1 00:00:02,767 --> 00:00:04,734 - (Narrator) They'll actually make these sperm, though 2 00:00:04,734 --> 00:00:06,484 the sperm production. 3 00:00:06,484 --> 00:00:09,785 It's not just simply a, here's one step-done. 4 00:00:09,785 --> 00:00:13,983 There's several different steps that must be required. 5 00:00:13,983 --> 00:00:17,821 You must go through mitosis and meiosis 6 00:00:17,821 --> 00:00:21,881 of cells inside the seminiferous tubules. 7 00:00:21,881 --> 00:00:24,047 So what's the purpose. Why? 8 00:00:24,047 --> 00:00:26,866 Well, we need to produce a large number of sperm. 9 00:00:26,866 --> 00:00:31,033 But the sperm must have half the number of chromosomes. 10 00:00:33,300 --> 00:00:36,690 The key thing here is this half number 11 00:00:36,690 --> 00:00:40,076 because the sperm are going to cause an 12 00:00:40,076 --> 00:00:44,172 individual with an egg. That's the idea of reproduction. 13 00:00:44,172 --> 00:00:48,205 If you take half of the chromosomes in the sperm, 14 00:00:48,205 --> 00:00:49,951 half in the egg. 15 00:00:49,951 --> 00:00:54,118 Once you combine, you end up with a full set of chromosomes. 16 00:00:55,238 --> 00:00:58,398 So that's why it's so important to have half the number. 17 00:00:58,398 --> 00:01:00,168 If a sperm or egg ever started 18 00:01:00,168 --> 00:01:02,751 with a full set of chromosomes. 19 00:01:03,709 --> 00:01:06,215 If there was fertilization. 20 00:01:06,215 --> 00:01:08,358 Well, that offspring would have three 21 00:01:08,358 --> 00:01:10,691 or four sets of chromosomes. 22 00:01:12,043 --> 00:01:14,513 Way above the normal amount. 23 00:01:14,513 --> 00:01:18,237 So to end up with a normal amount, the diploid, 24 00:01:18,237 --> 00:01:21,286 you want to have half the chromosomes to start, 25 00:01:21,286 --> 00:01:22,786 or called haploid. 26 00:01:25,184 --> 00:01:28,840 What you start with is a cell called spermatogonia. 27 00:01:28,840 --> 00:01:33,773 The figure 2n means it has the full set of chromosomes, 28 00:01:33,773 --> 00:01:34,690 two copies. 29 00:01:35,964 --> 00:01:38,467 From the spermatogonia you go to the primary spermatocytes, 30 00:01:38,467 --> 00:01:41,233 secondary spermatocyte, spermatid, sperm. 31 00:01:41,233 --> 00:01:44,106 You can see that you go from the 2n, 32 00:01:44,106 --> 00:01:46,145 both sets of chromosomes, to 1n. 33 00:01:46,145 --> 00:01:46,978 Half. 34 00:01:49,595 --> 00:01:51,308 Any cell that's not going to be 35 00:01:51,308 --> 00:01:53,688 actually be produced into a sperm 36 00:01:53,688 --> 00:01:55,422 is called a sertoli cell. 37 00:01:55,422 --> 00:01:58,422 It's meant to help support, nourish. 38 00:01:59,332 --> 00:02:00,981 So here you can see, top left, 39 00:02:00,981 --> 00:02:04,265 we have a cross-section through a teste. 40 00:02:04,265 --> 00:02:07,311 You can see that they bring out that seminiferous tubule 41 00:02:07,311 --> 00:02:09,832 Kind of enlarge it comes out. 42 00:02:09,832 --> 00:02:12,143 Cut it in half, you can see what the 43 00:02:12,143 --> 00:02:13,664 large scene in the bottom left looks like, 44 00:02:13,664 --> 00:02:15,677 the cross-section. 45 00:02:15,677 --> 00:02:17,479 But in the top-right, that's an 46 00:02:17,479 --> 00:02:19,460 artist rendition of what the wall of 47 00:02:19,460 --> 00:02:22,895 a seminiferous tubule would look like. 48 00:02:22,895 --> 00:02:25,600 Because see how they go from the cells from along the wall. 49 00:02:25,600 --> 00:02:27,987 They divide and divide and divide. 50 00:02:27,987 --> 00:02:31,381 Until eventually, they look like immature sperm. 51 00:02:31,381 --> 00:02:35,833 You're going through mitosis first, then meiosis. 52 00:02:35,833 --> 00:02:40,000 So you divide from one to two, two divides into four. 53 00:02:40,975 --> 00:02:45,092 So the idea of this meiosis, is taking one cell 54 00:02:45,092 --> 00:02:47,855 and eventually creating four from it. 55 00:02:47,855 --> 00:02:50,188 Four cells that are haploid. 56 00:02:51,369 --> 00:02:55,286 Four cells that half the amount of chromosomes. 57 00:02:56,617 --> 00:02:59,499 And all that material is going 58 00:02:59,499 --> 00:03:03,362 to be stored in each individual sperm. 59 00:03:03,362 --> 00:03:05,492 As you can see in the bottom right, 60 00:03:05,492 --> 00:03:08,045 the artists rendition of a sperm. 61 00:03:08,045 --> 00:03:11,761 You have the head units, which contains the chromosomes 62 00:03:11,761 --> 00:03:13,236 you have a mid-section, 63 00:03:13,236 --> 00:03:15,335 which is all energy, on the contrary, 64 00:03:15,335 --> 00:03:19,600 and you have a tail which helps with movement. 