Review Sheet Exercise 42 Anatomy of the Reproductive System
Chapter 42
Anatomy and Physiology of the Male Reproductive Organisation
By the cease of this section, you will exist able to:
- Describe the structure and role of the organs of the male reproductive system
- Describe the structure and function of the sperm cell
- Explain the events during spermatogenesis that produce haploid sperm from diploid cells
- Identify the importance of testosterone in male person reproductive role
Unique for its role in human reproduction, a gamete is a specialized sex cell conveying 23 chromosomes—one one-half the number in body cells. At fertilization, the chromosomes in one male gamete, called a sperm (or spermatozoon), combine with the chromosomes in 1 female gamete, chosen an oocyte. The function of the male person reproductive organisation (Figure i) is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this procedure, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In humans, the virtually important male androgen is testosterone. Several accessory organs and ducts assistance the process of sperm maturation and ship the sperm and other seminal components to the penis, which delivers sperm to the female person reproductive tract. In this department, we examine each of these unlike structures, and discuss the process of sperm product and transport.
Male Reproductive Organization
Figure 1: The structures of the male reproductive organization include the testes, the epididymides, the penis, and the ducts and glands that produce and carry semen. Sperm exit the scrotum through the ductus deferens, which is arranged in the spermatic cord. The seminal vesicles and prostate gland add together fluids to the sperm to create semen.
Scrotum
The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis (see Effigy two). This location is of import in sperm product, which occurs within the testes, and gain more than efficiently when the testes are kept 2 to 4°C below core trunk temperature.
The dartos muscle makes up the subcutaneous muscle layer of the scrotum ( Figure ). It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments, each housing i testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles, which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather (or water), moving the testes closer to the body and decreasing the surface surface area of the scrotum to retain rut. Alternatively, equally the environmental temperature increases, the scrotum relaxes, moving the testes farther from the body core and increasing scrotal surface surface area, which promotes heat loss. Externally, the scrotum has a raised medial thickening on the surface called the raphae.
The Scrotum and Testes
Effigy ii: This anterior view shows the structures of the scrotum and testes.
Testes
The testes (atypical = testis) are the male gonads—that is, the male reproductive organs. They produce both sperm and androgens, such as testosterone, and are active throughout the reproductive lifespan of the male person.
Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure 2). They are surrounded past 2 distinct layers of protective connective tissue (Figure 3). The outer tunica vaginalis is a serous membrane that has both a parietal and a sparse visceral layer. Below the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer roofing the testis itself. Not only does the tunica albuginea embrace the exterior of the testis, it also invaginates to course septa that divide the testis into 300 to 400 structures called lobules. Within the lobules, sperm develop in structures chosen seminiferous tubules. During the seventh month of the developmental flow of a male person fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity. This is called the "descent of the testis." Cryptorchidism is the clinical term used when one or both of the testes fail to descend into the scrotum prior to birth.
Anatomy of the Testis
Figure 3: This sagittal view shows the seminiferous tubules, the site of sperm product. Formed sperm are transferred to the epididymis, where they mature. They leave the epididymis during an ejaculation via the ductus deferens.
The tightly coiled seminiferous tubules form the bulk of each testis. They are composed of developing sperm cells surrounding a lumen, the hollow center of the tubule, where formed sperm are released into the duct system of the testis. Specifically, from the lumens of the seminiferous tubules, sperm move into the straight tubules (or tubuli recti), and from there into a fine meshwork of tubules chosen the rete testes. Sperm leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross the tunica albuginea.
Within the seminiferous tubules are half-dozen different jail cell types. These include supporting cells chosen sustentacular cells, as well equally five types of developing sperm cells called germ cells. Germ cell development progresses from the basement membrane—at the perimeter of the tubule—toward the lumen. Allow'due south wait more closely at these prison cell types.
Sertoli Cells
Surrounding all stages of the developing sperm cells are elongate, branching Sertoli cells. Sertoli cells are a type of supporting cell called a sustentacular prison cell, or sustentocyte, that are typically found in epithelial tissue. Sertoli cells secrete signaling molecules that promote sperm production and tin can control whether germ cells alive or dice. They extend physically effectually the germ cells from the peripheral basement membrane of the seminiferous tubules to the lumen. Tight junctions between these sustentacular cells create the blood–testis bulwark, which keeps bloodborne substances from reaching the germ cells and, at the aforementioned time, keeps surface antigens on developing germ cells from escaping into the bloodstream and prompting an autoimmune response.
