MALE REPRODUCTIVE SYSTEM

Penis

Penis is the male sexual organ; it is covered by a layer of elastic skin which stands behind its non-fixed size. Penis is split into the root, the body and the glans penis. Also, there is a loose layer of skin surrounding the glans; it is named the foreskin. The top of the glans includes the tube which works to move urine and semen out of the body. While the root of the penis is linked to the abdominal wall, the body, cylinder-shaped, represents the middle of the penis with three internal chambers composed of a spongy erectile tissue which is in turn divided into thousands of large spaces. When a male feels sexual arouse, blood fills in these spaces, causing the hardness and erection of the penis to occur. Thus, it is allowed to penetrate the vaginal track during sexual intercourse. The penis includes various sensitive nerve endings (Fig. 1).

Testicles and Scrotum

There are two egg-shaped testicles in males. In addition to producing sperm in a process called spermatogenesis, testicles are the glands which are responsible for giving the male characteristics through secreting various hormones including testosterone. The functioning of the testicles depends upon two hormones secreted by the pituitary gland in the brain: follicle-stimulating hormone (FSH) which maintains spermatogenesis and Luteinizing hormone (LH) which triggers the excretion of testosterone from the testes. Testicles are protected by an external vesicle or sac named the scrotum, which is composed of skin and muscle, and split into two divisions for the two testes. Both testicles and scrotum hang outside the body behind the penis. The scrotal muscle can be loose or tight, allowing the testes to move away from or closer to the abdomen. Due to the location, the temperature of the testes is somewhat cooler than that of the rest of the body, allowing sperm to live longer (Fig. 1). 

Epididymis 

Epididymis (plural epididymides) lie at the back of the testes. Males have two epididymides composed of a collection of small, coiled tubes functioning to connect testes to the vas deferens. Also, they collect and store sperm before the ejaculation of the seminal fluid (Fig. 2).

Ductus Deferens 

The ductus deferens or vas deferens is a long muscular tube. After sperm has been produced by testes and stored in epididymites, they are moved via peristalsis by the ductus deferens to the ejaculatory ducts where the urethra receives them (Fig. 3).

Ejaculatory Ducts 

When the ductus deferens joins the seminal vesicles, the ejaculatory ducts (ED) are formed. The two ED go through the prostate and travel into the urethra (Fig. 3).

Seminal Vesicles 

The seminal vesicle is a male sex gland highly participating in the secretion of seminal fluid which protects the sperm when it is ejaculated out of the body. They are two in males, and they lie near the prostate (Fig. 3).

Prostate

The prostate is a part of the male reproductive system. It is located beneath the bladder. As a small muscular gland, it acts to secrete some of the semen. While the prostate forms a frame around the urethra, it is surrounded by the muscles of the pelvic floor. When the ejaculation occurs, these muscles contract supporting the penile erection. The prostate also has the ability to convert protein secretions into smaller molecules through secreting an enzyme called protease or prostate-specific antigen. It explains the liquid texture of semen (Fig. 3).

Bulbourethral Glands 

Bulbourethral glands or Cowper’s glands are two pea-shaped organs in the male reproductive system. When man is sexually aroused, they produce pre-ejaculate which is a clear, sticky fluid which works to lubricate the urethra so the sperm can pass through (Fig. 3).

Urethra

The function of the urethra is important to both the urinary system and the male reproductive system. The tube which links the urinary bladder to the penis and remove the fluid out of the body is called urethra. Also, it is responsible for carrying semen in males (Fig. 3).

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It refers to the process of producing sperm which starts in the seminiferous tubules of the testis when spermatogonia, primitive stem cells, arise in the outer edge and divide rapidly to form the stem cell line. This line is produced and increased from birth until puberty. During adulthood, spermatogenesis starts, and the anterior pituitary gland produces increasing amounts of FSH. Millions of sperm are made daily, but only one sperm fertilizes an egg. In males, spermatogenesis continues throughout life (Fig. 4).

From puberty on, the division of a spermatogonium results two different types of stem cells: type A daughter cell, and type B daughter cell. While the tubule periphery retains type A cell which has the ability to keep the stem cell population, the tubule lumen receives the type B cell which develops to a primary sper­matocyte that can generate four sperm through meiosis. While different body cells have 46 chromosomes, the genetic material, spermatids or gametes in spermatogenesis include 23 chromosomes only. However, the normal number of 46 chromosomes is reestablished through the process of fertilization when the sperm and the egg (which also has 23 chromosomes) associate together to form the zygote, which is the fertilized egg. Through the process of mitosis, the subsequent body cells keep the normal number of 46 chromosomes (Fig. 4).

