Male Reproductive System Overview

Hello everyone! Now we start studying the reproductive system and these are our learning objectives. Gametes are an organism's reproductive cells and because of that gametes are also referred to as sex cells. The reproductive system of males and females produces gametes, stores gametes, nourishes gametes, and finally it transports gametes. For fertilization, the reproductive organs responsible for producing the gametes and also producing sex hormones are called gonads. In males, the gonads are the testes, and in females, the gonads are the ovaries. The gamete or sex cell produced by the testes is the sperm, and the gamete or sex cell produced by the ovaries is the oocyte. Now, in both males and females, gonads are associated with a system of ducts, which is collectively called reproductive tract. And these ducts receive, store, and carry the gametes from the gonads to the place where they're supposed to go. Also, as part of the reproductive system, we have several accessory glands, that secrete fluids into the ducts and we also have the external genitalia. One thing that's important to point out is that an adult male produces, in average, half a billion sperm cells per day and the sperm cells are stored and expelled out of the male body within semen during ejaculation. So semen just refers to the fluid at which the sperm cells, the male sex cells, are found. So when we say semen, it only refers to the fluid part. Now, males, once they reach puberty, they produce sperm cells every day throughout their lives. Whereas females only make oocytes before they are born. So a baby girl, on her very first day of life, already has all oocytes she'll ever have her entire life. And these oocytes will be dormant until the female reaches puberty, when they start to be released monthly throughout the female reproductive years. So, females are born with all oocytes they'll ever have their entire lives. They do not make new oocytes. Now, the fusion of the male and female gametes is called fertilization. And when fertilization happens, a zygote is formed. It's important to remember that a human cell has 46 chromosomes. So, when fertilization happens, a sperm carrying 23 chromosomes and an oocyte carrying 23 chromosomes result in a zygote with 46 chromosomes. which is exactly half from the father and half from the mother. In this video we will cover the male reproductive system and in the next video we will cover the female reproductive system and we will go into more details about each of them. Here we have a mid-sagittal cut through a male pelvic area. We see the pubic symphysis which is just between the two halves of the pelvis. Posterior to the pubic symphysis we find the urinary bladder. On the back of the urinary bladder, we see the seminal glands, also called seminal vesicles. Under the urinary bladder, we see the prostate gland, and inferior to the prostate, we find the bulbo-urethral gland. And these are the three accessory glands in the males. The male external genitalia is the penis and posterior to the penis we see the scrotum. The scrotum is this pouch of skin located outside of the male body. Within the scrotum, we find the testis. The testis is the male gonad. So, it is the organ that produces the sperm. Right next to the testis, on the posterior board of the testis, we find the epididymis. The epididymis is basically a storage site for sperm. Then we see here the vas deferens. also called ductus deferens, which is a muscular tube that extends up into the pelvic cavity and it goes back behind the urinary bladder where it meets up with the seminal gland. The seminal gland produces the majority of the volume of semen, approximately 60% of it. And in this fluid produced by the seminal glands, we find a high concentration of fructose, which is a very important source of energy for the sperm cells. Also, this secretion produced by the seminal glands is alkaline. And this alkaline secretion helps neutralize the acidity of the urethra because the acidity of the urethra could potentially damage sperm cells. Leaving the seminal gland, we see the ejaculatory duct. And the ejaculatory duct meets up with the prostatic urethra, which is right here within the prostate. The prostate is another gland and it produces the prostatic fluid. which contributes with 20 to 30 percent of the semen volume. So the prosthetic urethra receives the prosthetic fluid and also the fluid coming from the ejaculatory duct. After the prosthetic urethra we find the membranous urethra, which is this part of the urethra passing through the external urethral sphincter. And the external urethral sphincter is a band of skeletal muscle that when contracted, it prevents urine and semen from leaving. After the membranous urethra, we find the spongy urethra. And the spongy urethra receives this name because it is found within a structure called corpus spongiosum, which is a type of erectile tissue together with the corpus cavernosum that we see here. The corpus cavernosum is what engorges with blood, and contributes to the majority of the penile erection itself. Now, if you look here at the very beginning of the spongy urethra, in an area referred to as the base of the penis, there is another gland. And this gland is called bulbo urethral gland. The bulbo urethral gland produces a very small amount of semen, like 5% of it, but even though it is a small volume, This secretion produced by the bulbous urethral glands is very important because it lubricates the urethra and the tip of the penis. Lastly, we see the penis which is the copulation organ, and it is necessary that it gets engorged with blood during sexual arousal for copulation to happen. And at the tip of the penis we find the external urethral orifice. During developmental stages of a baby boy, So inside the mother's womb, the testes are found very up high in the abdomen. They are near the kidneys. And that's a long way from where the testes should be. And as fetal development continues, the testes descend into the scrotum. And that happens in a very interesting way. The two top pictures show where the testes of a two-month-old male fetus inside the mother's womb are located. Keep in mind that a two months old fetus is basically the size of a peanut. The testes are way up near the kidneys and the scrotum is all the way down. And you see here this cord named gubernaculum testis that basically attaches the testes down to the scrotum. The length of the gubernaculum testis is five millimeters throughout the development and And with that, when the fetus keeps growing, since the gubernaculum testis doesn't change in length, this allows the testis to end up in the right place at the end of the fetal development. And at birth, the testis should be located within the scrotum. Since the testis is targeted out up in the abdominal cavity and ends up inside the scrotum By the end of the fetal development, We say that the testes descend towards the scrotum. The scrotum or scrotal sac is a skin-covered sac that provides the testes with a cooler environment than body temperature. Sperm cells develop at a temperature that is slightly cooler than normal average body temperature. And in order to have a healthy sperm count, It is important for the temperature of the testes to be around 4 degrees Fahrenheit cooler than the average body temperature. So it makes sense that the testes which produce the sperm are located within a scrotum. which hangs outside of the pelvic area and it is more external to the pelvic cavity. This way the scrotum hanging out of the pelvic cavity helps with the cooling off of the testis with the external environment. In the scrotum we find a very important set of muscles, the dartus muscle and the cremaster muscle. These muscles are part of the scrotal wall. The D'Artes muscle is a layer of smooth muscle that when contracted it basically wrinkles the skin of the scrotal sac. So by wrinkling up the skin it reduces the scrotum surface area available for heat loss. Hence contraction of the D'Artes muscle binds up the scrotal skin leading to a reduction of the surface area of the scrotum and with that reduction in heat loss it warms up the testis. Now, the cremaster muscle is a very important muscle that actually pulls the scrotal sac close to the body