The Reproductive System

The gonads, testes and ovaries, are endocrine glands that secrete sex hormones.  However, the primary function of the gonads is not to produce hormones but to produce and store gametes-sperm and eggs.  Other organs in the male reproductive system prepare sperm for the possible fertilization of an egg.

IN HUMANS THE REPRODUCTIVE SYSTEM PRODUCES, STORES, NOURISHES, AND RELEASES SPECIALIZED SEX CELLS KNOWN AS GAMETES. .

The ways in which the Gametes are released make possible the fusion of Sperm (Male Gametes) and Egg (Female Gametes) in the process of FERTILIZATION.  From a Fertilized Egg, or ZYGOTE, come all the cells in a human body.

The TESTES, which are the PRIMARY Reproductive Organs of a MALE, begin to produce Steroid Hormones (Sex) known as ANDROGENS.  The tissue of the Embryo responds to these hormones by developing into the MALE REPRODUCTIVE ORGANS.

The OVARIES, or the PRIMARY Reproductive Organs of a FEMALE Embryo, produce Steroid Hormones (Sex) known as ESTROGENS. The tissue of the Embryo responds to these hormones by developing into the FEMALE REPRODUCTIVE ORGANS.

THE MALE AND FEMALE REPRODUCTIVE ORGANS DEVELOP FROM EXACTLY THE SAME TISSUES IN THE EMBRYO.

Puberty begins with a change in the Hypothalamus, the part of the Brain that regulates the secretions of the Pituitary Gland (GONADOTROPIN RELEASING HORMONE, GnRH).  This changes causes the Pituitary Gland to produce Increased Levels of TWO Hormones that affect the Gonads:     A.  Follicle Stimulating Hormone (FSH)     B. Luteinizing Hormone (LH)

As the Pituitary Gland begins to release FSH and LH, these Hormones stimulate the Testes to make the PRINCIPAL MALE SEX HORMONE TESTOSTERONE

Testosterone produces a number of SECONDARY SEX CHARACTERISTICS that appear in Males at Puberty – Voice Deepens, Beard Grows, and Body Hair.

Sperm are derived from Special Cells within the Testes that go through the process of MEIOSIS to form HAPLOID NUCLEI found in Mature Sperm.  The Chromosome number drops from 46 to 23, Four sperm cells result from each cell that begins meiosis

Developed Sperm travel from the Seminiferous Tubules into the EPIDIDYMIS. Within each Epididymis, a Sperm MATURES AND GAINS THE ABILITY TO SWIM AS ITS FLAGELLUM COMPLETES DEVELOPMENT.

Although most Sperm remain stored in each Epididymis, some leave the Epididymis and pass into through the VAS DEFERENS, a duct that extends from the Epididymis.

Each Vas Deferens enters the Abdominal Cavity, where it loops around the Urinary Bladder and merges with the Urethra.  In a Male, both Urine and Sperm exit the body through the Urethra.

In the Urethra, Sperm Mix with Fluids that are secreted by Three Exocrine Glands- the Seminal Vesicles, Bulbourethral Glands, and the Prostate Gland- to produce SEMINAL FLUID -which Protects and Nourishes the Sperm. THE COMBINATION OF SPERM AND SEMINAL FLUID IS KNOWN AS SEMEN.

The Vas Deferens merges with the URETHRA, the Tube that leads to the outside of the body through the PENIS. 300 - 400 million Sperm are released at one time.

THE PRIMARY REPRODUCTIVE ORGANS OF THE FEMALE ARE THE OVARIES. The Ovaries are located in the Lower Abdominal Cavity; the Ovaries USUALLY produce only ONE EGG or OVUM per month.

Puberty in females starts with changes in the Hypothalamus that causes the release of FSH and LH from the Pituitary Gland. FSH (follicle stimulating hormone) stimulates cells within the Ovaries to produce the Hormone ESTROGEN. Estrogen causes the reproductive system to complete its development, and also produce SECONDARY SEX CHARACTERISTICS - Enlargement of Breast and Reproductive Organs, Widening of the Hips, and growth of Body Hair.

Each Ovary contains about 400,000 PRIMARY FOLLICLES, which are clusters of cells surrounding a single ovum (egg). During her lifetime fewer than 500 Ova (Eggs) will actually be released, averaging one egg about every 28 days.

When a Follicle has completely matured, the Ovum (Egg) is released When a Follicle has completely matured, the Ovum (Egg) is released.  THIS PROCESS IS CALLED OVULATION

The Follicle literally ruptures, and the Ovum is swept from the Ovary into one of the TWO FALLOPIAN TUBES.  The Fallopian Tubes provide a way for an egg to travel from the Ovary to the Uterus

IT IS DURING ITS JOURNEY THROUGH THE FALLOPIAN TUBE THAT AN EGG CAN BE FERTILIZED.  An Egg must be fertilized within 48 hours of its release - after that, the egg begins to break down.  Unfertilized eggs dissolve in the Uterus.

After a FEW DAYS, the Ovum passes from the Fallopian Tube into the UTERUS.

The lower entrance to the Uterus is called the CERVIX The lower entrance to the Uterus is called the CERVIX.  A Sphincter Muscle in the Cervix controls the opening to the Uterus

Leading from the Cervix to the outside of the body is a muscular tube called the VAGINA or Birth Canal.