B3 Topic 1 The Menstrual Cycle and Reproductive cycle

Sperm: The function is to transport the male DNA to the female egg so that the DNA can combine. 

Adaptations of a sperm cell: They are small, but have a long tail to drive the sperm forward. They don't have much cytoplasm so they have less mass which means they can swim faster. The nucleus is haploid so it only has one copy of each chromosome. Mitochondria releases energy by breaking down the glucose so that the driving of the tail can be done and it occurs in the mid-section. Acrosome contains enzymes to digest the egg cell membrane so the sperm can penetrate the outer layers surrounding the eggs. 

Egg cell: The main function is to carry the female DNA and to nourish the developing embryo. 

Adaptations of egg cells: In the cytoplasm, there is nutrients so that the embryo can develop after fertilisation, but before it attaches to the uterus wall. A nucleus which is haploid so that when the egg is fertilised the resulting cell will have the right amount of chromosome. Granules are behind the cell membrane so that it changes the structure after fertilisation so not other sperm can penetrate the egg cell and kill the egg. 

Stages of Fertilisation:

1. The sperm cell and the egg cell are haploid so they have half the numbers of chromosomes.

2. When the sperm reaches the egg, the acrosomes release the enzymes so that it can break down the cells surrounding the egg so that the sperm can penetrate.

3. When the head reaches the cytoplasm, the tail and the mid section breaks off and the head enters the cytoplasm.

4. The granules release a substance behind the egg membrane so that no other sperm can enter.

5. The nucleus of the sperm head is released and passes through the cytoplasm to the egg nucleus. The sperm cell an egg cell fuse and a zygote are formed.

Menstrual cycle 

Hormones involved: 

FSH: stimulates the maturation of the egg follicles. (Follicles is an egg surrounded by cells). It also stimulates oestrogen production. 

Oestrogen: stimulates the growth and repair of the uterus lining so it causes it to thicken and grow and the development of the follicles. A high level of oestrogen stimulates a LH surge.

LH: the surge stimulate or triggers ovulation at day 14. The follicle ruptures and the egg is released. It also stimulates the remains of the follicle to develop into the structure called a corpus luteum- which secrets progesterone 

Progesterone:  maintains the thickness of the uterus lining and inhibits the production of FSH and LH. When the level of progesterone falls and there's a low oestrogen level, the uterus lining breaks down. A low progesterone level allows FSH to increase so the cycle starts again. 

Day 1-7: FSH is released from the pituitary gland which stimulates the maturation of the egg follicles. The maturation of the follicles stimulates oestrogen production which stimulates the growth and repair of the uterus lining and stimulates…