Fertilisation and pregnancy
Fertilisation is the fusion of a A cell that contains half the normal number of chromosomes. The male sex cell or gamete. nucleus and a haploid The female reproductive cell. nucleus to form a A cell that contains the normal number of chromosomes. (normal chromosome number) zygote.
A zygote is the first cell of a new individual. Fertilisation occurs in the A tube in the female reproductive organ through which an egg passes from an ovary to the uterus..
After fertilisation:
- The zygote travels down the oviduct dividing by A type of cell division that produces cells that are genetically identical to the parent cell and to each other. to form a ball of cells An organism in the early stages of development..
- When the embryo reaches the Also known as a womb. This is where the fertilised egg (ovum) develops., implantation occurs. This is when the embryo attaches to the thick uterus lining to receive nourishment.
- The The organ in the uterus of pregnant mammals that allows the transfer of nutrients and waste products between the mother and the fetus through the umbilical cord., The cord that connects the foetus to the placenta. It contains blood vessels., Bag surrounding the foetus in the uterus and containing the amniotic fluid. and The fluid surrounding a foetus that cushions it. form.
- The embryo When a cell becomes different in order to carry out a particular function. to produce a variety of tissues and organs.
- The embryo is referred to as a foetus when it begins to look more like a baby.
Placenta and umbilical cord
The placenta allows substances to The random movement of a substance from a region of high concentration to a region of low concentration from the mother’s blood to the foetus (e.g. oxygen and glucose).
Substances can also diffuse from the foetus to the mother’s blood (e.g. carbon dioxide and A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine.).
The placenta is adapted for diffusion by having:
- A large surface area between it and the uterus wall.
- Villi (finger like projections that extend into the uterus wall), which further increase the surface area of the placenta.
- A good blood supply.
The umbilical cord attaches the placenta to the foetus. It contains the umbilical artery and the umbilical vein.
The umbilical artery carries urea and carbon dioxide from the foetus to the mother’s blood.
The umbilical vein carries oxygen and nutrients from the mother’s blood to the foetus.
Belonging to the mother. blood and Belonging to the foetus. blood systems are close together but not joined. They are separated by thin membranes that allow diffusion to occur.
Amnion and amniotic fluid
The amnion is a membrane that forms around the embryo.
Amniotic fluid surrounds the embryo inside the amnion, cushioning and protecting the developing embryo.