Biology

Female Reproductive System

Big Picture

The female reproductive system consists of the female sex organs, the two most important of which are the uterus and the ovary. The female reproductive organ has many responsibilities that include the reception of sperm and support for a developing fetus during and post-birth. The female reproductive system develops before birth but doesn’t reach maturity until puberty. From puberty until around midlife, females will have a monthly menstrual cycle that will allow the female to have a child when an egg cell is fertilized by a sperm cell. When a woman reaches midlife, she undergoes menopause, meaning she will enter a non-reproductive state.

Key Terms

Reproductive System: The system of organs that produces gametes and secretes sex hormones.

Vulva: The external female reproductive organs.

Vagina: A mucous-lined muscular tract leading from the vulva to the uterus.

Uterus: Female sex organ where the fetus develops. Contraction of the uterus leads to childbirth.

Endometrium: The inner lining of the uterus.

Ovaries: Two egg-producing sex organs located on either side of the uterus. The ovaries also include endocrine glands that secrete estrogen.

Estrogen: Female sex hormone.

Follicle: Structure that houses and protects a maturing egg cell.

Fallopian Tubes: Two tubes that extend from the upper right and left corners of the uterus to the ovaries.

Oogenesis: The production of an egg cell.

Oogonium: A diploid reproductive cell that will undergo mitosis to produce primary oocytes.

Primary Oocyte: A diploid daughter cell that will begin but not complete meiosis during fetal development.

Ovulation: The release of the secondary oocyte from its follicle and from the ovary. The secondary oocyte will travel down the fallopian tube into the uterus.

Puberty: Period during which humans become sexually mature.

Luteinizing Hormone (LH): Pituitary gland hormone that stimulates the testes to secrete testosterone and the ovaries to secrete estrogen

Follicle-Stimulating Hormone (FSH): Pituitary gland hormone that stimulates the ovaries to secrete estrogen and follicles in the ovaries to mature.

Adolescent Growth Spurt: Period of rapid growth that occurs during puberty.

Menstrual Cycle: The physiological changes that occur monthly in non-pregnant, fertile females.

Menarche: The first menstrual cycle.

Menstruation: The shedding of the endometrium from the uterine wall.

Menopause: The transition from fertile to non-reproductive that occurs around midlife in women.

Female Reproductive Structures

Main structures of the female reproductive system:‍

  • The vulva include the labia (singular, labium), which protect the vagina and urethra. The vagina and urethra have openings in the vulva.
  • The vagina is tube-like and begins at the vulva and extends toward the uterus. The vagina facilitates reproduction and childbirth.
  • The uterus is shaped like an upside-down pear. The region where the uterus meets the vagina is called the cervix.
  • The uterus has a thick lining of tissues called endometrium.
  • On either side of the uterus are the ovaries.
  • Eggs produced by the ovaries are housed in follicles.
  • The fallopian tubes extend from the upper corners of the uterus. Each tube reaches (does not attach) one of the ovaries.

The breasts are also a part of the female reproductive system. The breasts are not involved in reproduction, but they do nourish a baby after birth. The breasts contain mammary glands that secrete milk.

Female Reproductive Structures
Image Credit: Mysid, Public Domain

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Biology

Female Reproductive System cont.

Egg Production

Oogenesis

  • Begins before birth, starts when a diploid oogonium undergoes mitosis to produce a primary oocyte
  • A diploid cell contains the usual number of chromosomes
  • The primary oocyte starts to go through meiosis I but does not complete meiosis until later
  • The primary oocyte remains in a resting state in an immature follicle
  • At birth, a female’s ovaries contain all the (immature) eggs she will ever produce

Maturation of a Follicle

  • Beginning during puberty, each month a follicle and its respective primary oocyte will mature
  • The primary oocyte will resume meiosis and form two haploid cells: a secondary oocyte, and a smaller cell called a polar body
  • A haploid cell contains half the usual number of chromosomes
Egg Production
Image Credit: Mysid, Public Domain

Ovulation and Fertilization

  • The follicle takes about 12-14 days to mature. After maturation, the follicle bursts open and releases the secondary oocyte from the ovary. This process is called ovulation.
  • The follicle, now called a corpus luteum, degenerates and breaks down.
  • A swaying tissue at the end of the fallopian tubes helps move eggs from the ovary into the tubes.
  • If the secondary oocyte is fertilized by a sperm cell as it travels through the fallopian tube, the secondary oocyte will finish meiosis to form one mature egg and another polar body. The polar bodies break down and disappear.
  • If the secondary oocyte is not fertilized, it will eventually break down.

Sexual Development

Development Before Birth

  • The absence of testosterone due to the lack of Y chromosome is what determines the development of female sex organs
  • During this time, immature eggs form in the ovaries, establishing all the egg cells a woman will have during her lifetime.

Changes During Puberty

  • Females generally reach puberty before males do. At around 10 years old (two years before boys), the immature sex organs of girls begin to mature.
  • Secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the pituitary glands initiate puberty. In response to these hormones, the ovaries secrete estrogen, which promotes the development of the reproductive organs and the breasts and the growth of pubic hair.

Adolescent Growth Spurt

  • Girls begin their adolescent growth spurt before boys do.
  • Girls tend to have shorter growth spurts than boyds do.
  • Most girls reach their full height by 15.

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Biology

Female Reproductive System Cont.

Sexual Development (cont.)

Menstrual Cycle

  • The menstrual cycle includes ovulation and menstruation.
  • Menarche is the first menstrual cycle. The timing of the first cycle depends on genetic and environmental factors.
  • The endometrium is shed from the body during mensturation. After menstruation, the endometrium will reform and grow again.
  • A follicle will start to mature in an ovary, and ovulation will occur around day 14 of the cycle.
  • The endometrium builds up in preparation for a fertilized egg.
  • If the egg is fertilized, the corpus luteum secrete a hormone that prevents the endometrium from breaking down. The endometrium helps nourish the egg.
  • If the egg is not fertilized, the endometrium will break down and be shed. A new menstrual cycle begins.
  • Since the number of eggs a woman will have during her lifetime is set at birth, the menstrual cycles will eventually stop. A woman then goes through menopause, which occurs around midlife, typically in the early fifties.
Menstrual Cycle

Notes

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