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Human Reproduction
Male Reproductive System
Female Reproductive System

The reproductive health needs of women and men change over time and are influenced by a variety of biological and situational factors. It is estimated that a woman spends approximately three decades of her life attempting not to become pregnant.  During this time, physical, behavioral and environmental factors may impact a woman’s or couple’s ability to become pregnant in the future. Additionally, the number of women and men choosing to delay having children continues to rise, increasing the demand for infertility treatments.

How does one protect one's fertility for future pregnancies? When a woman and her partner have difficulty becoming pregnant, what options do they have for improving their chances of becoming pregnant and having healthy children? In this section of the website you will find information on the science, ethics, and regulation of emerging reproductive health technologies including assisted reproductive technologies, prenatal and pre-implantation genetic diagnosis, and somatic cell nuclear transfer. RHTP is committed to exploring and addressing the implications these technologies have on the health and wellbeing of women and their families.

Human Reproduction1
Human reproduction depends on the union of male and female gametes or sex cells, ova in women and sperm in men.  Each sperm and ovum contains a half set of 23 chromosomes so when combined during fertilization they form a zygote with a full set of 46 unique chromosomes. 

Overview of the Male Reproductive System
The main male reproductive components are sperm and the male sex hormone testosterone, both produced in the testes.  This process is regulated by gonadotropic hormone pathways.  Every two to three hours, gonadotropin-releasing hormone (GnRH) is secreted from the hypothalamus which acts on the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).  Within the testes, FSH is directly involved in the production of sperm and LH is responsible for regulating testosterone, which in turn is also essential for sperm production. Once men reach puberty, their reproductive system employs this pathway to continuously secrete testosterone and produce sperm throughout their reproductive life.

Overview of the Female Reproductive System
The female reproductive system is more complex than the male counterpart, displaying cyclical swings in hormones with interrupted ova release.  The primary female reproductive organs are the ovaries which produce ova and secrete estrogen and progesterone, the female sex hormones.  Similar to the male, the female reproductive system is also controlled by the GnRH, FSH and LH pathways; however, the effects of FSH and LH differ throughout the female cycle.

The ovary is continuously rotating between the follicular stage and the luteal stage, named for the respective hormone that is most dominant in the particular phase. Although the duration and timing differ from woman to woman and cycle to cycle, the ovarian cycle is typically 28 days starting on the first day of menstruation.

  • Follicular stage: During the follicular stage (day 1 through day 14), estrogen and FSH are secreted in higher concentrations to maturate the follicles to release an ovum during ovulation.
  • Ovulation is triggered by a sudden spike in LH, usually around day 14, which marks the end of the follicular stage and the beginning of the luteal stage.  During ovulation, the ovum is released by the ovary and is picked up by the fallopian tube where it awaits fertilization.
  • Luteal stage: In the luteal stage (day 15-28), the follicles become luteal cells which form the corpus luteum, a group of cells that secrete progesterone.  Progesterone and LH are the dominant hormones in the luteal phase and are responsible for preparing the uterus for implantation of a fertilized ovum. 

If fertilization does not occur, the corpus luteum is degenerated and the cycle starts over with menstruation and the expulsion of the ovum.

Fertilization is all about timing.  In order for conception to occur, sperm and egg must unite in the fallopian tube within 24 hours following ovulation.  Sperm typically live in a woman’s body for 48 to 72 hours, but can survive for up to five days.

Thus, fertilization is more likely when sexual intercourse occurs up to five days before and one day after ovulation (days 9-15).  However, this timetable varies greatly from couple to couple, and should not serve as a guide to preventing pregnancy.  For more information on natural family planning please click here.

If fertilized, the egg, now called a zygote, moves into the uterus where it attaches to begin a pregnancy. 

Usually after one year of unprotected sexual intercourse, roughly 85 percent of couples will become pregnant.  Over the next three years, approximately half of the other 15 percent will conceive naturally.2


1 Sherwood, L.  Human Physiology From Cells to Systems. Fourth Edition.  Pacific Grove, CA:  Brooks/Cole, 2001.

2 Mayo Clinic.  Infertility.  Available at:  http://www.mayoclinic.com/health/infertility/DS00310/DSECTION=3
Accessed February, 2008.




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