in response to cold temperatures. And as I mentioned before, the testis need to be a little cooler than the body temperature, like 4 degrees Fahrenheit cooler. But if it is too cold, the cremaster muscle pulls the scrotal sac up close to the body to keep it warm. In other words, the cremaster muscle brings the scrotum closer or further away from the body based on temperature. The scrotum is divided into two chambers and we call each chamber scrotal cavity. And as you can see here, each testes is located inside a scrotal cavity. Now what divides the scrotum into scrotal cavities is the scrotal septum and this septum extends to the skin surface of the scrotum as the raphe of the scrotum. The testis is the male gonads, so it produces the sperm and the sperm is stored within the epididymis. So the sperm stays within the epididymis until they are released, but if the sperm is in the epididymis for too long, it was stored for long term, then the sperm is just reabsorbed by the immune system. Now, we see here associated with the testes and the epididymis a structure called spermatic cord. All of this is the spermatic cord, and it includes the cremaster muscle. If we look deep within the spermatic cord, we find the testicular artery that brings oxygen and nutrient-rich blood to the testes and scrotal tissue. And emerging from the testis, coming back up towards the pelvic cavity, we have a series of veins that form a plexus called Pampiniform Plexus. This plexus, this network of veins, surrounds the testicular artery. And what happens is that there is a heat exchange between the warm arterial blood that's going down towards the testes and the cooler venous blood that's going... towards the pelvic cavity within the pumpiniform plexus. And this helps to cool down the warm arterial blood that's going towards the testes. Hence, it helps to keep the testes cooler than the body temperature. We also find in the spermatic cord the autonomic nerves, which include sensory and motor nerves. And these nerves are involved with controlling the muscles that we find in the scrotum. as well as involved with sensations of pain and temperature. We see here the vas deferens or ductus deferens, which is actually a muscular tube that emerges from the epididymis. And during ejaculation, the vas deferens carries testicular fluid up towards the posterior part of the urinary bladder, where we find the seminal glands. Now, linking each scrotal chamber with the pelvic cavity. there is the inguinal canal. And this superficial inguinal ring that we see here marks the end of the inguinal canal. Then deep inside the body, marking the entrance of the inguinal canal, there is the deep inguinal ring. As you can see here, the spermatic cord passes through the superficial inguinal ring and after the spermatic cord passes through this ring, it goes through the inguinal canal and it reaches the pelvic cavity. And I'm pointing this out because this is clinically relevant. What happens is that structures within the pelvic cavity and abdominal cavity can herniate through the inguinal canal down into the scrotum. And that is... It's called inguinal hernia. Inguinal hernias are much more frequent in males than in females because in females the inguinal canal is very small. We will learn that passing through the inguinal canal of females there is basically the uterus round ligament and nerves. Consequently, the females' inguinal canal is much smaller than males because males have this wide spermatic cord passing through it. One example of inguinal hernia is when the mesenteric fat protrudes through the spermatic cord into the scrotum and if there is a lot of fat coming down to the scrotum it can affect proper blood flow and that can lead to the death of the scrotal tissue which is obviously not good. This diagram shows a horizontal section of the testes within the scrotum. At the outside part of the scrotum we find the skin. Underneath the skin we find the darts muscle, the muscle that wrinkles up the scrotal sac skin to reduce surface area and consequently it helps to reduce heat loss. Underneath the darts muscle we find the cremaster muscle that brings the testis closer or further away from the body depending on the temperature. The test is discovered by a serious membrane called Tunica vaginalis. And like all serous membranes, the tunica vaginalis has a visceral layer that surrounds the testis and a parietal layer on the outside. And between the visceral and the parietal layers, we find a cavity named scrotal cavity. So if the testis are covered by a serous membrane, the testis are actually lubricated and they can move around within the scrotum. Now the The testis itself is surrounded by a fibrous tissue called tunica albuginea. This tunica albuginea is a dense fibrous tissue that surrounds the outside of the testis and it invaginates. It goes deep down within the testis and creates what we call septum. All this septa divides the testis into lobules. Each one of these logos is filled with this coiled up tubes that we call seminiferous tubules. And within the seminiferous tubules is where the production of sperm actually takes place. So the septa divide the testes into lobules, and these lobules have the seminiferous tubules inside. All the septa converge towards the mediastinum of the testes, which is this area basically in the middle in between the testis and the epididymis. Remember that the sperm is produced in the seminiferous tubules of the testis and then it goes to the epididymis to be stored. So in the mediastinum we find what makes the connection between the seminiferous tubules and the epididymis and this connection is made by the retic testis and the efferent ductus. Efferent with E which means exiting the mediastinum area and entering the epididymis. So, in summary, sperm is produced inside the seminiferous tubules, then sperm goes into the rat testis, from there it goes into the efferent ductus, and then it goes into the epididymis that we see here. If we take a look at the seminiferous tubules, we find the germinal epithelium. we find the cells that will give rise to the sperm. These cells are stem cells and they are called spermatogonia. The process of producing sperm is called spermatogenesis. So as I mentioned before, the gonads, so the testes in males, they produce sex cells and also sex hormones. And what happens is that when males reach puberty, Testosterone, which is a sex hormone, starts being produced by cells called interstitial endocrine cells. And one of the things that testosterone does is to stimulate spermatogenesis. So testosterone stimulates the production of sperm. So when males reach puberty, the presence of testosterone stimulates the spermatogonia to divide, differentiate and mature giving rise to sperm. And as that happens, the differentiating cell goes towards the lumen of the seminiferous tubules. And from the lumen, sperm cells get transported through the seminiferous tubules towards the reticulitis and then to the efferent ductus. the epididymis which is the site of sperm storage. Now what's interesting is that because sperm cells do not start to develop until males reach puberty technically the sperm is considered a foreign cell by the body. So what happens is that if immune cells of a male encounter a sperm cell of the same male the immune cells would attack these sperm cells because they are considered foreign. And for this reason, males have the blood test barrier, a barrier that prevents sperm cells and immune cells from communicating. The blood test barrier basically isolates the seminiferous tubules from the general circulation and with that it avoids immune reactions against sperm cells. Making this blood testis barrier, we have cells called nurse cells that we see here in the seminiferous tubules. And these nurse cells are also known as Sertoli cells or sustentacular cells. And between these nurse cells, we have tight junctions, which packs these cells tightly together. And with that, they make the blood testis barrier. Nurse cells, as their name implies, are involved with nursing. And besides making up the blood testes barrier, these nurse cells are stimulated by the presence of sex hormones, like testosterone. And when nurse cells are stimulated, they promote the division of the spermatogonia, which