Male Reproductive System | Spermatogenesis — Transcript

Full transcript

1. 0:07all right engine nerd so what we're
2. 0:08going to do in this video is we're going
3. 0:09to talk about the brain testicular axis
4. 0:12okay so first off let's go ahead and
5. 0:13look at what specific organs are
6. 0:15involved here so if you look here what I
7. 0:17have zoomed in on right here this is the
8. 0:18hypothalamus so the hypothalamus is
9. 0:20basically the master endocrine regulator
10. 0:22right because he controls your pituitary
11. 0:24gland how does it do that so if we look
12. 0:27here at the hypothalamus so again what
13. 0:29is this right here this is the
14. 0:30hypothalamus just has a cons it's
15. 0:32consist of a uh hypothalamus consists of
16. 0:35a bunch of gray matter so basically
17. 0:38these nuclei that are lodged within
18. 0:40What's called the dianon of the cerebrum
19. 0:42right so it's a component of the dianon
20. 0:45the hypothalamus has these specific sets
21. 0:47of nuclei that are responsible for
22. 0:49secreting a hormone that's going to
23. 0:51regulate a lot of this cycle here what
24. 0:53is this hormone here called well the
25. 0:56hormone that these two nuclei are
26. 0:58actually secreting here is called
27. 1:02gonat tropin releasing hormone G&R okay
28. 1:07so that's g& RH and what nuclei are
29. 1:10secreting this this is actually going to
30. 1:13be let's say that this one over here is
31. 1:14the
32. 1:15pre-optic nucleus okay so the pre-optic
33. 1:18nucleus is secreting it and let's say
34. 1:20that this green nuclei over here that's
35. 1:23secreting this genr is actually called
36. 1:25the arcu nucleus so these are two nuclei
37. 1:28that are very very important being able
38. 1:30to secrete ganat tropen releasing
39. 1:32hormone now what does that gonadotropin
40. 1:34releasing hormone do you know it
41. 1:36actually moves to this nice little
42. 1:37portal system down through here it's
43. 1:38called the hypoy portal system it's a
44. 1:40blood vessel connection and look what
45. 1:42it's doing it circulates down through
46. 1:44that and it binds onto these receptors
47. 1:46on these specific cells what are these
48. 1:48cells here called these cells are called
49. 1:51gonat tropes so they're called
50. 1:54gonado
51. 1:56tropes okay or troughs but what this
52. 1:59gatr and releasing hormone does is it
53. 2:02binds onto the receptors on these
54. 2:04gonadotropes and triggers the production
55. 2:06of two very important hormones one of
56. 2:09the hormones is called luteinizing
57. 2:12hormone and the other hormone that's
58. 2:14secreted is called follicle stimulating
59. 2:18hormone okay so one's luteinizing
60. 2:20hormone and the other one's follicle
61. 2:21stimulating hormone now before we talk
62. 2:25about what these guys do we have to talk
63. 2:28about the interaction that's actually
64. 2:29all the physiological mechanisms that
65. 2:31are occurring in this area what is this
66. 2:33structure that I'm drawing right now you
67. 2:35know in the testes you have this
68. 2:38structure called the seminiferous
69. 2:40tubules the seminiferous tubules are
70. 2:42very very important why because that's
71. 2:44where spermatogenesis is occurring what
72. 2:46is spermatogenesis it's sperm production
73. 2:48okay so what I'm doing is as I'm zooming
74. 2:52in on one seminiferous tubal now
75. 2:54seminiferous tubal is primarily made up
76. 2:56of these very very important cells you
77. 2:58see these green cells right right here
78. 3:01these green cells are very important
79. 3:02cells and we're going to call these
80. 3:04green cells we're going to call these
81. 3:08C
82. 3:10cells or I can call them susten
83. 3:15cells and sometimes they even call them
84. 3:18just nurse
85. 3:19cells but either way you can pick which
86. 3:22one you like the best either way one of
87. 3:24these three cells is the name of these
88. 3:26cells that are making up the
89. 3:29seminiferous tubal now really important
90. 3:32in between them they have these proteins
91. 3:35that are linking them together and
92. 3:36keeping them very very tight to one
93. 3:38another or adhering one another right
94. 3:41what are these things called These are
95. 3:43called tight junctions or adhering
96. 3:46Junctions they're actually two different
97. 3:47types so we have what is it again tight
98. 3:52junctions and we have other ones which
99. 3:54are
