Normal Sexual Development:Explained in the easiest way

Added: 2026-05-11

[00:00:05]So hello everyone let's learn about normal sexual development.

[00:00:11]So to learn about the normal sexual development we need to learn two important things first. First of all, we will be talking about the PGC's or the primary germ cells and then we will be talking about the genital ridge because these are the two structures these are the two important structures from which the gonads are going to develop.

[00:00:43]The primordial germ cells they derived from the primordial germ cells are derived from the epiblasts.

[00:00:58]They are derived from the epiblast and they are present in the yolk sack.

[00:01:05]Rather we can say that they are present in the wall of the yolk sack.

[00:01:10]What happens that during the fifth week of the intrauterine life, the primordial germ cells will migrate through the dorsal recent entry.

[00:01:39]to the region of genital ridge by ammoid movements.

[00:01:58]Sorry.

[00:02:07]So let us first understand the primordial germ cells first. As we learned that the primordial germ cells they are derived from the epiblast.

[00:02:16]Epiblast if we try to recall that whenever there is we learned that we learned about the formation of the bilamina germ disk where the cells here they were known as the epiblast and the cells below they were known as the hypoblast.

[00:02:30]So, so these are the epiblasts which will later uh you know many things later let's not talk about this. Then these primary germ cells they're present in the yolk sack. I will draw a diagram so that things get clear.

[00:02:47]So this is the embryo and here we have the yuk sack.

[00:02:53]If the yuk means the embryo will be divided into the for gut, mid gut and hind gut.

[00:03:04]Now what is this genital ridge? Okay, before that we have learned that this primordial germ cells they if because this is the yolk sack. So the primordial germ cells they present inside the yuk sack. It is present in the walls of the yuk sack. Now it is going to try what did I what did we learn is that it is present in the yuk sack and in the fifth week of the intrauterine life it is present in the yolk sack and in the fifth week of the intrauterine life the pges the primordial junction cells will migrate through the dorsal mentry to the region of the genital ridge by the ammoid movements. So we are left with the understanding of the dorsal mentry.

[00:03:45]We learned that uh the genital the PG said they are present in the walls of the uk. Now what is this dorsal mentry the the tubes which are present these are the tubes means the intestines and all.

[00:04:00]So these are the tubes here and the tubes are connected to the posterior wall with the help of the fold of the paronium and what is that that is the dorsal misentry.

[00:04:13]Let us assume that this is the dorsal misentry and the primodial germ cells via okay so this is the dorsal mentry and the primordial germ cells from the yuk sac via the dorsal mentry it is going to reach this region now this region as I told you that this is the genital ridge now let us explain what this genital ridge is so did you understand the migration or have you all understood After the uh migration of the primordial gems which was initially present in the yuk sack in the fourth week sorry in the fifth week of the intrauterine life it is migrated through the dorsal masonentry to reach the genital ridge.

[00:04:57]Okay. Now let us understand what this genital ridge is. We if we again look into this diagram this genital ridge let us first of all understand what is the definition of the genital ridge.

[00:05:12]In the fifth week of the intrauterine life again here also it says that in the fifth week of the intrauterine life the selomic epithelium epithelium in the medial surface in the medial surface of the mison nephros proliferate to form to form the genital ridge. What is this?

[00:05:57]To form the genital ridge.

[00:06:01]So let's learn. So what the new words that we learned here is that we in the fifth week of the intrauterine life.

[00:06:11]So we have learned that in the fifth week of the intrauterine life as well the selomic epithelium which is present in the medial surface of the misphron will proliferate to form the genital ridge. Now what is this misone first of all we let me just magnify this posterior abdominal wall or the dorsal wall of the embryo. If this is the dorsal wall there are two important structures which are present in the dorsal wall. One is our very well-known dorsal leota. So this is the dorsal leota. Another important structure which we discuss is the misphrons. So this is the mispheros nephras and this is the dorsal.

[00:07:01]Now the epithelium which is lining in the medial side. This is the vis. So here there are the cells which are lining in the medial side of the misphron. So the cells which are lining in the medial side of the misphron that is known as the selomic epithelium.

[00:07:19]And it is the selomic epithelium which is going to proliferate.

[00:07:24]When this proliferate it is going to form suppose it is proliferating like this. So it is going to form a bulge on the posterior abdominal wall which is known as the genital ridge and nothing else.

[00:07:39]So it is forming a bulge. This is the medial part of the misanas which is forming a bulge on the posterior abdominal wall which is known as the genital ridge. So this is only known as the genital ridge.

