The male reproductive system

In simple terms, reproduction is the process by which organisms create descendants.

 This miracle is a characteristic that all living things have in common and sets them apart from nonliving things.

But even though the reproductive system is essential to keeping a species alive, it is not essential to keeping an individual alive.

In human reproduction, two kinds of sex cells or gametes are involved.

 Sperm, the male gamete, and a secondary oocyte (along with first polar body and corona radiata), the female gamete must meet in the female reproductive system to create a new individual.

 For reproduction to occur, both the female and male reproductive systems are essential. It is a common misnomer to refer to a woman’s gametic cell as an egg or ovum, but this is impossible.

 A secondary oocyte must be fertilized by the male gamete before it becomes an “ovum” or “egg”.

While both the female and male reproductive systems are involved with producing, nourishing and transporting either the oocyte or sperm, they are different in shape and structure.

 The male has reproductive organs, or genitals, that are both inside and outside the pelvis, while the female has reproductive organs entirely within the pelvis.

The male reproductive system consists of the testes and a series of ducts and glands. Sperm are produced in the testes and are transported through the reproductive ducts.

 These ducts include the epididymis, vas deferens, ejaculatory duct and urethra. The reproductive glands produce secretions that become part of semen, the fluid that is ejaculated from the urethra.

These glands include the seminal vesicles, prostate gland, and bulbourethral glands.

The purpose of the organs of the male reproductive system is to perform the following functions:
To produce, maintain, and transport sperm (the male reproductive cells) and protective fluid (semen)
To discharge sperm within the female reproductive tract during sex
To produce and secrete male sex hormones responsible for maintaining the male reproductive system

Parts of the male reproductive system

Penis

The penis is the male organ for sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-shaped end of the penis. The glans, which also is called the head of the penis, is covered with a loose layer of skin called foreskin.

(This skin is sometimes removed in a procedure called circumcision.) The opening of the urethra, the tube that transports semen and urine, is at the tip of the glans penis. The penis also contains a number of sensitive nerve endings.

Within the penis are masses of erectile tissue. Each consists of a framework of smooth muscle and connective tissue that contains blood sinuses, which are large, irregular vascular channels.

The body of the penis is cylindrical in shape and consists of three internal chambers. These chambers are made up of special, sponge-like erectile tissue.

 This tissue contains thousands of large spaces that fill with blood when the man is sexually aroused. As the penis fills with blood, it becomes rigid and erect, which allows for penetration during sexual intercourse.

The skin of the penis is loose and elastic to allow for changes in penis size during an erection .
Semen, which contains sperm, is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm).

 When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.

Scrotum

The two testicles are each held in a fleshy sac called the scrotum. The major function of the scrotal sac is to keep the testes cooler than thirty-seven degrees Celsius (ninety-eight point six degrees Fahrenheit).

The external appearance of the scrotum varies at different times in the same individual depending upon temperature and the subsequent contraction or relaxation of two muscles.

These two muscles contract involuntarily when it is cold to move the testes closer to the heat of the body in the pelvic region.

This causes the scrotum to appear tightly wrinkled. On the contrary, they relax in warm temperatures causing the testes to lower and the scrotum to become flaccid.

The temperature of the testes is maintained at about thirty-five degrees Celsius (ninety-five degrees Fahrenheit), which is below normal body temperature.

Temperature has to be lower than normal in order for spermatogenesis (sperm production) to take place.

The scrotum has a protective function and acts as a climate control system for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than the body temperature. Special muscles in the wall of the scrotum allow it to contract (tighten) and relax, moving the testicles closer to the body for warmth and protection or farther away from the body to cool the temperature.

The two muscles that regulate the temperature of the testes are the dartos and cremaster muscles:

Dartos Muscle

The dartos muscle is a layer of smooth muscle fibers in the subcutaneous tissue of the scrotum (surrounding the scrotum). This muscle is responsible for wrinkling up the scrotum, in conditions of cold weather, in order to maintain the correct temperature for spermatogenesis.

Cremaster Muscle

The cremaster muscle is a thin strand of skeletal muscle associated with the testes and spermatic cord. This muscle is a continuation of the internal oblique muscle of the abdominal wall, from which it is derived.

Testicles (testes)

 The testes are oval organs about the size of very large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord.

 Most men have two testes. The testes are responsible for making testosterone, the primary male sex hormone, and for producing sperm. Within the testes are coiled masses of tubes called seminiferous tubules. These tubules are responsible for producing the sperm cells through a process called spermatogenesis.

In the male fetus, the testes develop near the kidneys, then descend into the scrotum just before birth. Each testis is about 1 1/2 inches long by 1 inch wide. Testosterone is produced in the testes which stimulates the production of sperm as well as give secondary sex characteristics beginning at puberty.

Seminiferous Tubules

Each testis contains over 100 yards of tightly packed seminiferous tubules. Around 90% of the weight of each testes consists of seminiferous tubules.

The seminiferous tubules are the functional units of the testis, where spermatogenesis takes place. Once the sperm are produced, they moved from the seminiferous tubules into the rete testis for further maturation.

Epididymis 

The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the carrying and storage of the sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization. During sexual arousal, contractions force the sperm into the vas deferens

Urethra

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum and its opening, known as the meatus, lies on the tip of the glans penis. It is both a passage for urine and for the ejaculation of semen.

Seminiferous Tubules

Each testis contains over 100 yards of tightly packed seminiferous tubules. Around 90% of the weight of each testes consists of seminiferous tubules. The seminiferous tubules are the functional units of the testis, where spermatogenesis takes place.

 Once the sperm are produced, they moved from the seminiferous tubules into the rete testis for further maturation.

Interstitial Cells (Cells of Leydig)

In between the seminiferous tubules within the testes, are instititial cells, or, Cells of Leydig . They are responsible for secreting the male sex hormones (i.e., testosterone).

Sertoli Cells

A Sertoli cell (a kind of sustentacular cell) is a ‘nurse’ cell of the testes which is part of a seminiferous tubule.
It is activated by follicle-stimulating hormone, and has FSH-receptor on its membranes.
Its main function is to nurture the developing sperm cells through the stages of spermatogenesis. Because of this, it has also been called the “mother cell.” It provides both secretory and structural support.

Other functions During the Maturation phase of spermiogenesis, the Sertoli cells consume the unneeded portions of the spermatazoa.

Efferent ductules

The sperm are transported out of the testis and into the epididymis through a series of efferent ductules.

Blood Supply

The testes receive blood through the testicular arteries (gonadal artery). Venous blood is drained by the testicular veins. The right testicular vein drains directly into the inferior vena cava. The left testicular vein drains into the left renal vein.