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Reproductive System

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Reproductive System
Reproductive System

Female Reproductive System / Male Reproductive System

Image Credit: SEER Training Modules / U. S. National Institutes of Health, National Cancer Institute

Reproductive System

The reproductive system is necessary for the production of new living organisms. The ability to reproduce is a basic characteristic of life. In sexual reproduction, two individuals produce offspring that have genetic characteristics from both parents. The primary function of the reproductive system is to produce male and female sex cells and to ensure the growth and development of offspring. The reproductive system is comprised of male and female reproductive organs and structures. The growth and activity of these organs and structures is regulated by hormones. The reproductive system is closely associated with other organ systems, particularly the endocrine system and urinary system.

Reproductive System Organs

Both male and female reproductive organs have internal and external structures. Reproductive organs are considered to be either primary or secondary organs. The primary reproductive organs are the gonads (ovaries and testes), which are responsible for gamete (sperm and egg cell) and hormone production. The other reproductive structures and organs are considered secondary reproductive structures. Secondary organs aid in the growth and maturation of gametes and developing offspring.
  • Female Reproductive System

    Labia majora - Larger lip-like external structures that cover and protect sexual structures.

    Labia minora - Smaller lip-like external structures found inside the labia majora. They provide protection for the clitoris and for the urethra and vaginal openings.

    Clitoris - Very sensitive sexual organ located in front of the vaginal opening. It contains thousands of sensory nerve endings and responds to sexual stimulation.

    Vagina - Fibrous, muscular canal leading from the cervix (opening of the uterus) to the external portion of the genital canal.

    Uterus - Muscular internal organ that houses and nurtures female gametes after fertilization. Also called the womb, the uterus is where a developing fetus resides during pregnancy.

    Fallopian tubes - Uterine tubes which transport egg cells from the ovaries to the uterus. Fertilization typically occurs in these tubes.

    Ovaries - Female primary reproductive structures that produce gametes and sex hormones. There is one ovary on each side of the uterus.
  • Male Reproductive System

    The male reproductive system consists of sexual organs, accessory glands, and a series of duct systems that provide a pathway for fertile sperm cells to exit the body. Male reproductive structures include the penis, testes, epididymis, seminal vesicles, and prostate gland.

Reproductive System: Gamete Production

Gametes are produced by a two part cell division process called meiosis. Through a sequence of steps, the replicated DNA in a parent cell is distributed among four daughter cells. Meiosis produces gametes with one half the number of chromosomes as the parent cell. Because these cells have one half the number of chromosomes as the parent cell, they are called haploid cells. Human sex cells contain one complete set of 23 chromosomes. When sex cells unite during fertilization, the two haploid cells become one diploid cell that contains 46 chromosomes.

The production of sperm cells is known as spermatogenesis. This process occurs continuously and takes place within the male testes. Hundreds of millions of sperm must be released in order for fertilization to take place. Oogenesis (ovum development) occurs in the female ovaries. In meiosis I of oogenesis, daughter cells are divided asymmetrically. This asymmetrical cytokinesis results in one large egg cell (oocyte) and smaller cells called polar bodies. The polar bodies degrade and are not fertilized. After meiosis I is complete, the egg cell is called a secondary oocyte. The haploid secondary oocyte will only complete the second meiotic stage if it encounters a sperm cell and fertilization begins. Once fertilization is initiated, the secondary oocyte completes meiosis II and is then called an ovum. The ovum fuses with the sperm cell, and fertilization is complete. The fertilized ovum is called a zygote.

Sources:
  • SEER Training Modules, Introduction to the Reproductive System. U. S. National Institutes of Health, National Cancer Institute. Accessed 24 January 2014 (http://training.seer.cancer.gov/anatomy/reproductive/)

  • The Reproductive System. On-Line Biology Book. Updated 03/12/07 (http://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookREPROD.html)

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