( ( ( Filtration , ) ( reabsorption ( , ( secretion ( , ( and excretion ) ) ) ) ) ) . )
(ROOT (NP (NP (NNP Filtration)) (, ,) (NP (NN reabsorption) (, ,) (NN secretion) (, ,) (CC and) (NN excretion)) (. .)))
Filtration, reabsorption, secretion, and excretion.
(ROOT (S (NP (NP (DT The) (JJ main) (NNS functions)) (PP (IN of) (NP (NN epithelia)))) (VP (VBP are) (NP (NP (NN protection)) (PP (IN from) (NP (NP (DT the) (NN environment) (, ,) (NN coverage) (, ,) (NN secretion) (CC and) (NN excretion)) (, ,) (NP (NN absorption)) (, ,) (CC and) (NP (NN filtration)))))) (. .)))