This provides it mechanical strength to ensure that the trachea’s wall does not collapse during exhalation. The mucosa is smooth and moist with gaps filled by the trachealis muscle. The trachealis muscle is a combination of smooth muscle and fibroelastic tissue, and it ensures that the lumen of the trachea is constantly open, allowing free flow of air without obstruction. In addition it allows flexibility to the trachea, so during exhalation and inhalation it’s able to move (Peckham, 2003). The mucosa and submucosa are warm and so in turn will moisten the air to prevent the lungs from drying out. The trachea is lined with epithelial cells, and these cells are made up of goblet cells and ciliated epithelial cells. Goblet cells produce and secrete mucus which will line the trachea, and the mucus is present to trap dust and bacteria and this ensures that the air is filtered before reaching the lungs otherwise invasion of bacteria can lead to infection and further complications. The ciliated cells have a protective function and sweep the mucus along towards the stomach so it doesn’t block the …show more content…
Alveoli form a barrier between the air in the lungs and the blood in the capillaries, but because the membrane is only 0.5µm across there is a rapid rate of diffusion of oxygen in and carbon dioxide out. The alveolar surface consists of simple squamous epithelial type 1 cells. These form a single layer and this will ensure that gases can easily diffuse through. A small part of the alveolar surface is occupied by type 2 cells which are cuboidal shaped cells. There function is to repair the alveolar wall after damage and release alveolar fluid which includes surfactant. This is a complex of phospholipids and proteins, and is designed to reduce the surface tension of liquids. This is beneficial because it keeps the alveolar walls from sticking together during exhalation (source, 2010). Alveolar macrophages will line the alveolar wall and their main function is to engulf foreign particles. The alveolar wall is separated from the capillary wall by an interstitial space. Interstitial fluid will fill these pores between the cells. The fluid is designed to allow diffusion of gases across the respiratory