The sperm is composed of the nucleus which is the head of the sperm, and filaments which is the long tail.  The genetic material or the compacted DNA is found in the sperm head or the nucleus anterior to which the helmetlike acrosome exists.  The acrosomal membrane facilitates the penetration of the sperm into the capsule of follicle cells surrounding the ovum, through breaking down and secreting enzymes once the sperm gets closer to the egg.  Filaments or the long tail are tightly enveloped by mitochondria. The sperm is pushed and go through the female reproductive tract in whiplike movements through the Adenosine triphosphate (ATP) provided by mitochondria (Fig. 5).

The entire process from the formation of a primary spermatocyte to release of immature sperm in the tubule lumen takes 64 to 72 days. When the sperm reaches the lumen, they still lack the ability to carry out the process of fertilization. The tubules of the testes contract pushing sperm to the epididymis where the maturation of the sperm occurs through acquiring fertilizing power and increased motility (Fig. 2).

The testosterone is the most important hormonal product of the testes. During puberty, FSH continuously catalyzes the seminiferous tubules to produce sperm, and LH constantly invigorates the interstitial cells. As a result, testosterone is secreted continuously for the rest of a man’s life and its increasing level in the blood spurs the reproductive organs to reach their adult size Testosterone affects the male secondary sex characteristics, and hence called the masculinizing hormone. These characteristics refer to the features appearing in nonreproductive organs and stimulated by sex hormones such as increased hair growth all over the body, deepening of the voice, and enlarged skeletal muscles (Fig. 6). 

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It is a congenital abnormality in the sexual development of male births, characterized by the non-existence of one or both testes. 

Before birth, the testes are located near the kidney. When they move to the scrotum, it indicates that the sexual development will occur normally, and that sperm will be secreted optimally. If one or both testes fail to descend from this position into the scrotum before birth, cryptorchism occurs Premature babies are more susceptible to this condition than full term infants. This case can be fixed spontaneously through descending the undescended testicle by one year of age, or surgically via an orchiopexy (Fig. 7).

When the prostate gland is inflamed by bacteria, prostatitis happens. It coincides with urethritis or an infection of the lower urinary tract. Fever, dysuria, chills, urethral discharge and a tender prostate are the symptoms (Fig. 8).

 When there is a bacterial infection, such as gonorrhea or chlamydia, in the epididymis, epididymitis results. It can also happen as a result of prostatitis or other urinary tract infections. However, it can be due to a non-infectious source such as injury in some cases, especially in children (Fig. 9).

Erectile dysfunction or impotence occurs when a man is unable to get and keep a penile erection during sexual intercourse. Causes of the disease can be organic as in cardiovascular disease or diabetes. Also, it can happen as a side effect of various drugs. A nerve damage, after prostate surgery can lead to erectile dysfunction. In some cases, it is psychological in aetiology (Fig. 10).

It is a condition causing glandular breast tissue in boys and men to be larger than normal. When the level of oestrogen gets higher compared to that of androgen and/or testosterone, gynaecomastia appears (Fig. 11). 

It is cancer in the small walnut-shaped gland, Prostate. When happening, no symptoms appear for a period of time. However, bladder neck obstruction comes to the surface with developing the disease. Although it is one of the slowest growing malignancies, it can be fatal in few cases. It can spread to include the adjacent lymphnodes and bones in the spine and pelvis (Fig. 12).

It is the most prevalent malignant tumor in young men. Seminoma, teratoma and choriocarcinoma are the main types of testicular cancer which affects testes. It can be curable in cases of early detection and treatment with chemotherapy (Fig. 13).  

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  a. Spermatogonia

  b. Spermatogonium

  c. Spermatogenesis 

  d. Spermatids 

  a. Ductus Deferens

  b. Epididymis 

  c. Urethra

  d. Prostate

  a. Seminiferous tubules

  b. Epididymides

  c. Ductus deferens 

  d. Ejaculatory ducts 

  a. Seminal vesicles  

  b. Cowper’s glands 

  c. Ejaculatory ducts 

  d. Prostates gland 

  a. Gynaecomastia  

  b. Epididymitis  

  c. Cystocele 

  d. Cryptorchism