In terms of pronominal reference,

“…that…” (line 2) refers to “…blood…” (line 1).

“…which…” (line 11) refers to “…supplies…” (line 10).

“where…” (line 16) refers to “…networks” (line 15).

“…where…” (line 31) refers to “…routes…” (line 31).

“This…” (line 37) refers to “…behavior.” (line 37).