Germ Cells
The to the lowest degree mature cells, the spermatogonia (atypical = spermatogonium), line the basement membrane inside the tubule. Spermatogonia are the stem cells of the testis, which means that they are all the same able to differentiate into a diversity of different cell types throughout adulthood. Spermatogonia split up to produce primary and secondary spermatocytes, then spermatids, which finally produce formed sperm. The process that begins with spermatogonia and concludes with the product of sperm is chosen spermatogenesis.
Spermatogenesis
As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis (see Figure 3). The process begins at puberty, after which fourth dimension sperm are produced constantly throughout a human being'south life. 1 production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new bike starts approximately every sixteen days, although this timing is not synchronous beyond the seminiferous tubules. Sperm counts—the total number of sperm a human being produces—slowly decline after age 35, and some studies suggest that smoking tin lower sperm counts irrespective of age.
The process of spermatogenesis begins with mitosis of the diploid spermatogonia (Figure iv). Because these cells are diploid (2n), they each have a complete copy of the begetter'south genetic material, or 46 chromosomes. However, mature gametes are haploid (1n), containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular partition through the process of meiosis.
Spermatogenesis
Figure 4: (a) Mitosis of a spermatogonial stem prison cell involves a unmarried cell division that results in two identical, diploid girl cells (spermatogonia to primary spermatocyte). Meiosis has two rounds of jail cell division: main spermatocyte to secondary spermatocyte, and then secondary spermatocyte to spermatid. This produces four haploid daughter cells (spermatids). (b) In this electron micrograph of a cross-section of a seminiferous tubule from a rat, the lumen is the light-shaded area in the center of the image. The location of the main spermatocytes is well-nigh the basement membrane, and the early spermatids are approaching the lumen (tissue source: rat). EM × 900. (Micrograph provided past the Regents of University of Michigan Medical Schoolhouse © 2012)
Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte, the side by side phase in the procedure of spermatogenesis. As in mitosis, Dna is replicated in a master spermatocyte, before it undergoes a prison cell division called meiosis I. During meiosis I each of the 23 pairs of chromosomes separates. This results in 2 cells, called secondary spermatocytes, each with simply half the number of chromosomes. Now a 2d circular of cell sectionalisation (meiosis 2) occurs in both of the secondary spermatocytes. During meiosis II each of the 23 replicated chromosomes divides, similar to what happens during mitosis. Thus, meiosis results in separating the chromosome pairs. This second meiotic sectionalisation results in a total of four cells with only half of the number of chromosomes. Each of these new cells is a spermatid. Although haploid, early spermatids wait very similar to cells in the earlier stages of spermatogenesis, with a round shape, cardinal nucleus, and large corporeality of cytoplasm. A process called spermiogenesis transforms these early spermatids, reducing the cytoplasm, and commencement the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the terminate upshot of this process, which occurs in the portion of the tubule nearest the lumen. Somewhen, the sperm are released into the lumen and are moved along a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation.
Structure of Formed Sperm
Sperm are smaller than most cells in the trunk; in fact, the volume of a sperm jail cell is 85,000 times less than that of the female gamete. Approximately 100 to 300 meg sperm are produced each day, whereas women typically ovulate only i oocyte per month. As is truthful for virtually cells in the torso, the construction of sperm cells speaks to their role. Sperm have a distinctive head, mid-piece, and tail region (Figure 5). The head of the sperm contains the extremely compact haploid nucleus with very little cytoplasm. These qualities contribute to the overall small size of the sperm (the head is merely 5 μyard long). A structure chosen the acrosome covers well-nigh of the caput of the sperm cell as a "cap" that is filled with lysosomal enzymes important for preparing sperm to participate in fertilization. Tightly packed mitochondria fill the mid-piece of the sperm. ATP produced past these mitochondria will power the flagellum, which extends from the cervix and the mid-piece through the tail of the sperm, enabling it to move the entire sperm jail cell. The central strand of the flagellum, the axial filament, is formed from one centriole inside the maturing sperm jail cell during the final stages of spermatogenesis.
Structure of Sperm
Figure five: Sperm cells are divided into a head, containing DNA; a mid-piece, containing mitochondria; and a tail, providing motility. The acrosome is oval and somewhat flattened.
Sperm Ship
To fertilize an egg, sperm must exist moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female person reproductive tract.
