Table of Contents
The Male Reproductive System
The male sexual organs consist of the internal and external sexual organs. The internal organs include the testicles (testes), the epididymis, the sperm duct (vas deferens), the seminal vesicles (also called vesicular or seminal glands), the prostate gland (prostate) and the Cowper gland (bulbourethral glands). The external sexual organs include the penis and the scrotum. The testicles and the epididymis are counted as internal reproductive organs, as originally, they are located on the posterior abdomen wall and only descend down the abdomen through the inguinal canal during embryonic development.
Structure of the Testes
The testes have an oval shape with a diameter of approx. 5 cm. They are arranged in pairs and are suspended elastically in the scrotum. The testes form already in the womb. After the first 1 trimenon, the testeicles start to descend and remain in the groin until about the seventh month of pregnancy. During this time, the scrotum develops, which is connected with the inguinal canal in the abdomen through the processus vaginalis testis. After the descent of the testes is complete, the canal closes.
Internally, the scrotum possesses a connective tissue capsule, which is divided by approximately 200 walls. Thus, a large number of chambers are formed. These chambers hold the seminiferous tubules, which can be recognized as a bundle and exit into the excretory duct. These passages are a web-like complex system called the rete testis.
The seminiferous tubules are lined with the germinal epithelium which, in turn, is surrounded by connective tissue. Within the germinal epithelium are the so called Sertoli cells. Additionally, the maturing gametes are located here which later develop into the sperm cells. The Sertoli cells’ main function is to nourish the developing sperm cells. Without them, the body’s immune system would attack the sperm cells. Equally important are the Leydig cells whose task is to produce testosterone.
Spermatogenesis describes the process of producing spermatozoa, the male germ cells. The process is initiated during the initial stage of puberty and occurs in the seminiferous tubules of the testes. Thereby, the spermatozoa undergo various stages of development. It is a continuous process, similar to the oocytes maturation in women.
Development Stages of the Spermatozoa
An anatomical requirement for the spermatogenesis is the presence of the seminiferous tubules. They develop during puberty under the presence of the follicle stimulating hormone (FSH). The FSH binds to the sertoli cells, triggering the production of various mediators which, in turn, stimulate the spermatogenesis.
The development stages are:
- Spermatogonia Type A
- Spermatogonia Type B
- Primary spermatocytes
- Secondary spermatocytes
In the first stage, spermatogonia type A is formed from the primordial germ cells in the seminiferous tubules through mitotic division. The nucleus contains the diploid cells which themselves contain the diploid chromosome set and one chromatid per chromosome.
As a result of a further mitotic division, type B spermatogonia is engendered, leaving the basement membrane during the process. The primary spermatocytes are formed from type B and approach the seminiferous tubules. They duplicate the DNA which results in a meiotic division and, subsequently, in a second meiotic division. At this stage, they are secondary spermatocytes.
Until the process of spermatozoa production is complete, it is dependent on testosterone. Spermatozoa consist of a head and a tail. The nucleus of the head is highly condensed and partially covered by acrosome. This cap-like structure contains the enzymes that later play an important role when needed to break down the outer membrane of the ovum, which is necessary for fertilisation. In the tail, the mitochondria are located, providing energy to the cell and, therefore, enabling the spermatozoa to move at a speed of 7 to 25 cm per minute.
Duration of Spermatozoa Formation
The process of developing from an undifferentiated germ cell all the way to the spermatozoa takes between 60 to 70 days. It is a continuing process without interruption. On average, an adult man produces several hundred million spermatozoa per day. However, the temperature needs to be at about 35° C. When temperature increases, the production of the spermatozoa is inhibited. When temperature decreases, the testes are drawn closer to the body, while they hang lower when temperature is high. This movement is performed by the muscles of the scrotum.
The epididymis is located adjacent to the testes, within the scrotal sac and has two main functions: to store and to mature sperm. It contains the epididymal duct, the shape of which reminds of a highly convoluted tube. On the exterior, the tunica albuginea of testis and the epiorchium (lamina visceralis) are located.
The exception is the point where the epididymis and testes are joined together. The epiorchium is the inner sheet of the tunica vaginalis testis. The connection between epididymis and the testes is called the mesepididymis. It has the purpose of securing the testis in the scrotum. In the epididymis, there is connective tissue with plenty of nerve fibres and blood vessels. The sperm cells are pushed out of the testes through the seminiferous tubules into the tubules of the epididymis. From there they reach the vas deferens.