[00:07:59]So let us just understand this thing once again that I told you that for understanding the normal sexual development we need to understand two important structures. First of all there is the primordial germ cells there is the primordial germ cells and the genital ridge. Now the primordial germ cells they are derived from the epiblast. They're present in the yolk sack and during the fifth week of the intrauterine life this primordial germ cells will migrate from the yolk sack to the posterior abdominal wall with the help of the dorsal mentry and to the where in the posterior abdominal wall to the genital ridge region in the posterior abdominal wall and how is it going to go? It is going to go with the help of the ammoid movements. Then we learned about the genital ridge. What is the genital ridge? Again in the fifth week of the intrauterine life, the selomic epithelium which is covering the media.

[00:08:57]This is the silomic epithelium which is covering the medial side of the mison.

[00:09:02]This is the misanas. So the selomic epithelium which is covering the medial side of the mispheros is proliferating to form the genital ridge.

[00:09:12]Okay. Learning this two chapter is very important because we are now going to understand what happens and why are this important. So okay so where is it? So that means the genital ridge it is being formed from the misone.

[00:09:27]Important thing to notice that that this genital ridge as I told you that inside the genital ridge only. So that means by fifth week of the intrauterine life inside the genital ridge. Now in the genital ridge or you can write now the genital ridge has what does it have?

[00:09:50]It has the primordial germ cells which have migrated into it and it also has the selomic epithelium.

[00:09:59]The selomic epithelium it is basically formed from the misphron and this misphron is a part of the intra embbrronic misod sorry it is a part of the intermediate misodum or rather you can say that it has developed from the intermediate misodum just a quick recapitulation we have learned that suppose this is the noto cord this is the paragial misodm this is the intermediate misodum and this is the lateral plate misodum paraxial misodum, intermediate misodum and this is the lateral plate misodum.

[00:10:35]So the intermediate misodum which is present in the lumbar region. All right.

[00:10:41]Uh like it is the intermediate misodam not let's not talk about that but the intermediate misodam is also present in the form of this tube and what will happen it is going to thicken to form the nephrogenic cord. This intermediate misodam will thicken to form the nephrogenic cord and it is the different segments of the nephroenic cord which we talk about. It will get separated. These are the different segments. One is the mison then we have the metan metanros. This is going to form the kidneys. Okay. So this is just a small orientation of what the from where why are we telling that uh the misphron is originating from the med intermediate misod. All right. So genital ridge is having the PGCS and the salomic epithelium. This is the question. Okay. Next. Now why are we reading the genital ridge in so much details? What is the genital ridge? Yes.

[00:11:41]So the genital ridge was made up of the selomic epithelium. selomic epithelium and it had to primodial germ cells. Now remember that it is from the silomic epitheliums epithelium only that numerous fingerlike processes will be produced or if you if we just don't uh like think too much and we just need to understand like what is it then remember that it is from the genital ridge only the primitive sex chords will be formed that is the primitive sex chords will be formed and this primitive six chords they are by potential they are by potential which means means that they have the capacity to get converted or to differentiate either into the male gonuts or into the female gonuts. Now whether it is going to differentiate so from the genital ridge therefore it is going to differentiate to form the primitive six cords. It is because of the formation of the finger-like processes from the silomic epithelium.

[00:12:44]Now these primitive sex squads which are formed they are by potential and they have the capability to get converted into to differentiate into either the male gonut or the female gonut. So how who is going to determine that it is this that we know that the the males have the con chromosomal constitution is xy and female is x6x. The Y chromosome in the short term of chromosome number Y. SR Y gene which is also known as the TDF which is the distance determining factor. SRY gene which stands for SRY gene which stands for six related gene which stands for six related gene on chromosome on chromosome Y and TDF stands for testice determining factor.

[00:13:44]testice determining factor. Okay.

[00:13:49]So this SRY gene or the test is determining factor this particular gene where is it present? It is present in the short arm of chromosome number Y the short arm of chromosome Y. Now what is the specialtity of this gene that if this SRY gene is present what it does is that it is going to activate SX9 and this will result in the differentiation of this primary sex cords into testice right it is because of the presence of this SOX 9 gene means the sock 9 which is produced by the SRY gene and this SRY gene is present in the short term of chromosome Y. So males they're having the chromosomeal constitution is 466 Y is this Y chromosome in the short term of the chromosome Y what is present this SRY gene is present which is going to stimulate sock 9 which will result in the differentiation of the primitive 64 into testice. Now testice has two type of cells that is the cerolei cells and the latic cells. So as we know that it contains the certi cells and the liic cells. So the cerly cells it secretes under the influence of the epi the cery cells are going to secrete a hormone which is known as the antimmalarian hormone. Now this antimmalarial hormone what it does is that uh so we are talking about the male part first. This is known as the antimmalarian hormone or the malarian inhibiting substance.

