Sexual Behaviour and Sexual Response
Senior 2 · Biology
Sexual Behaviour and Sexual Response
Lesson 1 of 4
18 min
Between about 8 and 14 years of age, your body starts changing faster than at any time since you were a baby. You grow taller, your shape changes, and new feelings appear. This stage is called puberty: the time when the body matures and becomes able to reproduce. Every adult you know has been through it. Understanding what is happening, and why, makes the changes easier to manage and helps you look after your body with confidence.
Many activities in the body are controlled by hormones, chemical messengers made by glands and carried in the blood. Puberty begins when the pituitary gland, a pea-sized gland at the base of the brain, starts releasing two hormones (FSH and LH) into the blood. These travel to the sex organs, the gonads, and wake them up:
These sex hormones cause the changes of puberty. Differences present from birth, such as the reproductive organs themselves, are called primary sexual characteristics. The features that develop at puberty are secondary sexual characteristics.
| Girls (usually starting between about 8 and 13) | Boys (usually starting between about 9 and 14) |
|---|---|
| Breasts develop | Testes and penis grow larger |
| Hips widen and the body becomes curvier | Shoulders broaden and muscles grow |
| Hair grows under the arms and in the pubic area | Hair grows in the pubic area, under the arms, on the face and on the body |
| A growth spurt, usually earlier than in boys | A growth spurt, usually later and longer than in girls |
| The ovaries begin to release eggs (ovulation), and monthly periods begin. The first period is called menarche. | The testes begin to make sperm. Erections and the release of semen (ejaculation) begin, including during sleep: wet dreams, also called nocturnal emissions |
| A clear or white discharge from the vagina: a normal way the body keeps itself clean | The larynx (voice box) grows, so the voice "breaks" and becomes deeper |
| In both: more sweat and a stronger body odour, oilier skin and often acne (pimples) | |
Hormones affect the brain as well as the body. It is common to feel moods change quickly, to feel shy about your body, to want more independence from your family, and to begin feeling attracted to other people. These feelings are a normal part of growing up. Having a feeling does not mean you must act on it, and you remain in charge of what you do.
Uwase and her brother Gatete are both 12. Uwase has grown 8 cm this year and her breasts have begun to develop. Gatete has not changed at all, and an aunt says something must be wrong with him. Is she right?
Tip
Pituitary first, gonads second, changes third. In an exam, follow the chain: the pituitary gland releases hormones → the ovaries make oestrogen (girls) or the testes make testosterone (boys) → these hormones cause the secondary sexual characteristics.
Name the gland that starts puberty and the main sex hormone made in (a) girls and (b) boys.
Answer: The pituitary gland. (a) Oestrogen (made by the ovaries, together with progesterone); (b) testosterone (made by the testes).
State two changes of puberty that happen in both boys and girls.
Answer: Any two of: pubic and underarm hair grows; a growth spurt; more sweating and body odour; oily skin and acne; stronger emotions and new feelings of attraction.
Mugisha, 14, wakes to find his sheets damp and is worried he is ill. Explain what has happened.
Answer: He has had a wet dream (nocturnal emission). Since puberty his testes have been making sperm, and sometimes semen is released during sleep. This is completely normal and healthy and is not a sign of illness.
Why does a boy's voice become deeper during puberty?
Answer: Testosterone makes the larynx (voice box) grow larger and the vocal cords longer and thicker, so they vibrate more slowly and produce a lower sound. While this happens, the voice may "crack".
Remember
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