All right, everybody. Welcome to the uh to chapter 26 where we're going to be diving into the reproductive system. Specifically, we're going to be talking about the male reproductive system and next chapter we'll be talking about the female reproductive system. Um it is going to be a little bit of a long um lecture, less than an hour, I promise about maybe 48 minutes. So, make sure you answer the questions that are popping up. Make sure you ask questions if the if you have any questions, any any concerns, if you don't understand something and uh always let me know if you need any help. All right, see you later. So, at its core, what is the job of the reproductive system? Well, it has several key functions. Primarily, it is responsible for producing, storing, nourishing and transporting gamts. Now, the term gamut is a general one and it is crucial to understand that these are different depending on whether we're talking about biological males or biological females. In biological males, the gamuts are sperm and in biological females, they are oytes, which you might also know as eggs. The whole point of these gamuts is for fertilization to happen. Fertilization, simply put, is the union of a sperm and an egg. When these two cells come together, they form a single cell called a zygote. Now, when we look at how the reproductive system is organized, we can break it down into several key components that you'll see in both the male and female systems, although the specific structures will differ. First, we have the gonuts. These are primary reproductive organs. In biological males are the testes and inbiological females are the ovaries. Their main jobs are to produce gamts, sperm and eggs and also to produce hormones that regulate reproductive functions. Next, we have the reproductive tract. This is essentially a series of tubes or or ducts that are responsible for receiving, storing and transporting the gamuts. In a specific for females, the reproductive tract is also where embryogenesis or fetal development will happen. Then we have the accessory glands. These are structures that will secrete various fluids that play important roles in supporting the gamuts and facilitating fertilization. Finally, we have the external genitalia which are the external reproductive structures. All right. So, let's now turn our attention specifically to the anatomy of the male reproductive system. We're going to focus on this slide on the internal structures. However, we're going to start with one external structure, the escroton. As you can see in this diagram, the skuron is a sackl like structure that houses both the testes which are the oval grade structures here as well as the epidmies which is the kind of hole structure that is located on the top and the back of the testes. So in anatomical terms the epidemies are located superiorly and posteriorly to the testes. The basic pathway of a sperm is that they are produced in the testes. From there they then travel into a into and through the epidmies. After the epidmies the sperm then moves into a tube called the doctor's deference. sometimes called the vast differences, the the vast difference. And you can see one of these on each side. They are pair structures. The doctor's difference then carries the sperm up and eventually leads to the ejaculatory duct. And finally, the sperm will exit the body through the urethra. It is also important to note that there are several accessory organs which are glands that contribute fluids to the semen. This includes the seminal gland also sometimes called the seinal vesicle, the prostate gland and the bulthrow gland also known as the copers gland. These glands secrete their fluid into the ejaculary ejaculatory ducts and the urethra. Here you can see the seminal gland and the point where it forms the ejaculatory duct. Then the prostate gland situated around the urethra and then down here are the bulbal glands. All of these contribute various components to the ejaculate. And then of course we have the penis which is an erectile organ that plays a crucial role in delivering a sperm and we'll discuss this anatomy in a later slide. Here you can see the seminal gland and the point where it forms the ejaculatory duct. Then the prostate gland situated around the urethra and then down here are the bulbal glands. All of these contribute various components to the ejaculate. And then of course we have the penis which is an erectile organ that plays a crucial role in delivering a sperm and we'll discuss this anatomy in a later slide. Now let's look at the testes in another angle. You'll notice that they do not reside within the body cavity. Instead, they hang inside this external pouch of skin known as the scrotum. There is a very important reason for this location. Sperm development is a delicate process and requires a specific temperature around 96.6° 6° F which is a slightly cooler than the body temperature. This is why the testes are located outside the abdominal cavity within the scrotum to provide this optimal thermal environment for a sperm production. within the struct within the scrotum each testice is actually housed in its own separate scrotal cavity. So even though they are in the same external pouch they are they are in distinct compartments. You can see here that the scrotum is divided externally by a race ridge called the rafi which visually marks the boundary between these two escroal chambers. Also connected to the testes are these paired structures called the spermatic cords. You have one on the left and