How do Organisms Reproduce? · Lesson 12 of 14
Female Reproductive System
“Egg release, fertilisation and development each have their own address.”
• Identify the main female reproductive organs. • Trace egg and sperm movement. • Distinguish ovulation fertilisation and implantation. • Explain embryo and foetus development. • Describe placental exchange. • Explain the role of the uterus and birth contractions.
The female reproductive system produces eggs, receives sperm and provides a protected environment in which an embryo can implant and develop. Each stage occurs at a particular location.
Ovaries Oviducts And Uterus
Ovaries contain immature eggs from birth and produce reproductive hormones. After puberty, usually one egg matures and is released during a cycle. The egg enters an oviduct or fallopian tube. The two oviducts connect to the uterus, a muscular elastic organ that opens through the cervix into the vagina.
| Part | Main role |
|---|---|
| Ovary | Produces and releases eggs; produces hormones |
| Fallopian tube | Carries egg; usual site of fertilisation |
| Uterus | Receives implanted embryo and supports development |
| Cervix | Lower opening of uterus |
| Vagina | Receives sperm and forms the birth passage |
Ovulation Fertilisation And Implantation
Ovulation is the release of a mature egg from an ovary.
Implantation is the attachment and embedding of an early embryo in the thickened uterine lining.
Sperm deposited in the vagina move through the cervix and uterus toward an oviduct. If a sperm fuses with the egg there, fertilisation forms a zygote. The zygote divides repeatedly while travelling toward the uterus, becoming an embryo. Implantation occurs when the embryo embeds in the prepared uterine lining.
Placenta And Development
The placenta is a disc-like exchange organ attached to the uterine wall. Embryonic villi project into spaces supplied with maternal blood, producing a large surface. Oxygen, glucose and other nutrients cross toward the embryo, while carbon dioxide and other wastes cross toward maternal blood. The two blood supplies are brought close but do not simply mix freely.
The placenta is a temporary exchange organ connecting the developing embryo with the uterine environment for transfer of nutrients, gases and wastes.
As organs develop, the embryo is called a foetus. Development inside the uterus takes about nine months. At birth, coordinated rhythmic contractions of uterine muscles help push the baby through the cervix and vagina.
Problem
Arrange ovulation, fertilisation, implantation and development.
- 1.Ovulation releases an egg from an ovary.
- 2.Fertilisation may occur in the fallopian tube.
- 3.The dividing embryo travels to the uterus.
- 4.Implantation embeds it in the uterine lining.
- 5.Continued development produces a foetus.
Problem
Sperm reach the uterus but cannot enter either fallopian tube. Which step is directly prevented?
- 1.The egg normally lies in or moves through a fallopian tube.
- 2.Fertilisation usually occurs there.
- 3.Sperm cannot reach the egg.
- 4.Fertilisation is therefore prevented, even though sperm entered the uterus.
Problem
Why does the placenta have villi surrounded by maternal blood spaces?
- 1.Villi create a very large surface area.
- 2.Thin exchange barriers bring embryonic and maternal circulations close.
- 3.Concentration differences drive transfer of gases and dissolved materials.
- 4.Large area supports sufficient nutrient supply and waste removal without free blood mixing.
Fertilisation and implantation are different. Fertilisation forms the zygote, usually in a fallopian tube; implantation happens later in the uterus.
Quiz
Where does fertilisation usually occur?
What is ovulation?
Where does implantation occur?
What is a key placental function?
What causes birth movement?
Practice Problems
- Trace an egg from ovary to uterus.
- Distinguish ovulation, fertilisation and implantation.
- Trace sperm to the usual site of fertilisation.
- Explain four adaptations or functions of the placenta.
- Predict the consequence if implantation occurs but placental exchange remains poorly developed.
Key Takeaways
• Ovaries produce and release eggs. • Fallopian tubes carry eggs and are the usual fertilisation site. • The uterus supports implantation and development. • Ovulation fertilisation and implantation are separate events. • A zygote divides to form an embryo. • The placenta provides a large exchange surface. • Maternal and embryonic blood do not freely mix. • Uterine contractions help accomplish birth.