Unit 12 Reproduction in humans
Key unit competence: Analyse the process of reproduction, pregnancy and childbirth in humans and the care needed for a healthy mother and baby.
Key ideas
- Male reproductive system: testes (make sperm and the hormone testosterone) in the scrotum (keeps them cooler than body temperature); epididymis (stores sperm); sperm duct (vas deferens); seminal vesicles, prostate gland and Cowper's gland (make fluids that nourish and carry sperm, forming semen); urethra and penis.
- Female reproductive system: ovaries (make ova and the hormones oestrogen and progesterone); oviducts (fallopian tubes) (carry the ovum; fertilisation happens here); uterus (womb, where the embryo develops; lined by the endometrium); cervix (neck of the uterus); vagina (birth canal).
- Gametes: the sperm has a head with a haploid nucleus and an acrosome (enzymes to penetrate the ovum), a middle piece with many mitochondria, and a tail for swimming. The ovum is large, with a haploid nucleus, cytoplasm with food stores and a jelly coat.
- The menstrual cycle (about 28 days): days 1–5 menstruation (lining shed); oestrogen rebuilds the lining; ovulation about day 14 (an ovum is released, triggered by LH); progesterone keeps the lining thick; if no fertilisation, progesterone falls and menstruation starts again. FSH from the pituitary stimulates follicle growth.
- Fertilisation: a sperm fuses with the ovum in the oviduct, forming a diploid zygote. The zygote divides by mitosis into a ball of cells (embryo) that moves to the uterus and implants in the endometrium about a week later.
- Pregnancy (gestation) lasts about 40 weeks (9 months). The placenta (from embryo and uterus tissues) allows exchange: oxygen, glucose, amino acids, antibodies pass from mother to fetus; CO₂ and urea pass from fetus to mother. Blood of mother and fetus does not mix. The umbilical cord connects the fetus to the placenta; the amnion and amniotic fluid protect the fetus from shocks.
- The placenta also makes hormones (progesterone) that maintain pregnancy, and acts as a barrier to some pathogens. Some harmful substances still cross: alcohol, nicotine, some drugs and viruses such as HIV and rubella.
- Childbirth (labour): the hormone oxytocin causes strong contractions of the uterus; the cervix dilates; the baby is pushed out head first; then the placenta (afterbirth) is expelled. Delivery should be in a health facility with skilled attendants.
- Antenatal care: regular check-ups (at least four visits, more now recommended), balanced diet rich in iron, folic acid, calcium and protein, tetanus vaccination, HIV testing and PMTCT, malaria prevention (nets), no smoking or alcohol, rest. Postnatal care: exclusive breastfeeding for six months (antibodies, perfect nutrition), vaccination of the baby, family planning, check-ups for mother and baby.
Common misconceptions
- "Fertilisation happens in the uterus." No: fertilisation usually happens in the oviduct; the embryo then implants in the uterus.
- "Mother's blood flows into the baby." No: maternal and fetal blood are separate; substances are exchanged by diffusion and active transport across the placenta.
- "A woman can only get pregnant during menstruation." No: the most fertile time is around ovulation, mid-cycle.
- "Drinking a little alcohol in pregnancy is harmless to the baby." No: alcohol crosses the placenta and can damage the developing brain.
Worked examples
Example 1. Explain how the placenta is adapted for exchange between mother and fetus.
Solution
It has many villi giving a large surface area; the barrier between maternal blood and fetal capillaries is thin (short diffusion distance); there is a rich blood supply on both sides keeping a steep gradient; maternal blood flows in spaces around the villi, so the two bloods stay separate.
Example 2. Explain why menstruation stops when a woman becomes pregnant.
Solution
After implantation the embryo and placenta produce hormones that keep progesterone levels high. Progesterone keeps the endometrium thick so the embryo can develop; since the lining is not shed, menstruation does not occur, and no new ovum is released.
Practice questions
Name four parts of the male reproductive system and give the function of each.