one on the right of the uh right testes. And these are crucial because they connect the abdominal cavity directly to the testes. Think of them as pathways in and out. These spermatic cords are not just simply strings. They are complex structures composed of layers of fascia, connective tissue and muscle all forming a protective sheath. Importantly, this course not only provide a physical connection but also enclose the doctor's deference, the tube we talked about earlier that carries a sperm as well as various blood vessels that supply the testes and remove waste and also nerves that provide innervation. Now let's take a look inside the testes to see how it is organized. If we were to take a cross-section, you'd see that the interior of the testes is divided into compartments by these partitions called septa. These septa essentially subdivide the testes into numerous wedge shaped areas called lobules. And within each of these lobules is where the magic of a sperm production begins. Each lobule contains tightly coiled tubes called seminifpheros tubules. These are the functional units of the testes where a sperm are actually produced. Now these seminifpherous tubules do not just end abruptly. They will begin to uncoil and eventually lead into shorter straighter tubes called a straight tubules. These straight tubules then interconnect with each other in a network of channels known as the retestes. You can see here how these seminifpherous tubules start to become a straight tubules. Follow them as they leave the lobule and enter this interconnected network. This is the retest. The retestes then connects to a series of a small ducks called ephine ductules. These epherendocules are the passageway that takes the newly formed sperm out of the testes and into the next structure in the reproductive tract which is the epidmies that we mentioned earlier. So to recap the flow within the testes, a sperm are produced in the seminifpherous tubules. They then move into the straight tubules, then through the network of the retest and finally exit the testes via the epherent ductles to reach the epidemis. If we were to zoom in even further and look microscopically at the walls of the seminifpherous tubules, we will see different types of cells. One important type is the espermatogonia. These are essentially the stem cells for a sperm. They are immature cells that will eventually undergo a process of differentiation to become mature sperm cells. Interestingly, these spermatogonia are formed during embryionic development, but they remain dormant until puberty. Once puberty hits, they are stimulated to undergo a process called a spermatogenesis. This is the actual production of a sperm. Looking at a cross-section of a seminar stubio, you can see that the process of a spermatogenesis occurs in a specific direction from the outside towards the inside. The espermatogonia are located on the periphery closest to the outer wall of the tubio. As these cells mature and develop into a sperm, they gradually move towards the center of the tubule which is called the lumen. So the most mature sperm cells will be found in the lumen of the seminifpherous tubules. Now in the spaces that exist between the seminifpherous tubules we find another important cell called the inter interstitial cells. They are also known as the leic cells. These interstatial cells have a very crucial endocrine function. They are responsible for secretreting male sex hormones and the primary hormone they produce is testosterone. So while the seminifpherous tubules are busy producing sperm, the insertial cells in the surrounding tissue are producing the hormones that regulate male reproductive development and function. You can see here that the cluster of insertial cells nested in the connective tissue between the borders of the seminifpherous tubules. And right at the edge of the tubule, you can see the spermatogonia, the starting point of a sperm development. Now that we have mentioned the insertial cells or leic cells which produce male sex hormones, the main player here, the most significant one is testosterone. Testosterone has a wide range of effects through the male body. It is absolutely essential for stimulating spermatogenesis. the very process of a sperm production we just discussed. It also promote promotes the maturation of a sperm ensuring they develop the necessary characteristics for fertilization. Furthermore, testosterone plays a crucial role in maintaining the accessory reproductive organs, keeping them functioning properly. It is also responsible for the development of secondary sex characteristics during puberty. Things like increased male muscle mass depending sorry deepening of the voice and the growth of body hair. Beyond the reproductive system itself, testosterone also stimulates growth and metabolism in general and even influences sex behavior and sexual drive. And just to give you an idea of its chemical nature, here you can see the molecular structure of testosterone. You will notice it is derived from an aster steroid base meaning it is a type of lipid synthesized from cholesterol which accounts for this characteristic ring structure of hydrocarbons. As we discussed briefly, spermatogenesis is a process of forming a sperm cells and is a continuous process that begins in the outermost layer of the seminifpherous tubules. It all starts with a spermatogonium espermatogonia in the plural sense which are deployed as stem cells. These spermatogonia undergo mitosis to produce more spermatogonia ensuring a