( ( When ( ( this ( smooth muscle ) ) contracts ) ) ( , ( ( ( the flow ) ( of urine ) ) ( begins . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT this) (JJ smooth) (NN muscle)) (VP (VBZ contracts)))) (, ,) (NP (NP (DT the) (NN flow)) (PP (IN of) (NP (NN urine)))) (VP (VBZ begins)) (. .)))
When this smooth muscle contracts, the flow of urine begins.
(ROOT (S (NP (JJ Smooth) (NN muscle)) (VP (VBZ regulates) (NP (NP (NN air) (NN flow)) (PP (IN in) (NP (NNS lungs))))) (. .)))
Smooth muscle regulates air flow in lungs.