100. 3:55called
101. 3:57adherence Junctions
102. 4:00why am I mentioning this okay and we'd
103. 4:03also have these ones right here right so
104. 4:04this would be a junction here and this
105. 4:07would be one joining right here these
106. 4:09are very very important proteins they're
107. 4:11actually called claudins and audin
108. 4:13proteins and they're very very important
109. 4:15of being able to link these actual cells
110. 4:17together if it's TI Junctions it's
111. 4:19claudin and Udin if it's adherin it's
112. 4:22actually cadherin molecules but neither
113. 4:24here nor there these molecules are
114. 4:26linking the cells tightly to one another
115. 4:28what is that doing that's separating
116. 4:31this actual if you will seminiferous
117. 4:33tubule into two compartments one
118. 4:36compartment over here we're going to
119. 4:37call the basil compartment because it's
120. 4:40closest you see these black cells right
121. 4:41here consisting of connective tissue
122. 4:43cells these black cells here is the
123. 4:45basil lamina and then right here is the
124. 4:48blood vessels that are going to be
125. 4:49supplying the seminiferous tubules so
126. 4:52the basil lamina look if it's on this
127. 4:54side it's the basil compartment if it's
128. 4:56on this side it's closer to this Central
129. 4:58space which is called the Lumen so this
130. 5:01is called the ad luminal compartment
131. 5:04okay specifically this part right here
132. 5:06so basil compartment and then add
133. 5:08luminal compartment and then down here
134. 5:10is the Lumen okay now let's see what's
135. 5:14actually happening in this area right
136. 5:16here we have some cells that are
137. 5:17actually going to be formed here these
138. 5:19are stem cells very very important stem
139. 5:21cells okay let's look at these guys
140. 5:23right here so let's say this one is a
141. 5:26diploid stem cell and it's 2 N so that's
142. 5:29what diploid means right it has 46
143. 5:30chromosomes 23 maternal 23 paternal what
144. 5:35happens is this spermatogonium right so
145. 5:38what am I calling this it's a
146. 5:41spermato
147. 5:43gonium heck of a name right and then
148. 5:44what does it do it splits into two
149. 5:47different types of cells but look what
150. 5:49these cells are here look they're two in
151. 5:52and two in whenever I start with a stem
152. 5:55cell and I separate it into two
153. 5:57identical daughter cells that's called m
154. 5:59osis so what just happened right here
155. 6:02this event right here is called
156. 6:05mitosis okay now we're actually going to
157. 6:09rename these now we're going to rename
158. 6:12this one a type a cell so we're going to
159. 6:15call this one a type a cell and we're
160. 6:18going to call this one a type B
161. 6:22cell what happens is the type A Cell
162. 6:25that's formed by mitosis from this
163. 6:28spermatogonium is actually going to come
164. 6:30back up so it's actually going to look
165. 6:32at this it comes back up to the basil
166. 6:33lamina and it just actually gets reused
167. 6:36it becomes the next spermatogonium and
168. 6:38just continues to keep replicating the B
169. 6:42actually is going to move out of this
170. 6:44basil compartment into the ad luminal
171. 6:46compartment how there's a lot of
172. 6:48chemicals that are secreted right these
173. 6:51these actual cells these spermatogonium
174. 6:53cells and other different cells nearby
175. 6:54are secreting chemicals and what these
176. 6:56chemicals are doing is they're telling
177. 6:58the sust ular cells to open up the tight
178. 7:01junctions kind of like a gate why do we
179. 7:03need these tight junctions there anyway
180. 7:05what's their significance it's not just
181. 7:07to hold the cells tightly together you
182. 7:09want to know what's really important
183. 7:10about
184. 7:11it if we separate these these actual
185. 7:15these compartments when I'm making sperm
186. 7:17because that's what I'm doing I'm making
187. 7:18sperm down here that sperm is developed
188. 7:22when when are we actually making sperm
189. 7:23we're making it during the puberty
190. 7:25process right now our immune system is
191. 7:28actually being able to has to recognize
192. 7:30any type of self antigens in the actual
193. 7:33thymus gland right our tea cells our te-
194. 7:34cells undergo that selective process
195. 7:36right but it occurs before puberty so
196. 7:40whenever someone starts making sperm
