Human Physiology – Reproduction: Spermatogenesis

>>Dr. Ketchum: In this video lecture we are going to be studying sperm and their development. Okay, so just starting out with the sperm. And remember that sperm are the male gamete, and also be sure that you understand that sperm are also called spermatozoa. That’s the same thing. So if you hear the term spermatozoa, we are referring to sperm. Okay, so let’s look at the morphology and what some of the important structures are associated with the sperm. So you have three different regions: there’s the head, the midpiece, and the tail.

So the head contains a couple of important things, and number one those are the chromosomes. And so what I would like to ask you is how many autosomes are there in the head, and how many sex chromosomes? So if you want to pause the video for a moment and think about that, then I’ll give you the answer in just a minute. Okay, so remember sperm are haploid. And because they’re haploid that means they’re one n, so that means we’re going to have 22 autosomes and one sex chromosome. Okay, also associated with the head is the area called the acrosome.

The acrosome contains the enzymes that are necessary for fertilization, and we’re going to come back to the acrosome and how sperm fertilized the egg later. Then there’s the midpiece, the next region of the sperm. And the midpiece contains the mitochondria. Why are the mitochondria important for sperm? So if you remember, the mitochondria are the powerhouse for the cell. So that’s going to produce ATP. Sperm are motile, and they need the ATP in order to generate that energy to move. The last component of the sperm or the last segment is the tail. The tail is called the flagellum, and so this is what the sperm use in order to propel themselves. So when we talk about motility of the sperm, essentially, you can think about the flagellum whipping.

And its whip-like motion is what propels the sperm, or causes the sperm to move. So how are those sperm produced? We’re going to look at spermatogenesis. So this is the process of sperm production; how the sperm are actually produced. So keep in mind that sperm production is associated with the Sertoli cells, and remember that the Sertoli cells are associated with the seminiferous tubules. And so where we’re going to begin is at the basement membrane, okay.

And then you have a Sertoli cell here on the left; you have a Sertoli cell here on the right, and we’re going to be talking about spermatogenesis that’s occurring between the Sertoli cells. So we’re going to start with a germ cell. So the germ cells are the spermatogonia. Germ cells are diploid—two n. Now remember that you have two different compartments when it comes to these Sertoli cells. You have what’s called the basal compartment.

So if you recall that’s from the tight junction toward the basement membrane, and the other compartment is called the luminal compartment. So that extends from the tight junction to the lumen. We’re going to start at the basal compartment with the spermatogonia and as the sperm migrates toward the lumen, they’re undergoing development. So beginning with the spermatogonia, males are born with a finite number of spermatogonia. And so the thing here though is that these spermatogonia can undergo mitosis. And so they continually, repeatedly divide; they are dividing indefinitely after puberty. In males, they keep producing spermatogonia throughout their life. After they undergo mitosis, then the spermatogonia are going to develop into primary spermatocytes, and they do that by undergoing mitosis.

So those primary spermatocytes then they are also diploid, because whenever a cell undergoes mitosis the next—the cells that’re derived from that are identical. So these have to be diploid cells. Primary spermatocytes then undergo meiosis one. So when they undergo meiosis one, they’re going to produce secondary spermatocytes. Secondary spermatocytes are haploid, so they are one n. Secondary spermatocytes then undergo meiosis two to become spermatids, and then spermatids undergo a maturation and development stage. So they have to mature and develop to become spermatozoa, a.k.a. sperm. So this is your gamete, the male gamete. Okay, this process spermatogenesis began with the spermatogonia, mitosis took place, you produce primary spermatocytes, then meiosis one occurred to produce secondary spermatocytes, then meiosis two occurred to produce spermatids. Then the spermatids matured and developed into gametes, male gametes—spermatozoa. And all of this process was occurring as, as the cells were migrating from the basal compartment toward the luminal compartment.

And once this process is over, the sperm are actually in the lumen of the seminiferous tubule. And I put a little note for here that approximately 50 to 500 million sperm are actually ejaculated— or that’s per ejaculation..

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