Reproduction and Contraception
Human Reproduction
Puberty
Puberty is the process of physical and sexual maturation triggered by hormones released from the pituitary gland.
In males:
- Testosterone (from testes) causes: growth of facial and body hair, deepening voice, muscle development, sperm production, growth spurt
In females:
- Oestrogen (from ovaries) causes: breast development, widening hips, pubic and underarm hair, menstruation begins, growth spurt
The Male Reproductive System
| Structure | Function |
|---|---|
| Testes | Produce sperm and testosterone |
| Scrotum | Holds testes outside the body at a slightly lower temperature (needed for sperm production) |
| Sperm duct (vas deferens) | Carries sperm from the testes to the urethra |
| Urethra | Carries sperm (and urine, at different times) out of the body |
| Prostate and seminal vesicles | Produce seminal fluid that nourishes and carries sperm |
| Penis | Delivers sperm into the female reproductive system |
The Female Reproductive System
| Structure | Function |
|---|---|
| Ovaries | Produce eggs (ova) and hormones (oestrogen and progesterone) |
| Oviducts (fallopian tubes) | Carry the egg from the ovary to the uterus; site of fertilisation |
| Uterus (womb) | Where the fertilised egg implants and the fetus develops; has a muscular wall and a thick lining rich in blood vessels |
| Cervix | Ring of muscle at the base of the uterus; keeps the fetus in place during pregnancy |
| Vagina | Where sperm are deposited; birth canal |
Fertilisation and Development
1. During sexual intercourse, sperm are deposited in the vagina
2. Sperm swim through the cervix and uterus into the oviduct
3. If an egg is present, one sperm may penetrate the egg membrane → fertilisation
4. The nuclei of the sperm and egg fuse, forming a zygote with 46 chromosomes (23 from each parent)
5. The zygote divides by mitosis to form a ball of cells called an embryo
6. The embryo implants in the thick uterus lining (implantation)
7. The placenta develops to supply the fetus with oxygen and nutrients via the mother's blood
Contraception
Contraception prevents pregnancy. Methods are divided into hormonal, barrier, and other categories.
Hormonal methods (prevent ovulation or implantation):
| Method | How it works | Effectiveness |
|---|---|---|
| Combined pill | Contains oestrogen + progesterone; stops FSH release → no egg matures → no ovulation | >99% |
| Progesterone-only pill | Thickens cervical mucus; may also stop ovulation | ~99% |
| Injection | Slow-release progesterone; lasts 8-13 weeks | >99% |
| Implant | Small rod inserted under skin; releases progesterone for up to 3 years | >99% |
| IUS | Inserted in uterus; releases progesterone locally for 3-5 years | >99% |
| Contraceptive patch | Releases oestrogen + progesterone through the skin | >99% |
Barrier methods (physically prevent sperm reaching the egg):
| Method | How it works | Additional benefit |
|---|---|---|
| Male condom | Thin sheath over the penis; collects sperm | Protects against STIs |
| Female condom | Inserted into vagina; lines it | Protects against STIs |
| Diaphragm/cap | Placed over the cervix; used with spermicide | Does not protect against STIs |
Other methods:
| Method | How it works |
|---|---|
| IUD (copper coil) | Copper device inserted in uterus; prevents implantation and is toxic to sperm; lasts 5-10 years |
| Spermicide | Chemical that kills sperm; used with barrier methods |
| Surgical sterilisation | Vasectomy (male) — sperm ducts cut; Tubal ligation (female) — oviducts cut or blocked; permanent |
| Natural family planning | Monitoring body temperature and cervical mucus to predict fertile days; avoiding intercourse during those days |
| Abstinence | Not having sexual intercourse; 100% effective |
Advantages and Disadvantages
Hormonal methods:
- Very effective
- Do not interrupt sex
- But: side effects possible (mood changes, headaches, weight gain, blood clot risk)
- Do NOT protect against STIs
- Must remember to take pills regularly
Barrier methods:
- Condoms protect against STIs
- No hormonal side effects
- But: less effective if not used correctly; can interrupt spontaneity
Surgical methods:
- Very effective and permanent
- But: difficult to reverse; permanent decision
Assisted Reproductive Technology
For couples who have difficulty conceiving:
- Clomifene — a drug that stimulates ovulation (given to women who do not ovulate regularly)
- IVF (covered in the endocrine system note) — eggs fertilised outside the body and implanted
Exam Tips
- Know at least one example of each type of contraception (hormonal, barrier, surgical)
- Only condoms protect against both pregnancy AND STIs — this is a common exam point
- Be able to evaluate different methods — weigh up effectiveness, side effects, convenience, and STI protection