197. 7:42it's at puberty if by chance let's say
198. 7:45that they have a sperm cell let's say
199. 7:47here's a sperm cell and some of the
200. 7:49antigens from the sperm cell leak out
201. 7:52into the blood what is it going to do
202. 7:54it's going to activate the immune system
203. 7:56and the immune system is going to start
204. 7:57coming and attacking our own test
205. 7:59right that's not good so what these
206. 8:02tight junctions between these ctoi cells
207. 8:05are doing is it's forming forming a
208. 8:07barrier between the blood and the testes
209. 8:11so we call that the blood testes barrier
210. 8:14okay and the reason why is you want to
211. 8:15prevent these sperm cells or their
212. 8:17antigens from leaking into the
213. 8:18bloodstream and activating our immune
214. 8:20system okay now these chemicals that are
215. 8:24secreted what happens it opens up these
216. 8:26tight junctions so now the tight
217. 8:28junctions open up
218. 8:31and now look what happens here so now
219. 8:32these type Junctions are open this type
220. 8:35B cell is going to move into the ad
221. 8:37luminal compartment now so now it moves
222. 8:39into the ad luminal compartment once it
223. 8:42moves into the ad luminal compartment
224. 8:43it's no longer considered to be a type B
225. 8:45cell we actually going to call this one
226. 8:48a primary spermato site so it's called a
227. 8:51primary
228. 8:54spermato
229. 8:56site okay let's redraw him here and
230. 9:00again what what state is this guy in
231. 9:01he's two in and what was this one two in
232. 9:04here's where it's going to get
233. 9:05interesting so we're just going to put
234. 9:07here primary speratti side but I'm going
235. 9:08to put two in
236. 9:09here he's going to undergo a process
237. 9:12where he's going to split into two
238. 9:14different cells but look what these
239. 9:16cells are now holy frick they're hloy so
240. 9:20now this was diploid and I went to hloy
241. 9:23whenever you go from a do a stem cell
242. 9:25that's diploid to two daughter cells
243. 9:27that are hloy this is called meiosis
244. 9:31one
245. 9:33meiosis
246. 9:35one okay but this was a primary
247. 9:37spermatocyte he divided into two of
248. 9:39these cells what should these be called
249. 9:41secondary spermatocytes so these are
250. 9:43called secondary
251. 9:46spermatocytes
252. 9:48okay we're on a roll guys hang in there
253. 9:50with me okay now what happens these
254. 9:53secondary spermatocytes look what they
255. 9:54do they're like hey we're not done we're
256. 9:57going to keep freaking dividing and look
257. 9:58what he divides into he divides into a
258. 10:01haid he divides into a haid he divides
259. 10:04into a haid and he divides into a haid
260. 10:06they're frecking things up here right
261. 10:08now look we got four haid daughter cells
262. 10:12whenever you go from two haid stem cells
263. 10:16to four haid daughter cells that is
264. 10:19called meiosis 2
265. 10:23meiosis
266. 10:24two okay what's actually happening is
267. 10:29that this primary speratti side it's
268. 10:31replicating so it had so for example
269. 10:33here if I were to show you like really
270. 10:34kind of like a little bit real quick
271. 10:35review of what's Happening Here let's
272. 10:37say here's the
273. 10:39chromosome what's happening is you're
274. 10:41replicating so originally you only had
275. 10:43one chromosome there you replicate it
276. 10:44right still have one chromosome but it's
277. 10:46just a replicated
278. 10:47version what
279. 10:49happens is let me actually make this
280. 10:51cell bigger
281. 10:52here is I could take a chromosome let's
282. 10:55say this is chromosome number four from
283. 10:57the maternal side and over here I draw
284. 11:00uh the paternal chromosome of
285. 11:04four what happens is these are called
286. 11:06diads right they come together and fuse
287. 11:10like right around the actual tips and
288. 11:12they they do what's called a crossover
289. 11:13or synapsis where they cross over some
290. 11:15of their genetic material now in mitosis
291. 11:17what you do is you separate them at the
292. 11:19centromere but in meiosis I'm not
293. 11:22separating them at the centr so when
294. 11:24these guys link together they're
295. 11:25actually going to link together and do
296. 11:26what's called recombination or crossover
297. 11:28or synapsis when they're linked they're