leads to the production of sperm cells. And the nurse cells also provide nutrients for the sperm cell development. So you can think of nurse cells like a protective and dedicated mother of sperm cells. Nurse cells make the blood testes barrier, they stimulate the production of sperm cells, and they nourish sperm cells during their development. And this is how sperm cells look like. They have a head, a neck, and a tail, and they do not have a lot of organelles. In the head of a sperm cell, we find a nucleus with the 23 pairs of chromosomes. And we also find in the head the acrosome. The acrosome contains digestive enzymes that break down the wall of the oocyte, allowing fertilization to happen. In the neck of a sperm cell, we find mitochondria, which provides energy for the flagellum, for the tail to move around. So the mitochondria provides ATP that powers the flagellum, which is the tail of the sperm cell. This is the only flagellum found in the human body. And this flagellum is very important because it enables the motility of the sperm cell. Now, sperm cells lack energy reserves like glycogen, and they absorb nutrients from the surrounding fluid where they are living at that moment. And the nutrients that sperm cells like the most is fructose, which is a simple sugar, a monosaccharide found in the seminal fluid, the fluid secreted by the seminal glands. Until recently, It was believed that during fertilization the sperm only brought the nucleus to the egg. So we used to say that the male contribution to the zygote was only the 23 pairs of chromosomes and no other organelle besides the nucleus was transferred from the sperm to the egg. And having that in mind we could affirm that all the mitochondria in our body came from the egg and not from the sperm. And that's why we used to say that all mitochondria in our body came from our mother. And obviously, inside the mitochondria, we have the mitochondrial DNA. And the fact that mitochondria was always inherited from our mother, who inherited hers from her mother, and so on, this enabled genealogical researchers to trace maternal lineage far back in time. However, on December 2018, A scientific paper was published showing compelling evidence that this long-held belief may not always be true. The scientific paper presented evidence for biparental inheritance of mitochondrial DNA in three unrelated families. Now, as you can imagine, lots of attention has been given to the possibility of paternal transmission of mitochondrial DNA. The test produces around 1500 sperm cells per second. So, in a day, several million sperm cells are produced. After all these sperm cells leave the seminiferous tubules, they are stored in this pretty convoluted system of tubules called epididymis. And the epididymis is anatomically divided in head, body, and tail. When the sperm leaves the seminiferous tubules, it goes to the rat testis and then to the efferent ductus. And the efferent ductus connects the head, of the epididymis. In a period of two weeks, sperm cells travel from the head of the epididymis to the tail of the epididymis, which connects to the ductus deferens, the muscular tube that goes up through the spermatic cord into the pelvic cavity. Now, one interesting thing is that when the sperm cells reach the epididymis. Even though the sperm is physically mature, it is not functionally mature. And what I mean by not functionally mature is that the sperm cannot move. It cannot swim on its own. Basically, the first time the sperm is able to move on its own, it is when the sperm cells get in contact with the... secretion produced by the seminal glands, which has a high concentration of fructose. And when that happens, the sperm becomes able to swim on its own. However, the swimming is not full power yet. The swimming is not enough to fertilize an egg. And the sperm cell just becomes fully capable of fertilization after it undergoes a process called capacitation. And capacitation happens outside of the male reproductive system. Capacitation just happens when the sperm gets in contact with secretions produced by the female reproductive system. Now, when the sperm undergoes capacitation, which happens inside the female reproductive system, the sperm tail is capable of beating very vigorously, and with that, the sperm is ready it is capable of fertilizing an egg. So what happens is that for the period of two weeks, approximately two weeks, that sperm cells are within the epididymis. The epididymis needs to ensure the sperm cells are kept in a good environment and because of that, lining up the lumen of the epididymis, we find a distinctive, pseudo-stratified columnar epithelium with long stereocilia. This stereocilia increases the surface area available for the absorption and secretion to adjust the testicular fluid composition at which the sperm is being stored in the epididymis. And with that, it ensures that the testicular fluid is kept at its prime and the sperm that leaves the epididymis is very healthy. The epididymis contributes with approximately 5% of the total volume of the semen. This picture is just to show you how it all looks in a cadaver. We see here the tunica vaginalis, which is the serous membrane that reduces friction and allows the testis to move around within the scrotum. And then we see the testis and directly surrounding the testis we see the tunica albuginea. And the tunica albuginea is The swamp goes deep. into the testis and form the septa that divides the testis into the lobules and the lobules is what contains the seminiferous tubules that actually produces the sperm. And we also see here the head, body, and tail of the epididymis and the spermatic cord that connects the scrotal chamber with the pelvic cavity. So, we just learned that lining the lumen of the epididymis we have the pseudostratified columnar epithelium with stereocilia. Now, when sperm is within the ductus deferens, due to muscular contraction of the ductus deferens that is made of smooth muscle, the sperm travels up through the spermatic cord and then through the inguinal canal into the pelvic cavity. Then, it goes behind the urinary bladder, where the sperm reaches the ampulla of the doctor's deference. which is this enlarged part that we see here. Also, in the posterior side of the urinary bladder, we find the seminal glands. The seminal glands produce the seminal fluid, and this fluid contributes to about 60% of the volume of the semen. The seminal fluid is a slightly alkaline, viscous, whitish-yellow type of fluid, and this fluid contains fructose that provides energy to the sperm. So, fructose is metabolized and converted to ATP, which sperm can use to power the flagellum, which is used for propulsion, for swimming. Now, since the seminal gland contributes with approximately 60% of the semen volume, and the secretion is alkaline, this fluid can neutralize the acidity of the urethra and also the acidity of the vagina. In this way, the sperm can be happy and healthy during its trip. Now, the duct that leaves the seminal gland is called excretory duct. When each ampulla of the ductus deferens joins with an excretory duct from the seminal gland, when this conversion happens, we have the ejaculatory duct. And in the ejaculatory duct is where the secretion coming from the ductus deferens is mixed with the secretion of the seminal glands. And then the sperm that was immobile now becomes mobile. So you can think of the seminal gland secretion as the sperm's energy drink. When the sperm gets in contact with the fluid secreted by the seminal glands, the sperm becomes mobile and it is ready to swim for its life. But remember, even though the sperm is mobile after it gets in contact with the seminal gland fluid, it. The sperm is still not capable of fertilizing an egg. The sperm just becomes capable of fertilizing an egg after it undergoes capacitation. And capacitation just happens after the sperm gets in contact with secretions present in the female reproductive system. Now, the ejaculatory duct goes to the prostate gland. And in the prostate gland, we have the production of the prostatic fluid. The prostatic fluid makes up 20 to 30% of semen. It contains citric acid, which is a nutrient for the sperm, and it contains an antibiotic that prevents male urinary tract infections. Now, the