pregnancy

where does fertilisation occur

oviduct/fallopian tube

fertilisation definition

fusion of the sperm nucleus with the egg nucleus to form a diploid zygote

restores the diploid number of chromosomes

fertilisation process

sperm needs to penetrate the egg

sperm released enzymes from its acrosome to break down part of the egg membrane

only 1 sperm allowed to enter egg

implantation process

cilia lining the inner surface of oviduct sweep the zygote along the oviduct towards the uterus, aided by the peristaltic movements of the oviduct

how is the embryo formed

after the diploid zygote is formed, it divides (by mitosis) to form a ball of cells, called the embryo

when does implantation occur

day 7-8, embryo is embedded in the endometrium

when does the embryo reach the uterus

5 days for the embryo, which develops into a blastocyst, to reach the uterus

when does the embryo become the foetus

12-14 weeks, organs are fully formed, placenta and amniotic sac start to develop

blood supply of mother and foetus

not continuous, kept separate by placenta

blood group of mother and foetus may be different. if mixing of blood occurred, agglutination would occur, and is life threatening to mother and foetus

the blood pressure of the mother is much higher than the fetus, and if blood systems were continuous, the high pressure would kill the foetus

exchange of substances in the placenta

occurs via diffusion

useful molecules like oxygen and food substances (glucose, amino acids), will diffuse from the mother’s blood into the foetus’s blood

excretory and metabolic waste products (urea and carbon dioxide) will diffuse from the foetus’s blood into the mother’s blood

protective antibodies from the mother can diffuse from the mother’s blood into the foetus’s blood

placenta

organ of exchange that allows nutrient uptake, waste product elimination and gas exchange between the developing foetus and the mother’s blood supply

secretes progesterone

villi within the placenta

increases surface area to volume ratio which increases the rate of diffusion of various substances across the placenta

what is the umbilical cord consisted of

two umbilical arteries, transport deoxygenated blood and waste substances (eg. urea) away from the foetus towards the placenta

one umbilical vein, transport blood rich in nutrients (eg. glucose, amino acids) and oxygen from the placenta towards the foetus

amniotic sac

as placenta develops, an amniotic sac begins to form and encases the embryo

thin and transparent membrane that contains amniotic fluid and embryo

amniotic fluid

liquid that surrounds and cushions the foetus during pregnancy

amniotic fluid functions

1) protects the foetus by cushioning against blows (shock absorber)

2) allows the foetus to move freely during pregnancy

3) lubricates and reduces friction in the vagina or birth canal during birth