Trachea Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. This is one of the factors that may limit their size. A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helices. Taenidia provide strength and flexibility to the trachea. In the head, thorax, or abdomen, tracheae may also be connected
Traditional Chinese medicines derived from the human body centuries after Li Shizhen considered the bioethical and biomedical dilemmas of using human drugs, 20th-century technological and medical advances have raised new related questions of organ transplants, transplantation medicine, organ trade, tissue banks, human cloning, and the commodification of human body parts (Awaya 1999, Nie 2002, Scheper-Hughes and Wacquant 2002). Traditional Chinese medicines derived from the human body Li Shizhen's (1597) "Bencao gangmu", the classic materia medica of traditional Chinese medicine (TCM), included 35 human drugs, including organs, bodily fluids, and excreta. Crude drugs derived from the human body were commonplace in the early history of medicine. Some of these