Sexual reproduction is a naturally gifted process by which human beings as well as other higher animals produce their offspring. This process involves the meeting of a male cell with a female cell to produce a fertilized egg which grows and develops into a new creature. The growth of a human body inside its mother’s womb, starting from the fertilization of cells till the birth, is a nine-month long process.
To begin with, a fertilized egg is formed by the union of male and female sex cells called sperm and ovum respectively. The fertilized egg is termed as zygote. It settles inside a specific place in the mother’s body called the uterus. Almost immediately after it is formed, the zygote begins to divide – and in less than 30 hours two cells are formed, called blastomers. These two cells are absolutely alike. The repeated cell division, rapidly increase the number of blastomers. But then all these cells are not alike. Some are muscle cells, some are bone cells some others are nerve cells, blood cells and so on. In short, all the different kinds of cells that make up a human body are present.
About two weeks after the fertilized egg begins to divide, the new cells start forming special body parts – the brain, heart and lungs etc. After about two months, the eyes, ears, a nose and a mouth start developing in the unborn baby. By this time it even has tiny legs and arms. It has a complete heart that beats and sends blood through its body. But it is surprising to note that even at this stage it is less than an inch long and weighs about one gram. Now its major function is to grow. At this stage it is called ‘foetus’. The foetus floats in the amniotic fluid surrounding it and receives nourishment through the umbilical cord.
For seven more months, the baby keeps developing in its mother’s body. The foetus grows at the rate of about 1.5 mm each day, doubling its length during the third month. It reaches almost half of its full-term length by the end of the fifth month, i.e. 25 cm (10 inches).
The weight gain begins in the seventh month when ordinary white fat gets deposited under the skin, all over the body. In addition to this, during the last few weeks in the womb, a special form of fat, called the brown fat, gets deposited across the shoulders and at other places on the upper body. By the end of the nine months (the normal pregnancy period) the foetus would probably weigh somewhere between 3 and 4 kg and be about 50 cm (20 inches) in length. This way the growth of a baby inside the mother’s womb reaches its completion and after birth a new life grows amongst us.