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A single sperm penetrates the mother’s egg, this cell is called a zygote.As it travels down the Fallopian tube the zygote divides to form a ball of cells.When it has formed a group of inner cells with an outer shell it is called a “blastocyst”.The inner cells eventually become the embryo while the outer group of cells become the membranes that nourish and protect it.
By the 6th day the blastocyst implants into the uterine wall and sticks here tightly, by this time the lining of the uterus has grown and is ready to provide nourishment via the mother’s blood stream. It puts down tiny roots which eventually become the placenta.
The cells of the embryo divide rapidly and begin to take on specific functions, this process called differentiation produces the varied cell types that make up a human being.Three layers of cells develop; the ectoderm, the endoderm and the mesoderm.
The amniotic sac is formed. The neural tube should close by the end of week 4, if it does not close properly spinal cord defects occur. By the 5th week the main parts of the brain; the forebrain, midbrain and hindbrain, develop further. Arm and leg buds are visible.
Feet and hands can be seen to develop. The tiny heart will start to beat rapidly. Beginning of formation of the lungs. ‘Reflex’ motion starts.By the end of the sixth week the basic development of the five brain vesicles is complete.
By the end of the 8th week of gestation (10th week of pregnancy) the basic components and organs of your baby are formed, the blueprint for your baby is complete. Facial features including external features of ears develop. Between 8 to 10 weeks all of the basic parts of the brain are in place.
The fetus reaches a length of about 3.2 inches. Eyes are formed but not ‘connected’ by the visual cortex. The first synapses start to form in the brain. The head is now half the size of the fetus. The fetus can make a fist with its fingers. ‘Deliberate’ motion starts.
The fetus reaches a length of about 6 inches.Lanugo (fine hair) develops on the head. Some bodily functions will start now, such as swallowing and urination. Taste buds are forming, baby can ‘taste’ amniotic fluid. The brain is multiplying at a rate of 250,000 cells per minute.
The fetus reaches a length of about 8 inches. The ears are fully formed; ‘hearing’ is possible. Lanugo covers the entire body. The fetus responds to touch around week 22. A waxy substance ‘vernix’ is covering its skin to stop it getting waterlogged by amniotic fluid. The mother can usually feel the fetus move.
The fetus reaches a length of 11.2 inches. Eye components are well developed. The myelination process begins; this means that the axons (the ‘wires’ that connect the brain cells) gain their fatty protective covering.
The fetus reaches a length of 15 inches.From week 25 the brain undertakes another phase of rapid growth. Eyes will open and start blinking around week 26. Nervous system is developed sufficiently to control some body functions. A baby born at this time has a 90% chance of survival.
The fetus reaches a length of up to 17 inches. (between 15 – 17). From week 28 the fetus is swallowing up to a litre a day of amniotic fluid. Around week 29 apoptosis begins; the brain's natural ‘pruning’ process. Rapid breathing movements occur. By week 32 nearly every part of the body is sensitive to heat, cold, pressure and pain. The fetus begins storing iron, calcium and phosphorus.