MALE REPRODUCTIVE SYSTEM PDF

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Overview of Male. Reproductive Physiology. Terry R. Brown, Ph.D. Department of Biochemistry & Molecular Biology. Johns Hopkins Bloomberg School of Public. MALE REPRODUCTIVE ORGANS. Accessory sex glands. Gld. vesiculosa. Prostate. Gld. bulbourethralis. Penis. Corpus cavernosum. Corpus spongiosum. Human reproduction. Male Reproductive System. Organs: 2 Testes – produce sperm and sex hormones. Hormones influence sperm production and secondary .


Male Reproductive System Pdf

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Anatomy of Male Reproductive System. Major Organs. External sexual organs: penis and scrotum. Internal structures form continuous tube: Testes epididymus. •Ejaculatory duct. •Urethra. Associated glands. •Seminal vesicles (paired). • Prostate. •Bulbourethral glands (paired). External genital organs. •Scrotum. • Penis. 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 .

This is the reason why the testes are located in a bag of skin called the scrotal sacs or scrotum that hangs below the body and where the evaporation of secretions from special glands can further reduce the temperature.

In many animals including humans the testes descend into the scrotal sacs at birth but in some animals they do not descend until sexual maturity and in others they only descend temporarily during the breeding season. A mature animal in which one or both testes have not descended is called a cryptorchid and is usually infertile. The problem of keeping sperm at a low enough temperature is even greater in birds that have a higher body temperature than mammals.

The testes consist of a mass of coiled tubes the seminiferous or sperm producing tubules in which the sperm are formed by meiosis see diagram Cells lying between the seminiferous tubules produce the male sex hormone testosterone.

When the sperm are mature they accumulate in the collecting ducts and then pass to the epididymisbefore moving to the sperm duct or vas deferens. The two sperm ducts join the urethra just below the bladder, which passes through the penis and transports both sperm and urine. Ejaculation discharges the semen from the erect penis. It is brought about by the contraction of the epididymis, vas deferens, prostate gland and urethra.

Diagram Accessory Glands[ edit ] Three different glands may be involved in producing the secretions in which sperm are suspended, although the number and type of glands varies from species to species. Seminal vesicles are important in rats, bulls, boars and stallions but are absent in cats and dogs.

When present they produce secretions that make up much of the volume of the semen, and transport and provide nutrients for the sperm. The prostate gland is important in dogs and humans. It produces an alkaline secretion that neutralizes the acidity of the male urethra and female vagina.

The secretions may lubricate, flush out urine or form a gelatinous plug that traps the semen in the female reproductive system after copulation and prevents other males of the same species fertilizing an already mated female.

The Penis[ edit ] The penis consists of connective tissue with numerous small blood spaces in it. These fill with blood during sexual excitement causing erection. Penis Form And Shape[ edit ] Dogs, bears, seals, bats and rodents have a special bone in the penis which helps maintain the erection see diagram In some animals e. In many animals the shape of the penis is adapted to match that of the vagina.

Anatomy and Physiology of Animals/Reproductive System

Some have spines, warts or hooks on them to help keep them in the vagina and copulation may be extended to help retain the semen in the female system. Sperm[ edit ] Sperm are made up of three parts: a head consisting mainly of the nucleus, a midpiece containing many mitochondria to provide the energy and a tail that provides propulsion see diagram Some may be dead while others are inactive or deformed with double, giant or small heads or tails that are coiled or absent altogether.

When there are too many abnormal sperm or when the sperm concentration is low, the semen may not be able to fertilize an egg and the animal is infertile.

Sperm do not live forever. They have a definite life span that varies from species to species. They survive for between 20 days guinea pig to 60 days bull in the epididymis but once ejaculated into the female tract they only live from 12 to 48 hours.

When semen is used for artificial insemination, storage under the right conditions can extend the life span of some species. Artificial Insemination[ edit ] In many species the male can be artificially stimulated to ejaculate and the semen collected. It can then be diluted, stored and used to inseminate females.

