( Just ( ( prior ( to ovulation ) ) ( , ( ( the endometrium ) ( ( begins ( ( ( to thicken ) and ) ( to ( ( ( expand ( in response ) ) ( to ( ( the release ) ( of estrogen ) ) ) ) ( from ( the ovaries ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (ADVP (RB Just)) (PP (RB prior) (PP (TO to) (NP (NN ovulation)))) (, ,) (NP (DT the) (NN endometrium)) (VP (VBZ begins) (S (VP (VP (TO to) (VP (VB thicken))) (CC and) (VP (TO to) (VP (VB expand) (PP (IN in) (NP (NN response))) (PP (TO to) (NP (NP (DT the) (NN release)) (PP (IN of) (NP (NN estrogen))))) (PP (IN from) (NP (DT the) (NNS ovaries)))))))) (. .)))
Just prior to ovulation , the endometrium begins to thicken and to expand in response to the release of estrogen from the ovaries.
(ROOT (S (NP (NNP Ovulation)) (VP (VBZ occurs) (SBAR (IN before) (S (NP (DT the) (NN endometrium)) (VP (VBZ thickens) (PP (IN in) (NP (JJ estrous) (NNS cycles))))))) (. .)))