prostate produces the PSA, the prostatic-specific antigen. And this antigen is basically enzyme that helps liquefy semen. So this enzyme makes the semen more liquidy. Liquid enough that the sperm can swim around it. But nowadays PSA is very famous because it is a prostate cancer biomarker. Because the blood levels of PSA is often elevated in men with prostate cancer. PSA levels can be elevated in other situations besides cancer, such as benign prostatic hyperplasia or in case of inflammation of the prostate. But since 1994, FDA approved the PSA test in conjunction with rectal exam to test a symptomatic man for prostate cancer. The last pair of glands males have is the bulbourethral gland. And these glands are located at the base of the penis, very, very close to the external urethral sphincter, which is also known as urogenital diaphragm. The bulbourethral gland secretion contributes with 5% of the semen. And the secretion is thick, sticky, alkaline mucus secretion that helps neutralize the acidity of the urethra, not as much as the seminal gland one, because the seminal glands contribute with 60% of the semen, and the bulburethral glands just contribute with 5% of the semen. But most importantly, the function of this secretion of the bulburethral glands is that it lubricates the tip of the penis, as well as the lining of the urethra. and with that diminishing the amount of sperm cells damaged during ejaculation. So this is the trip that sperm cells do until they leave the male body and the semen, the fluid at which the sperm cells are kept on, is modified until basically it leaves the male body. Five percent of the semen comes from the epididymis, then 60 percent of it comes from the seminal glands, around 30% of it comes from the prostate gland and 5% from the pulmonary urethral gland. And during ejaculation, a male releases from 2 to 5 mLs of semen. And in a male with a healthy sperm count, we can find from 50 to 150 million sperm cells in each mL of semen. In other words, 5 mLs of semen could contain 750 million sperm cells. Now, the last thing we need to talk about is the copulation organ, the penis. The penis and the scrotum form the external genitalia. The elongated portion of the penis is the body or shaft of the penis, and the tip of the penis is the glands which surrounds the external urethral orifice. The prepuce or foreskin surrounds the glands, and the prepuce attaches to the neck of the glands. The erectile tissue of the penis is formed by the corpus spongiosum and two corpus cavernosum. The plural of corpus cavernosum is corpora cavernosa that you see here. And if we take a look at this frontal section of the penis, we can see that the glands of the penis is made of corpus spongiosum, which kind of enlarges, goes to the sides, and forms the glands of the penis. And the corpus spongiosum surrounds the entire spongi urethra, and that's the reason why the spongi urethra is called spongi urethra. The glands of the penis is corpus spongiosum, but the body of the penis consists of corpus spongiosum and two corpus cavernosum. Each corpus cavernosum extends along the length of the penis until the neck of glands. But if we look at the base of the penis, we see that the corpus cavernosum forms what is called crux of penis. And the corpus spongiosum forms the bulb of penis. And here we have a better view of what I just mentioned. At the base of the penis, there is the bulb of penis, which is formed by the corpus spongiosum. And there is the crux of penis which is formed by the corpus cavernosum. Each cross of penis is bound to the ischiorhomus through connective tissue ligaments. Forming the male pelvic floor, there are two muscles, the ischiocavernosus and the bulboespongiosus. Now pay attention to the name of these muscles. Ischium cavernosus, based on the name, the origin is a Deischium. and the insertion is on the corpus cavernosum of the penis. And the bulbospongiosus origin is at the bulb of penis, and its insertion is at the corpus spongiosum. So keep in mind that both of these muscles are intimately linked to the penis. Now look at this. If we analyze a cross-section of the penis, we see that corpus spongiosum surrounds the spongiorithra, And we see that there are two parts. paired corpus cavernosum. Each corpus cavernosum surrounds a deep artery of the penis. So during an erection, what happens is that there is an increased blood flow through these erectile tissues, which fill them up with blood. But to keep these erectile tissues filled with blood, there is also a decrease in blood outflow. Because if there is an increase in the inflow of blood NAD. decrease of the outflow of blood, then blood starts to accumulate inside the erectile tissues and fill in all these spaces. And that's what creates an erection. So there is no bone in a human penis. And what makes the penis hard during copulation is actually the engorgement of blood within these erectile tissues. So the main purpose of the corpus cavernosum is to engorge with blood and it actually contributes the majority of the erection itself. And the main purpose of the corpus spondyosum, which surrounds the urethra, is to keep the urethra open. Because if there was no tissue actually supporting the urethra externally during an erection, the urethra could get closed and then no semen would go out. No semen would be able to leave the body during an ejaculation. Now if you see here there are some large veins on the dorsal surface of the penis and the constriction of these veins is what prevents the blood that's within the erectile tissue of the penis from leaving the penis and going back to the heart. And what prevents the blood from leaving the penis is the contraction of the ischiocavernosus and the bulbospongiosus muscles. So when these two muscles contract, they compress the veins of the penis and with that blood remains within the erectile tissues and the penis is erect. Now since the bulbospongiosus inserts at the corpus the spongiosum that surrounds the spongiurethra. Rhythmic contraction of the bulbospongiosus muscle pushes the semen that is within the urethra towards the external urethral orifice. And the semen is ejected out of the body. Now, obviously, if there is urine inside of the male urethra, the bulbospongiosus muscle aids in the urine ejection. So, bulbospongiosus muscle aids in the semen and also in the urine ejection. Now, erection is triggered by the nervous system. And an increase in the parasympathetic response, so the autonomic nervous system related to rest and digest, is what actually stimulates an erection. And the parasympathetic does that by stimulating vasodilation. And if you vasodilate, you decrease the resistance, and you increase blood flow to the erectile tissue, and with that, the penis gets erected. And that's why guys that have performance anxiety, they have difficulty achieving an erection. Because they actually need to be relaxed. They need to have their parasympathetic autonomic nervous system working to have an erection. Now, the ejaculation is a different process. The ejaculation is controlled by the sympathetic autonomic nervous system. And during ejaculation, the sympathetic nervous system stimulates rhythmic contractions of smooth muscle in the epididymis and ductus deferens which helps propel semen out of the epididymis up into the ductus deferens and so on. Now I spent the entire video telling you the pathway sperm cells follow until it's ejected out of the male body and in my last slide I have a mnemonic that I hope it will help you to remember it and here it is. The mnemonic is 7UP. S stands for seminiferous tubules, which is the place where sperm cells are actually produced. Then sperm cells they move to the epididymis. From the epididymis, sperm cells go into the vas deferens. When the vas deferens joins with the excretory duct, it forms the ejaculatory duct and the N of the 7UP is nothing but that's the way the mnemonic works. After the ejaculatory duct, the sperm cell goes into the urethra, more specifically the prosthetic urethra, and after that it passes the membranous urethra and then it reaches the spongy urethra which is within the penis. And we have here U for urethra and P for penis. And that was it for this video. Please let me know if you have any questions. Bye!