298. 11:32called a tetrad but individually they're
299. 11:36called
300. 11:39diads why am I mentioning that so that
301. 11:41you can really understand what's really
302. 11:42happening versus in this versus mitosis
303. 11:45so in mitosis you separate these at the
304. 11:47centret so you get two chromosomes going
305. 11:48to these cells and then one going to
306. 11:50that cell too right if it was mitosis in
307. 11:53meiosis this whole diad is going to one
308. 11:56cell this whole diad is going into the
309. 11:58other cell the only thing that's
310. 12:00happening that's different is that some
311. 12:01of the genetic material is crossing over
312. 12:04so for example here just to finish this
313. 12:06off let's say I had one cell over here
314. 12:08one cell over here all that's happening
315. 12:11is I'm going to redraw this chromosome
316. 12:13over here look what's different I'm
317. 12:16going to draw a piece of blue in here
318. 12:18that piece of blue was from that
319. 12:19chromosome but now I'm going to redraw
320. 12:21this blue chromosome over here you see
321. 12:23how we got two diads in each corner all
322. 12:26that happened is is I swapped a little
323. 12:27bit of the genetic material right there
324. 12:29that's all that's happening and then
325. 12:31these guys will get separated so now
326. 12:32we're going into four haid guess what
327. 12:34I'm going to separate that at the Cent
328. 12:36mirr and that at the Cent mirror I'm
329. 12:37going to se upate that at the Cent
330. 12:39mirror and then I'm going to get how
331. 12:40many of these chromosomes I'm going to
332. 12:42get one here one here one here one here
333. 12:44that's how I get these four hloy
334. 12:47daughter
335. 12:48cells these are now
336. 12:50called spermatids so these are called
337. 12:56spermatids then what happens is these
338. 12:59spermatids are going to turn into some
339. 13:01more motile and functional sperm cells
340. 13:04so now look what's G to happen
341. 13:06here you see how now they're becoming
342. 13:08more well-formed sperm they have a head
343. 13:11they have a mid piece they have a tail
344. 13:13they have the acrosome all that stuff so
345. 13:16when they're going from spermatids to
346. 13:18what are these guys called These are
347. 13:20called spermatozoa
348. 13:23spermato
349. 13:25zoa when you go from spermatids to
350. 13:28spermatozoa zoa this is a specific
351. 13:30process they call it
352. 13:32spermiogenesis so it's called
353. 13:36spero
354. 13:38Genesis now this whole process starting
355. 13:42from a primary speratti site to a
356. 13:44secondary
357. 13:45spermatocysts to spermatozoa that whole
358. 13:49process in general is called
359. 13:51spermatogenesis though so if I were to
360. 13:53highlight from here all the way from
361. 13:54this point here all the way down this is
362. 13:57called spermatogenic genis
363. 14:01spermato
364. 14:03Genesis okay technically what you could
365. 14:06do is you could separate right here you
366. 14:07see where it comes to spermatids I could
367. 14:09make a little line there and I could say
368. 14:11from primary to this to the actually
369. 14:13getting to the point of like the
370. 14:14spermatids is called early
371. 14:16spermatogenesis and then from the
372. 14:18spermatids that the spero I could call
373. 14:20late spermatogenesis but I'm just going
374. 14:21to say this whole thing is
375. 14:23spermatogenesis and the spermatia the
376. 14:25spermatozoa is spermiogenesis okay now
377. 14:29that we've done that I have to explain a
378. 14:30couple more things about these susten
379. 14:32acular cells so you notice how all this
380. 14:34stuff is happening it's not happening on
381. 14:36its own there's got to be these FSH and
382. 14:38this LH they got to be doing something
383. 14:40let's see what they're doing now okay so
384. 14:44over here let's focus on LH first let's
385. 14:46see what LH is doing first because he's
386. 14:48going to be doing some really really
387. 14:50important stuff with a very very
388. 14:52important metabolic hormone for males so
389. 14:55luteinizing hormone comes over here and
390. 14:57it acts on a specific cell what is this
391. 15:00cell here called this specific cell is
392. 15:03actually called a liting cell or an
393. 15:05interstitial cell so this cell right
394. 15:07here is called the LI dig cells or again
395. 15:10the interstitial cells what lutenizing