continuous supply. Some of these spermatogonia will then differentiate and develop into deploy primary espermatocytes. Now these primary expertes are the cells that will undergo meiosis. That a special type of cell division that reduces the chromosome number by half. Remember that meiosis involves two rounds of division or two rounds of cell division. So in a single deploy primary experimental site, this will undergo meiosis one and then meiosis 2 to ultimately generate four spermatits. And these esperats are now hloid meaning they contain only half the number of chromosomes as the original espermatogonium and primary espermatite. So to recap the initial stages we start with a deployed espermatogonium. It develops into a deploy primary esperatto site which then undergoes meiosis to produce four hloid esperatids. The spermatids that we just talked about are not yet mature functional sperm cells. They need to undergo a final stage of development called esper esperiogenesis. This is a process where the hloid espermatids undergo a significant physical maturation to transform into the familiar structure of a sperm cell. So you have these relatively round espermits that through esperioenesis they will develop the characteristic head midpace midpiece and tail that we associate with a mature sperm. During esperioenesis, the developing espermatites are actually embedded within a specialized cells called nurse cells, which are also known as certoly cells. These nerve cells play a crucial supportive role in the entire process of espertogenesis. As the spermatites mature, they undergo a dramatic transformation. They will lose most of their organels, unnecessary cellular machineries and the majority of the cell cytoplasma to become more streamline and motile. If we look at the stages of spermatogenesis here, you can see that the early spermatites still retain a significant amount of cytoplasma and various organels. But as they complete spermatogenesis and become mature sperm, they shed this excess material. These nerve cells embedded within the walls of the seminifpherous tubules are essential for this maturation process. They provide nourishment, remove waste products and secrete factors that help the spermatus develop properly. We will actually dive into the specific functions of these nerve cells in more detail on the next slide. But just to quickly review the overall process we have covered so far. It begins with a espermatogonium which undergoes meiosis to produce espermatids and then these esperats undergo esper mioenesis a physical maturation process facilitated by the nurse cells resulting in the formation of mature sperm. Now let's dive deeper into these fascinating nerve cells or certoly cells. They surround the developing sperm. They have several critical functions beyond just providing physical support. One of their key roles is in the maintenance of the blood testice barrier. This barrier is actually quite similar in concept to the blood brain barrier that we have talked about in the nervous system. Essentially, it isolates the seminifpherous tubules from the general blood circulation. Why is that important? Well, the fluid environment inside the lumen, the central cavity of the seminifpherous tubules is very different from the insertial fluid that surrounds these tubules. The developing sperm actually begin to express cell surface markers as they mature. These markers will be recognized as nonself by the male's immune system. So without this barrier, this developing a sperm will likely be attacked and destroyed by the immune system. The blood testice barrier formed by tight junctions between the nerve cells ensure that these two fluid environments remain strictly separate. This creates a protected environment within the seminifpherous tubules where the developing sperm are bathed in fluids specifically tailored to nourish them and support their maturation without interference from the general circulation. So what does a mature sperm cell actually look like? It is a highly specialized cell with three main components. The head, the middle piece, and the tail. The head is the command center containing the chromosomes, the male's genetic contribution. It is also feature sorry it also features a caplike structure at its anterior end called the acrosome. The acrosome is essentially a membrane bound vesicle a little compartment filled with enzymes that are absolutely crucial for fertilization. These enzymes help the sperm to penetrate the outer layers of the egg. The process of acrosomal reaction is quite complex. If you are interested in this part of fertilization and early development, we will cover this in a later lecture. Connected to the head by a short neck is the middle piece. This region is packed with mitochondria and also contains centrioles. So you may be asking why so much mitochondria. Well, let's remember what mitochondria is used for. Mitochondria is the powerhouse of the cell responsible for producing energy in the form of ATP. This energy is essential for the movement of the third component, the tail. The tail of the sperm is essentially a flagelum, a wipe, a whiplike structure that propels the sperm forward. It moves it, it moves in a characteristic undulating crocrew like motion. And the energy required for this movement is given by ATP. This is supplied by the numerous mitochondria located in the middle piece right behind the head. Let's take a moment to recall the path that a sperm takes as they travel from their site of rep of production to the initial storage