Respiratory cilia. Transmission electron micrograph (TEM) of a section through cilia from the respiratory epithelium of the lung. The inside of each cilium contains precisely arranged microtubules (dark rings) known as the axoneme, which supports the cilia, whilst allowing it to bend. The axoneme consists of a central unit containing two single microtubules and nine peripheral doublet microtubules. The cilia, along with mucous, act to trap potential pathogens and foreign particles, preventing infection.