Xing Fan, Ph.D., Assistant Professor, Neurosurgery and Cell & Developmental Biology

This is a section from the testes of a mouse. The testes have two major functions in the male: it is the site of sperm development and it is an important producer of androgens, or sex hormones (the most important of which is testosterone). The large roundish structure in the center of this image is a seminiferous tubule, the site of sperm production. The round brown cells are early spermatids while the small elongated structures in the center of the tubule are late spermatids, ready to be released into the tubule lumen to begin their journey to the epididymis, where they are stored before ejaculation. The Leydig cells that produce testosterone lie just outside of the seminiferous tubules (e.g., the brownish cells in the upper left hand corner). They produce about 7 mg of testosterone a day to promote differentiation of the sperm and also to maintain the secondary sexual characteristics (low-pitched voice, beard, etc.). Skeletal growth, distribution of subcutaneous fat as well as behavior, including libido, are also influenced by testosterone from Leydig cells.