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Reproduction

A quick re-visit to your high-school biology class.

At birth, the ovaries of every baby girl contain almost half a million single-cell eggs, each of these is a potential human life. These eggs do not ripen until the menstrual cycle begins at puberty. During ovulation, an egg is released from an ovary and is drawn into the fallopian tube to travel towards the womb. When a man ejaculates during sexual intercourse he deposits semen, that contain millions of sperm, into the woman’s vagina.

The sperm must be vigorous enough to be able to leave the vagina for the cervix and uterus as soon as possible. In the acid environment of the vagina, they can perish quickly. In the cervix, they can survive in the mucus for five or six days. Only 2,000 or so sperm survive the journey up through the vagina, cervix and womb into the fallopian tubes.

Only one sperm can penetrate the outer layers of the egg and fertilise it. When this occurs, chemical changes triggered by enzymes prevent the entry of any other sperm.

As the nucleus of the sperm fuses with the nucleus of the egg to make one single cell, your baby’s entire genetic coding is determined for life.

This one cell, called a zygote, contains 23 chromosomes supplied by the egg and 23 chromosomes supplied by the sperm. As the cell begins to rapidly multiply it becomes a cluster of cells called a morula, the Latin word meaning “mulberry”. It travels towards the womb and floats about for a few days before it is ready to embed itself in the endometrial tissue of the womb wall. Here it will stay for nine lunar months, miraculously developing into a tiny human in preparation for birth.

During each lunar month in a menstruating woman’s life, her body prepares for pregnancy. As an egg is released and travels down the fallopian tubes towards the womb, hormones instruct the lining of the womb to thicken and blood flow to increase in anticipation of receiving a fertilised egg. Most women become aware of this as the abdominal area and breasts swell and emotional levels fluctuate.

Throughout a woman’s childbearing years, she may carry as many as 4,000 ripe eggs, but usually only one a month reaches maturity and is capable of being fertilised. Only some 375 eggs mature throughout a woman’s lifetime.

If the egg is not fertilised within a few days, it is shed, along with the lining of the uterus, during menstruation. Usually, eggs are released from alternate ovaries each month although sometimes one ovary may become more active for a few months. Occasionally, one ovary may not be functioning, or perhaps an ovary or part of the fallopian tube has been surgically removed. In both these cases, the other ovary will take over.    

   
   

   




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