Sexual intercourse is the normal method for human reproduction. The main goal of sexual intercourse is for the male sex cell (sperm) to unite with the female sex cell (egg) in a process called fertilization. The structure of the male and female reproductive organs (genitals) makes it possible for fertilization to take place inside of the woman's body.
The female reproductive system allows women to produce female sex cells (eggs, ova), to have sexual intercourse, to carry and nourish the fertilized egg while it develops, and to give birth to offspring. The male reproductive system allows men to produce male sex cells (spermatozoa, sperm) and to fertilize the egg, resulting in pregnancy.
Anatomy of the Female Reproductive Tract
The female reproductive system consists of internal organs and external organs. Internal female reproductive organs include the ovaries, the fallopian tubes, the uterus (womb), and the vagina. External female reproductive organs include the vulva (e.g., labia majora, labia minora) and the clitoris.
The ovaries produce and store female sex cells (eggs, ova). At birth, the ovaries already contain hundreds of thousands of eggs. During puberty, the pituitary gland in the brain begins making hormones that stimulate the ovaries to produce female sex hormones (e.g., estrogen). These hormones result in female sexual maturity and cause the periodic release of an ovum into the fallopian tube (called ovulation).
If the egg is not fertilized by a male sex cell (sperm), it is discharged from the body through the vagina, along with blood and tissue from the lining of the uterus (called menstruation). Menstruation occurs in sexually mature women about every 28 days and ovulation occurs approximately 14 days before the next menstrual period.
Anatomy of the Male Reproductive Tract
The male reproductive system also consists of internal organs and external organs. Internal male reproductive organs include ducts (e.g., epididymes, vas deferens) and glands (e.g., prostate gland, seminal vesicles), and external male reproductive organs include the penis and the testicles (testes).
The penis is made up of the shaft (main part of the organ) and the glans (tip of the organ, sometimes called the head). The shaft of the penis contains cylinder-shaped vascular tissue (called the corpora cavernosa) and erectile tissue. It also contains the urethra (tube through which urine and semen are expelled), arteries and veins, and nerves. An opening in the glans penis (called the meatus) allows urinate and semen to be expelled from the body.
The testicles, also called the testes, are oval-shaped organs that produce male sex cells (spermatozoa, sperm) and male hormones (e.g., testosterone). Normally, sexually mature males produce millions of sperm cells every day. The testicles are located in a sac located at the base of the penis, which is called the scrotum.
Internal structures in the male reproductive system include the epididymes, the vas deferens, the prostate gland, and the seminal vesicles. The epididymes (singular is epididymis) are small tubes that connect each testicle to the vas deferens. After sperm are produced in the testes, they are stored in the epididymes for 46 weeks until they mature.
The vas deferens is connected to a walnut-sized gland called the prostate gland. The prostate produces substances (e.g., prostate specific antigen [PSA]) that combine with sperm to form seminal fluid.
The seminal vesicles are located near the prostate gland. These sac-like organs produce a thick fluid that mixes with the seminal fluid produced by the prostate and sperm produced by the testes to form semen (also called ejaculate).
When a male becomes sexually aroused (stimulated), tissue in the penis becomes filled with blood, causing the organ to become stiff and hard (called an erection). An erection allows the man's penis to penetrate the woman's vagina during sexual intercourse.
Additional sexual stimulation may result in the propulsion of semen out of the male's body through the opening in the penis (called ejaculation). Each ejaculate may contain as many as 500 million sperm.
If ejaculation occurs during sexual intercourse, semen may enter the vagina, allowing sperm to move through the lower part of the uterus (called the cervix) and into the body of the organ. If a woman who is sexually mature has sexual intercourse with a male within several days of ovulation, a sperm may unite with a mature egg in the fallopian tube (called fertilization or conception), resulting in pregnancy.
Once the egg has been fertilized, the cells (called a zygote) travel from the fallopian tube to the uterus and implant in the uterine lining (called implantation). These cells continue to develop for about 280 days (9 months)first into a larger collection of cells (called a blastocyst), then into an embryo and placenta, and finally, after 8 weeks, into a fetus. The resulting offspring contains genetic material from both the male and the female.