The reproductive system of males and females produces gametes, stores gametes, nourishes gametes, and finally it transports gametes. For fertilization, the reproductive organs responsible for producing the gametes and also producing sex hormones are called gonads. In males, the gonads are the testes, and in females, the gonads are the ovaries.

The gamete or sex cell produced by the testes is the sperm, and the gamete or sex cell produced by the ovaries is the oocyte. Now, in both males and females, gonads are associated with a system of ducts, which is collectively called reproductive tract. And these ducts receive, store, and carry the gametes from the gonads to the place where they're supposed to go.

Also, as part of the reproductive system, we have several accessory glands, that secrete fluids into the ducts and we also have the external genitalia. One thing that's important to point out is that an adult male produces, in average, half a billion sperm cells per day and the sperm cells are stored and expelled out of the male body within semen during ejaculation. So semen just refers to the fluid at which the sperm cells, the male sex cells, are found. So when we say semen, it only refers to the fluid part. Now, males, once they reach puberty, they produce sperm cells every day throughout their lives.

Whereas females only make oocytes before they are born. So a baby girl, on her very first day of life, already has all oocytes she'll ever have her entire life. And these oocytes will be dormant until the female reaches puberty, when they start to be released monthly throughout the female reproductive years.

So, females are born with all oocytes they'll ever have their entire lives. They do not make new oocytes. Now, the fusion of the male and female gametes is called fertilization. And when fertilization happens, a zygote is formed.

It's important to remember that a human cell has 46 chromosomes. So, when fertilization happens, a sperm carrying 23 chromosomes and an oocyte carrying 23 chromosomes result in a zygote with 46 chromosomes. which is exactly half from the father and half from the mother. In this video we will cover the male reproductive system and in the next video we will cover the female reproductive system and we will go into more details about each of them.

Here we have a mid-sagittal cut through a male pelvic area. We see the pubic symphysis which is just between the two halves of the pelvis. Posterior to the pubic symphysis we find the urinary bladder.

On the back of the urinary bladder, we see the seminal glands, also called seminal vesicles. Under the urinary bladder, we see the prostate gland, and inferior to the prostate, we find the bulbo-urethral gland. And these are the three accessory glands in the males. The male external genitalia is the penis and posterior to the penis we see the scrotum.

The scrotum is this pouch of skin located outside of the male body. Within the scrotum, we find the testis. The testis is the male gonad.

So, it is the organ that produces the sperm. Right next to the testis, on the posterior board of the testis, we find the epididymis. The epididymis is basically a storage site for sperm. Then we see here the vas deferens. also called ductus deferens, which is a muscular tube that extends up into the pelvic cavity and it goes back behind the urinary bladder where it meets up with the seminal gland.

The seminal gland produces the majority of the volume of semen, approximately 60% of it. And in this fluid produced by the seminal glands, we find a high concentration of fructose, which is a very important source of energy for the sperm cells. Also, this secretion produced by the seminal glands is alkaline.

And this alkaline secretion helps neutralize the acidity of the urethra because the acidity of the urethra could potentially damage sperm cells. Leaving the seminal gland, we see the ejaculatory duct. And the ejaculatory duct meets up with the prostatic urethra, which is right here within the prostate. The prostate is another gland and it produces the prostatic fluid. which contributes with 20 to 30 percent of the semen volume.

So the prosthetic urethra receives the prosthetic fluid and also the fluid coming from the ejaculatory duct. After the prosthetic urethra we find the membranous urethra, which is this part of the urethra passing through the external urethral sphincter. And the external urethral sphincter is a band of skeletal muscle that when contracted, it prevents urine and semen from leaving.

After the membranous urethra, we find the spongy urethra. And the spongy urethra receives this name because it is found within a structure called corpus spongiosum, which is a type of erectile tissue together with the corpus cavernosum that we see here. The corpus cavernosum is what engorges with blood, and contributes to the majority of the penile erection itself. Now, if you look here at the very beginning of the spongy urethra, in an area referred to as the base of the penis, there is another gland. And this gland is called bulbo urethral gland.

The bulbo urethral gland produces a very small amount of semen, like 5% of it, but even though it is a small volume, This secretion produced by the bulbous urethral glands is very important because it lubricates the urethra and the tip of the penis. Lastly, we see the penis which is the copulation organ, and it is necessary that it gets engorged with blood during sexual arousal for copulation to happen. And at the tip of the penis we find the external urethral orifice. During developmental stages of a baby boy, So inside the mother's womb, the testes are found very up high in the abdomen. They are near the kidneys.

And that's a long way from where the testes should be. And as fetal development continues, the testes descend into the scrotum. And that happens in a very interesting way. The two top pictures show where the testes of a two-month-old male fetus inside the mother's womb are located. Keep in mind that a two months old fetus is basically the size of a peanut.

The testes are way up near the kidneys and the scrotum is all the way down. And you see here this cord named gubernaculum testis that basically attaches the testes down to the scrotum. The length of the gubernaculum testis is five millimeters throughout the development and And with that, when the fetus keeps growing, since the gubernaculum testis doesn't change in length, this allows the testis to end up in the right place at the end of the fetal development.

And at birth, the testis should be located within the scrotum. Since the testis is targeted out up in the abdominal cavity and ends up inside the scrotum By the end of the fetal development, We say that the testes descend towards the scrotum. The scrotum or scrotal sac is a skin-covered sac that provides the testes with a cooler environment than body temperature. Sperm cells develop at a temperature that is slightly cooler than normal average body temperature.

And in order to have a healthy sperm count, It is important for the temperature of the testes to be around 4 degrees Fahrenheit cooler than the average body temperature. So it makes sense that the testes which produce the sperm are located within a scrotum. which hangs outside of the pelvic area and it is more external to the pelvic cavity. This way the scrotum hanging out of the pelvic cavity helps with the cooling off of the testis with the external environment. In the scrotum we find a very important set of muscles, the dartus muscle and the cremaster muscle.

These muscles are part of the scrotal wall. The D'Artes muscle is a layer of smooth muscle that when contracted it basically wrinkles the skin of the scrotal sac. So by wrinkling up the skin it reduces the scrotum surface area available for heat loss. Hence contraction of the D'Artes muscle binds up the scrotal skin leading to a reduction of the surface area of the scrotum and with that reduction in heat loss it warms up the testis.

Now, the cremaster muscle is a very important muscle that actually pulls the scrotal sac close to the body in response to cold temperatures. And as I mentioned before, the testis need to be a little cooler than the body temperature, like 4 degrees Fahrenheit cooler. But if it is too cold, the cremaster muscle pulls the scrotal sac up close to the body to keep it warm.

In other words, the cremaster muscle brings the scrotum closer or further away from the body based on temperature. The scrotum is divided into two chambers and we call each chamber scrotal cavity. And as you can see here, each testes is located inside a scrotal cavity.