396. 15:12hormone does is it acts on this litig
397. 15:14cell which triggers some specific
398. 15:17signals to the nucleus and it makes a
399. 15:19specific Mo it makes these actual
400. 15:21enzymes right so it's actually going to
401. 15:23make some specific enzymes what is he
402. 15:24going to do this enzyme is going to
403. 15:28catalyze a spef specific reaction he's
404. 15:30going to have his hand out here and his
405. 15:32hand is actually going to catalyze the
406. 15:34conversion of
407. 15:37cholesterol all the way to
408. 15:41testosterone to go through the whole
409. 15:43pathway is not necessary but it
410. 15:46basically what this enzyme is doing is
411. 15:47these enzymes is it's helping to
412. 15:50catalyze the conversion of cholesterol
413. 15:51to testosterone and then where's the
414. 15:53testosterone going to go it's where's it
415. 15:55going to go it's going to do it's going
416. 15:56to come out here and it's it's going to
417. 15:59act in this vicinity and I'm going to
418. 16:00explain how in a
419. 16:02second okay but before we do that we
420. 16:04have to say what FSH is doing over here
421. 16:07so let's draw a receptor over here for
422. 16:09FSH let's say here is this
423. 16:13receptor for
424. 16:15FSH and look what happens here the FSH
425. 16:19is going to come over here and it's
426. 16:20going to do what it's going to bind into
427. 16:23this receptor similar thing it's going
428. 16:26to send signals to the nucleus
429. 16:29and this nucleus is actually going to
430. 16:31synthesize a new protein and this new
431. 16:34Protein that's actually going to be made
432. 16:37is called Androgen bonding protein and
433. 16:41this Androgen bonding protein is
434. 16:43actually going to get bound it's
435. 16:44actually going to get secreted out here
436. 16:46now I'm going to explain what happens so
437. 16:48this whole process spermatogenesis it
438. 16:51requires the presence of two different
439. 16:54molecules this one right here which is
440. 16:55called testosterone
441. 16:59and this molecule here which is called
442. 17:02Androgen bonding protein now what's the
443. 17:06function of Androgen bonding protein
444. 17:08well you know testosterone is actually
445. 17:09very lipophilic which means it loves
446. 17:11lipids so it's not very good at
447. 17:13dissolving into a water soluble like
448. 17:16environment Androgen bonding protein
449. 17:18helps testosterone to be less lipophilic
450. 17:21so it actually is going to want to stay
451. 17:22in this vicinity and if testosterone is
452. 17:25very concentrated in this vicinity it's
453. 17:27going to help for these sperms
454. 17:29sperm cells to develop so it's going to
455. 17:31help the spermatogenic process so
456. 17:33testosterone is very important in all of
457. 17:35these steps here it drives this step and
458. 17:38this step and this step right so it's
459. 17:41stimulating all of
460. 17:43these processes of spermatogenesis but
461. 17:47all Androgen bonding protein does is it
462. 17:49helps to be able to keep the
463. 17:50testosterone in this vicinity and keep
464. 17:53it very very uh soluble and highly
465. 17:57concentrated now
466. 18:00susten acular cells or the CI cells
467. 18:02they're not just opening up their tight
468. 18:04junctions they're also doing some other
469. 18:06stuff in here they're passing a lot of
470. 18:08nutrients because these cells are going
471. 18:10to go on a very long journey to the
472. 18:12epidemis so they have to have enough
473. 18:14nutrients and metabolic products to be
474. 18:16able to carry out that process so these
475. 18:19susten acular cells are providing
476. 18:20nutrients to the sperm cells you know
477. 18:22you see this process where they went
478. 18:24from spermatids to spermatozoa it also
479. 18:26helps the spermiogenic process because
480. 18:28what happening is it's taking this sperm
481. 18:31which was just like a Big immotile Blob
482. 18:34and look what it turns it into it turns
483. 18:36it into a well-defined sperm cell that
484. 18:39has very very important structures that
485. 18:40I need to talk about here because it's
486. 18:42very very essential all right this part
487. 18:44right here is called the head of the
488. 18:46sperm this part right here is called the
489. 18:49mid
490. 18:50piece and then this last part back here
491. 18:53is called the tail and each one of these