Part of the Epididymis
From the lumen of the seminiferous tubules, the immotile sperm are surrounded by testicular fluid and moved to the epididymis (plural = epididymides), a coiled tube attached to the testis where newly formed sperm keep to mature (come across Figure 3). Though the epididymis does not take up much room in its tightly coiled state, it would exist approximately 6 m (20 anxiety) long if straightened. Information technology takes an average of 12 days for sperm to motility through the coils of the epididymis, with the shortest recorded transit time in humans being i day. Sperm enter the head of the epididymis and are moved along predominantly past the contraction of smooth muscles lining the epididymal tubes. As they are moved forth the length of the epididymis, the sperm further mature and acquire the ability to motility nether their own power. Once within the female reproductive tract, they will utilize this ability to move independently toward the unfertilized egg. The more mature sperm are then stored in the tail of the epididymis (the final section) until ejaculation occurs.
Duct Organization
During ejaculation, sperm get out the tail of the epididymis and are pushed by shine muscle contraction to the ductus deferens (also called the vas deferens). The ductus deferens is a thick, muscular tube that is arranged together inside the scrotum with connective tissue, claret vessels, and nerves into a structure called the spermatic cord (see Figure ane and Effigy 2). Because the ductus deferens is physically accessible inside the scrotum, surgical sterilization to interrupt sperm delivery can exist performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is called a vasectomy, and it is an effective form of male nascency control. Although it may be possible to reverse a vasectomy, clinicians consider the process permanent, and propose men to undergo it simply if they are sure they no longer wish to male parent children.
Lookout man the video linked to below to learn about a vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm practise non get out through the vas, either because the human has had a vasectomy or has not ejaculated, in what region of the testis practise they remain?
From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the intestinal wall. From hither, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder where information technology dilates in a region chosen the ampulla (meaning "flask").
Sperm brand upwardly simply 5 per centum of the last volume of semen, the thick, milky fluid that the male ejaculates. The bulk of semen is produced past three critical accessory glands of the male reproductive arrangement: the seminal vesicles, the prostate, and the bulbourethral glands.
Seminal Vesicles
As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle (run into Figure 1). The paired seminal vesicles are glands that contribute approximately 60 percentage of the semen volume. Seminal vesicle fluid contains big amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female person reproductive tract.
The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct, a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.
Prostate Gland
Equally shown in Figure 1, the centrally located prostate gland sits inductive to the rectum at the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, the prostate is formed of both muscular and glandular tissues. It excretes an alkali metal, milky fluid to the passing seminal fluid—now called semen—that is critical to first coagulate and then decoagulate the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing fourth dimension for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm tin then laissez passer farther into the female person reproductive tract.
The prostate normally doubles in size during puberty. At approximately age 25, information technology gradually begins to enlarge over again. This enlargement does not unremarkably crusade problems; withal, abnormal growth of the prostate, or beneficial prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a awareness that the float has not emptied completely. By age 60, approximately xl percent of men have some caste of BPH. By age 80, the number of affected individuals has jumped to equally many equally 80 percent. Treatments for BPH attempt to relieve the pressure level on the urethra and so that urine tin menstruation more normally. Mild to moderate symptoms are treated with medication, whereas astringent enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.
Another mutual disorder involving the prostate is prostate cancer. According to the Centers for Illness Control and Prevention (CDC), prostate cancer is the second most common cancer in men. However, some forms of prostate cancer grow very slowly and thus may non ever require handling. Aggressive forms of prostate cancer, in dissimilarity, involve metastasis to vulnerable organs similar the lungs and brain. There is no link between BPH and prostate cancer, only the symptoms are like. Prostate cancer is detected past a medical history, a claret examination, and a rectal examination that allows physicians to palpate the prostate and check for unusual masses. If a mass is detected, the cancer diagnosis is confirmed by biopsy of the cells.
Bulbourethral Glands
The final addition to semen is made past ii bulbourethral glands (or Cowper's glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to make clean urine residues from the penile urethra. The fluid from these accompaniment glands is released after the male person becomes sexually aroused, and soon before the release of the semen. It is therefore sometimes called pre-ejaculate. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick upward sperm already present in the urethra, and therefore information technology may be able to cause pregnancy.
Watch the video linked to below to explore the structures of the male reproductive system and the path of sperm, which starts in the testes and ends equally the sperm get out the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?
The Penis
The penis is the male person organ of copulation (sexual intercourse). It is flaccid for non-sexual deportment, such equally urination, and turgid and rod-like with sexual arousal. When erect, the stiffness of the organ allows it to penetrate into the vagina and eolith semen into the female reproductive tract.
Cantankerous-Exclusive Anatomy of the Penis
Figure 6: Three columns of erectile tissue brand upwardly most of the volume of the penis.