For example bull semen can be diluted and stored for up to 3 weeks at room temperature. Unfortunately the semen of chickens, stallions and boars can only be stored for up to 2 days. Dilution of the semen means that one male can be used to fertilise many more females than would occur under natural conditions.

There are also advantages in the male and female not having to make physical contact. It means that owners of females do not have to download expensive males and the possibility of transmitting sexually transmitted diseases is reduced.

Routine examination of the semen for sperm concentration, quality and activity allows only the highest quality semen to be used so a high success rate is ensured. Since the lifespan of sperm in the female tract is so short and ova only survive from 8 to 10 hours the timing of the artificial insemination is critical. The Female Reproductive Organs[ edit ] The female reproductive system consists of a pair of ovaries that produce egg cells or ova and fallopian tubes where fertilisation occurs and which carry the fertilised ovum to the uterus.

Growth of the foetus takes place here. The cervix separates the uterus from the vagina or birth canal, where the sperm are deposited see diagram The Ovaries[ edit ] Ovaries are small oval organs situated in the abdominal cavity just ventral to the kidneys.

Most animals have a pair of ovaries but in birds only the left one is functional to reduce weight see below. The ovary consists of an inner region medulla and an outer region cortex containing egg cells or ova. These are formed in large numbers around the time of birth and start to develop after the animal becomes sexually mature.

A cluster of cells called the follicle surrounds and nourishes each ovum. The Ovarian Cycle[ edit ] The ovarian cycle refers to the series of changes in the ovary during which the follicle matures, the ovum is shed and the corpus luteum develops see diagram Numerous undeveloped ovarian follicles are present at birth but they start to mature after sexual maturity. In animals that normally have only one baby at a time only one ovum will mature at once but in litter animals several will. The mature follicle consists of outer cells that provide nourishment.

Inside this is a fluid-filled space that contains the ovum. A mature follicle can be quite large, ranging from a few millimetres in small mammals to the size of a golf ball in large animals.

It bulges out from the surface of the ovary before eventually rupturing to release the ovum into the abdominal cavity. Once the ovum has been shed, a blood clot forms in the empty follicle. This develops into a tissue called the corpus luteum that produces the hormone progesterone see diagram If the animal becomes pregnant the corpus luteum persists, but if there is no pregnancy it degenerates and a new ovarian cycle usually.

It is surrounded by few layers of follicle cells and a tough membrane called the zona pellucida see diagram These changes influence the behaviour and body changes of the female see diagram It stimulates the follicle to develop. However, some forms of prostate cancer grow very slowly and thus may not ever require treatment.

Aggressive forms of prostate cancer, in contrast, involve metastasis to vulnerable organs like the lungs and brain. There is no link between BPH and prostate cancer, but the symptoms are similar. Prostate cancer is detected by a medical history, a blood test, and a rectal exam 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. The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly 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 up sperm already present in the urethra, and therefore it may be able to cause pregnancy.

Watch this video to explore the structures of the male reproductive system and the path of sperm, which starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct? The penis is the male organ of copulation sexual intercourse.

It is flaccid for non-sexual actions, such as urination, and turgid and rod-like with sexual arousal. When erect, the stiffness of the organ allows it to penetrate into the vagina and deposit semen into the female reproductive tract.

The shaft of the penis surrounds the urethra Figure 6. The shaft is composed of three column-like chambers of erectile tissue that span the length of the shaft. Together, these make up 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 end of the penis, called the glans penis , has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation see Figure 1. The skin from the shaft extends down over the glans and forms a collar called the prepuce or foreskin. The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive skin of the glans penis.

A surgical procedure called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth. Both sexual arousal and REM sleep during which dreaming occurs can induce an erection. Penile erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the penis than is leaving in the veins.

During sexual arousal, nitric oxide NO is released from nerve endings near blood vessels within the corpora cavernosa and spongiosum. Release of NO activates a signaling pathway that results in relaxation of the smooth muscles that surround the penile arteries, causing them to dilate.

