Cilia. Coloured transmission electron micrograph TEM of a cross section through cilia circles, from the lining epithelium of the human trachea, or windpipe. Cilia in the trachea are hair_like projections that beat rhythmically to move mucus away from the gas_exchanging parts of the lungs, up towards the throat where it can be swallowed or coughed up. They project in parallel rows, with 300 on each cell, measuring up to 10 micrometres in length. Each cilium contains a central core axoneme, which consists of twenty microtubules arranged as a central pair, surrounded by nine peripheral doublets as seen.