Definition is a rhetorical mode that can be used in something smaller or shorter than a full paper. You can use extended definition for several paragraphs only in a paper of much greater length. You also can add to a paper a one-paragraph definition--like a brief encyclopedia definition.
The research group, headed by Dr. Lukas Sommer at the Swiss Federal Institute of Technology, has identified a heretofore unknown role for the TGF cell-to-cell signaling pathway in the pathogenesis of DiGeorge syndrome.
A different siderotic scenario of locoregional character,2 is caused by mutations that affect cell iron utilization and result in intracellular foci of siderosis that damages cells of organs such as brain, heart, endocrine glands, or bone marrow (Figure), 6 and ensuing dysfunctions.