A LIFE INTO A LIFE 

Fertilization and development of foetus 

FERTILIZATION 

 It is the union of human egg and sperm occurring in the fallopian tubes.

 The result of this union is the production of a zygote cell or fertilized egg.

The sperm on entering the female reproductive system releases enzymes from its acrosome region present in the head region that disintegrates the corona radiata and zona pellucida layer of the ovum, thereby out of million sperms, only one sperm fuses with the female pronucleus.

The sperm head containing the nucleus enters the ovum, thereby degenerating the middle piece and the tail region.

* video of fertilization *

IMPLANTATION 

After fertilization, the fertilized egg propels through the tube towards the uterus.

The cells of the zygote divide repeatedly as the zygote moves down the fallopian tube.

The zygote enters the uterus in 3 to 5 days .

In the uterus, the cells continue to divide, becoming a hollow ball of cells called a blastocyst.

Between 5th and 8th day after fertilization, the blastocyst attaches to the lining of the uterus, usually near the top.

This process is called Implantation, is completed by 9th or 10th day.

DEVELOPMENT OF BLASTOCYST

•  The wall of  blastocyst is one cell thick except in one area, where it is three or four cells thick.
• The inner cells develop into an embryo and the outer cells burrow into the wall of the uterus and develop into placenta.
• The placenta produces several hormones that help maintain the pregnancy.
• The placenta also carries oxygen and nutrients from mother to foetus and waste materials from foetus to mother.
• Some of the cells from placenta form an outer layer chorion around the developing blastocyst.
• Other cells develop into an inner layer amnion, which forms the amniotic sac.
• The amniotic sac fills with an amniotic fluid and expands to envelope the developing embryo, which floats within it.

DEVELOPMENT OF EMBRYO

•  The next stage in development is the embryo, which develops within the amniotic sac, under the lining of the uterus on one side.
• This stage is characterized by the formation of most internal organs and external body structures.
• Most organs form to begin to form about 3 weeks after fertilization, which equals 5 weeks of pregnancy.
• At this time, the embryo elongates, first suggesting a human shape.
• Shortly, thereafter, the area that will become the brain and spinal cord begin to develop.
• The heart and blood vessels begin to develop earlier by about Day 16.

Embryo at 8 weeks 

DEVELOPMENT OF FOETUS AND PLACENTA 

• At the end of the 8th week after fertilization, the embryo is considered a foetus.
• During this stage, the structures that have already formed grow and develop.
• By 12 weeks of pregnancy- the foetus fills the entire uterus.
• By about 14 weeks - the sex is identified.
• By about 16-20 weeks - typically the pregnant woman can feel the foetus moving.
• Women who have been pregnant before typically feel movements about 2 weeks earlier than women who are pregnant for the first time.
• By about 24 weeks- the fortus has a chance of survival outside the uterus
• The lungs continue to mature until near the time of delivery
• The brain accumulates new cells throughout pregnancy and the first year of life after birth.
• As, the placenta develops, it extends tiny hair like projections into the wall of the uterus.
• The projections branch and rebranch in a complicated treelike arrangement.
• This arrangement greatly increases the area of contact between the wall of the uterus and the placenta, so that more nutrients and waste materials can be exchanged.
• The placenta is fully formed by 18 to 20 weeks but continues to grow throughout pregnancy.
• At delivery, it weighs about 1 pound.

PARTURITION

Parturition, also called birth or childbirth, process of bringing forth a child from the uterus or womb.

It takes place after the gestation period of 9 months.

Stages of pregnancy in the mother's womb ..... * this video will help you to understand the stages of foetal development *

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