Placenta, umbilical cord and amnion

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  • Placenta, umbilical cord and amnion
    • Placenta
      • begins to develop at implantation and after approximately 12 weeks, it is a thick, disc-like structure with finger-like projections called villi that extend deep into the wall of the uterus.
      • site of exchange by the process of diffusion
      • provides important adaptions for diffusion:
        • the rich blood system of the mother runs in a counter-current system to that of the foetus so there will always be a concentration gradient which allows diffusion into the foetal blood
        • the blood systems of the mother and foetus are close together, separated by a thin membrane but not joined, reducing the length of the pathway for diffusion
        • the villi provide a large surface area for exchange of dissolved nutrients, oxygen, carbon dioxide and urea
      • amnion contains amniotic fluid
      • umbilical cord:
        • umbilical artery: carries urea, carbon dioxide and other wastes back to the mother
        • umbilical vein: carries oxygen, glucose, amino acids and other nutrients from the mother to the foetus
    • exchange of materials by diffusion only takes place in the placenta
    • the role of the umbilical cord is the transport these materials to or from the foetus in the blood vessels of the umbilical artery and the umbilical vein
    • the amnion contains amniotic fluid which cushions the foetus, supporting it during development and protecting it against mechanical shock and temperature fluctuations


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