Show answer
Testes: make sperm and testosterone. Scrotum: keeps testes cool. Sperm duct: carries sperm. Prostate/seminal vesicles: make fluid for semen. Urethra: carries semen out. Penis: deposits sperm.
Common mistake: Saying the prostate makes sperm.
Name four parts of the female reproductive system and give the function of each.
Show answer
Ovaries: make ova and hormones. Oviducts: carry ovum, site of fertilisation. Uterus: where the embryo develops. Cervix: neck of uterus, dilates in birth. Vagina: receives sperm, birth canal.
Common mistake: Saying fertilisation occurs in the ovary.
Describe how a sperm is adapted to its function.
Show answer
Tail for swimming; middle piece with many mitochondria for energy; acrosome with enzymes to penetrate the ovum; haploid nucleus carrying genes; small and streamlined.
Common mistake: Saying the sperm has chloroplasts.
Outline the main events of a 28-day menstrual cycle.
Show answer
Days 1–5 menstruation; oestrogen rebuilds the lining; ovulation about day 14; progesterone keeps lining thick; if no fertilisation, progesterone falls and menstruation begins again.
Common mistake: Placing ovulation on day 1.
State four functions of the placenta.
Show answer
Passes oxygen and food to the fetus; removes CO₂ and urea; passes antibodies; produces hormones (progesterone); acts as a barrier to some pathogens.
Common mistake: Saying blood flows directly from mother to fetus.
State four practices of good antenatal care.
Show answer
Regular check-ups; balanced diet with iron and folic acid; tetanus vaccine; HIV test and PMTCT; sleeping under a net; avoid alcohol, smoking and drugs; rest.
Common mistake: Advising to stop eating to keep the baby small.
State three advantages of breastfeeding.
Show answer
Complete nutrition; contains antibodies; clean and at correct temperature; free; promotes bonding; helps the uterus return to normal.
Common mistake: Saying formula is always better.
Describe what happens during childbirth.
Show answer
Oxytocin causes uterus contractions; the cervix dilates; the amnion breaks; the baby is pushed out head first through the vagina; the umbilical cord is tied and cut; the placenta is expelled.
Common mistake: Forgetting the placenta (afterbirth).
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The embryo develops in the: a. implantation 2. Which substance can cross the placenta and harm the fetus? b. iron 3. A nutrient especially important in pregnancy to prevent anaemia is: c. uterus 4. The attachment of the embryo to the uterus wall is: d. Alcohol Show answer
1 → c (uterus) · 2 → d (Alcohol) · 3 → b (iron) · 4 → a (implantation)
- It implants in the endometrium.
- Nicotine and some drugs also cross.
- The mother's blood volume increases.
- It happens about a week after fertilisation.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
protects the fetus from shocks · store urine before it leaves · keep them cooler than body temperature · sperm duct (vas deferens)- Amniotic fluid .
- The tube that carries sperm from the testis towards the urethra is the .
- The scrotum holds the testes outside the body to .
Show answer
1: protects the fetus from shocks · 2: sperm duct (vas deferens) · 3: keep them cooler than body temperature
- The fetus floats in it.
- Vasectomy cuts this tube.
- Sperm develop best slightly below 37 °C.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Ovulation in a 28-day cycle happens around day: a. testes 2. Human pregnancy lasts about: b. oviduct 3. Sperm are produced in the: c. 14 4. Fertilisation normally takes place in the: d. 40 weeks Show answer
1 → c (14) · 2 → d (40 weeks) · 3 → a (testes) · 4 → b (oviduct)
- An ovum is released.
- About nine months.
- The testes also make testosterone.
- The zygote then moves to the uterus.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
umbilical cord · oxytocin · ovaries · testosterone- Ova are produced in the .
- The hormone that causes strong contractions during labour is .
- The structure joining the fetus to the placenta is the .
Show answer
1: ovaries · 2: oxytocin · 3: umbilical cord
- Usually one ovum per cycle.
- It is released by the pituitary.
- It contains blood vessels.