Testicular histology

Most of the testicle, if you look at it under the microscope, is made of tubes: the seminiferous tubules, tightly coiled on themselves, and it is inside them that sperm develop. But the space around those maturing cells is not empty.

Wrapping around every stage of those cells are long, branched cells, the Sertoli cells, which are support cells: they physically support the ones that are maturing, like the scaffolding that surrounds a building under construction, and they also release signaling molecules that drive sperm production. They are inside the tube. Outside, in the space left between one tubule and the next, other cells live: the Leydig cells, which are also called interstitial cells because of where they sit, that is, in the interstices, the gaps. And the Leydig cells have a job of their own: they are the ones that make testosterone. Two neighborhoods, two jobs: inside the tube, cells are made; between the tubes, hormones are made.