492. 18:55consists of some very specific
493. 18:56structures the head obviously consist to
494. 18:59the DNA but there's another thing in
495. 19:01there which is extremely important
496. 19:02without this we would not be able to
497. 19:05form uh fertilized ooms right this green
498. 19:08structure I drew is called what called
499. 19:09an acrosome and it's very very essential
500. 19:12for it has hydrolytic enzymes that'll
501. 19:14eat through specific types of things
502. 19:16within the egg the mid piece consists of
503. 19:19mitochondria okay so let me actually
504. 19:21write this down what was that green
505. 19:22structure it was called the
506. 19:25acrosome then this mid piece consists of
507. 19:28Mito mondria and the mitochondria is
508. 19:31extremely important because that's
509. 19:33what's going to have the it's going to
510. 19:34utilize the ATP it's it's actually going
511. 19:37to form ATP from different types of uh
512. 19:40maybe carbohydrate molecules or
513. 19:42different types of nutrient sources that
514. 19:43the CI cells are providing and then the
515. 19:46tail is actually going to be considered
516. 19:48to be what you actually call this
517. 19:49flagella right so it's going to be made
518. 19:51up of microt
519. 19:53[Music]
520. 19:54tubules and then at the base of it
521. 19:56you'll have what's called a basil body
522. 19:57right this is in like a this Fel is in a
523. 20:009 plus2 Arrangement okay so this right
524. 20:03here is spermiogenesis going from an
525. 20:05immotile spermed to a little bit not yet
526. 20:08but a little bit motile sperm cell the
527. 20:12the H CI cells help this process to
528. 20:15occur that's spermiogenic process what
529. 20:18else okay you know testosterone doesn't
530. 20:20just go right to the actual the
531. 20:23seminiferous tubules to help sperm
532. 20:24production it also goes into the blood
533. 20:27and acts on different Tiss isues also so
534. 20:29it can also act on other tissues that
535. 20:31we're not going to discuss but I'll just
536. 20:32put here other
537. 20:36tissues okay and it can exert its
538. 20:38effects on that but like anything
539. 20:42elevated testosterone levels are
540. 20:43obviously not good for the body so this
541. 20:46let's say that there's High T levels
542. 20:49testosterone what's going to happen
543. 20:51testosterone is actually going to come
544. 20:53up here it's going to go up to the
545. 20:54actual hypothalamus watch this and it's
546. 20:58going to exert a a negative feedback
547. 20:59mechanism on hypothalamus you know where
548. 21:01else it can exert a negative feedback
549. 21:03here at the anti pituitary what's that
550. 21:05going to do if you inhibit this
551. 21:06hypothalamus you're going to make less
552. 21:08G&R if you make less G&R you're going to
553. 21:10make less luteinizing hormone less
554. 21:12luteinizing hormone makes less
555. 21:14testosterone okay that's
556. 21:17important now who controls the FSH you
557. 21:20see these little like black little
558. 21:22sensors here they're picking up sperm
559. 21:24levels so these susten acular cells are
560. 21:27they're weird they have the ability to
561. 21:28pick up levels of sperm if the sperm
562. 21:31starts getting really really high the
563. 21:34high sperm production these susac cells
564. 21:37will be able to detect that when they
565. 21:39detect that they actually secrete a
566. 21:42specific chemical so let's say this
567. 21:45actual CI cell picks up that signal
568. 21:48right so it picks up that signal s sends
569. 21:51signals to the nucleus and the nucleus
570. 21:53makes a hormone uh that's called inhibin
571. 21:59and what does inhibin
572. 22:00do it comes up here watch this now it's
573. 22:04going to come up and it's going to exert
574. 22:06a negative feedback mechanism on the
575. 22:08hypothalamus and it's going to exert a
576. 22:11negative feedback mechanism on the
577. 22:13anterior pituitary what's that going to
578. 22:15do that's going to inhibit the release
579. 22:17of G&R that's going to inhibit the
580. 22:19release of FSH if there's less FSH
581. 22:23you'll have less ABP if there's less ABP
582. 22:26testosterone won't be concentrated
583. 22:28enough and spermatogenesis will actually
584. 22:31decrease okay all right guys in this
585. 22:34video we covered a lot of information I
586. 22:36hope it all made sense until next time
587. 22:38Ninja nerds