Now what divides the scrotum into scrotal cavities is the scrotal septum and this septum extends to the skin surface of the scrotum as the raphe of the scrotum. The testis is the male gonads, so it produces the sperm and the sperm is stored within the epididymis. So the sperm stays within the epididymis until they are released, but if the sperm is in the epididymis for too long, it was stored for long term, then the sperm is just reabsorbed by the immune system.

Now, we see here associated with the testes and the epididymis a structure called spermatic cord. All of this is the spermatic cord, and it includes the cremaster muscle. If we look deep within the spermatic cord, we find the testicular artery that brings oxygen and nutrient-rich blood to the testes and scrotal tissue. And emerging from the testis, coming back up towards the pelvic cavity, we have a series of veins that form a plexus called Pampiniform Plexus.

This plexus, this network of veins, surrounds the testicular artery. And what happens is that there is a heat exchange between the warm arterial blood that's going down towards the testes and the cooler venous blood that's going... towards the pelvic cavity within the pumpiniform plexus. And this helps to cool down the warm arterial blood that's going towards the testes.

Hence, it helps to keep the testes cooler than the body temperature. We also find in the spermatic cord the autonomic nerves, which include sensory and motor nerves. And these nerves are involved with controlling the muscles that we find in the scrotum. as well as involved with sensations of pain and temperature.

We see here the vas deferens or ductus deferens, which is actually a muscular tube that emerges from the epididymis. And during ejaculation, the vas deferens carries testicular fluid up towards the posterior part of the urinary bladder, where we find the seminal glands. Now, linking each scrotal chamber with the pelvic cavity.

there is the inguinal canal. And this superficial inguinal ring that we see here marks the end of the inguinal canal. Then deep inside the body, marking the entrance of the inguinal canal, there is the deep inguinal ring. As you can see here, the spermatic cord passes through the superficial inguinal ring and after the spermatic cord passes through this ring, it goes through the inguinal canal and it reaches the pelvic cavity.

And I'm pointing this out because this is clinically relevant. What happens is that structures within the pelvic cavity and abdominal cavity can herniate through the inguinal canal down into the scrotum. And that is... It's called inguinal hernia. Inguinal hernias are much more frequent in males than in females because in females the inguinal canal is very small.

We will learn that passing through the inguinal canal of females there is basically the uterus round ligament and nerves. Consequently, the females' inguinal canal is much smaller than males because males have this wide spermatic cord passing through it. One example of inguinal hernia is when the mesenteric fat protrudes through the spermatic cord into the scrotum and if there is a lot of fat coming down to the scrotum it can affect proper blood flow and that can lead to the death of the scrotal tissue which is obviously not good.

This diagram shows a horizontal section of the testes within the scrotum. At the outside part of the scrotum we find the skin. Underneath the skin we find the darts muscle, the muscle that wrinkles up the scrotal sac skin to reduce surface area and consequently it helps to reduce heat loss. Underneath the darts muscle we find the cremaster muscle that brings the testis closer or further away from the body depending on the temperature. The test is discovered by a serious membrane called Tunica vaginalis.

And like all serous membranes, the tunica vaginalis has a visceral layer that surrounds the testis and a parietal layer on the outside. And between the visceral and the parietal layers, we find a cavity named scrotal cavity. So if the testis are covered by a serous membrane, the testis are actually lubricated and they can move around within the scrotum. Now the The testis itself is surrounded by a fibrous tissue called tunica albuginea. This tunica albuginea is a dense fibrous tissue that surrounds the outside of the testis and it invaginates.

It goes deep down within the testis and creates what we call septum. All this septa divides the testis into lobules. Each one of these logos is filled with this coiled up tubes that we call seminiferous tubules.

And within the seminiferous tubules is where the production of sperm actually takes place. So the septa divide the testes into lobules, and these lobules have the seminiferous tubules inside. All the septa converge towards the mediastinum of the testes, which is this area basically in the middle in between the testis and the epididymis. Remember that the sperm is produced in the seminiferous tubules of the testis and then it goes to the epididymis to be stored.

So in the mediastinum we find what makes the connection between the seminiferous tubules and the epididymis and this connection is made by the retic testis and the efferent ductus. Efferent with E which means exiting the mediastinum area and entering the epididymis. So, in summary, sperm is produced inside the seminiferous tubules, then sperm goes into the rat testis, from there it goes into the efferent ductus, and then it goes into the epididymis that we see here.

If we take a look at the seminiferous tubules, we find the germinal epithelium. we find the cells that will give rise to the sperm. These cells are stem cells and they are called spermatogonia.

The process of producing sperm is called spermatogenesis. So as I mentioned before, the gonads, so the testes in males, they produce sex cells and also sex hormones. And what happens is that when males reach puberty, Testosterone, which is a sex hormone, starts being produced by cells called interstitial endocrine cells. And one of the things that testosterone does is to stimulate spermatogenesis. So testosterone stimulates the production of sperm.

So when males reach puberty, the presence of testosterone stimulates the spermatogonia to divide, differentiate and mature giving rise to sperm. And as that happens, the differentiating cell goes towards the lumen of the seminiferous tubules. And from the lumen, sperm cells get transported through the seminiferous tubules towards the reticulitis and then to the efferent ductus. the epididymis which is the site of sperm storage.

Now what's interesting is that because sperm cells do not start to develop until males reach puberty technically the sperm is considered a foreign cell by the body. So what happens is that if immune cells of a male encounter a sperm cell of the same male the immune cells would attack these sperm cells because they are considered foreign. And for this reason, males have the blood test barrier, a barrier that prevents sperm cells and immune cells from communicating. The blood test barrier basically isolates the seminiferous tubules from the general circulation and with that it avoids immune reactions against sperm cells. Making this blood testis barrier, we have cells called nurse cells that we see here in the seminiferous tubules.

And these nurse cells are also known as Sertoli cells or sustentacular cells. And between these nurse cells, we have tight junctions, which packs these cells tightly together. And with that, they make the blood testis barrier. Nurse cells, as their name implies, are involved with nursing.

And besides making up the blood testes barrier, these nurse cells are stimulated by the presence of sex hormones, like testosterone. And when nurse cells are stimulated, they promote the division of the spermatogonia, which leads to the production of sperm cells. And the nurse cells also provide nutrients for the sperm cell development. So you can think of nurse cells like a protective and dedicated mother of sperm cells.

Nurse cells make the blood testes barrier, they stimulate the production of sperm cells, and they nourish sperm cells during their development. And this is how sperm cells look like. They have a head, a neck, and a tail, and they do not have a lot of organelles.

