MALE REPRODUCTIVE SYSTEM

THE REPRODUCTIVE SYSTEM

The purpose of the male and female reproductive systems is to continue the human species by the production of offspring. The male and female reproductive systems produce gametes, that is, sperm and egg cells, and ensure the union of gametes in fertilization following sexual intercourse. In women, the uterus provides the site for the developing embryo/fetus until it is sufficiently developed to survive outside the womb.

THE MALE REPRODUCTIVE SYSTEM

The male reproductive system includes the scrotum, testes, spermatic ducts, sex glands, and penis. These organs also work together to deliver semen out of the body and into the vagina where it can

fertilize egg cells to produce offspring.

Unlike the female reproductive system, most of the male reproductive system is located outside of the body. These external structures include the penis, scrotum, and testicles.

Functions of the Male Reproductive System

1.      To produce sperm

2.      To maintain and transport sperm 

3.      To produce and secrete male sex hormone e.g testosterone

4.      To discharge sperm within the female reproductive tract during sex

Parts Of The Male Reproductive System

The Scrotum

The scrotum is a sac-like organ made of skin and muscles that contains the testes as well as many nerves and blood vessels. It is made up of 2 side-by-side pouches with a testes located in each pouch

The scrotum acts as a "climate control system" for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than body temperature (about 2-4°C lower than the body temperature). Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth or farther away from the body to cool the temperature.

The Testes

The 2 testes, also known as testicles, located in the scrotum, responsible for the production of sperm and testosterone. Each testis is oval in shape and about 1.5 inches long by 1 inch wide (4 cm by 2.5 cm) and is divided internally into lobes. Each lobe contains several seminiferous tubules, in which spermatogenesis takes place.

It is connected to the abdomen by a spermatic cord and cremaster muscle. The cremaster muscles contract and relax along with the scrotum to regulate the temperature of the testes. In the male fetus, the testes develop near the kidneys, then descend into the scrotum just before birth.

NB: Cryptorchidism is the condition in which the testes fail to descend, and the result is sterility unless the testes are surgically placed in the scrotum.

DIAGRAM OF THE TESTIS

EPIDIDYMIS

The epididymis (plural: epididymides) is a tube about 20 feet (6 m) long that is coiled on the posterior surface of each testis. Sperm produced in the testes moves into the epididymis. The length of the epididymis delays the release of the sperm, allows them time to mature and develop functional flagella.

Smooth muscle in the wall of the epididymis propels the sperm into the ductus deferens.

SPERMATIC CORDS

A pair of spermatic cords connects the testes to the abdominal cavity. The spermatic cords contain the ductus deferens along with nerves, veins, arteries, and lymphatic vessels that support the function of the testes.

It connects to the abdominal cavity through the inguinal canal.

DUCTUS DEFERENS/ VAS DEFERENS

The ductus deferens is a muscular tube that carries sperm superiorly from the epididymis into the abdominal cavity to the ejaculatory duct. The ductus deferens is wider in diameter than the epididymis and uses its internal space to store mature sperm. The smooth muscles of the walls of the ductus deferens are used to move sperm towards the ejaculatory duct through peristalsis.

EJACULATORY DUCTS

Each of the two ejaculatory ducts receives sperm from the ductus deferens and the secretion of the seminal vesicle on its own side. During ejaculation, both ejaculatory ducts open and expel sperm and the secretions from the seminal vesicles into the single urethra.

SEMINAL VESICLES

The paired seminal vesicles are posterior to the urinary bladder. Their secretion contains fructose to provide an energy source for sperm and is alkaline to enhance sperm motility. The duct of each seminal vesicle joins the ductus deferens on that side to form the ejaculatory duct.

PROSTATE GLAND

A muscular gland just below the urinary bladder, which is about 1.2 inches high by 1.6 inches wide by 0.8 inch deep (3 cm by 4 cm by 2 cm). It surrounds the first inch of the urethra.

The prostate produces a large portion of the fluid that makes up semen. This fluid is alkaline and milky white in colour and contains enzymes, proteins, and other chemicals to support and protect sperm during ejaculation. The prostate also contains smooth muscle tissue that can constrict to prevent the flow of urine or semen.

BULBOURETHRAL GLANDS/ COWPER’S GLANDS

The bulbourethral glands are about the size of peas and are located below the prostate gland; they empty into the urethra. Their alkaline secretion coats the interior of the urethra just before ejaculation, which neutralizes any acidic urine that might be present.

NB: Why are the secretions of the male reproductive system alkaline?

This is necessary because the cavity of the female vagina has an acidic pH created by the normal flora, the natural bacterial population of the vagina. The alkalinity of seminal fluid helps neutralize the acidic vaginal pH and permits sperm motility.

URETHRA
The urethra is a long muscular tube through which semen passes from the ejaculatory duct to the exterior of the body. It’s about 8 to 10 inch long. The urethra passes through the prostate and ends at the external urethral orifice located at the tip of the penis. Urine exiting the body from the urinary bladder also passes through the urethra.

PENIS

The penis is the male external sexual organ located superior to the scrotum and inferior to the umbilicus. The penis is roughly cylindrical in shape and contains the urethra and the external opening of the urethra.

Its distal end is called the glans penis and is covered with a fold of skin called the prepuce or foreskin. Circumcision is the surgical removal of the foreskin.

Large pockets of cavernous (erectile) tissue in the penis allow it to fill with blood and become erect. The erection of the penis causes it to increase in size and become turgid. The function of the penis is to deliver semen into the vagina during sexual intercourse. In addition to its reproductive function, the penis also allows for the excretion of urine through the urethra to the exterior of the body.

SEMEN

Semen consists of sperm and the secretions of the seminal vesicles, prostate gland, and bulbourethral glands. It has a thick sticky consistency and slightly alkaline with an average pH of about 7.4.

In healthy adult males, semen contains around 100 million sperm cells per milliliter. These sperm cells fertilize oocytes inside the female fallopian tubes. During ejaculation, approximately 2 to 4 mL of semen is expelled.

SPERMATOGENESIS

Spermatogenesis is the process of producing sperm and takes place in the testes and epididymis of adult males. Within each testis are seminiferous tubules that contain spermatogonia, which are stem cells that generate sperm. A spermatogonium divides into spermatocytes.

Each diploid spermatocyte goes through the process of meiosis I and splits into 2 haploid secondary spermatocytes. The secondary spermatocytes go through meiosis II to form 4 haploid spermatid cells.

The spermatid cells then go through a process known as spermiogenesis where they grow a flagellum and develop the structures of the sperm head. After spermiogenesis, the cell is finally a sperm cell, or spermatozoa. The spermatozoa are released into the epididymis where they complete their maturation and become able to move on their own.

Spermatogenesis is regulated by hormones. Follicle-stimulating hormone (FSH) from the anterior pituitary gland initiates sperm production, and testosterone, secreted by the testes when stimulated by luteinizing hormone (LH) from the anterior pituitary, promotes the maturation of sperm. Inhibin, also produced by the testes, decreases the secretion of FSH.

Sperm production begins at puberty (10 to 14 years of age), and millions of sperm are formed each day in the testes. Although sperm production diminishes with advancing age, there is usually no complete cessation, as there is of egg production in women at menopause.

MATURED SPERM

FERTILIZATION

Fertilization is the process by which a sperm combines with an oocyte, or egg cell, to produce a fertilized zygote. The sperm released during ejaculation must first swim through the vagina and uterus and into the fallopian tubes where they may find an oocyte. After encountering the oocyte, sperm next have to penetrate the outer corona radiata and zona pellucida layers of the oocyte. Sperm contain enzymes in the acrosome region of the head that allow them to penetrate these layers. After penetrating the interior of the oocyte, the nuclei of these haploid cells fuse to form a diploid cell known as a zygote. The zygote cell begins cell division to form an embryo.