The Female Reproductive System Part II

In the reproductive cycle, both men and women produce gametes or reproductive germ cells. Females produce gametes known as ova (singular ovum) that are larger than male gametes (spermatozoon). The presence of both gametes is required for fertilization to take place.

Fertilization is caused by the fusion of gametes i.e. the fusing of a sperm with an ovum, eventually leading to the development of an embryo. The process of fertilization and nurturing the embryo till it is developed enough to be born, is the role of the female reproductive system.

Briefly, this is how it works.

Both males and females have gonads or sexual organs which are different in shape and structure and without which reproduction would not be possible. In the male, the gonads refer to the testicles and in the female, the ovaries. Unlike the male, the female's reproductive system is internal and is housed entirely within the pelvic area.

A woman is born with her entire supply of egg cells (around 400,000) which are contained in the ovaries and remain inactive until she approaches puberty. At this time, the pituitary gland which is situated in the central section of the brain starts producing hormones that stimulate the ovaries into producing female sex hormones that cause her to become sexually mature.

Nearing the end of puberty, as part of a monthly period known as her menstrual cycle, during ovulation, one of her ovaries releases a single egg into one of her fallopian tubes. This is where the sperm fuses with the ova and fertilization takes place. If fertilization does not take place, then the ovum is expelled from the body through the uterus in a process called menstruation or period. The menstrual flow consists of tissues and blood from the inner lining of the uterus or endometrium and lasts for around 3 to 5 days in most cases. The range for the monthly cycle is between 23 to 35 days, but on an average is usually 28 days.

The ovaries produce the hormone estrogen that causes the endometrium to thicken and become rich with blood in anticipation of fertilization being successful. During intercourse, the male inserts his penis into the female's vagina and when he ejaculates, he deposits semen consisting of seminal fluid and between 75 to 900 million sperm into the vagina. Each sperm consisting of a head and a lashing tail that helps it swim, races up the vagina, through the cervix and uterus and up the fallopian tube to the waiting ovum. Only one of the millions of sperm will be able to successfully fuse with the ovum and successfully fertilize the egg. The fertilized egg is known as a zygote.

The ovaries produce the hormone progesterone to keep the uterus lining thick and blood-rich and about a week after fertilization, the zygote develops into a multicelled unit known as a blastocyst that burrows and fuses with the lining of the uterus. This fusing-with-the-endometrium process is known as implantation and the blastocyst uses the endometrium to draw all the nutrients it requires.

As the blastocyst continues to get nourished, it enters into a new stage of development i.e. the embryonic stage. The inner cells of the blastocyst transform into what is known as the embryonic disk which will eventually form into a baby. The outer cells change into thin membranes that surround the embryonic disk. The disk cells multiply thousands of times over and shift to new positions to form the embryo. Around eight weeks later, the embryo though still tiny, has developed and formed most of its parts including the brain, nerves, heart, blood, stomach, intestines, muscle and skin.

The embryo now enters the fetal stage which lasts up to delivery and continues to grow and develop. It exists inside the amniotic sac which contains amniotic fluid that acts as a shock absorber and receives its nourishment and oxygen from the mother’s blood through the placenta and the umbilical cord that connects it to the lining of the uterus.

Pregnancy normally lasts for up to nine months at the end of which the baby is fully formed and ready to exit from the womb. The pituitary gland produces the hormone oxytocin which encourages the uterus walls to contract in order to push the baby out. This process is known as labor contractions. With the contractions the baby’s head begins to press on the cervix which starts to expand to let it through to the vagina. The mucus that had plugged the cervix to keep the uterus sterile, starts getting loose and when the ‘mother’s water breaks’ comes out through the vagina along with the amniotic fluid and the baby. The umbilical cord connecting the baby to the mother is cut. After the baby is born, the contractions continue (a process known as the afterbirth) until the placenta and all remaining membranes and fluid are also expelled and the birthing process is complete.