Human reproductive organs, fertilisation and growth of the embryo
The testes make sperms; the ovaries make eggs. A sperm fertilises the egg in the fallopian tube, and the embryo grows in the uterus for about 280 days.
Male reproductive organs
| Organ | Job |
|---|---|
| Testes (two) | Make sperms and the hormone testosterone. They lie outside the abdomen in a pouch of skin, the scrotum. It is about 2 °C cooler than the body, and sperms need this lower temperature to stay alive. |
| Vasa deferentia (singular: vas deferens) | Two sperm ducts. Each carries sperms up from a testis into the body; they join to form the ejaculatory duct. |
| Ejaculatory duct and urethra | Lead the sperms out. The urethra is the common passage for urine and sperms. (Your NIOS lesson's table gives this job to the ejaculatory duct, which in fact opens into the urethra.) |
| Penis | A muscular organ that transfers sperms into the female body |
Female reproductive organs
| Organ | Job |
|---|---|
| Ovaries (two) | Make ova (eggs) and the hormones oestrogen and progesterone. A girl is born with a fixed number of immature eggs, which begin to mature at puberty. |
| Fallopian tubes (two oviducts) | Carry the egg from the ovary to the uterus; fertilisation happens here |
| Uterus (womb) | The embryo implants and grows here |
| Cervix | The narrow opening, or neck, of the uterus |
| Vagina | The passage from the cervix to the outside |
From fertilisation to birth
- 1Gametes: sperms are made in the testes, and an egg (ovum) matures in an ovary under FSH from the pituitary.
- 2LH from the pituitary makes the ovary release the egg, which enters the fallopian tube.
- 3★Fertilisation: a sperm meets the egg in the fallopian tube, and their nuclei fuse inside the egg. The fertilised egg is the zygote.
- 4The zygote divides again and again as it moves down, forming a ball of cells with a cavity, the blastocoel.
- 5This ball embeds (implants) in the thick, blood-rich wall of the uterus. It is now the embryo, and later the foetus.
- 6The foetus grows inside the uterus for about 280 days (about nine months), taking food and oxygen from the mother's blood through the uterus wall.
- 7Birth: the hormone oxytocin, from the posterior pituitary, makes the uterus contract, and the baby is born.
★ key step
Hormones of reproduction
- FSH (follicle stimulating hormone, from the anterior pituitary): makes an egg mature in the ovary.
- LH (luteinising hormone, from the anterior pituitary): makes the ovary release the egg. Your NIOS lesson links LH with the thickening of the uterus lining; that lining is in fact built up by oestrogen and progesterone from the ovary.
- Oestrogen and progesterone (from the ovaries): bring the female secondary sexual characters.
- Testosterone (from the testes): brings the male secondary sexual characters.
- Oxytocin (from the posterior pituitary): makes the uterus contract to deliver the baby.
- If the egg is not fertilised, it breaks down, and the thickened lining of the uterus is shed in menstruation. Periods stop during pregnancy because the embryo is attached to that lining.
How to draw the human reproductive systems
- Male: draw the urinary bladder as a rounded bag at the top centre. Draw the urethra running down from it through the penis.
- Below, draw the scrotum as a pouch holding an oval testis.
- Draw the vas deferens as a tube looping up from the testis, over the bladder, and joining the urethra through the ejaculatory duct. Glands that add fluid (the seminal vesicle and prostate) may also be shown.
- Female: draw an upside-down, pear-shaped uterus in the centre.
- From each upper corner, draw a curved tube, the fallopian tube (oviduct), ending in a funnel near an oval ovary.
- Mark the narrow lower end of the uterus as the cervix, and draw the vagina below it. Label every part in both diagrams.
Pregnant women are advised regular check-ups, a nutritious diet and iron tablets, because the growing baby takes its food and oxygen from the mother's blood. Government health centres in India offer these check-ups and tablets.
1 marks: “Where does fertilisation take place in the human female?” In the fallopian tube (oviduct).
2 marks: “Why do the testes lie in the scrotum, outside the abdomen?” Sperms are formed and stay alive at a temperature about 2 °C lower than body temperature. The scrotum keeps the testes cooler.
3 marks: “List, in order, the events from fertilisation to the birth of a baby.” The egg is released into the fallopian tube; a sperm fuses with it to form a zygote; the zygote divides into a ball of cells; it implants in the uterus wall as an embryo, then a foetus; it grows for about 280 days; oxytocin makes the uterus contract, and the baby is born.
Path of the egg: Ovary → Fallopian tube → Uterus → Cervix → Vagina. Fertilisation happens on the way, in the fallopian tube.