The shaft of the penis surrounds the urethra (Figure 6). The shaft is composed of three cavalcade-like chambers of erectile tissue that span the length of the shaft. Each of the 2 larger lateral chambers is called a corpus cavernosum (plural = corpora cavernosa). Together, these brand upwardly the bulk of the penis. The corpus spongiosum, which can be felt as a raised ridge on the erect penis, is a smaller chamber that surrounds the spongy, or penile, urethra. The cease of the penis, chosen the glans penis, has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation (see Effigy 1). The skin from the shaft extends down over the glans and forms a neckband called the prepuce (or foreskin). The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive peel of the glans penis. A surgical process called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth.
Both sexual arousal and REM slumber (during which dreaming occurs) tin induce an erection. Penile erections are the result of vasocongestion, or engorgement of the tissues because of more than arterial blood flowing into the penis than is leaving in the veins. During sexual arousal, nitric oxide (NO) is released from nerve endings well-nigh blood vessels inside the corpora cavernosa and spongiosum. Release of NO activates a signaling pathway that results in relaxation of the polish muscles that surround the penile arteries, causing them to dilate. This dilation increases the amount of blood that can enter the penis and induces the endothelial cells in the penile arterial walls to also secrete NO and perpetuate the vasodilation. The rapid increment in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the sparse-walled penile venules, preventing venous drainage of the penis. The result of this increased blood flow to the penis and reduced blood return from the penis is erection. Depending on the flaccid dimensions of a penis, information technology tin can increment in size slightly or profoundly during erection, with the average length of an erect penis measuring approximately 15 cm.
Disorders of the...
Male Reproductive System
Erectile dysfunction (ED) is a condition in which a human being has difficulty either initiating or maintaining an erection. The combined prevalence of minimal, moderate, and complete ED is approximately twoscore pct in men at age xl, and reaches nearly lxx percent past 70 years of age. In addition to aging, ED is associated with diabetes, vascular disease, psychiatric disorders, prostate disorders, the use of some drugs such every bit certain antidepressants, and issues with the testes resulting in low testosterone concentrations. These concrete and emotional weather condition can lead to interruptions in the vasodilation pathway and result in an inability to achieve an erection.
Recollect that the release of NO induces relaxation of the smooth muscles that environment the penile arteries, leading to the vasodilation necessary to achieve an erection. To opposite the process of vasodilation, an enzyme called phosphodiesterase (PDE) degrades a key component of the NO signaling pathway called cGMP. There are several dissimilar forms of this enzyme, and PDE blazon v is the blazon of PDE found in the tissues of the penis. Scientists discovered that inhibiting PDE5 increases blood menstruation, and allows vasodilation of the penis to occur.
PDEs and the vasodilation signaling pathway are plant in the vasculature in other parts of the torso. In the 1990s, clinical trials of a PDE5 inhibitor called sildenafil were initiated to treat hypertension and angina pectoris (chest pain caused by poor blood flow through the eye). The trial showed that the drug was non effective at treating center atmospheric condition, merely many men experienced erection and priapism (erection lasting longer than 4 hours). Considering of this, a clinical trial was started to investigate the power of sildenafil to promote erections in men suffering from ED. In 1998, the FDA approved the drug, marketed equally Viagra®. Since approval of the drug, sildenafil and similar PDE inhibitors now generate over a billion dollars a year in sales, and are reported to be constructive in treating approximately 70 to 85 percentage of cases of ED. Importantly, men with health bug—particularly those with cardiac disease taking nitrates—should avoid Viagra or talk to their doctor to find out if they are a candidate for the use of this drug, as deaths have been reported for at-risk users.
Testosterone
Testosterone, an androgen, is a steroid hormone produced past Leydig cells. The alternate term for Leydig cells, interstitial cells, reflects their location between the seminiferous tubules in the testes. In male embryos, testosterone is secreted by Leydig cells by the seventh week of development, with peak concentrations reached in the second trimester. This early release of testosterone results in the anatomical differentiation of the male sexual organs. In childhood, testosterone concentrations are low. They increase during puberty, activating characteristic physical changes and initiating spermatogenesis.
Functions of Testosterone
The connected presence of testosterone is necessary to keep the male reproductive system working properly, and Leydig cells produce approximately 6 to seven mg of testosterone per twenty-four hours. Testicular steroidogenesis (the manufacture of androgens, including testosterone) results in testosterone concentrations that are 100 times higher in the testes than in the apportionment. Maintaining these normal concentrations of testosterone promotes spermatogenesis, whereas depression levels of testosterone tin can lead to infertility. In addition to intratesticular secretion, testosterone is also released into the systemic circulation and plays an important role in musculus development, os growth, the evolution of secondary sexual activity characteristics, and maintaining libido (sex drive) in both males and females. In females, the ovaries secrete small amounts of testosterone, although near is converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes.
