在下列这段话中分别为啥意思：
Parenchyma / Stroma: The parenchyma of an organ consists of that tissue which conducts the specific function of the organ and which usually comprises the bulk of the organ. Stroma is everything else -- connective tissue, blood vessels, nerves, ducts. The parenchyma / stroma distinction provides a convenient way to circumvent the listing of tissue types when discussing an organ.