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Anatomy and Physiology Unit 9: Reproductive system and development

The reproductive systems produce gametes and hormones, and after fertilization the embryo develops with support from the placenta.

Covers: Male reproductive anatomy and hormones, female reproductive anatomy, ovarian and menstrual cycles, fertilization, pregnancy and the placenta, embryonic development, birth

Study guide

The reproductive system produces gametes (sex cells) through meiosis and makes sex hormones. In males, the testes produce sperm in the seminiferous tubules and make testosterone in interstitial (Leydig) cells. Sperm mature in the epididymis, travel through the vas deferens and urethra, and mix with fluids from the seminal vesicles, prostate gland and bulbourethral glands to form semen. FSH and LH from the anterior pituitary control sperm production and testosterone release.

In females, the ovaries produce eggs (oocytes) and the hormones estrogen and progesterone. Each month, the ovarian cycle matures a follicle; a surge of LH triggers ovulation, the release of an egg into the uterine (fallopian) tube. The empty follicle becomes the corpus luteum, which secretes progesterone to prepare the uterine lining (endometrium). If no pregnancy occurs, the corpus luteum breaks down, hormone levels fall and the endometrium sheds in menstruation. The uterus is a muscular organ where a fertilized egg implants, and the cervix connects it to the vagina.

Fertilization usually happens in the uterine (fallopian) tube when a sperm joins an egg, forming a zygote with a full set of chromosomes. The zygote divides into a blastocyst, which implants in the endometrium about a week later. The placenta forms from embryonic and maternal tissue; it lets nutrients, oxygen and wastes diffuse between the mother's and the embryo's blood without the bloods mixing, and it makes hormones such as hCG (detected by pregnancy tests) and progesterone. The umbilical cord connects the fetus to the placenta. Many substances, including alcohol, nicotine and some drugs, can cross the placenta and harm the developing embryo, especially during the first trimester, when organs form. Birth (labor) is driven by positive feedback: oxytocin from the posterior pituitary causes uterine contractions, which trigger more oxytocin release.

Key ideas

• Testes make sperm and testosterone; ovaries make eggs, estrogen and progesterone.
• An LH surge triggers ovulation.
• Fertilization usually occurs in the uterine (fallopian) tube.
• The placenta exchanges materials between mother and fetus and makes hormones.
• Labor is controlled by a positive-feedback loop involving oxytocin.

Formulas and rules

Common mistakes

• Thinking fertilization happens in the uterus; it usually happens in the uterine tube.
• Thinking the mother's and fetus's blood mix in the placenta; they don't.

Words to know

Gamete

A sex cell (sperm or egg) with half the chromosomes.

Testes

Male gonads that produce sperm and testosterone.

Seminiferous tubules

Tubules in the testes where sperm are made.

Epididymis

Duct where sperm mature and are stored.

Vas deferens

Duct that carries sperm toward the urethra.

Prostate gland

Gland that adds fluid to semen.

Ovary

Female gonad that produces eggs, estrogen and progesterone.

Follicle

A structure in the ovary containing a developing egg.

Ovulation

Release of an egg from the ovary.

Corpus luteum

Structure formed from a follicle that secretes progesterone.

Endometrium

The lining of the uterus.

Menstruation

Shedding of the endometrium when pregnancy doesn't occur.

Uterine tube

Tube carrying the egg to the uterus; usual site of fertilization.

Zygote

The cell formed when sperm and egg join.

Implantation

Attachment of the blastocyst to the uterine lining.

Placenta

Organ that exchanges materials between mother and fetus.

hCG

Hormone made by the embryo and placenta, detected by pregnancy tests.

Oxytocin

Hormone that causes uterine contractions during labor.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.