Command of Testosterone
The regulation of testosterone concentrations throughout the torso is critical for male person reproductive function. The intricate coaction between the endocrine organisation and the reproductive system is shown in Figure 7.
Regulation of Testosterone Production
Figure vii: The hypothalamus and pituitary gland regulate the product of testosterone and the cells that assistance in spermatogenesis. GnRH activates the anterior pituitary to produce LH and FSH, which in turn stimulate Leydig cells and Sertoli cells, respectively. The system is a negative feedback loop because the end products of the pathway, testosterone and inhibin, interact with the activity of GnRH to inhibit their own production.
The regulation of Leydig cell production of testosterone begins outside of the testes. The hypothalamus and the pituitary gland in the brain integrate external and internal signals to command testosterone synthesis and secretion. The regulation begins in the hypothalamus. Pulsatile release of a hormone called gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the endocrine release of hormones from the pituitary gland. Binding of GnRH to its receptors on the inductive pituitary gland stimulates release of the 2 gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These ii hormones are critical for reproductive role in both men and women. In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis. FSH as well stimulates the Sertoli cells to produce hormones called inhibins, which function to inhibit FSH release from the pituitary, thus reducing testosterone secretion. These polypeptide hormones correlate straight with Sertoli jail cell role and sperm number; inhibin B tin can be used equally a marker of spermatogenic activity. In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone.
A negative feedback loop predominantly controls the synthesis and secretion of both FSH and LH. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the inductive pituitary to secrete LH into the bloodstream. In the testis, LH binds to LH receptors on Leydig cells and stimulates the release of testosterone. When concentrations of testosterone in the blood reach a critical threshold, testosterone itself will bind to androgen receptors on both the hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH and LH, respectively. When the claret concentrations of testosterone in one case again decline, testosterone no longer interacts with the receptors to the same degree and GnRH and LH are once again secreted, stimulating more testosterone production. This aforementioned process occurs with FSH and inhibin to control spermatogenesis.
Aging and the...
Male Reproductive System
Declines in Leydig cell activity tin occur in men offset at 40 to fifty years of historic period. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known every bit male menopause. While the reduction in sex steroids in men is akin to female menopause, there is no articulate sign—such as a lack of a menstrual period—to announce the initiation of andropause. Instead, men report feelings of fatigue, reduced muscle mass, low, anxiety, irritability, loss of libido, and insomnia. A reduction in spermatogenesis resulting in lowered fertility is besides reported, and sexual dysfunction tin also be associated with andropausal symptoms.
Whereas some researchers believe that certain aspects of andropause are difficult to tease apart from crumbling in general, testosterone replacement is sometimes prescribed to alleviate some symptoms. Contempo studies have shown a do good from androgen replacement therapy on the new onset of low in elderly men; however, other studies caution against testosterone replacement for long-term treatment of andropause symptoms, showing that high doses tin sharply increment the hazard of both eye disease and prostate cancer.
Chapter Review
Gametes are the reproductive cells that combine to form offspring. Organs called gonads produce the gametes, along with the hormones that regulate homo reproduction. The male person gametes are called sperm. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that brand up most of the testis. The scrotum is the muscular sac that holds the testes exterior of the body cavity.
Spermatogenesis begins with mitotic division of spermatogonia (stem cells) to produce primary spermatocytes that undergo the two divisions of meiosis to become secondary spermatocytes, so the haploid spermatids. During spermiogenesis, spermatids are transformed into spermatozoa (formed sperm). Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature. During ejaculation, sperm go out the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum. The ampulla of the ductus deferens meets the seminal vesicle, a gland that contributes fructose and proteins, at the ejaculatory duct. The fluid continues through the prostatic urethra, where secretions from the prostate are added to form semen. These secretions help the sperm to travel through the urethra and into the female reproductive tract. Secretions from the bulbourethral glands protect sperm and cleanse and lubricate the penile (spongy) urethra.
The penis is the male organ of copulation. Columns of erectile tissue called the corpora cavernosa and corpus spongiosum fill with claret when sexual arousal activates vasodilatation in the blood vessels of the penis. Testosterone regulates and maintains the sex activity organs and sex activity drive, and induces the physical changes of puberty. Interplay between the testes and the endocrine system precisely control the production of testosterone with a negative feedback loop.
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