location within the male reproductive track. We started in the seminifpherous tubules. Then the sperm moves into the estra tubule followed by the network of the retestes then through the efferent doctors and finally they arrive at the epidmies. Now the epidmis itself is not just one uniform structure. It is divided into three distinctive regions. the head, the body and the tail. The head of the epidmies is the initial receiving point for the sperm coming from the ephine ductals. That makes logical sense as they lead directly into it. The body of the epidemis is characterized by tightly coiled tubes that continue to to transport the sperm towards the tail. As we reach the tail of the epidmis, these coil tubes will begin to straighten out and transition into the next part of the dog system which is the doctor's deference or bus difference. It is important to understand that the male reproductive tract this entire network of tubes is involved in more than just transport. It is also crucial for the functional maturation, nourishment and storage while still transporting the sperm. The key components we have discussed so far in this track are the epidmies with its head, body and tail followed by the doctor's deference. Continuing from the doctor's deference, we will eventually reach the ejaculatory dot and finally the urethra that share path passageway. So we have reached the epidmies and as I mentioned before it has those three distinctive parts the head the body and the tail. But the epidemis is more than just a passive storage tube for a sperm. It has several important functions. Firstly, it plays a role in monitoring the composition of the fluid that is produced by the seminifpherous tubules. It is not just blindly accepting everything that comes its way. Secondly, the epidmis acts as a recycling center for damaged sperm. If a sperm is malformed or has died, they are broken down and reabsorbed here. And thirdly, it is a crucial site for the storage of a sperm and also for their further maturation. This maturation process is what I allude to I allude to on the previous slide. The sperm undergoes changes within the epidmies that contribute to the ability to become motile and f fertilize an egg. Although the final step capacitation occurs later. Just to reiterate the journey we have tra so far is a sperm are produced within the seminifpherous tubules. Then they travel through the straight tubules. Then the retestes the then the ephine ductals and finally they arrive and are processed within the epidmis. From the tail of the epidmis, the sperm then enters the dock's deference, which is another tubular structure also commonly known as the vast difference. The doctor's deference serves as a major transport pathway leading towards the urethra. If we were to trace the path of the doctor's deference, it begins at the tail of the epidmis down in the scrotum. It then ascends into the abdominal cavity by by passing through the inguinal canal, a passageway in the abdominal wall. Once inside the abdomen, it curves around the urinary bladder and then ure the tube carrying urine from the kidney to the bladder. It then descends back down a pass and passes through the prostate gland eventually joining with the duct of the seinal gland to form the ejaculatory dot. So think of the dog difference as a significant detour that takes the sperm up and around before heading towards their exit route. Now let's turn our attention to the various accessory glands of the male reproductive system. These glands secrete fluids that mix with the sperm to form semen. We have three main sets of glands to consider. the seinal gland also known as the seinal vesicles, the prostate gland and the bulbthrol glands which are also called the copers glands. It is helpful to note that I have listed them roughly in the order that the sperm will encounter these secretions during ejaculation. First we have the seinal glands which are located here posterior to the bladder you can see the dctor's deference coming in to join with the duct of the seinal gland. Then inferior to the bladder we have prostate gland surrounding the initial portion of the urethra. And finally, located inferior to the prostate gland are the bulbthro glands situated near the base of the penis before the urethra exits the pelvic cavity. The seinal glands or seminal vesicles are responsible for producing a significant portion of the semen volume about 60%. The fluid they secrete known as seinal fluid plays a crucial role in enabling the sperm to become motile to start swimming. This fluid is rich in several key components including fructose which serves as a energy source for the sperm. prostaglandins which are hormone like substances that can help with a smooth muscle contraction in the female reproductive tract and chlorine factors which contribute to the initial coagulation of a sperm after ejaculation. The seminal fluid empties into the doctor's deference during the process of ejaculation just before it joins with the ejaculatory duct. The prostate gland which surrounds the upper portion of the urethra just below the bladder contributes another significant portion of the semen volume. accounting for about 20 to 30%. The fluid produced by the prostate gland also known as prostatic fluid contains this contains various enzymes that play important role in supporting the sperm after ejaculation. Some of these enzymes help to nurse the sperm providing them with nutrients as a favorable environment. Interestingly, prostatic fluid also contains enzymes that