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.
V. Toxicants and Blood-Testis Barrier Function. Environmental toxicants, such as heavy metals (e.g., cadmium), that caused testicular injury (Parizek and Zahor, 1956; Parizek, 1960; Chiquoine, 1964) and BTB disruption (Setchell and Waites, 1970) were first reported more than 5 decades ago.RP1 was found to be expressed at relatively high levels in the mouse testis versus other organs. It is detected in Sertoli cells, spermatogonia, round and elongating/elongated spermatids, and even spermatozoa (Stride et al., 1996), but mostly in Sertoli cells and Leydig cells of humans and mice (Flens et al., 1996).