REPRODUCTIVE SYSTEM FUNCTIONS 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.  

Male Reproductive System The TESTES (PRIMARY MALE REPRODUCTIVE ORGANS) develop within the Abdominal Cavity. Just before birth the Testes descend through a canal into an external sac called the SCROTUM. The Testes (two egg-shaped structures) remain in the Scrotum, outside the body, where the temperature is about 3 degrees C Cooler than the body internal temperature. Sperm development in the Testes Requires the Lower Temperature.

The Testes are clusters of hundreds of Tiny Tubules called SEMINIFEROUS (sehm-uh-NIHF-er-uhs) TUBULES (28 in), which means "SEED BEARING".  Sperm Form through Meiosis in the specialized lining of this extensive network of tubules.

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. A Mature Sperm consists of THREE Regions:     A.  HEAD - which contains the Nucleus (The 23 Chromosomes) and enzymes that help the sperm penetrate the protective layers that surround and egg cell. (acrosome)     B.  MID PIECE - packed with energy releasing Mitochondria (energy source).  The mitochondria supply the energy that is required for sperm to reach an egg.     C.  TAIL – Consists of a Single, Powerful FLAGELLUM that propels the sperm.

Developed Sperm travel from the Seminiferous Tubules into the EPIDIDYMIS (20ft) where sperm mature and gain a flagellum. Although most Sperm remain stored in each Epididymis, some leave the Epididymis and pass into through the VAS DEFERENS, (18 in) 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 glands- the Seminal Vesicles, Bulbourethral Glands, and the Prostate Gland- to produce SEMINAL FLUID -which Protects and Nourishes the Sperm.

When the male is sexually excited, the Autonomic Nervous System prepares the male organs to deliver sperm (Erect). Sperm are Ejected from the Penis by Contractions of Smooth Muscles Lining the Vas Deferens.  This process is called ejaculation. Because ejaculation is regulated by the Autonomic Nervous System, it is not completely voluntary. 300 - 400 million Sperm are released in the Reproductive tract of a female during a single Ejaculation. Most sperm are killed by the acidic environment of the female reproductive tract. Only a few Sperm reach the site of fertilization.

The combination of sperm and seminal fluid make SEMEN. Sperm make up only 10 Percent of Semen, 90 percent is the fluid secreted by the Three Glands. Semen has a high concentration of Fructose to be used by Sperm as an energy source. To increase sperm survival, semen also contains alkaline fluids that help to neutralize the acidic environment of the female's vagina. To help sperm move through the female reproductive system, semen also contains Prostaglandins that Stimulate contractions of smooth muscles that line the female reproductive tract.

Between 100 and 200 million sperm are present in 1 milliliter of semen or about 5 MILLION sperm per drop. The Vas Deferens merges with the URETHRA, the tube that leads to the outside of the body through the PENIS. The Penis is the male reproductive organ that makes it possible for sperm to be delivered to the body of the female.

Female Reproductive System

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. Each time an egg is released, the body must be prepared to nourish a developing embryo.

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. The FUNCTION of a Follicle is to prepare a Single Ovum for release into the part of reproductive system where it can be Fertilized.  Ova mature within their follicles.  The maturing eggs become large, highly complex cells, growing nearly 75,000 times larger than sperm. When a Follicle has completely matured, the Ovum (Egg) is released.  THIS PROCESS IS CALLED OVULATION. If TWO Eggs mature, Fraternal, or Non Identical Twins may result.

The Follicle literally ruptures, and the Ovum is swept from the Ovary into one of the two uterine (fallopian) tubes.  The Fallopian Tubes provide a way for an egg to travel from the Ovary to the Uterus. The Ovum is moved through the fluid filled Fallopian Tubes by Cilia attached to the cells that line the walls of the tube.

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 lining of the Uterus is specially designed to receive a Fertilized Ovum. 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.

Menstrual Cycle Pituitary gland secretes FSH FSH stimulates maturation of follicle Follicular cells produce & secrete estrogen which causes the uterine lining to thicken Pituitary gland secretes a surge of LH which stimulates ovulation (release of egg) Follicular cells become corpus luteum cells which secrete estrogen & progesterone. Estrogen continues stimulating uterine lining to thicken Progesterone stimulates uterine lining to become glandular & vascular. Both inhibit the secretion of FSH & LH

9. If egg not fertilized, corpus luteum degenerates & stops secreting estrogen & progesterone. 10. Blood vessels in uterine lining constrict 11. Uterine lining disintegrates & sloughs away producing a menstrual flow. 12. Pituitary gland again secretes FSH & LH, cycle repeats.