As a member, you'll also get unlimited access to over 79,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.
Try it risk-freeAlready registered? Log in here for access
Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.
While many fetal developmental processes are similar between males and females, there is one particular process that is quite different. Yes, as you may have guessed, I'm talking about the development of the male and female external genitalia!
Now, even though you probably guessed that's what I was referring to, did you also know that both males' and females' genitals actually start out the same? You see, just like the internal gonads, the testes and ovaries, developed from the same fetal structure, the external reproductive organs also develop from the same set of tissues. Up until about 2-2.5 months after conception (or fertilization), males and females look the same, even on the outside!
 |
But obviously, even though they may start out looking the same, they end up looking quite different. So, how does this happen? What is it that makes these initially identical tissues develop into gender-specific structures? Well, it all comes down to one little word - hormones, specifically the hormones produced by the gonads.
You see, once the internal gonads have developed, the male's testes start producing a hormone called testosterone. This happens between weeks 7-9 of gestation and is the beginning of the steps leading to the differences in male and female development. This process is known as sexual differentiation and can officially be defined as the process of developing sex- or gender-specific tissues, organs, and functions, and while this can refer to many different developmental processes, in this lesson, we are focusing on the sexual differentiation of the external genitals.
So, let's start at the beginning! Okay, not all the way at the beginning - that would be when fertilization occurs. Let's skip ahead to about the end of month two/beginning of month three. You may remember that the entire process of fetal development takes about nine months, or 40 weeks. By the end of month two, there are already differences between males and females. However, these differences are only on the inside. By now, the internal gonads have developed into either testes or ovaries. However, the external structures still look pretty much the same.
Both males and females start out in what is called a state of undifferentiation, where their tissues look exactly the same and even have the same potential to develop into either male or female parts! They both kinda look like the picture below - neither male nor female.
 |
But, once the male's testes start producing testosterone, things begin to change! Testosterone is released from the testes into the bloodstream. Testosterone is a male steroid hormone that is part of a class of hormones called androgens. Another hormone in this class is dihydrotestosterone, or DHT for short. While testosterone is important for many aspects of male development, about 5% of testosterone is converted into DHT. And, it is DHT that's the main hormone required for normal external development of the male genitals.
Now, in order for DHT to be able to carry out its effects on the external tissues, it has to be able to bind to them. It does that by binding to receptors for androgens known as androgen receptors. You can think of it kind of like a lock and key method. The receptor is like the lock, and, like any lock, it can only be opened by certain keys. And, the keys for our androgen receptor locks are the androgen hormones, like testosterone and DHT. Each of these has a unique structure, allowing it to fit into and activate the receptor.
 |
Once the DHT has bound to its receptors, it begins to carry out its job. You may remember from other lessons that hormones act like messengers, and the message DHT is carrying are instructions for the genital tissues of the male. These instructions direct the development, or differentiation, of the undifferentiated tissues. Without testosterone, DHT, or androgen receptors, the undifferentiated tissues would end up following more of a female path of differentiation.
So, what are these changes I keep talking about? Well, first let's divide our tissues into three different sections: the genital tubercle at the top, the labioscrotal swellings on the side, and the urethral folds in the middle.
 |
Under the influence of androgens, mostly DHT, the male tissues will enlarge and fuse to create the penis and the scrotum. In comparison, the female tissues will develop into the female genitals in the absence of androgens.
1. First, in both sexes, the urethral folds elongate and fuse. This splits the cloacal membrane, located in between the urethral folds, into the urogenital membrane up at the top and the anal membrane below.
2. Then, in step two, things start to change. Around week 10-11, the male and female genitals are distinctly different. The genital tubercle in males has elongated, moving away from the anal opening and beginning to form the shaft and head of the penis, while in females it moves inward, closer to the anal opening, and begins to form the clitoris.
3. Over the next few weeks, the urethral folds in the male will fuse all the way, forming the urethra inside the penile shaft. However, in females they do not fuse. Instead, they will begin to form the labia minora, the inner skin folds of the vaginal area.
4. By week 16-18, genital differentiation is almost complete and the fetus can be visually identified as a male or female during the ultrasound. The last few steps of genital differentiation include:
Even though the main process of sexual differentiation is completed by week 20, the genitals will continue to grow as the baby grows and increases in size. In males, the testes will start to descend into the scrotum around the end of month three, and by birth, both testes have usually relocated into the scrotal sac.
And there you have it: the process of male and female sexual differentiation! Kind of amazing, isn't it, how we all start out looking just the same but end up looking so different? And remember, it's all under the process of hormones!
Let's take a quick moment to review. Until about the end of month two, males and females all look the same. But once the male's testes start producing testosterone, it all changes. Sexual differentiation of the genital tissues begins around week 7-9 and continues all the way up to week 20 of gestation. This process occurs under the influence of the androgen DHT in males and in the complete absence of androgens in females.
DHT causes the genital tissues in the males to enlarge and elongate, forming the shaft and head of the penis. These tissues then fuse to complete the formation of the shaft and to form the male's scrotal sac.
In the absence of hormones, the female's genital tissues do not fuse but instead move further apart, forming the labia minora and labia majora folds that surround the vaginal opening. And instead of elongating like in the males, the tissue forming the female's clitoris shrinks.
And of course, the differences between males and females don't stop there! The hormones that males and females produce also lead to sexual differentiation of the brain, which might help explain why men and women think and act differently.
At the end of this lesson, you should be able to:
To unlock this lesson you must be a Study.com Member.
Create your account
Already a member? Log In
BackAlready registered? Log in here for access
Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.
To learn more, visit our Earning Credit Page
Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.
Back To Course
UExcel Anatomy & Physiology: Study Guide & Test Prep20 chapters | 243 lessons | 19 flashcard sets
{{courseNav.course.topics.length}} chapters | {{courseNav.course.mDynamicIntFields.lessonCount}} lessons | {{course.flashcardSetCount}} flashcard set{{course.flashcardSetCoun > 1 ? 's' : ''}}
Next Lesson
Watch 5 minute video clips, get step by step explanations, take practice quizzes and tests to master any topic.
Study.com has a library of 750,000 questions and answers for covering your toughest textbook problems
I love the way expert tutors clearly explains the answers to my homework questions. Keep up the good work!
- Maritess, College StudentStudy.com video lessons have helped over 30 million students.
"I learned more in 10 minutes than 1 month of chemistry classes"
- Ashlee P.
"I learned more in 10 minutes than 1 month of chemistry classes"
- Ashlee P.
"I aced the CLEP exam and earned 3 college credits!"
- Clair S.
Over 65 million users have prepared for {{displayNameByProductKey[registrationData.product || testPrepCocoon]}} and other exams on Study.com
"The videos have changed the way I teach! The videos on Study.com accomplish in 5 minutes what would take me an entire class."
- Chris F.
Over 65 million users have prepared for {{displayNameByProductKey[registrationData.product || testPrepCocoon]}} and other exams on Study.com
