Final answer:
Sertoli cells are elongate, branching sustentacular cells that surround developing sperm cells in the seminiferous tubules. They secrete signaling molecules, create the blood-testis barrier, and support sperm production.
Step-by-step explanation:
Sertoli cells are elongate, branching sustentacular cells that surround developing sperm cells in the seminiferous tubules. They secrete signaling molecules that promote sperm production and extend physically around the germ cells from the basement membrane to the lumen. The tight junctions between Sertoli cells create the blood-testis barrier, preventing bloodborne substances from reaching the germ cells and stopping surface antigens on germ cells from escaping into the bloodstream.