The prostate is located beneath the urinary bladder and surrounds the urethra. The urethra transports urine and sperm. The Cowper’s glands, the seminal vesicles and the prostate all permanently release small amounts of secretions which dilute the sperm concentrate in the vas deferens.
This way, the secretion and sperm are ejected through the urethra simultaneously. After the prostate, the urethra passes the pelvic floor, the penis and the glans. Shortly before ejaculation, the secretion of the Cowper’s glands also cleans the urethra. This way, the acidic environment in the vaginal tract is neutralised, prolonging the lifespan of the sperm and providing mobility for them.
Erection and Sexual Intercourse
Without erection, sexual intercourse would be impossible. The erection is prompted by stimuli (visual or physical). Subsequently, the corpus cavernosa fills with (arterial) blood. At the same time, due to stimulation of previously smooth muscles, the venous drainage of the blood is prevented. This process can take place within a few seconds. During ejaculation, the smooth muscle contracts in:
- Vas deferens
- Seminal vesicle
Through the pressure, the seminal fluid is pushed into the urethra. With the contraction of the pelvic floor, 60 to 120 million spermatozoa are released.
Hormones Influencing the Male Reproductive System
The hormones controlling the male sexual organs are the Androgenic and gonadotropic hormones of the pituitary gland. Testosterone is an androgen and is produced in the Leydig cells of the testes. The hormone FSH (follicle stimulating hormone) and LH (luteinizing hormone – lutropin) are formed in the pituitary gland. They also play a crucial role in the female hormonal balance. In men, however, they only affect the tissue of the testis. The effect of testosterone is considerably more complex. It influences:
- Accessory glands
- Secondary sexual characteristics
- Sexual behaviour
- General metabolism
FSH and LH are important for the sperm production and testosterone formation. LH thereby indirect affects the Leydig cells. The production of LH and FSH is constant in men. Cyclical fluctuations do not occur.
Pathology of the Male Reproductive System
One of the most common complications that can occur with the testes are problems with the testis’ descent. Therefore, checking for this complication is part of the voluntary examinations which are conducted on newly born males all the way through to adolescence. One possible disorder occurs when the testes do not completely descend into the scrotum. This problem should be observed and corrected through a surgical procedure to move the testes into place if necessary.
Another complication is present when the inguinal canal does not close after the descent of the testes. This results in an inguinal hernia which can lead to abdominal organs being forced through the canal. In this case, too, a surgical intervention might be necessary.
Impotence actually describes the inability to reproduce (sterility). However, as an erection is crucial for performing the sexual act, the term impotence is currently also used to describe erectile dysfunctions. Common medications against the erectile dysfunction directly influence the physiological process of blood accumulation in the corpus cavernous. They do not act sexually stimulating.
This means that without sexual stimulation, even with the intake of potency-enhancing drugs, there is no erection. Impotence can have many causes. Increasing age may decrease the ability to achieve or maintain erection, but also stress and relationship problems can cause erectile dysfunction. In addition to that, several diseases can be the reason for an erectile dysfunction. One common example for this is diabetes.
If a woman is unable to conceive, in approx. 30 % of cases, this is due to fertility problems among men. Infertility can be caused by low sperm count or immotile sperm. In a normal healthy fertile man, at least 30 % of sperm per ejaculation should be formed normally, while at least 50 % should be sufficiently mobile. Abnormalities are an important indication of an existing infertility. The quality of sperm decreases with age. Further factors can affect sperm quality adversely. These include:
- Mumps with testes infection
- Injury of the testes
- Heavy smoking
- High alcohol consumption
- Varicose Veins
- Overheating the testes
The infertility can also be congenital. The quality of sperm can easily be determined by a simple test.
Popular Exam Questions on Male Reproductive System
The correct answers can be found below the references.
1. Tubuluri seminiferous are…
- …deferent ducts of the testes.
- …the Cowper’s glands.
- …another word for inguinal canal.
- …seminiferous tubules.
- …supplying vessels of the germinal epithelium.
2. Procedure in the testes:
- The acrosome covers the head of the spermatozoa partially.
- The Cowper’s glands clean the urethra before ejaculation.
- Testosterone does not act on the accessory glands.
- Sperm pass from the epididymis into the vas deferens.
- Androgen is produced in the Leydig cells.
3. Which statement is true?
- Primary spermatocytes arise from Type B.
- FSH has no effect on testosterone.
- LH has no effect on testosterone.
- LH only plays a role in women.
- The epiorchium is the outer sheet of the tunica vaginalis testis.