One class that I've found really interesting so far in vet school is reproduction. I have enjoyed learning about the how animals develop into phenotypical females and males, and how this massive bull gained it's primary sex characteristics such as it's testes.
The first testes-unique cells to differentiate are the Sertoli cells, which are stimulated to develop by the Testes Determining Factor on the y chromosome. These cells are critical for spermatogenesis following sexual maturation. In the embryo, these cells secrete AMH (Anti-Müllerian hormone) which initiates degeneration of the female reproductive ducts and causes leydig cells to differentiate. Leydig cells synthesize and release testosterone, which is necessary to promote differentiation and growth of male duct system. Testosterone also promotes masculinization of the external genitals and sex glands.
How cool is that? 🐮