Themes and Trends in Physiology, Biochemistry and Investigative Andrology

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 increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-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, it can increase in size slightly or greatly during erection, with the average length of an erect penis measuring approximately 15 cm. Male Reproductive System Erectile dysfunction ED is a condition in which a man has difficulty either initiating or maintaining an erection. The combined prevalence of minimal, moderate, and complete ED is approximately 40 percent in men at age 40, and reaches nearly 70 percent by 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 as certain antidepressants, and problems with the testes resulting in low testosterone concentrations. These physical and emotional conditions can lead to interruptions in the vasodilation pathway and result in an inability to achieve an erection.

Recall that the release of NO induces relaxation of the smooth muscles that surround the penile arteries, leading to the vasodilation necessary to achieve an erection. There are several different forms of this enzyme, and PDE type 5 is the type of PDE found in the tissues of the penis. Scientists discovered that inhibiting PDE5 increases blood flow, and allows vasodilation of the penis to occur. PDEs and the vasodilation signaling pathway are found in the vasculature in other parts of the body.

In the s, 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 heart. The trial showed that the drug was not effective at treating heart conditions, but many men experienced erection and priapism erection lasting longer than 4 hours. Because of this, a clinical trial was started to investigate the ability of sildenafil to promote erections in men suffering from ED.

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 effective in treating approximately 70 to 85 percent of cases of ED. Importantly, men with health problems—especially those with cardiac disease taking nitrates—should avoid Viagra or talk to their physician to find out if they are a candidate for the use of this drug, as deaths have been reported for at-risk users.

Testosterone, an androgen, is a steroid hormone produced by 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. The continued presence of testosterone is necessary to keep the male reproductive system working properly, and Leydig cells produce approximately 6 to 7 mg of testosterone per day.

Testicular steroidogenesis the manufacture of androgens, including testosterone results in testosterone concentrations that are times higher in the testes than in the circulation. Maintaining these normal concentrations of testosterone promotes spermatogenesis, whereas low levels of testosterone can lead to infertility.

In addition to intratesticular secretion, testosterone is also released into the systemic circulation and plays an important role in muscle development, bone growth, the development of secondary sex characteristics, and maintaining libido sex drive in both males and females.

In females, the ovaries secrete small amounts of testosterone, although most is converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes. The regulation of testosterone concentrations throughout the body is critical for male reproductive function. The intricate interplay between the endocrine system and the reproductive system is shown in Figure 7.

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 control 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 anterior pituitary gland stimulates release of the two gonadotropins: These two hormones are critical for reproductive function in both men and women. In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis.

FSH also 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 directly with Sertoli cell function and sperm number; inhibin B can be used as a marker of spermatogenic activity. In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone.

Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream.

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 blood concentrations of testosterone once 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 same process occurs with FSH and inhibin to control spermatogenesis. Male Reproductive System Declines in Leydig cell activity can occur in men beginning at 40 to 50 years of age. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known as male menopause.

While the reduction in sex steroids in men is akin to female menopause, there is no clear sign—such as a lack of a menstrual period—to denote the initiation of andropause.

Instead, men report feelings of fatigue, reduced muscle mass, depression, anxiety, irritability, loss of libido, and insomnia. When erect, the stiffness of the organ allows it to penetrate into the vagina and deposit semen into the female reproductive tract. The shaft of the penis surrounds the urethra Figure 6.

The shaft is composed of three column-like chambers of erectile tissue that span the length of the shaft. Together, these make up 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 end of the penis, called the glans penis , has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation see Figure 1. The skin from the shaft extends down over the glans and forms a collar called the prepuce or foreskin. The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive skin of the glans penis.

A surgical procedure called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth. Both sexual arousal and REM sleep during which dreaming occurs can induce an erection.

Penile erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the penis than is leaving in the veins. During sexual arousal, nitric oxide NO is released from nerve endings near blood vessels within the corpora cavernosa and spongiosum.

Release of NO activates a signaling pathway that results in relaxation of the smooth 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 increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-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, it can increase in size slightly or greatly during erection, with the average length of an erect penis measuring approximately 15 cm. Male Reproductive System Erectile dysfunction ED is a condition in which a man has difficulty either initiating or maintaining an erection. The combined prevalence of minimal, moderate, and complete ED is approximately 40 percent in men at age 40, and reaches nearly 70 percent by 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 as certain antidepressants, and problems with the testes resulting in low testosterone concentrations.

