( ( A ( portal vessel ) ) ( ( is ( ( a ( blood vessel ) ) ( that ( ( ( links ( two ( capillary beds ) ) ) , ) ( in ( ( ( this case ) , ) ( ( the ( capillary bed ) ) ( of ( ( the ( median eminence ) ) ( with ( ( the ( capillary bed ) ) ( in ( the adenophypophysis ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ portal) (NN vessel)) (VP (VBZ is) (NP (NP (DT a) (NN blood) (NN vessel)) (SBAR (WHNP (WDT that)) (S (VP (VBZ links) (NP (CD two) (JJ capillary) (NNS beds)) (, ,) (PP (IN in) (NP (NP (DT this) (NN case)) (, ,) (NP (NP (DT the) (JJ capillary) (NN bed)) (PP (IN of) (NP (NP (DT the) (JJ median) (NN eminence)) (PP (IN with) (NP (NP (DT the) (JJ capillary) (NN bed)) (PP (IN in) (NP (DT the) (NNS adenophypophysis))))))))))))))) (. .)))
A portal vessel       is a blood vessel that links two capillary beds, in this case, the       capillary bed of the median eminence with the capillary bed in the       adenophypophysis.
(ROOT (S (NP (JJ Portal) (NNS veins)) (VP (VBP carry) (NP (NP (NN blood)) (PP (IN between) (NP (NP (NNS pairs)) (PP (IN of) (NP (JJ capillary) (NNS beds))))))) (. .)))