The Big Picture
Human reproduction begins when a male sex cell and a female sex cell unite. The male and female reproductive systems have different structures that support this process.
You need to know the main reproductive structures, what they do, and how sperm and an egg move through the reproductive systems. You also need to understand menstruation, ovulation, and fertilization.
Quick tip: Tap, click, or press Enter on any term with a dotted underline and an ⓘ icon to see its plain-English definition.
Start Here If You’re Overwhelmed
Focus on these core ideas:
- The testes produce sperm and testosterone.
- The ovaries contain eggs and produce estrogen and progesterone.
- menstruation happens when the lining of the uterus breaks down and leaves the body through the vagina.
- Ovulation usually occurs on or about day 14 of the menstrual cycle.
- Fertilization happens when a sperm and an ovum unite into one cell.
- A sperm has 23 chromosomes and an ovum has 23 chromosomes. The fertilized cell has 46 chromosomes.
Jump to:
Course Notes: Key Ideas You Need to Know
The Basic Idea of Reproduction
Human reproduction involves the union of two sex cells:
- The male sex cell is the sperm.
- The female sex cell is the ovum, or egg.
The different structures of the male and female reproductive systems allow reproduction to occur.
The Male Reproductive System
Testes and Scrotum
The testes, also called testicles, are the male sex glands or gonads. There are two testes.
The testes have two important functions:
- They produce sperm.
- They produce testosterone.
Testosterone is a male hormone. A hormone is a chemical substance produced by cells of specialized glands and released into the bloodstream.
Testosterone supports the functioning of the reproductive organs and the development of male secondary sex characteristics.
The testes hang between the thighs at the base of the penis. They are held inside the scrotum, a sac made of skin and muscle.
How Sperm Travels
Sperm follows a pathway through several structures.
- Sperm is produced in the testes.
- Sperm travels from each testis to the epididymis.
- Sperm then travels through the vas deferens .
- Each vas deferens eventually joins a seminal vesicle.
- The ducts of the seminal vesicles join to form the ejaculatory duct.
- The ejaculatory duct passes through the prostate gland and joins the urethra.
The epididymis is a coiled tube located on the top and side of the testis. It is about 6 m, or 20 ft., long.
Seminal Vesicles and Semen
The two seminal vesicles store sperm and produce semen.
Semen is the fluid that carries sperm from the male reproductive tract.
Prostate Gland and Urethra
The prostate gland lies just below the bladder. It is shaped like a doughnut.
The prostate adds fluid to semen. This fluid helps increase sperm mobility .
The urethra runs through the prostate and continues through the penis. It serves as the outlet for both urine and semen.
Penis
The penis is located outside the body and contains erectile tissue.
During sexual arousal, blood fills this tissue. The penis becomes enlarged, hard, and erect.
During sexual intercourse, the erect penis can enter the vagina. Semen containing sperm is then released into the vagina.
The Female Reproductive System
Ovaries and Ovulation
The female gonads are two ovaries. These almond-shaped glands are located on each side of the uterus in the pelvic cavity.
The ovaries contain ova, or eggs. These are the female sex cells.
During the reproductive years, one ovum is released about once each month. This release is called ovulation.
The ovaries also produce the hormones estrogen and progesterone. These hormones support reproductive system function and the development of female secondary sex characteristics.
Fallopian Tubes
After an ovum leaves an ovary, it travels through a fallopian tube.
A fallopian tube lies on each side of the uterus and attaches to the uterus at one end.
The fallopian tubes also play an important part in fertilization because sperm and an ovum can unite there.
Uterus
The uterus is a hollow, muscular organ shaped like a pear.
It sits in the centre of the pelvic cavity:
- behind the bladder
- in front of the rectum
The main part of the uterus is called the fundus.
The narrow neck of the uterus is the cervix.
The tissue lining the uterus is called the endometrium. It contains many blood vessels.
If fertilization occurs, the fertilized cell can implant in the endometrium. The uterus provides the place where the developing fetus receives nourishment and grows.
Vagina
The cervix projects into a muscular canal called the vagina.
The vagina:
- opens to the outside of the body
- sits just behind the urethra
- receives the penis during sexual intercourse
- forms part of the birth canal
Glands in the vaginal wall produce secretions that keep the vagina moist.
In young girls, a membrane called the hymen partly covers the external vaginal opening. The hymen can break for different reasons.
Vulva
The external female genitalia are called the vulva.
The vulva includes several structures.
Mons pubis: A rounded pad of fatty tissue over a bone called the symphysis pubis. It is covered with hair in the adult female.
Labia majora and labia minora: Two folds of tissue on either side of the vaginal opening.
Clitoris: A small, sensitive organ made of erectile tissue. It becomes hard during sexual stimulation.
Mammary Glands
The mammary glands are located in the breasts.
They contain glandular tissue and fat. After childbirth, they produce and release milk.
Milk travels through ducts that open into the nipple.
Menstruation and the Menstrual Cycle
The endometrium contains a rich blood supply that can nourish a developing fetus.
If pregnancy does not occur, the endometrium breaks down and leaves the body through the vagina. This process is called menstruation.
The menstrual cycle occurs about every 28 days.
Beginning of the Cycle
The first day of the menstrual cycle begins with menstruation.
Blood leaves the uterus through the vaginal opening. Menstrual flow usually lasts 3 to 7 days.
Ovulation
During the next phase, an ovum matures inside an ovary and is released.
Ovulation usually happens on or about day 14 of the menstrual cycle.
Preparing the Endometrium
The ovaries release estrogen and progesterone.
These hormones cause the endometrium to thicken in preparation for a possible pregnancy.
If pregnancy does not occur:
- Estrogen and progesterone decrease.
- Blood supply to the endometrium decreases.
- The endometrium breaks down.
- The lining leaves the body through the vagina.
- Another menstrual cycle begins.
Fertilization
Fertilization is the joining of a sperm and an ovum into one cell.
A sperm contains 23 chromosomes. An ovum also contains 23 chromosomes.
When they unite, the fertilized cell contains 46 chromosomes.
How Sperm Reaches the Ovum
During sexual intercourse, millions of sperm are deposited in the vagina.
The sperm travel:
- through the cervix
- through the uterus
- into the fallopian tubes
If a sperm joins an ovum in a fallopian tube, fertilization occurs and pregnancy may result.
The fertilized ovum then travels down the fallopian tube toward the uterus.
After a short time, the fertilized cell implants in the thick endometrium and grows during pregnancy.
Fast Review
Keep your review focused on the main structures, pathways, and numbers.
- The testes produce sperm and testosterone.
- Sperm travels from each testis to the epididymis, then through the vas deferens.
- Each vas deferens joins a seminal vesicle. The seminal vesicle ducts form the ejaculatory duct, which joins the urethra.
- The seminal vesicles store sperm and produce semen.
- The ovaries contain ova and produce estrogen and progesterone.
- Ovulation is the release of an ovum from an ovary.
- The endometrium is the tissue lining the uterus.
- menstruation occurs when the endometrium breaks down and leaves through the vagina.
- The menstrual cycle occurs about every 28 days, and menstrual flow usually lasts 3 to 7 days.
- Ovulation usually occurs on or about day 14.
- Fertilization occurs when a sperm and an ovum unite.
- A sperm and an ovum each contain 23 chromosomes. The fertilized cell contains 46 chromosomes.
- After fertilization in a fallopian tube, the fertilized ovum travels toward the uterus and implants in the endometrium.
Final Pep Talk
There are many structures and pathways in this topic, so review them in small groups instead of trying to hold every name at once. Learn the order first, then go back and strengthen the terms that still feel unfamiliar.