In the head of a sperm cell, we find a nucleus with the 23 pairs of chromosomes. And we also find in the head the acrosome. The acrosome contains digestive enzymes that break down the wall of the oocyte, allowing fertilization to happen.

In the neck of a sperm cell, we find mitochondria, which provides energy for the flagellum, for the tail to move around. So the mitochondria provides ATP that powers the flagellum, which is the tail of the sperm cell. This is the only flagellum found in the human body.

And this flagellum is very important because it enables the motility of the sperm cell. Now, sperm cells lack energy reserves like glycogen, and they absorb nutrients from the surrounding fluid where they are living at that moment. And the nutrients that sperm cells like the most is fructose, which is a simple sugar, a monosaccharide found in the seminal fluid, the fluid secreted by the seminal glands.

Until recently, It was believed that during fertilization the sperm only brought the nucleus to the egg. So we used to say that the male contribution to the zygote was only the 23 pairs of chromosomes and no other organelle besides the nucleus was transferred from the sperm to the egg. And having that in mind we could affirm that all the mitochondria in our body came from the egg and not from the sperm.

And that's why we used to say that all mitochondria in our body came from our mother. And obviously, inside the mitochondria, we have the mitochondrial DNA. And the fact that mitochondria was always inherited from our mother, who inherited hers from her mother, and so on, this enabled genealogical researchers to trace maternal lineage far back in time.

However, on December 2018, A scientific paper was published showing compelling evidence that this long-held belief may not always be true. The scientific paper presented evidence for biparental inheritance of mitochondrial DNA in three unrelated families. Now, as you can imagine, lots of attention has been given to the possibility of paternal transmission of mitochondrial DNA. The test produces around 1500 sperm cells per second. So, in a day, several million sperm cells are produced.

After all these sperm cells leave the seminiferous tubules, they are stored in this pretty convoluted system of tubules called epididymis. And the epididymis is anatomically divided in head, body, and tail. When the sperm leaves the seminiferous tubules, it goes to the rat testis and then to the efferent ductus.

And the efferent ductus connects the head, of the epididymis. In a period of two weeks, sperm cells travel from the head of the epididymis to the tail of the epididymis, which connects to the ductus deferens, the muscular tube that goes up through the spermatic cord into the pelvic cavity. Now, one interesting thing is that when the sperm cells reach the epididymis. Even though the sperm is physically mature, it is not functionally mature. And what I mean by not functionally mature is that the sperm cannot move.

It cannot swim on its own. Basically, the first time the sperm is able to move on its own, it is when the sperm cells get in contact with the... secretion produced by the seminal glands, which has a high concentration of fructose.

And when that happens, the sperm becomes able to swim on its own. However, the swimming is not full power yet. The swimming is not enough to fertilize an egg.

And the sperm cell just becomes fully capable of fertilization after it undergoes a process called capacitation. And capacitation happens outside of the male reproductive system. Capacitation just happens when the sperm gets in contact with secretions produced by the female reproductive system.

Now, when the sperm undergoes capacitation, which happens inside the female reproductive system, the sperm tail is capable of beating very vigorously, and with that, the sperm is ready it is capable of fertilizing an egg. So what happens is that for the period of two weeks, approximately two weeks, that sperm cells are within the epididymis. The epididymis needs to ensure the sperm cells are kept in a good environment and because of that, lining up the lumen of the epididymis, we find a distinctive, pseudo-stratified columnar epithelium with long stereocilia. This stereocilia increases the surface area available for the absorption and secretion to adjust the testicular fluid composition at which the sperm is being stored in the epididymis.

And with that, it ensures that the testicular fluid is kept at its prime and the sperm that leaves the epididymis is very healthy. The epididymis contributes with approximately 5% of the total volume of the semen. This picture is just to show you how it all looks in a cadaver.

We see here the tunica vaginalis, which is the serous membrane that reduces friction and allows the testis to move around within the scrotum. And then we see the testis and directly surrounding the testis we see the tunica albuginea. And the tunica albuginea is The swamp goes deep. into the testis and form the septa that divides the testis into the lobules and the lobules is what contains the seminiferous tubules that actually produces the sperm.

And we also see here the head, body, and tail of the epididymis and the spermatic cord that connects the scrotal chamber with the pelvic cavity. So, we just learned that lining the lumen of the epididymis we have the pseudostratified columnar epithelium with stereocilia. Now, when sperm is within the ductus deferens, due to muscular contraction of the ductus deferens that is made of smooth muscle, the sperm travels up through the spermatic cord and then through the inguinal canal into the pelvic cavity. Then, it goes behind the urinary bladder, where the sperm reaches the ampulla of the doctor's deference. which is this enlarged part that we see here.

Also, in the posterior side of the urinary bladder, we find the seminal glands. The seminal glands produce the seminal fluid, and this fluid contributes to about 60% of the volume of the semen. The seminal fluid is a slightly alkaline, viscous, whitish-yellow type of fluid, and this fluid contains fructose that provides energy to the sperm.

So, fructose is metabolized and converted to ATP, which sperm can use to power the flagellum, which is used for propulsion, for swimming. Now, since the seminal gland contributes with approximately 60% of the semen volume, and the secretion is alkaline, this fluid can neutralize the acidity of the urethra and also the acidity of the vagina. In this way, the sperm can be happy and healthy during its trip.

Now, the duct that leaves the seminal gland is called excretory duct. When each ampulla of the ductus deferens joins with an excretory duct from the seminal gland, when this conversion happens, we have the ejaculatory duct. And in the ejaculatory duct is where the secretion coming from the ductus deferens is mixed with the secretion of the seminal glands. And then the sperm that was immobile now becomes mobile. So you can think of the seminal gland secretion as the sperm's energy drink.

When the sperm gets in contact with the fluid secreted by the seminal glands, the sperm becomes mobile and it is ready to swim for its life. But remember, even though the sperm is mobile after it gets in contact with the seminal gland fluid, it. The sperm is still not capable of fertilizing an egg.

The sperm just becomes capable of fertilizing an egg after it undergoes capacitation. And capacitation just happens after the sperm gets in contact with secretions present in the female reproductive system. Now, the ejaculatory duct goes to the prostate gland.

And in the prostate gland, we have the production of the prostatic fluid. The prostatic fluid makes up 20 to 30% of semen. It contains citric acid, which is a nutrient for the sperm, and it contains an antibiotic that prevents male urinary tract infections. Now, the prostate produces the PSA, the prostatic-specific antigen. And this antigen is basically enzyme that helps liquefy semen.

So this enzyme makes the semen more liquidy. Liquid enough that the sperm can swim around it. But nowadays PSA is very famous because it is a prostate cancer biomarker.

