Question from M. Selvakumaran, Chennai
As we breathe in dust-laden air our respiratory system starts its filtering and expulsion mechanism from the nose itself. The small hairs present in our nose act as filters stopping bigger dust particles and smaller dust particles will be expelled by sneezing. The dust and particles adhering to dust will be washed away by the watery mucous that is secreted by the nasal mucosal layer. From here the dust that is smaller in particle size reaches bronchi and branchioles through wind pipe, trachaea and will be expelled in the form of mucous secreted by the cells lining these air passages. The dust surrounded by the mucus will be pushed upwards with the help of cilia present in the bronchioles and bronchi and comes out in cough, spit from the throat. Still smaller particles of dust might reach the alveoli (where exchange of oxygen and carbon dioxide takes place). Here macrophages take care of the defense mechanism by surrounding the minute dust particles. As there are no cilia in this region, this dust can only come out in the form of spit or it will be sent out through the digestive system. Dust can be laden with inorganics like silica dust, carbon (soot) or organic dyes, pigments or biological materials such as spores, bacteria, viruses, pollen and others, This can be injurious to our lungs. As per the latest guide lines by the air quality monitoring authorities respirable suspended particulate matter should not exceed 75 ppm on a 24 hourly basis. In sensitive areas such as hospitals it should not exceed 50ppm.
Dr. T. Bhavani,
Bengaluru