These physical and emotional conditions can lead to interruptions in the vasodilation pathway and result in an inability to achieve an erection. Recall that the release of NO induces relaxation of the smooth muscles that surround the penile arteries, leading to the vasodilation necessary to achieve an erection.

There are several different forms of this enzyme, and PDE type 5 is the type of PDE found in the tissues of the penis. Scientists discovered that inhibiting PDE5 increases blood flow, and allows vasodilation of the penis to occur.

PDEs and the vasodilation signaling pathway are found in the vasculature in other parts of the body. In the s, 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 heart. The trial showed that the drug was not effective at treating heart conditions, but many men experienced erection and priapism erection lasting longer than 4 hours. Because of this, a clinical trial was started to investigate the ability of sildenafil to promote erections in men suffering from ED.

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 effective in treating approximately 70 to 85 percent of cases of ED. Importantly, men with health problems—especially those with cardiac disease taking nitrates—should avoid Viagra or talk to their physician to find out if they are a candidate for the use of this drug, as deaths have been reported for at-risk users.

Testosterone, an androgen, is a steroid hormone produced by 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. The continued presence of testosterone is necessary to keep the male reproductive system working properly, and Leydig cells produce approximately 6 to 7 mg of testosterone per day.

Testicular steroidogenesis the manufacture of androgens, including testosterone results in testosterone concentrations that are times higher in the testes than in the circulation. Maintaining these normal concentrations of testosterone promotes spermatogenesis, whereas low levels of testosterone can lead to infertility. In addition to intratesticular secretion, testosterone is also released into the systemic circulation and plays an important role in muscle development, bone growth, the development of secondary sex characteristics, and maintaining libido sex drive in both males and females.

In females, the ovaries secrete small amounts of testosterone, although most is converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes.

The regulation of testosterone concentrations throughout the body is critical for male reproductive function. The intricate interplay between the endocrine system and the reproductive system is shown in Figure 7. 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 control 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 anterior pituitary gland stimulates release of the two gonadotropins: These two hormones are critical for reproductive function in both men and women.

In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis. FSH also 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 directly with Sertoli cell function and sperm number; inhibin B can be used as a marker of spermatogenic activity.

In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream. 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 blood concentrations of testosterone once 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 same process occurs with FSH and inhibin to control spermatogenesis.

Male Reproductive System Declines in Leydig cell activity can occur in men beginning at 40 to 50 years of age. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known as male menopause. While the reduction in sex steroids in men is akin to female menopause, there is no clear sign—such as a lack of a menstrual period—to denote the initiation of andropause. Instead, men report feelings of fatigue, reduced muscle mass, depression, anxiety, irritability, loss of libido, and insomnia.

A reduction in spermatogenesis resulting in lowered fertility is also reported, and sexual dysfunction can also be associated with andropausal symptoms. Whereas some researchers believe that certain aspects of andropause are difficult to tease apart from aging in general, testosterone replacement is sometimes prescribed to alleviate some symptoms.

Recent studies have shown a benefit from androgen replacement therapy on the new onset of depression in elderly men; however, other studies caution against testosterone replacement for long-term treatment of andropause symptoms, showing that high doses can sharply increase the risk of both heart disease and prostate cancer. Gametes are the reproductive cells that combine to form offspring. Organs called gonads produce the gametes, along with the hormones that regulate human reproduction.

The male gametes are called sperm. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that make up most of the testis. The scrotum is the muscular sac that holds the testes outside 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, then 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 exit the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum.Testicular steroidogenesis the manufacture of androgens, including testosterone results in testosterone concentrations that are times higher in the testes than in the circulation.

Watch this video to explore the structures of the male reproductive system and the path of sperm that starts in the testes and ends as the sperm leave the penis through the urethra. 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.

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. The hormone is produced by the foal and placenta, and is only present when there is a living foal.

Male Reproductive Function and Semen

Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature. When the blood concentrations of testosterone once 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.

Within the lobules, sperm develop in structures called seminiferous tubules.