Since we recently discussed the process of oogenesis, it only seemed right that we also cover spermatogenesis! Both are a type of gametogenesis which is the umbrella term for the production of sex cells. Spermatogenesis is not quite as difficult, but there are some nomenclature things that can be easy to get confused with.
At the time of birth, males already have spermatogonia. These are the primordial germ cells that will eventually develop into mature sperms. Mature sperms are known as spermatozoa. Some people use the memory device that “spermatazoa zoom to the egg.” As long as it works, right?
The spermatogonia lie dormant in the testes until puberty. Once again, there is a reason kids going through puberty are so damn awkward. There is a lot of new things going on in the body, including the start of spermatogenesis. This 74 day cycle (approximately) will normally last from now until death.
So, enter your almighty pituitary gland. It’s going to stimulate to release the same enzymes as in oogenesis – Follicle Stimulating Hormone (FSH) and Lutenizing Hormone (LH). Both of these are going to work their way down to where LH stimulates the leydig cells to begin creating testosterone. Testosterone, along with FSH, stimulates the actual spermatogenesis process.
Spermatogenesis has three stages: spermatocytogenesis, spermatidogenesis, and spermiogenesis. See how that can get confusing? Make particular note, though, of the name of the stage and how it relates to the name of the gamete at that point. If you can get that straight, you’ll keep this straight. You can also remember it as we’re going from the longest word to the shortest.
- SPERMATOCYTOGENESIS
At the start of this process, we have the spermatogonia that the male was born with. The first phase is turning them into spermatocytes. Now look at the name of the stage. Make sense? It’s the beginning (genesis) of spermatocytes – spermatocytogenesis. First, the spermatogonia go through mitosis resulting in two daughter cells that are genetically identical. Next, they go through the meiosis I to begin the process of developing genetic variance.
- SPERMATIDOGENESIS
Alright, so we started the process of developing genetic variance. In spermatidogenesis, we’re going to finish meiosis II, fully forming our haploid cells. These are called…can you guess? Look at the name. Yup, spermatids. I’d say more here, but that is pretty much all that happens!
- SPERMIOGENESIS
At this point, we’ve never left the sertoli cells, we have our haploid spermatids but we can’t really get anywhere. They’re not quite ready for moving or fertilizing. Enter spermiogenesis. The name thing doesn’t work quite as well since we’re making spermatazoa, but if you can recognize that spermatazoa is the goal and spermiogenesis is the final step, we should be good.
So from here, we go into the lumen of seminiferous vesicles and get carried to the epididymis for our mature spermatozoa to get mobile and look like sperm as we think of it. We’re going to see the formation of the acrosome, which aids in penetrating eggs protective lining. The nucleus will be condensed and the neck, middle piece and tail will form. That neck is loaded with mitochondria, too. It takes a tremendous amount of energy to swim that hard for that long! We’re also going to shed some other things that are just weighing the spermatozoa down. The metaphor would be how you might put a big motor in a car and take out the seats and anything else that adds unnecessary weight.
The last thing that happens in this process goes all the back to the role of FSH. It helped to start this process, but it’s also going to help to finish it. FSH stimulates the sertoli cells to make inhibin. Inhibin is the negative feedback that the pituitary gland is looking for to slow this process down. So the more FSH that is released, the more inhibin that gets released, the more the pituitary gland is told to stop releasing FSH (and LH!)
And that is pretty much how it happens! Of course, there are some extra details that you may want to fill in for yourself, but our goal is to provide you with a good framework for understanding the concept. So, remember the types of sperm you’re making or look to the order of the stages to help you keep track of everything. Best of luck!