Spermatogenesis: from Spermatogonium to Spermatid (Nursing)

00:00 Now, let's discuss the specifics of gamete formation in the male reproductive system.

00:07 This is referred to as spermatogenesis.

00:10 Spermatogenesis is the production of sperm or spermatozoa, in the seminiferous tubules of the testes.

00:20 Again, spermatogenesis is going to occur in the seminiferous tubules of the testes.

00:27 First, you have spermatogenic cells which are going to give rise to sperm.

00:33 and this is going to happen in three steps.

00:37 First, we're going to have mitosis of stem cells known as spermatogonia.

00:44 These are going to form 2 spermatocyte known as primary spermatocyte.

00:51 Because this is mitosis these two new cells are genetically identical to their spermatogonium and they are diploid.

01:02 After mitosis of the spermatogonia we have meiosis.

01:07 In this process, these primary spermatocyte will undergo Meiosis I in order to form secondary spermatocyte and then they will undergo Meiosis II to form spermatids.

01:23 After this, the spermatids will become sperm cells by way of a process known as spermiogenesis.

01:34 So let's take a closer look at this process.

01:38 First, starting with the mitosis of spermatogonia, we're going to form our primary spermatocyte.

01:46 Spermatogenesis begins at puberty with our spermatogonia.

01:52 These are stem cells that are located at the epithelial basal lamina portion of the testes in the seminiferous tubules.

02:02 Each mitotic division of the spermatogonia is going to yield two cells: a Type A daughter cell and a Type B daughter cell.

02:13 The Type A cells will maintain the germ cell line at the basal lamina and stay at that area.

02:22 The Type B cells, however, will move toward the lumen and develop into primary spermatocytes.

02:32 Next, we have meiosis.

02:35 In this process, these spermatocytes will now be converted to spermatids.

02:41 In Meiosis I, the primary spermatocyte which is diploid is going to undergo Meiosis I forming 2 secondary spermatocytes that are now haploid.

02:54 In Meiosis II, the secondary spermatocytes will rapidly undergo Meiosis II to become 2 spermatids that are also haploid.

03:04 So all together, from the original spermatogonium we end up with 4 spermatids.

03:14 Spermatids are small, nonmotile cells that are going to be found close to the lumen of the tubule.

03:24 Now that we have our spermatids, we undergo the third process of spermatogenesis, which is spermiogenesis or the formation of sperm.

03:35 Spermatids are going to contain the correct haploid chromosome number needed for fertilization, but these are nonmotile.

03:46 In spermiogenesis, we're going to streamline the process where the spermatid is going to elongate loses excess cytoplasm and form a tail in order to become our spermatozoan or sperm.

04:02 Now, let's examine this in the context of the testes.

04:07 Spermatogenesis takes place in the seminiferous tubules of the testes where we have spermatogonia and supporting cells known as sustentocytes or Sertoli cells.

04:19 Recall that the spermatogonium which are sperm forming stem cells undergo mitosis just beneath the basal lamina, and produce diploid cells.

04:32 While the Type A cells will remain at the basal lamina, the type B cells will become primary spermatocytes.

04:41 Also, we have tight junctions between the sustenocytes that are going to prevent leakage of substances from the blood between these cells and block access to these developing sperm.

04:56 This is what's referred to as the Blood-testis barrier.

05:00 This is important because it prevents the immune system from attacking the spermatogenic cells.

05:11 The Type B cells will undergo meiosis I and II.

05:16 This will then form haploid early spermatids that are way from the basal lamina, and toward the lumen of the seminiferous tubule.

05:28 The early spermatids will now begin to form what will eventually become our spermatozoa or sperm.

05:36 This is going to happen through the process of spermiogenesis.