Human Reproductive System and Sexual Maturation
Senior 1 · Biology
Human Reproductive System and Sexual Maturation
Lesson 1 of 5
25 min
In Primary 6 you learned the names of the main reproductive organs. In Senior 1 you will ask harder questions. Why do the testes hang outside the body, when almost every other organ is kept warm inside it? Where exactly does a sperm cell meet an egg cell, and what path does each take to get there?
To answer, you will follow two journeys on labelled diagrams: the journey of a sperm cell, and the journey of an egg cell. As in every part of biology, we use the correct scientific names, calmly and with respect. Doctors and nurses use these words every day.
Definition
Reproductive system: the group of organs that produce sex cells and sex hormones and, in females, that shelter and nourish a developing baby.
Gonad: an organ that makes sex cells and sex hormones. The male gonads are the testes (one is a testis); the female gonads are the ovaries.
Gamete (sex cell): a cell that joins with another gamete at fertilisation. Male gametes are sperm cells; female gametes are egg cells (ova; one is an ovum).
Fertilisation: the joining of the nucleus of a sperm cell with the nucleus of an egg cell, forming a zygote, the first cell of a new individual.
Figure 1: The male reproductive system, side view cut through the middle (simplified; not to scale).
| Part | Function |
|---|---|
| Testes (in the scrotum) | Make sperm cells, from puberty onwards, inside many tiny coiled tubes; make the hormone testosterone. |
| Scrotum | A bag of skin that holds the testes outside the abdomen, where they stay about 2 °C cooler than the rest of the body; sperm need this lower temperature to develop normally. |
| Epididymis | A long coiled tube on the back of each testis, where sperm are stored and finish maturing. |
| Sperm duct (vas deferens) | Carries sperm from the epididymis, up over and behind the bladder, to the urethra. |
| Seminal vesicles and prostate gland | Add fluid to the sperm. The fluid gives the sperm nutrients (food for energy) and a suitable pH. Sperm plus this fluid is called semen. |
| Urethra | A tube through the penis that carries urine out of the body and, in adults, semen. A ring of muscle makes sure the two never pass together. |
| Penis | Carries the urethra to the outside of the body. |
Worked example 1: the journey of a sperm cell
List, in order, the structures a sperm cell passes through from where it is made to where it leaves the body, and say what happens at each.
Check: the bladder is not on the route. The sperm duct passes around it, and joins the urethra below it, inside the prostate gland.
Figure 2: The female reproductive system, front view cut through the middle (simplified; not to scale).
| Part | Function |
|---|---|
| Ovaries | Contain egg cells from before birth; from puberty, usually release one mature egg about once a month (ovulation); make the hormones oestrogen and progesterone. |
| Oviducts (fallopian tubes) | The funnel at the end, with its finger-like fimbriae, catches the egg released from the ovary. Tiny beating hairs (cilia) and muscle in the wall move the egg towards the uterus. Fertilisation usually happens here. |
| Uterus (womb) | A hollow organ about the size of a fist, with a thick muscle wall. Its lining (the endometrium) thickens every month, ready to receive a fertilised egg; a baby develops here during pregnancy. The muscle pushes the baby out at birth. |
| Cervix | The narrow neck at the lower end of the uterus, opening into the vagina. |
| Vagina | A muscular tube from the cervix to the outside of the body. Menstrual blood leaves through it, and it is the birth canal. |
The outer parts are called the vulva. In females the urethra (for urine) has its own separate opening, in front of the opening of the vagina.
Definition
Ovulation: the release of a mature egg cell from an ovary.
Endometrium: the lining of the uterus, rich in blood vessels, which thickens each month and is shed during menstruation if no pregnancy begins.
Semen: the fluid that leaves the male body, made of sperm cells mixed with fluid from the seminal vesicles and prostate gland.
Worked example 2: the journey of an egg cell
Describe what happens to an egg cell after ovulation (a) if it is fertilised and (b) if it is not.
Worked example 3: name the organ from its job
| Clue | Reasoning | Organ |
|---|---|---|
| Makes male gametes and testosterone | a male gonad | testis |
| Where fertilisation usually happens | the egg is still travelling towards the uterus | oviduct |
| Keeps sperm about 2 °C below body temperature | it holds the testes outside the abdomen | scrotum |
| Its lining receives a fertilised egg | the thick endometrium | uterus |
| Carries both urine and semen, never at the same time | the shared tube in the penis | urethra |
| Feature | Male | Female |
|---|---|---|
| Gonads | two testes, outside the abdomen | two ovaries, inside the abdomen |
| Gametes | sperm cells, made in millions every day from puberty | egg cells, all present before birth; usually one released a month from puberty |
| Tubes that carry gametes | epididymis, sperm ducts, urethra | oviducts |
| Main sex hormone | testosterone | oestrogen and progesterone |
| Other role | glands add fluid to make semen | uterus shelters and nourishes a developing baby |
Important
Your body belongs to you. Knowing the correct names helps you explain a health problem to a nurse or doctor, and helps you tell a trusted adult clearly if anyone touches you in a way that is wrong. Any sexual touching of a child is abuse and a crime, and it is never the child's fault. Tell a parent, teacher or other trusted adult, or call the free child-abuse line 116 (Rwanda Investigation Bureau).
Warning
Common mistakes. (1) Mixing up the urethra (carries urine out of the body) with the ureters (carry urine from the kidneys to the bladder). (2) Thinking a baby grows in the stomach: it grows in the uterus. (3) Saying the ovary is where fertilisation happens: it usually happens in the oviduct. (4) Thinking the bladder is part of the route of sperm: the sperm duct passes around it.
Tip
Memory hook: "Make, Store, Carry, Add, Leave". For sperm: Make (testis), Store (epididymis), Carry (sperm duct), Add fluid (seminal vesicles and prostate), Leave (urethra). For the egg: Release (ovary), Catch (funnel), Meet (oviduct), Settle (uterus).
Practice: structure and function
Key points
Sources and credits
Figures 1 and 2, the tables, the worked examples and the practice questions are written by Ganzaa.
