human_reference_atlas Homo sapiens lobar bronchus http://upload.wikimedia.org/wikipedia/commons/d/df/Illu_quiz_lung05.jpg MA:0000437 EHDAA:8203 EHDAA:8225 secondary bronchus EHDAA:4963 EHDAA:4985 AS SCTID:245509008 secondary bronchus EHDAA:8187 Wikipedia:Secondary_bronchus bronchi lobaris FMA:7406 EHDAA:4993 EHDAA:8213 secondary bronchus EHDAA:8175 secondary bronchi uberon lobar bronchi They have relatively large lumens that are lined by respiratory epithelium. There is a smooth muscle layer below the epithelium arranged as two ribbons of muscle that spiral in opposite directions. This smooth muscle layer contains seromucous glands. Irregularly arranged plates of hyaline cartilage surround the smooth muscle. These plates give structural support to the bronchus and maintain the patency of the lumen. UBERON:0002183 NCIT:C32998 EMAPA:32696 The lobar bronchus is the major airway within the respiratory tree that starts by division of the principal bronchi on both sides and ends at the point of its own subdivision into tertiary or segmental bronchi[GO]. UMLS:C0225653 EHDAA:4955 EHDAA:4977 bronchus tracheobronchial tree