Fig. 4.

Schematic overview of C₁₉steroid biosynthesis in the testes. The testes produce C₁₉ steroids via the classical Δ⁵ pathway in the Leydig cells. Due to abundant HSD3B2 and HSD17B3, and the lack of aromatase, T is the major product making the testes the only steroidogenic organ secreting significant amounts of an active androgen (black box). Major pathways are indicated by bold arrows and arrows are labelled with the major isoform of the enzyme responsible for the reaction.