Learning outcomes:
3.8
describe the structure and explain the function of the male and female reproductive systems - b
3.9
understand the roles of oestrogen and progesterone in the menstrual cycle
3.10
describe the role of the placenta in the nutrition of the developing embryo
3.11
understand how the developing embryo is protected by amniotic fluid
3.12
understand the roles of oestrogen and testosterone in the development of secondary sexual characteristics.
Male reproductive System:
male.GIF
Female reproductive system:
female.GIF

Pregnancy:

When the egg and sperm fuse (fertilisation) the resulting zygote begins to divide by mitosis (see next section) and becomes an embryo. The embryo quickly develops a placenta, which brings the mother’s blood supply very close to the foetus’ blood supply. The two blood streams never mix (otherwise the mother‟s white blood cells would attack the foetus!), but they are close enough for diffusion to occur.

Diffuse from foetus to mother - CO2, water, urea
Diffuse from mother to foetus - O2, glucose, amino acids, minerals
The placenta is adapted for diffusion in much the same way as other exchange organs, i.e. it has;

- Huge surface area (it has lots of villi-like projections)
- Only a few cells thick
- Blood supplies keep the concentration gradients high
- Counter-current system (this one is an A-level idea… look it up?!)

As well as the placenta the embryo also develops an amnion (membrane sac, which fills up with amniotic fluid). This helps cushion the embryo and protects it.

Reproductive Hormones:

During puberty boys make testosterone in their testes and girls make oestrogen in their ovaries.

Testosterone:
- Causes testes to drop & penis to enlarge
- Triggers spermatogenesis (sperm manufacture)
- Causes growth of pubic and body hair
- Causes larynx to enlarge (voice deepens)
- Causes muscles to grow

Oestrogen:
- Triggers menstruation to begin
- Causes maturation of vagina
- Causes breasts to grow
- Causes growth of pubic and body hair
- Causes hips to widen
menstr.GIF
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