Spermiogenesis: from Spermatids to Sperm (Nursing)

00:01 So on spermiogenesis, the spermatids are going to be converted into sperm.

00:08 The major regions of an actual sperm include the head, which is the genetic region that's going to contain the nucleus, as well as a helmet-like acrosome that contains hydrolytic enzymes that will help the sperm penetrate the egg during fertilization.

00:29 Next you have the midpiece or the neck of the sperm, which is going to be its metabolic region.

00:36 This portion is going to contain a large number of mitochondria that produce the ATP that will be necessary to move the tail.

00:46 And finally, we have the tail, which is going to be the local motive region that's going to include flagella that allow the sperm to swim.

00:59 So if we look closely at spermiogenesis it starts when our spermatid is going to have acrosomal enzymes packaged into vesicles by way of the Golgi apparatus of the cell.

01:15 Following this, the acrosomes begin to form at the anterior end of the nucleus, while centrioles gather on the opposite side of the nucleus.

01:27 Next, the centrioles which are where microtubules are formed from will begin to form the flagellum on the posterior end of the cell.

01:40 After this, energy producing mitochondria, then begin to cluster around the portion of the flagellum closest to the nucleus.

01:53 The excess cytoplasm is no longer needed and is now going to begin to slough off and the spermatid is now beginning to take shape into a sperm cell.

02:05 Once the excess cytoplasm has been shed, the immature sperm is released from the systentocyte into the lumen of the seminiferous tubule.

02:18 The immature sperm and the lumen of the seminiferous tubule has three main portions: The head, where the acrosome is located and the nucleus is located, the neck or midpiece, where the mitochondria are located, and the flagella or tail that was produced from the centriole.

02:39 The sustentocytes are also very important in the process of spermatognesis.

02:45 So synocytes are the large supporting cells in the seminiferous tubules, also referred to as Sertoli cells.

02:54 They extend through the wall of the tubule, and surround developing cells.

03:00 These are going to provide nutrients and signals to the dividing cells and move the cells along toward the lumen away from the basal lamina.

03:12 These cells also secrete testicular fluid into the lumen for the transport of sperm.

03:20 And this fluid is going to contain androgen hormones as well as metabolic acids.

03:28 The sustentocytes or Sortoli cells also phagocytizes any faulty germ cells so that we don't make a mistake, and divide and eventually send off faulty cells.

03:41 And it's also going to phagocytizes excess cytoplasm as the spermiogenesis take place.

03:49 Finally, the sustentocytes are going to produce chemical mediators that regulates the process of spermatogenesis.

03:57 This includes mediators such as inhibin as well as androgen binding protein, or ABP.

04:05 We'll discuss that later in the course.

04:09 So, if we take a look at the sustentocytes we find that sustentocytes contain tight junctions that divide the tubule into two compartments.

04:22 The basal compartment which is closest to the basal lamina is where the spermatogonia, and the primary spermatocytes are going to be located.

04:33 And the second compartment is the Adluminal compartment.

04:37 This is the area where meiotically active cells, and the tubule lumen are located.

04:46 Next we have the Blood-testis Barrier.

04:49 This barrier is formed by tight junctions that separate the basal compartment close to the basal lamina from the adluminal compartment closer to the lumen of the tubule.

05:03 This is going to prevent sperm antigens from escaping into the blood, and causing activation of the immune system.

05:13 Recall that sperm are not formed until puberty.

05:18 So as the immune system is being developed, it will not be able to recognize this sperm as "self".

05:26 So, sperm need to be kept separated from the rest of the body in order to avoid being attacked by the immune system.

05:38 So notice that the spermatogonia are in the basal compartment above the tight junction and are not protected by the blood-testis barrier.

05:49 This is okay, because these would be recognized by our immune system since they've been there since development.

05:57 It's the cells and the adluminal compartment that needs to be protected from getting into the blood since these are not formed until after puberty.

06:08 So the entire process from spermatogonia to sperm takes about 64 to 72 days if conditions are hospitable.

06:21 Even at the end of this process, the sperm are still unable to swim.

06:26 But it's the pressure of the testicular fluid that pushes these immobile sperm into the epididymis.

06:36 It is in the epididymis, where they gain their motility and their ability to fertilize.