Human Reproduction

Human Reproduction

Human reproduction is any form of sexual reproduction resulting in the of a child, typically involving sexual intercourse between a man and a woman .

The male reproductive is made up of a pp system contains two main divisions: the penis, and the testes, the latter of which is where sperm are produced. In humans, both of these organs are outside the abdominal cavity.

The female reproductive system likewise contains two main divisions: the vagina and uterus, which act as the receptacle for the semen, and the ovaries, which produce the female's ova. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the fallopian tube into the uterus.

Pregnancy is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta, which is attached to the fetus' abdomen via an umbilical cord. This drain of nutrients can be quite taxing on the female, who is required to ingest slightly higher levels of calories. In addition, certain vitamins and other nutrients are required in greater quantities than normal, often creating abnormal eating habits.

The ovum is picked up by the fallopian tube on the same sideEvery month a mature ovum is released from either one of a woman’s two ovaries. (There are two fallopian tubes on either side of the uterus near the ovaries. See image ). The tubes have long fingerlike projections called fimbria which it uses, rather like hands to pick up the ovum.

The ovum then moves through the tube, propelled along by long hairs growing from cells in the tubes. Intercourse has to take place within this narrow time frame (1-2 days before ovulation

or immediately after ovulation), for a pregnancy to occur. At every intercourse a normal man deposits 2 – 5 mililitre of semen in the upper part of the vagina (see diagram). Each mililitre of semen normally contains about 50 – 200 million of sperms.

All the sperm deposited in the vagina cannot swim into the uterus. Some die off in the vagina, some get entangled in the cervical mucous and some manage to swim just into the cervix before dying. But it is believed that even these sperms help in causing pregnancy by changing the acidity (‘ph’) of the vagina or by acting on the cervical mucous so that other sperms can penetrate it and reach the ovum.

Only about 1 % of the total number of sperms deposited in the vagina make the journey. Hundreds of sperm (estimated to be around 300) surround the ovum in the tube. They press against the membrane of the ovum attempting to penetrate it and fertilize the ovum. Finally one sperm succeeds. At once a chemical reaction is triggered off in the wall of the ovum, making it impenetrable to any other sperm. No other sperm can enter the ovum now.

Theoretically, it is from the 2-celled to the 16-celled stages that the cells can be separated from each other and allowed to develop into clones of each other (identical twins).

The development of the embryo continues until at the end of 9th months of pregnancy (40 weeks or 280 days), a fully formed baby, capable of leading a life independent from its mother is ready to be born.