Hi everyone. And today we'll be starting Module 3 in Unit 1 Biology, which is all about reproduction. And we'll be starting with sexual reproduction in humans. So just a general breakdown.
So humans are either male or female. And the process of reproduction begins in the female as eugenicists, whereas the males make sperm via spermatogenesis. So this is called gametogenesis. Okay, these are the gametes. Alright, the next step.
is fertilization of the eggs by the sperm, right? And in order for this to happen, in the female, there's the ovarian cycle and the uterine cycle. And finally, to prevent pregnancy, there's contraception. Okay, so after fertilization, it leads to pregnancy, where it will be introduced to the fetus, the placenta, as well as the mother.
And later on, we'll be talking about contraceptive methods. So let's begin by taking a look at the diagram of the male and female reproductive system. So here's a picture of the male reproductive system.
We have the testis, and it is contained in the scrotum. So sperm is made here. So sperm is made in the epididymis. And after that, the sperm travels via the vas deferens. You can see this blue arrow here.
It goes all the way up. It does not enter the urinary bladder. This is behind the bladder, right?
However, the prostate gland, which is this organ here, adds fluid to the spume. The bulbarithral gland, which are these glands here, also add fluid to the spume. And then, when all these fluids are added to the spume, it is called semen. Alright?
The seminal vesicles. can see in this diagram but they just put it here right um also adds fluid to these birds so semen will now travel by the urethra and then out of the penis in ejaculation okay now this is a diagram of the female reproductive system so eggs are made in the ovary they travel via the ov duct or the fallopian tube then they go over here and are implanted in the wall of the uterus called the endometrium. Alright, this is first of all, this is if fertilization occurs and fertilization usually occurs in the fallopian tube. Alright, if fertilization does not occur then menstruation will eventually occur which is shedding of the endometrium which we'll talk about in another class.
Okay, so again the myriod-propyl system is made up of these glands here. Well, not glands, but organs. So you can take a look at what they are and what they do.
You can take a screenshot and you can read it. I'll give you time to take your screenshots now. So these are all the elements of the male reproductive system.
It's very important that you know the function as well as the structure of these glands and structures. So let's take a look at spermatogenesis. So spermatogenesis occurs in the seminiferous.
and mitosis as well as meiosis are involved here so if you forgot what mitosis and meiosis are you can go back to the previous video in unit two and take a look at that all right so testosterone controls spermatogenesis from the onset of puberty in the meal the hypothalamus which is in the brain releases a hormone called gonadotropin releasing hormone this hormone then travels to the um the anterior pituitary gland. The anterior pituitary gland now then releases two of its own hormones, luteinizing hormone LH and follicle stimulating hormone called FSH. So LH would enter the bloodstream, travel to the interstitial cells where it fits into receptors there.
Now there are cells called lydic cells and the LH causes the lydic cells to manufacture testosterone and it is releasing to the bloodstream. Defects of testosterone causes the development of secondary sexual characteristics, the stimulation of soteri cells so that spermatogenesis will be facilitated, and also stimulation of the germinal epithelial cells so that spermatogenesis can occur. Now, as I said before, FSH is also required for spermatogenesis.
It will travel from the anterior pituitary gland to the soteri cells, and it will cause them to increase their activity. would quicker develop sperm and also secret fluid into the seminiferous tubules. So this is a diagrammatic representation here of how the hormones work.
So you can see the hypothalamus in the brain here, releases gonadotropin-releasing hormones. causing the anterior pituitary gland to release FSH and LH. LH acts on the LADIG cell, so L for LH, L for LADIG. Very easy.
And the LADIG cells actually produce the testosterone, and that leads to spermatogenesis. The FSH and S-fuscitol cells produce hormones and are also involved in spermatogenesis. This is an entire negative feedback system.
When there is a lot of testosterone, it will negatively feedback on the pituitary and hypothalamus and say, Hey, we have enough testosterone. There is no need to keep releasing your hormones. The opposite will be true if it is low. Alright, this is a diagram.
representation of how mitosis and meiosis works in somatogenesis. Initially, we have the somatogonial cell and this keeps dividing via mitosis, producing the somatogonium first. Then the somatogonium will divide and make more of themselves and the pleuralis cause somatogonia.
Another mitotic division will cause the development of the primary spermatozoite it is here so this these names are very important to remember primary spermatozoite here my male sister clues now so the the important thing is the chromosome number so initially we had 46 chromosomes the 2n number right or the diploid number of um chromosomes and after meiosis one we know that the diploid becomes haploid so there's half the number of chromosomes now right so two N divides into N and N as the daughter cells. Meiosis 2 will occur and two more daughter cells will be produced. And these are called spermatids. So they are almost mature.
And after the Sotoli cells secrete their substances and hormones, it causes the spermatozoids to develop into sperm cells. And sperm cells are also haploid, 23. Because remember, they need to go and combine with the ugonium now, or the ovum, to make a 47. chromosome number cell in fertilization. Okay?
