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An alveolus consists of an epithelial layer of simple squamous epithelium (very thin, flattened cells), [13] and an extracellular matrix surrounded by capillaries. The epithelial lining is part of the alveolar membrane, also known as the respiratory membrane, that allows the exchange of gases.
The upper respiratory tract can refer to the parts of the respiratory system lying above the vocal folds, or above the cricoid cartilage. [4] [5] The larynx is sometimes included in both the upper and lower airways. [6] The larynx is also called the voice box and has the associated cartilage that produces sound.
The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES) [6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here. [7]
The thinning of the mucus layer ultimately affects the periciliary liquid layer, which becomes dehydrated, compromising ciliary function, and impairing mucociliary clearance. [ 16 ] [ 17 ] A respiratory therapist can recommend airway clearance therapy which uses a number of clearance techniques to help with the clearance of mucus.
The blood–air barrier or air–blood barrier, (alveolar–capillary barrier or membrane) exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood , and from blood entering the alveoli .
The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital tract.
Ciliated pseudostratified columnar epithelium is the type of respiratory epithelium found in the linings of the trachea as well as upper respiratory tract, which allows filtering and humidification of incoming air. [1] Non-ciliated pseudostratified columnar epithelia are located in the prostate [2] and membranous part of male vas deferens.
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue .