The Reproductive System

2. The Reproductive System

The reproductive system is unique among the organ systems. The organs of this system vary greatly between the sexes. Male and female children do not differ remarkably in body form until they reach the age of puberty. At this time, under the influence of hormones, striking changes occur in several systems. The voice gradually changes in the male to a deeper masculine tone; the beard becomes a little stronger; pubic, axillary and body hair develop; and the body gradually assumes the characteristics of the adult male. The body form of the adult male develops increased musculature, with broader shoulders and narrow hips. The female at puberty develops a feminine contour due largely to deposition of subepidermal fat and she mammary glands become larger. The internal and external genitalia approach maturity, and the gonads begin to produce mature sex cells.

2.1 Female Reproductive System

The internal reproductive organs of the female are the ovaries, fallopian tubes (or oviducts), the uterus and the vagina. The ova arise and develop in the ovaries. When they are mature, they rupture from the surface of the ovary and pass down the fallopian tubes to the uterus. If the ovum is fertilized during is passage down the oviduct, the developing blastocyst becomes implanted in the lining of the uterus. If it remains unfertilized, it soon breaks down and becomes lost in mucous secretion. The uterus leads into the vagina, which is a narrow passageway opening to the exterior.

2.1.1 Ovaries

The paired ovaries lie on either side of the uterus and below the fallopian tubes. The internal structure of the ovary consists of a connective-tissue framework, which supports the developing germ cells, muscle cells, blood vessels and nerves.

The ova develop within the ovarian follicle. The various stages of oogenesis are passed there, and the developing ovum in one of the more mature follicles is in reality a primary oocyte. Follicles develop under the influence of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) originating in the pituitary gland. From puberty to menopause, mature follicles approach the surface of the ovary and rupture mature ova through the surface at fairly regular monthly intervals in the process known as ovulation. Ovulation occurs about the middle of the 28-day menstrual cycle, but the follicle cells persist, undergoing a transformation into the corpus luteum.

2.1.2 Corpus Luteum

After ovulation, the follicular cells enlarge and increase in numbers so that the number of cell layers increases. The cavity of the old follicle becomes filled with blood, but the blood is gradually resorbed as new cell layers fill in the cavity. Connective tissue and blood vessels grow in from a connective-tissue layer surrounding the old follicle. A yellowish thick-walled body called the corpus luteum replaces the old follicle. The cell cytoplasm contains a lipid substance known as lutein. In the period between ovulation and menstruation the corpus luteum secretes the hormones progesterone and estrogen, which exert a sustaining influence on the lining of the uterus. If the ovum is not fertilized, the corpus luteum begins to degenerate toward the end of the menstrual cycle and menstruation follows. If the ovum is fertilized, the corpus luteum of pregnancy reaches the height of its development about the third month, after which it begins to degenerate.

2.1.3 Fallopian Tubes

The tubes that conduct the ova from the ovaries to the uterus are usually called oviducts in animals. In humans they are more commonly referred to as fallopian tubes, or uterine tubes. They lie in a horizontal position above the ovaries. The far ends near the ovaries flare out in a funnel-like fashion. The funnels bear fringed processes called fimbriae which aid in guiding the ovum into the tube.

2.1.4 Uterus

The uterus is a thick-walled organ located in the upper part of the pelvic region. Its function is to receive the blastocyst and to provide protection and nourishment to the developing embryo and fetus after implantation. The position of the uterus varies, but it is usually tipped forward over the urinary bladder. The lower part of the uterus is more cylindrical in shape and is called the cervix. Its external orifice opens into the vagina.

2.1.5 Vagina

A canal leading from the vestibule of the external genitalia to the cervix of the uterus is called the vagina. The vagina receives the penis of the male during sexual intercourse; a seminal emission releases sperm near the external orifice of the uterus. At childbirth the vagina becomes greatly distended to form the birth canal from the cervix to the exterior.

The external orifice of the virginal vagina is partially closed off by a fold of membrane known as the hymen.

2.2 Male Reproductive System

2.2.1 Testes

Spermatogenesis takes place in the testes. The testes descend from an abdominal position before birth and come to lie in a sac called the scrotum. Occasionally the testes fail to descend into the scrotum, a condition known as cryptorchism. Undescended testes are almost invariably sterile, although they produce the male sex hormone.

2.2.2 Epididymis

Immature sperm are not motile but are propelled up through the convoluted tubules into a network of fine tubules and on into the ducts of the epididymis. The epididymis is a body containing a tightly convoluted tubule and is located behind the testis.

2.2.3 Vas Deferens

The duct of the epididymis is continuous with a larger duct, the ductus deferens or vas deferens, which leads the sperm away from the testis. The vas deferens extends upward from the testis through the spermatic cord. It passes through the inguinal canal, over the pubic arch, and behind the urinary bladder to terminate in the ejaculatory duct. The right and left ejaculatory ducts open into the urethra within the prostate gland. They are much smaller ducts than the vas deferens and only two centimeters long.

2.2.4 Seminal Vesicles

The seminal vesicles are lobulated sacs located behind the surface of the bladder. They secrete a fluid that forms a part of the semen. The fluid passes down a small duct and enters the ejaculatory duct. It is thought to contribute to the viability of the spermatozoa.

2.2.5 Prostate Gland

The prostate gland is a muscular and glandular organ that is located below the bladder and in front of the rectum. The base of the urethra passes ‘through it. The prostatic secretion is alkaline, somewhat milky, and contributes to the odor of semen. The base of the urethra runs almost vertically through the anterior portion of the gland when the body is in a standing position.

2.2.6 Penis

The penis is the copulatory organ of the male. The body of the penis is composed of three longitudinal columns of erectile tissue. Erectile tissue is composed of blood spaces, which ordinarily are not distended with blood, the penis then being soft and flaccid. Sexual excitement causes blood to pour into these spaces faster than it is drained away by the veins. As a result the walls of the tissue become distended with blood, and the penis becomes hard and erect. It is in this condition that it is inserted into the vagina in the act of sexual intercourse. After sexual excitement has passed, blood is drained out of the erectile tissue and the penis becomes soft again. Erectile tissue is also present in the clitoris.

The smooth tip of the penis is the glans portion and is covered by loose skin called the foreskin or prepuce. Sometimes the foreskin covers the glans too tightly or, becomes adherent if this area is not cleansed properly. Circumcision is an operation to remove the foreskin. The operation may be complete or partial. The area behind the glans contains modified sebaceous glands that secrete a soft, whitish substance, which soon deteriorates. The reason given by physicians for performing circumcision is to expose the surface of the glans and make it easier to clean the area where the secretion has collected. This is an unnecessary and cruel operation. Daily cleansing of this area will keep it clean so that secretions will not collect. You need not worry about the skin becoming adherent if you keep this area clean.