Histology of the alveoli Flashcards
What does the alveoli consist of?
Type I and II pneumocytes that lie on the basement membrane, and also alveolar macrophages.
What does the alveolar wall contain considerable amounts of?
Elastin
What is the function of the elastin within the alveoli?
It allows the lungs to stretch to accommodate inspired air, it recoils to its original shape, allowing air to be expelled and it acts as support, attaching airways with no cartilage firmly to the connective tissue of the lung.
What are type I pneumocytes?
Very thin, flattened cells, with flattened nuclei which allow gaseous diffusion that are joined together by tight junctions.
Type I pneumocytes represent about __% of the number of alveolar cells but __% of the surface area lining the alveoli.
40
90
Type II pneumocytes represent __% of the number of alveolar cells but only __% of the surface area lining the alveoli.
60
5-10
Type II pneumocytes secrete surfactant, what is surfactant?
A detergent which reduces alveolar surface tension, preventing collapse of the alveoli during expiration and facilitating inspirational expansion.
What do some type II pneumocytes act as?
Precursor stem cells for type I pneumocyte.
What is the structure of type II pneumocytes?
They are rounded in shape and contain numerous mitochondria.
What is the function of alveolar macrophages?
They patrol the alveolar spaces and the intreralveolar septa (the walls of the alveoli) and can pass freely between the two. They phagocytose inhaled debris and pathogens.
What happens to alveolar macrophages after they phagocytose?
They may pass into the lymphatic system or adhere to mucus-coated ciliated epithelium and continue up the mucosillary escalator to the trachea where they are cleared by coughing up.
