( TPA ( ( ( ( ( must ( be ( administered ( within ( ( ( about three ) hours ) ( of ( a stroke ) ) ) ) ) ) ) , ) and ) ( ( is only ) ( effective ( for ( ( ischemic attacks ) ( involving ( ( blood clots ) ( in ( the brain ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP TPA)) (VP (VP (MD must) (VP (VB be) (VP (VBN administered) (PP (IN within) (NP (NP (QP (RB about) (CD three)) (NNS hours)) (PP (IN of) (NP (DT a) (NN stroke)))))))) (, ,) (CC and) (VP (VBZ is) (ADVP (RB only)) (ADJP (JJ effective) (PP (IN for) (NP (NP (JJ ischemic) (NNS attacks)) (PP (VBG involving) (NP (NP (NN blood) (NNS clots)) (PP (IN in) (NP (DT the) (NN brain)))))))))) (. .)))
TPA must be administered within about three hours of a stroke, and is only effective for ischemic attacks involving blood clots in the brain.
(ROOT (S (NP (CD Three) (NNS steps)) (VP (VBP are) (VP (VBN involved) (PP (IN in) (NP (NN blood) (NN clotting))))) (. .)))
Three steps are involved in blood clotting.