65 00:03:19,600 --> 00:03:22,704 Now we've gone through the production of sperm, in general. 66 00:03:22,704 --> 00:03:24,872 Let's talk about testosterone, 67 00:03:24,872 --> 00:03:28,485 the major hormone of the male reproductive system. 68 00:03:28,485 --> 00:03:30,630 Testosterone is produced by the 69 00:03:30,630 --> 00:03:33,464 interstitial cells of the testes. 70 00:03:33,464 --> 00:03:38,340 "Inter" or in between means these interstitial cells 71 00:03:38,340 --> 00:03:41,423 are between the seminiferous tubules. 72 00:03:42,459 --> 00:03:45,706 Testosterone is going to help control the growth, 73 00:03:45,706 --> 00:03:47,021 the functionality, 74 00:03:47,021 --> 00:03:50,403 of all male reproductive tissues. 75 00:03:50,403 --> 00:03:54,583 It causes the secondary sexual characteristics to develop. 76 00:03:54,583 --> 00:03:57,071 It stimulates more aggressive behavior 77 00:03:57,071 --> 00:03:59,313 in males than females. 78 00:03:59,313 --> 00:04:02,944 It helps to stimulate sexual behaviors. 79 00:04:02,944 --> 00:04:06,064 So most things you attribute to male sexuality 80 00:04:06,064 --> 00:04:08,314 is because of testosterone. 81 00:04:10,797 --> 00:04:14,964 But it also deals with the rate of sperm formation. 82 00:04:16,330 --> 00:04:19,558 So its talking about how fast are sperm produced. 83 00:04:19,558 --> 00:04:22,161 Is it efficient or is it inefficient? 84 00:04:22,161 --> 00:04:25,911 Is there too much or too little testosterone? 85 00:04:27,422 --> 00:04:30,528 But testosterone itself has to be regulated. 86 00:04:30,528 --> 00:04:33,552 It must be kept in a proper amount. 87 00:04:33,552 --> 00:04:37,478 So you have these hormones called GnRH. 88 00:04:37,478 --> 00:04:39,932 The full name is gonadotropin-releasing hormone. 89 00:04:39,932 --> 00:04:42,670 But the abbreviation is just fine. 90 00:04:42,670 --> 00:04:44,298 These things come from the hypothalmus, 91 00:04:44,298 --> 00:04:46,131 it's up in your brain. 92 00:04:47,809 --> 00:04:51,892 You also have LH, it comes from pituitary glands. 93 00:04:52,840 --> 00:04:57,007 You have FSH, coming from the pituitary gland as well. 94 00:04:58,005 --> 00:05:00,750 Both LH, luteinizing hormone and 95 00:05:00,750 --> 00:05:04,252 FSH, follicle-stimulating hormone 96 00:05:04,252 --> 00:05:06,542 come from the anterior pituitary 97 00:05:06,542 --> 00:05:10,379 and deal with testosterone production. 98 00:05:10,379 --> 00:05:12,042 But if you notice, 99 00:05:12,042 --> 00:05:15,625 only LH can stimulate testerone production. 100 00:05:17,121 --> 00:05:20,937 FSH, actually helps with the helper cells, 101 00:05:20,937 --> 00:05:22,437 the sertoli cells. 102 00:05:24,590 --> 00:05:27,771 And then we have this hormone called inhibin. 103 00:05:27,771 --> 00:05:29,514 I'm willing to bet you can probably 104 00:05:29,514 --> 00:05:31,833 figure out what inhibin does. 105 00:05:31,833 --> 00:05:34,148 Yeah, inhibin inhibits. 106 00:05:34,148 --> 00:05:36,898 It inhibits the secretion of FSH. 107 00:05:38,741 --> 00:05:41,024 So by reducing FSH production, 108 00:05:41,024 --> 00:05:45,191 you also reduce overall production of testosterone. 109 00:05:47,469 --> 00:05:51,036 So here's the same thing, just more in a visual form. 110 00:05:51,036 --> 00:05:55,504 We start with the hypothalmus, producing that GnRH, 111 00:05:55,504 --> 00:05:59,102 which then we can get luteinizing hormone, or LH, 112 00:05:59,102 --> 00:06:02,320 FSH, follicle-stimulating produced. 113 00:06:02,320 --> 00:06:04,561 They come down the testes and 114 00:06:04,561 --> 00:06:09,424 in their own ways help to trigger testosterone production. 115 00:06:09,424 --> 00:06:13,641 While testosterone production helps with sperm production. 116 00:06:13,641 --> 00:06:15,173 Well you can see all these dotted lines, 117 00:06:15,173 --> 00:06:17,019 or dashed lines going back up. 118 00:06:17,019 --> 00:06:20,418 Those are all negative feedback. 119 00:06:20,418 --> 00:06:22,927 Too much of any one of these steps, 120 00:06:22,927 --> 00:06:24,286 goes back up and triggers that 121 00:06:24,286 --> 00:06:26,869 you stop producing the hormone. 122 00:06:28,224 --> 00:06:32,909 So enough testosterone tells LH to stop producing. 123 00:06:32,909 --> 00:06:37,892 Enough inhibin will help stop the production of FSH. 124 00:06:37,892 --> 00:06:39,684 So it's all about this negative feedback. 125 00:06:39,684 --> 00:06:40,990 It's like, hey we've got enough. 126 00:06:40,990 --> 00:06:42,547 Slow down. Back off. 127 00:06:42,547 --> 00:06:44,547 You don't want too much.