Because the blood levels of PSA is often elevated in men with prostate cancer. PSA levels can be elevated in other situations besides cancer, such as benign prostatic hyperplasia or in case of inflammation of the prostate. But since 1994, FDA approved the PSA test in conjunction with rectal exam to test a symptomatic man for prostate cancer. The last pair of glands males have is the bulbourethral gland. And these glands are located at the base of the penis, very, very close to the external urethral sphincter, which is also known as urogenital diaphragm.

The bulbourethral gland secretion contributes with 5% of the semen. And the secretion is thick, sticky, alkaline mucus secretion that helps neutralize the acidity of the urethra, not as much as the seminal gland one, because the seminal glands contribute with 60% of the semen, and the bulburethral glands just contribute with 5% of the semen. But most importantly, the function of this secretion of the bulburethral glands is that it lubricates the tip of the penis, as well as the lining of the urethra.

and with that diminishing the amount of sperm cells damaged during ejaculation. So this is the trip that sperm cells do until they leave the male body and the semen, the fluid at which the sperm cells are kept on, is modified until basically it leaves the male body. Five percent of the semen comes from the epididymis, then 60 percent of it comes from the seminal glands, around 30% of it comes from the prostate gland and 5% from the pulmonary urethral gland.

And during ejaculation, a male releases from 2 to 5 mLs of semen. And in a male with a healthy sperm count, we can find from 50 to 150 million sperm cells in each mL of semen. In other words, 5 mLs of semen could contain 750 million sperm cells. Now, the last thing we need to talk about is the copulation organ, the penis.

The penis and the scrotum form the external genitalia. The elongated portion of the penis is the body or shaft of the penis, and the tip of the penis is the glands which surrounds the external urethral orifice. The prepuce or foreskin surrounds the glands, and the prepuce attaches to the neck of the glands.

The erectile tissue of the penis is formed by the corpus spongiosum and two corpus cavernosum. The plural of corpus cavernosum is corpora cavernosa that you see here. And if we take a look at this frontal section of the penis, we can see that the glands of the penis is made of corpus spongiosum, which kind of enlarges, goes to the sides, and forms the glands of the penis.

And the corpus spongiosum surrounds the entire spongi urethra, and that's the reason why the spongi urethra is called spongi urethra. The glands of the penis is corpus spongiosum, but the body of the penis consists of corpus spongiosum and two corpus cavernosum. Each corpus cavernosum extends along the length of the penis until the neck of glands.

But if we look at the base of the penis, we see that the corpus cavernosum forms what is called crux of penis. And the corpus spongiosum forms the bulb of penis. And here we have a better view of what I just mentioned. At the base of the penis, there is the bulb of penis, which is formed by the corpus spongiosum.

And there is the crux of penis which is formed by the corpus cavernosum. Each cross of penis is bound to the ischiorhomus through connective tissue ligaments. Forming the male pelvic floor, there are two muscles, the ischiocavernosus and the bulboespongiosus.

Now pay attention to the name of these muscles. Ischium cavernosus, based on the name, the origin is a Deischium. and the insertion is on the corpus cavernosum of the penis.

And the bulbospongiosus origin is at the bulb of penis, and its insertion is at the corpus spongiosum. So keep in mind that both of these muscles are intimately linked to the penis. Now look at this. If we analyze a cross-section of the penis, we see that corpus spongiosum surrounds the spongiorithra, And we see that there are two parts. paired corpus cavernosum.

Each corpus cavernosum surrounds a deep artery of the penis. So during an erection, what happens is that there is an increased blood flow through these erectile tissues, which fill them up with blood. But to keep these erectile tissues filled with blood, there is also a decrease in blood outflow. Because if there is an increase in the inflow of blood NAD.

decrease of the outflow of blood, then blood starts to accumulate inside the erectile tissues and fill in all these spaces. And that's what creates an erection. So there is no bone in a human penis. And what makes the penis hard during copulation is actually the engorgement of blood within these erectile tissues.

So the main purpose of the corpus cavernosum is to engorge with blood and it actually contributes the majority of the erection itself. And the main purpose of the corpus spondyosum, which surrounds the urethra, is to keep the urethra open. Because if there was no tissue actually supporting the urethra externally during an erection, the urethra could get closed and then no semen would go out. No semen would be able to leave the body during an ejaculation.

Now if you see here there are some large veins on the dorsal surface of the penis and the constriction of these veins is what prevents the blood that's within the erectile tissue of the penis from leaving the penis and going back to the heart. And what prevents the blood from leaving the penis is the contraction of the ischiocavernosus and the bulbospongiosus muscles. So when these two muscles contract, they compress the veins of the penis and with that blood remains within the erectile tissues and the penis is erect.

Now since the bulbospongiosus inserts at the corpus the spongiosum that surrounds the spongiurethra. Rhythmic contraction of the bulbospongiosus muscle pushes the semen that is within the urethra towards the external urethral orifice. And the semen is ejected out of the body.

Now, obviously, if there is urine inside of the male urethra, the bulbospongiosus muscle aids in the urine ejection. So, bulbospongiosus muscle aids in the semen and also in the urine ejection. Now, erection is triggered by the nervous system.

And an increase in the parasympathetic response, so the autonomic nervous system related to rest and digest, is what actually stimulates an erection. And the parasympathetic does that by stimulating vasodilation. And if you vasodilate, you decrease the resistance, and you increase blood flow to the erectile tissue, and with that, the penis gets erected. And that's why guys that have performance anxiety, they have difficulty achieving an erection.

Because they actually need to be relaxed. They need to have their parasympathetic autonomic nervous system working to have an erection. Now, the ejaculation is a different process. The ejaculation is controlled by the sympathetic autonomic nervous system. And during ejaculation, the sympathetic nervous system stimulates rhythmic contractions of smooth muscle in the epididymis and ductus deferens which helps propel semen out of the epididymis up into the ductus deferens and so on.

Now I spent the entire video telling you the pathway sperm cells follow until it's ejected out of the male body and in my last slide I have a mnemonic that I hope it will help you to remember it and here it is. The mnemonic is 7UP. S stands for seminiferous tubules, which is the place where sperm cells are actually produced. Then sperm cells they move to the epididymis. From the epididymis, sperm cells go into the vas deferens.

When the vas deferens joins with the excretory duct, it forms the ejaculatory duct and the N of the 7UP is nothing but that's the way the mnemonic works. After the ejaculatory duct, the sperm cell goes into the urethra, more specifically the prosthetic urethra, and after that it passes the membranous urethra and then it reaches the spongy urethra which is within the penis. And we have here U for urethra and P for penis. And that was it for this video.

Please let me know if you have any questions. Bye!

Transcript for:Male Reproductive System Overview

Transcript for:
Male Reproductive System Overview