( ( ( The ( smooth muscle ) ) ( of ( arteriolar walls ) ) ) ( ( forms ( ( pre-capillary sphincters ) ( which ( ( regulate ( blood flow ) ) ( through ( the ( capillary bed ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ smooth) (NN muscle)) (PP (IN of) (NP (NN arteriolar) (NNS walls)))) (VP (VBZ forms) (NP (NP (JJ pre-capillary) (NNS sphincters)) (SBAR (WHNP (WDT which)) (S (VP (VB regulate) (NP (NN blood) (NN flow)) (PP (IN through) (NP (DT the) (JJ capillary) (NN bed)))))))) (. .)))
The smooth muscle of arteriolar walls forms pre-capillary sphincters which regulate blood flow through the capillary bed.
(ROOT (NP (NP (NP (DT The) (ADJP (RB precapillary) (JJ sphincters)) (NN regulate)) (PRN (-LRB- -LRB-) (PRP s) (-RRB- -RRB-))) (NP (NP (DT the) (NN passage)) (PP (IN of) (NP (NP (NN blood)) (PP (IN into) (NP (JJ capillary) (NNS beds)))))) (. .)))