[00:15:30]Antimalarian hormone anti-malarian hormone or the malarian inhibiting substance inhibiting substance. What is what it does is that this is going to cause the regression of the malarian duct. the duct which is responsible for demarian or the paramisine duct and this is because this parameric duct is responsible for producing the female reproductive tract.

[00:16:09]It regresses the malarian duct and it leaves the remnants. The remnants of which are important to remember that is it forms prostatic utricleon hydrated of moragi moragi moragi and one more thing that is appendix of testus.

[00:16:43]of test.

[00:16:47]So not only does it cause the regression of the validian duct but it also hence helps in the abdominal descent of the testice the testice. Okay. So this is what the certy cells do.

[00:17:09]The ladic cells they're going to produce testosterone and this testosterone is produced in the 8th week of the intrauterine life intrauterine life. The function of the testosterone it is as follows. First of all the testosterone because we we saw that the certly cell we saw that the cerly cell it produced the antimmalarian hormone which suppressed or which yeah right which suppressed the growth of which duct? The malarian duct sorry it suppressed the growth of the malarian duct or the paramisic duct which is which was supposed to develop into the female internal genital organs.

[00:17:59]Now because the antim because the parameionic duct has been suppressed so this testosterone is going to stimulate the growth of the misonic duct or the wolfian duct.

[00:18:13]Now because this duct is going to grow it is going to grow into what? It is going to grow into the male internal genital organs. So this is how the male internal genital organs are going to develop. that is the criiferous tubule, epitidis all these structures. Next what the testosterone does is that under the influence of the five alpha reductase enzyme five alpha reductase enzyme the testosterone is converted into dihydrotestosterone and it is this dihydrotestosterone which is responsible for causing the masculinization of the male of the masculinization of the external genitalia.

[00:19:01]The external genitalia during the during the stage of development. This external genitalia also has the bipotential capability to get converted into the male or the female external genitalia.

[00:19:14]But under the influence of the testosterone with the dihydro uh dihydrotestosterone is formed which causes the masculineization of the external genitalia. Okay. The other functions are that it is going to have a negative feedback on the G&R hormone due to which the G&R will decrease and the FS FH and LH are also going to sorry the FSH and LH are also going to decrease. And the other function which the testosterone has is that it causes the descent of the testice. The scrutal distance. Certainly cells did something.

[00:19:56]It did the abdominal descent of the testice. Testosterone causes the scrotal descent of the testice.

[00:20:05]Here we learned this is the function of the testosterone. And it is with the help of this testosterone only that we saw that the male internal genital organs are being formed. The external genitalia they are getting converted into the male one that is a masculinization is happening and it also causes the scrotal dist descent of the testice. So with this we complete the development of the male genital organs of the male reproductive system. Now if we talk about the female reproductive system then we know that it is very clear female. Now we talk about female which is 46x6. Now because there is no Y chromosome there is no Y chromosome that is why there will be no certly cells. I mean sorry first of all let's not go to certi cell because there is no Y chromosome. Obviously there will not be the SRY gene. If there is no SRY gene, there will be no sle cell. No sly cell.

[00:21:05]If there is no sle cell, there will not be any anti the antimmalarian hormone will not develop means it will not be produced. So that means what will happen? The the malarian duct is going to malarian duct grows and it is going to form the female internal genital organs.

[00:21:30]genital organs along with that because no certly cells are present antimarian hormones are not produced. Similarly, no leic cells are present.

[00:21:45]No leic cells are present and because no leic cells are present so no testosterone and if there is no testosterone so there will not be masculineization of the external genitalia. So no masculinization of external genitalia.

[00:22:03]External genitalia. So what will happen?

[00:22:07]Female external genitalia will be produced. External genitalia is produced.

[00:22:19]So this is how that in if so this is how that if yes. So in the absence of the Y chromosome in females how the female internal genital organs are formed and how the external genitalia female external genitalia is produced because of the absence of the SRY gene. Now one more thing is that now because there is no testosterone testosterone was causing the growth of the wolfian duct. So if there is no testosterone this is the testosterone I'm sorry for my handwriting. So because there is no testosterone so one more thing is going to happen that is the wolfian duct is not going to form. So wolfian duct will regress.

[00:23:07]Wolfian duct regresses to leave the remnant and the remnants which are produced are epooron paruoronoron and the gartner's duct duct.

[00:23:37]So this is how with this we complete the development of the male and the female external genital layer. Thank you for your patient listening.