Veylora
AnatomyIntermediate2D simulation~15 min

Human Reproductive System

Reproduction is how every living thing passes on its genes. In humans, two specialised systems produce sex cells (gametes), and a carefully timed set of hormones prepares the body for a possible pregnancy. Explore the anatomy, step through the monthly cycle, and follow the first ten days after fertilisation.

Female anatomy
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Press Start to play through the cycle.

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Press Start to watch the first ten days.

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How to use this simulator

  1. Choose a view. In the anatomy views, click any structure to learn its function, and compare the magnified egg and sperm cells.
  2. In Menstrual cycle, press Start or drag the day slider and watch the hormones, the ovary and the uterine lining change together.
  3. Turn on A fertilised egg implants to see how hCG and progesterone keep the lining and stop menstruation.
  4. In Fertilisation, press Start to follow the early embryo from fertilisation in the tube to implantation in the uterus.

What the reproductive system does

The reproductive systems produce gametes (eggs and sperm), make sex hormones that control development and fertility, and, in females, support a developing baby. Unlike other body systems, they are not needed for an individual to survive, but they are essential for the species. They become fully active atpuberty, when rising hormone levels cause the body to mature.

Female reproductive anatomy

  • Ovaries: two almond-sized glands that store immature eggs and release one, usually each month. They also make oestrogen and progesterone.
  • Fallopian tubes: carry the egg from the ovary to the uterus; fertilisation usually happens here.
  • Uterus: a muscular organ with a lining (the endometrium) where an embryo can implant and grow.
  • Cervix: the neck of the uterus, opening into the vagina.
  • Vagina: a muscular canal from the cervix to the outside of the body, also the birth canal.

Male reproductive anatomy

  • Testes: make sperm and testosterone. They sit outside the abdomen in the scrotum, which keeps them slightly cooler, as sperm production needs.
  • Epididymis: a long coiled tube where sperm mature and are stored.
  • Vas deferens (sperm ducts): carry sperm towards the urethra.
  • Seminal vesicles and prostate gland: add fluids that provide energy and protect sperm, forming semen.
  • Urethra: carries urine or semen out of the body through the penis.

Gamete production

Gametes are made by meiosis, a type of cell division that halves the chromosome number from 46 to 23. Sperm production (spermatogenesis) begins at puberty and continues throughout life, producing millions of sperm a day; each takes about 74 days to form. Egg production (oogenesis) starts before birth: a baby girl is born with all her immature eggs, and from puberty one usually matures each month untilmenopause. Each gamete is adapted to its job: the sperm has a tail and many mitochondria; the egg is large with a food store.

Reproductive hormones

The hypothalamus and pituitary gland in the brain control reproduction. The pituitary releases FSH (follicle-stimulating hormone) and LH (luteinising hormone), which act on the ovaries and testes. The ovaries respond by making oestrogen and progesterone; the testes make testosterone. These sex hormones cause the changes of puberty and control the menstrual cycle and sperm production, often through feedback loops.

The menstrual cycle

The cycle lasts about 28 days on average, but anywhere from about 21 to 35 days is common. During thefollicular phase, FSH makes a follicle grow and oestrogen rebuilds the uterine lining. A surge of LH triggers ovulation, the release of an egg, around the middle of the cycle. In theluteal phase, the empty follicle becomes the corpus luteum, which makes progesterone to keep the lining ready. If there is no pregnancy, hormone levels fall and the lining is shed duringmenstruation, a period, which marks day 1 of the next cycle.

Fertilisation and early development

If a sperm meets the egg in a fallopian tube, enzymes in the sperm’s acrosome help it through the egg’s outer layer. Once one sperm enters, the egg’s coat changes to block others. The nuclei combine to form a zygote, which divides repeatedly as it travels to the uterus, becoming a ball of cells (morula) and then a hollowblastocyst. About six to ten days after fertilisation it implants in the uterine lining and begins to make hCG, the hormone detected by pregnancy tests. Over the following weeks the placenta forms and the embryo’s organs begin to develop.

Health and medicine

Understanding the reproductive system underpins fertility treatments such as IVF (in vitro fertilisation), contraception, which works by preventing ovulation, fertilisation or implantation, and screening for conditions such as testicular and cervical cancer. Hormone levels such as FSH and LH are measured to investigate fertility and puberty. Talking to a doctor or nurse is the right step for any personal health question.

