratory tract and male reproductive system).

Is Respiratory Epithelium Keratinised?

No, the respiratory epithelium is not keratinised. Usually, it is a pseudostratified ciliated columnar epithelium with mucus-secreting goblet cells. This type of epithelium is appropriate for its function in the respiratory tract. This includes trapping and removing particles and pathogens while breathing.

However, keratinisation is a maturation process when cells generated in the basal layer go to the stratum corneum, where they degenerate and shed.

Your body’s health and activities depend heavily on epithelial tissue. Respiratory epithelium helps to preserve homeostasis and avoid inflammation. With the help of the respiratory epithelium, airways remove debris, pathogens, and allergens while breathing. The functions of this type of epithelium are humidification and warming, oxidant defence and injury response, filtration, and gas exchange.

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