The male reproductive system

Male reproductive structures and their function:

The female reproductive system

Female reproductive structures and their function:

Fertilisation is the?fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)

• It occurs in the?oviducts
• Gametes have?adaptations?to increase the chances of fertilisation and successful development of an embryo

Comparing sperm and egg cells

Comparison of Male & Female Gametes

• After fertilisation in the?oviduct, the zygote travels towards the?uterus
• This takes about 3 days, during which time the zygote will divide several times to form a ball of cells known as an?embryo
• In the uterus, the embryo embeds itself in the thick lining (implantation) and continues to grow and develop
• The gestation period for humans is?9 months
• Major?development of organs?takes place within the?first 12 weeks, during which time the embryo gets nutrients from the mother by?diffusion through the uterus lining
• After this point the organs are all in place, the?placenta?has formed and the embryo is now called a?fetus
• The remaining gestation time is used by the fetus to?grow bigger in size

The fetus in the uterus

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• The fetus is surrounded by an?amniotic sac?which contains?amniotic fluid?(made from the mother’s blood plasma)
• This protects the fetus during development by?cushioning it from bumps?to the mother’s abdomen
• The?umbilical cord?joins the fetus’s blood supply to the?placenta?for exchange of nutrients and removal of waste products

• During the gestation period the fetus develops and grows by gaining the?glucose, amino acids, fats,?water?and?oxygen?it needs from the mother’s blood
• The bloods run opposite each other, never mixing, in the?placenta
• The fetus’s blood connects to and from the placenta by the?umbilical cord
• The mother’s blood also absorbs the?waste?from the fetus’s blood in the placenta; substances like?carbon dioxide?and?urea?are removed from the fetus’s blood so that they do not build up to dangerous levels
• Movement of all molecules across the placenta occurs by?diffusion?due to?difference in concentration gradients
• The placenta is adapted for this diffusion by having a large surface area?and a?thin wall?for efficient diffusion
• The placenta acts as a?barrier?to prevent toxins and pathogens getting into the fetus’s blood
• Not all?toxin molecules?or?pathogenic organisms?(such as?viruses, eg?rubella) are stopped from passing through the placenta (this usually depends on the size of the molecule)
• This is why pregnant women are advised?not to smoke during pregnancy?as molecules like?nicotine?can pass across the placenta
• After the baby has been born, the?umbilical cord is cut?– this does not hurt as there are no nerves in it, just two blood vessels
• It is tied off to prevent bleeding and shrivels up and falls off after a few days leaving the belly button behind
• The placenta detaches from the uterus wall shortly after birth and is pushed out due to contractions in the muscular wall of the uterus - known as the?afterbirth

The placenta