Genes and Inheritance PDF

GENES AND INHERITANCE. 1 2 3 4 5 6 7 8 9 10 11 12 13 14  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...

GENES AND INHERITANCE. 1 2 3 4 5 6 7 8 9 10 11 12 13 14  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 foetus The remaining gestation time is used by the fetus to grow bigger in size The gestation period for humans is 9 months 15  The fetus is surrounded by an amniotic sac which contains amniotic fluid (madez 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 16  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. 17 18 19 20 21