Educational model only. The diagrams are simplified schematics, and the cycle shows an idealised 28-day pattern with relative hormone levels; real cycles vary widely between people and from month to month. This simulator is not medical advice and cannot be used to track fertility or plan or prevent pregnancy. See oureducational and medical disclaimer.

Key terms

Gamete
A sex cell (egg or sperm) containing 23 chromosomes.
Ovulation
The release of an egg from an ovary.
Zygote
The single cell formed when an egg and sperm fuse.
Implantation
The embedding of the early embryo in the uterine lining.

Key takeaways

  • Testes make sperm and testosterone; ovaries release eggs and make oestrogen and progesterone.
  • Gametes are made by meiosis and carry 23 chromosomes.
  • FSH, LH, oestrogen and progesterone coordinate the menstrual cycle, with ovulation around mid-cycle.
  • Fertilisation happens in a fallopian tube; the embryo implants in the uterus about a week later.

Model note: hormone curves show relative levels for an idealised cycle; units and timings differ between people.

Knowledge check

Human Reproductive System: test your understanding

Answer each question to get instant feedback and an explanation. Use the simulator to check your thinking.

8 questions3 basic3 intermediate2 advanced

0 of 8 answered

  1. Q1BasicWhere are sperm cells produced?
    Show answer

    Answer: B. In the testes

    Sperm are made in the coiled seminiferous tubules of the testes, then mature in the epididymis.

  2. Q2BasicWhere does fertilisation usually take place?
    Show answer

    Answer: C. In a fallopian tube

    The egg is fertilised in the fallopian tube, then the early embryo travels to the uterus over about five days.

  3. Q3BasicHow many chromosomes does a human egg or sperm cell contain?
    Show answer

    Answer: B. 23

    Gametes are made by meiosis and contain half the usual number. When they join, the zygote has the full 46.

  4. Q4IntermediateWhich hormone surge triggers ovulation?
    Show answer

    Answer: B. Luteinising hormone (LH)

    High oestrogen causes the pituitary gland to release a surge of LH around day 14, and the follicle releases its egg about a day later.

  5. Q5IntermediateWhat is the main role of progesterone in the second half of the cycle?
    Show answer

    Answer: B. To keep the uterine lining thick and ready for an embryo

    Progesterone from the corpus luteum maintains the lining. When it falls (no pregnancy), the lining is shed as a period.

  6. Q6AdvancedIn the simulator, switch on pregnancy. Why does menstruation not happen?
    Show answer

    Answer: B. The implanted embryo releases hCG, which keeps the corpus luteum making progesterone, so the lining is maintained

    hCG is also the hormone detected by pregnancy tests. Later, the placenta takes over making progesterone.

  7. Q7IntermediateWhat does the seminal vesicle add to semen?
    Show answer

    Answer: B. A sugary fluid that gives sperm energy

    Seminal vesicles add fructose-rich fluid; the prostate adds an alkaline fluid. Together they make up most of the volume of semen.

  8. Q8AdvancedWhat is a blastocyst?
    Show answer

    Answer: B. A hollow ball of cells, about five days after fertilisation, that implants in the uterus

    Its inner cell mass becomes the embryo; its outer layer helps form the placenta.

References and further reading

  1. Betts, J. G., et al. (2022). Anatomy and Physiology 2e, Chapter 27: The Reproductive System. OpenStax. openstax.org (opens in a new tab)
  2. Betts, J. G., et al. (2022). Anatomy and Physiology 2e, Section 28.2: Embryonic Development. OpenStax. openstax.org (opens in a new tab)
  3. Moore, K. L., Persaud, T. V. N., & Torchia, M. G. (2019). The Developing Human: Clinically Oriented Embryology (11th ed.). Elsevier.
  4. Reed, B. G., & Carr, B. R. (2018). The Normal Menstrual Cycle and the Control of Ovulation. In Endotext. MDText.com. ncbi.nlm.nih.gov (opens in a new tab)

This page is an educational model, not medical advice. Found an error? Let us know. See our educational disclaimer.

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