So you can see that it begins at the outer edge of the seminiferous tibia where the somatogonium are, and as they mature and mature and mature, they mature sperm in the lumen of the seminiferous tibia. Alright? So we go from the outer edge into the lumen or the center of it. Okay?
Let's focus on the female reproductive system now. So it consists of the ovary, the oocyte, the fallopian. the anterior butyros, cervix and vagina. So less structures here to remember in the female reproductive system.
You can take your screenshot there. So let's take a look at the female version now, which is eugenesis. So ugonia stuffed, right, they are the germinal epithelial cells. Okay, and they also divide by mitosis. So it's almost a copy of spermatogenesis.
They are eventually deployed, and they are in the ovaries. Now the primary oocyte now is also deployed, just like the sperm, right? Okay, so now right at this...
This point is where meiosis I begins. Alright, and the primary oocyte will remain at prophase I in meiosis I for many years. Alright, so the primary follicle is larger than a primordial follicle. Alright, so a primordial follicle is simply a primary oocyte and it's surrounded by a layer of other cells. Okay, the primary follicle is simply the primary oocyte with more cells surrounding it.
Alright, and those cells. are called granulosa cells and they produce sex hormones. The secondary follicle now is where things get very important.
So it contains a secondary oocyte and that is haploid. In contrast to spermatogenesis, when meiosis occurs, there's not a straight division of the follicle. So there's one proper follicle or a secondary follicle.
and then there's a polar body which is which is of no use and it eventually degenerates right you will see a diagrammatic representation where I explain it better okay and then finally meiosis II will occur after fertilization so the graphene follicle Now is the mature follicle and that contains the secondary oocyte. Remember the secondary oocyte has completed meiosis 1 and is now haploid. Okay. The secondary oocyte will remain at metaphase 2 of meiosis until 49. by mitosis to form the primary oocyte.
This is present at birth before puberty. It is arrested in prophase 1 of meiosis 1. Now at puberty it will start to complete meiosis 1 and it will be stuck at meiosis 2 now. At meiosis 2 we have the secondary oocyte and then we have a polar body. So the secondary oocyte is the important cell here.
The polar body will simply degenerate. And this is where it changes from diploid to haploid now, so 23 chromosomes there. Only at ovulation and fertilization will it complete meiosis II and form a fertilized egg, which will add the 23 chromosomes from the sperm, the 23 from the egg, and make a 46 chromosome egg. And there's another polar body here, by the way, after meiosis II. So in contrast to the sperm, which you will get from the sperm, four sperm per um spermato-ugonium there's only one over per ugonium all right the the polar bodies degenerate right and also on the right hand side you can see the size of the oocytes so you can see the cells surrounding the oocyte here these are so cells that's what that's the granulosa cells all right um just a note on the copious luteum If the egg is not fertilized, the corpus luteum will simply degenerate.
We will go into this in another video where we learn about the ovarian cycle and the menstrual cycle as well. This table is a nice reminder of the steps of eugenesis and the number of chromosomes at each step. This is essentially how the hormones work. Eugenesis begins at the 6th week.
or fetal development right so even before you are born eugenicist is there all right um so The ubonia will enter meiosis I and they are known as primary oocytes. When meiosis I is completed, the secondary oocyte and the first polar body are formed and this is where it is haploid as well. The secondary oocyte is in metaphase II of meiosis and it has to wait until fertilization can occur to complete the meiotic division. During the process of eugenesis, at puberty, GnRH, just like in the meal, will be released by the hypothalamus.
And travel to the anterior pituitary gland and you will get an increase in FSH. FSH is going to travel to the ovaries and they will target the primordial follicles there and cause them to develop into primary follicles and each month only one of these will mature and others will start to degenerate. So by the time a woman is at puberty there's a predetermined amount of eggs that she has the potential to meet. All right and as the prime primary follicles enlarge, they produce estrogen. Estrogen also works to enlarge the primary follicle and encourages the completion of the meiotic division.
So it's only at puberty you will get FSH and estrogen, and that is what will trigger the completion of meiosis 1. Now, this is going a little bit into the ovarian cycle, but fear not, I will release that video very soon explaining the ovarian cycle in detail. Alright, now this is is a very nice table of the sperm versus the egg in terms of structure. Okay, this is a common exam question and you can take a look at it.
It's very simple comparing the structures of the sperm and the egg. All right, just one little note on the hypothalamic pituitary ovarian axis. Big words, but it's simply a diagrammatic representation of what I've been telling you all along, where the hypothalamus produced the GnRH, the pituitary is released. It's releasing its LH and its FSH and it's targeting the ovary. The ovary produces two hormones called estrogen and progesterone.
So it will negatively feed back on the pituitary gland and the hypothalamus if there is enough estrogen and progesterone, just like in spermatogenesis. Okay. And this is essentially what... is a nice typed out note of what I've been telling you of eugenicists and the hypothalamic pituitary ovarian axis so you can take a screenshot of that and you can have a read of it. Alright, so this was a short video on sexual reproduction in humans.
We will then go into the ovarian cycle, the uterine cycle, and also contraception and pregnancy in another class.