Structure And Function Of Male Reproductive System Pdf
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The major function of the reproductive system is to ensure survival of the species. Other systems in the body, such as the endocrine and urinary systems, work continuously to maintain homeostasis for survival of the individual. An individual may live a long, healthy, and happy life without producing offspring, but if the species is to continue, at least some individuals must produce offspring.
Human reproductive system , organ system by which humans reproduce and bear live offspring.
Unique for its role in human reproduction, a gamete is a specialized sex cell carrying 23 chromosomes—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 one female gamete, called an oocyte. The function of the male reproductive system Figure The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In humans, the most important male androgen is testosterone.
Human reproductive system
Unique for its role in human reproduction, a gamete is a specialized sex cell carrying 23 chromosomes—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 one female gamete, called an oocyte. The function of the male reproductive system Figure The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology.
In humans, the most important male androgen is testosterone. Several accessory organs and ducts aid the process of sperm maturation and transport the sperm and other seminal components to the penis, which delivers sperm to the female reproductive tract.
In this section, we examine each of these different structures, and discuss the process of sperm production and transport. The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis see Figure 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 one 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 area of the scrotum to retain heat. Alternatively, as the environmental temperature increases, the scrotum relaxes, moving the testes farther from the body core and increasing scrotal surface area, which promotes heat loss.
Externally, the scrotum has a raised medial thickening on the surface called the raphae. They produce both sperm and androgens, such as testosterone, and are active throughout the reproductive lifespan of the male.
Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum see Figure They are surrounded by two distinct layers of protective connective tissue Figure The outer tunica vaginalis is a serous membrane that has both a parietal and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer covering the testis itself. Not only does the tunica albuginea cover the outside of the testis, it also invaginates to form septa that divide the testis into to structures called lobules.
Within the lobules, sperm develop in structures called seminiferous tubules. During the seventh month of the developmental period of a male fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity.
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 called the rete testes.
Sperm leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross the tunica albuginea. Inside the seminiferous tubules are six different cell types.
These include supporting cells called sustentacular cells, as well as 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. Surrounding all stages of the developing sperm cells are elongate, branching Sertoli cells. Sertoli cells are a type of supporting cell called a sustentacular cell, or sustentocyte, that are typically found in epithelial tissue.
Sertoli cells secrete signaling molecules that promote sperm production and can control whether germ cells live or die. They extend physically around 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 barrier , which keeps bloodborne substances from reaching the germ cells and, at the same time, keeps surface antigens on developing germ cells from escaping into the bloodstream and prompting an autoimmune response.
Spermatogonia are the stem cells of the testis, which means that they are still able to differentiate into a variety of different cell types throughout adulthood. Spermatogonia divide to produce primary and secondary spermatocytes, then spermatids, which finally produce formed sperm. The process that begins with spermatogonia and concludes with the production of sperm is called spermatogenesis. As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis see Figure One production cycle, from spermatogonia through formed sperm, takes approximately 64 days.
A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm counts—the total number of sperm a man produces—slowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age. The process of spermatogenesis begins with mitosis of the diploid spermatogonia Figure However, mature gametes are haploid 1 n , containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.
Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte , the next stage in the process of spermatogenesis.
As in mitosis, DNA is replicated in a primary spermatocyte, before it undergoes a cell division called meiosis I. During meiosis I each of the 23 pairs of chromosomes separates. This results in two cells, called secondary spermatocytes, each with only half the number of chromosomes. Now a second round of cell division meiosis II 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 division 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 look very similar to cells in the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm.
A process called spermiogenesis transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which occurs in the portion of the tubule nearest the lumen.
Eventually, 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. Sperm are smaller than most cells in the body; in fact, the volume of a sperm cell is 85, times less than that of the female gamete. Approximately to million sperm are produced each day, whereas women typically ovulate only one oocyte per month.
As is true for most cells in the body, the structure of sperm cells speaks to their function. Sperm have a distinctive head, mid-piece, and tail region Figure The head of the sperm contains the extremely compact haploid nucleus with very little cytoplasm. Tightly packed mitochondria fill the mid-piece of the sperm.
ATP produced by these mitochondria will power the flagellum, which extends from the neck and the mid-piece through the tail of the sperm, enabling it to move the entire sperm cell. The central strand of the flagellum, the axial filament, is formed from one centriole inside the maturing sperm cell during the final stages of spermatogenesis.
To fertilize an egg, sperm must be 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 reproductive tract. Though the epididymis does not take up much room in its tightly coiled state, it would be approximately 6 m 20 feet long if straightened. It takes an average of 12 days for sperm to move through the coils of the epididymis, with the shortest recorded transit time in humans being one day.
Sperm enter the head of the epididymis and are moved along predominantly by the contraction of smooth muscles lining the epididymal tubes. As they are moved along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use 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.
During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens also called the vas deferens. The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord see Figure Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt sperm delivery can be 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 birth control. Although it may be possible to reverse a vasectomy, clinicians consider the procedure permanent, and advise men to undergo it only if they are certain they no longer wish to father children. Watch this video 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 do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain? From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the abdominal wall. Sperm make up only 5 percent of the final volume of semen , the thick, milky fluid that the male ejaculates.
The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands. As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle see Figure The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume.
Seminal vesicle fluid contains large amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female 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.
As shown in Figure About the size of a walnut, the prostate is formed of both muscular and glandular tissues. It excretes an alkaline, 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 time for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm can then pass farther into the female reproductive tract. The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again.
This enlargement does not usually cause problems; however, abnormal growth of the prostate, or benign 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 sensation that the bladder has not emptied completely. By age 60, approximately 40 percent of men have some degree of BPH.
By age 80, the number of affected individuals has jumped to as many as 80 percent.
Male reproductive system
The male reproductive system includes the penis, scrotum, testes, epididymis, vas deferens, prostate, and seminal vesicles. The penis and the urethra are part of the urinary and reproductive systems. The scrotum, testes testicles , epididymis, vas deferens, seminal vesicles, and prostate comprise the rest of the reproductive system. The penis consists of the root which is attached to the lower abdominal structures and pelvic bones , the visible part of the shaft, and the glans penis the cone-shaped end. The opening of the urethra the channel that transports semen and urine is located at the tip of the glans penis. The base of the glans penis is called the corona. In uncircumcised males, the foreskin prepuce extends from the corona to cover the glans penis.
The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body and within the pelvis. The main male sex organs are the penis and the testicles which produce semen and sperm , which, as part of sexual intercourse , fertilize an ovum in the female's body; the fertilized ovum zygote develops into a fetus , which is later born as an infant. The corresponding system in females is the female reproductive system. The penis is the male intromittent organ. It has a long shaft and an enlarged bulbous-shaped tip called the glans penis , which supports and is protected by the foreskin.
What can male reproductive anatomy tell us about pregnancy in the different species? Learning Outcomes: Identify male reproductive anatomical structures of.
Structure of the Male Reproductive System
The male reproductive system includes the scrotum, testes, spermatic ducts, sex glands, and penis. These organs work together to produce sperm, the male gamete, and the other components of semen. These reproductive organs also work together to deliver semen out of the body and into the vagina where it can fertilize egg cells to produce offspring. The scrotum is a sac-like organ made of skin and muscles that houses the testes. It is located inferior to the penis in the pubic region.
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