help to prevent coagulation of the semen within the vagina allowing the sperm to maintain their moility and continue their journey towards the egg. Finally, we have the bulb glands, also known as the copers glands. These are relatively small glands contributing about 5% of the total semen volume. They are located at the base of the penis. Their primary secretion is a thick sticky alkaline mucus that is re released into the urethra used before ejaculation. This secretion serves two main purposes. First, it helps to neutralize any residual urinary acids that might still be present in the urethra, creating a more favorable environment for the passage of a sperm. Remember that urine is acidic and could be damaging the sperm. Second, this moccus also helps to lubricate the tip of the penis, facilitating its entry into the female reproductive tract. So what exactly is released during ejaculation? A typical ejaculation involves a volume of about two to five milliliters of semen. This semen is a complex mixture containing a sperm cells and the concentration can be quite high ranging from about 20 to 100 millions sperm per milliliter. In addition to the sperm, semen is comprised of seinal fluid which is the combined secretions from all the accessory glands. We have discussed the seinal gland, the prostate gland and the bulbthral glands as well as some contributing contributions from the epidemis. Lemon also contains various enzymes. One enzyme in particular plays an interesting role in helping to dissolve the moccas within the vagina which can sometimes act as a physical barrier to a sperm for entry. Thus aiding the sperm in their journey towards the egg. Let's take a closer look at the external anatomy of the male reproductive system, specifically the penis. The penis can be divided into three main regions. The root which is the attached base, the body also commonly refer as the shaft and the glands penis which is the expanded distal end or the head of the penis. The root of the penis is responsible for anchoring the penis to the pelvic structure specifically attached to the ramy of the pelvis. The bony part of the pelvis. The body or shaft is primarily composed of erectile tissue which we will examine closely in a moment. The erectile tissue consists of corpus espongium corpus espongosum and the corpora cavernosa. Finally, the gland's penis is the enlarged tip of the penis and it surrounds the external urethral orifice which is the opening through which both urine and semen exit the body. The shaft of the penis is characterized by three cylindrical columns of erectile tissue that are highly supplied with blood vessels. There are two corpora cavernosa located on the posterior side of the penis and a single corpus espongiosum situated anteriorly. A key feature of the corpus espongiosum is that it surrounds the urethra as it passes through the penis. The erectile tissue itself contains numerous vascular spaces under normal non-arousal conditions. These spaces contain relatively little blood and the smooth muscle in the walls of the associated arteries are contracted. However, when sexual stimulation occurs, this smooth muscle in the arterial walls relaxes. This relaxation causes the arteries to dilate dilate leading to a significant increase in blood flow into the vascular spaces within erectile tissue. Both the corpora cavernosa and the corpus espongiosum are filled with blood. As these spaces become engorged with blood, the erectile penis expands and becomes rigid resulting in erection. The penis also features a full of a skin that surrounds the tip known as the prepus or more commonly known as the foreskin. You can see here how it covers the gland's penis and attaches to the neck used below the head. The inner surface of the prepuse contains a specialized prep glands also sometimes called tyson glands. These glands secrete a waxy oily substance known as smeckma. This primary function of the propuse and this esmema is to moisturize and lubricate the cavity between the foreskin and the glands penis ensuring smooth movement and preventing irritation. Smeckma itself is essentially a combination of shed epithelial cells, skin oils and moisture. You may have heard of a surgical procedure called circumcision. This pro procedure involves a surgical removal of the prepuse the foreskin tissue that we use have discussed. Like all systems in the body, the male reproductive system also undergoes changes with age. Men experience a gradual period known as the male climacteric sometimes referred as andropause which signifies a decline in the efficiency of various reproductive functions. One of the key changes during this time is the testosterone levels begin to decline. However, it is important to note that this decline is typically more gradual compared to the more rapid drop in estrogen levels that women experience during menopause. The male climacteric generally occurs between the ages of 50 and 60, although the timing and extent can vary. Along with the hormonal changes, there is often a notable reduction in sexual activity in older men and this is likely due at least in part to the gradual decrease in testosterone levels which can affect libido and erectile function. So, like I promised, this is only a 47 and 38 seconds, um, video. So, I'm just going to say goodbye so you can go on and I promise less than an hour. So, uh, make sure that you watch this again and again, um, so you can get the material. And if you have any questions, concerns, please let me know. See you in the next video.