Organ development
Brain - The first thing to develop is the brain, around 18 days the neural tube, which
is the foundation of the spinal cord and brain, starts to form. By six weeks the brain is outgrowing the rest of the
body. As the month progresses the brain becomes more and more complex. From 29 weeks the baby is aware of their surroundings.
By 32 weeks the brain is as advanced as a newborn's. By the end of the pregnancy the babies brain has grown around 100 billion
neurons.
Heart - At around three weeks the baby's heart is a clump of cells the size of a seed.
It springs into life after 22 days. By six weeks it has compartments and valves. By week five the heart is pumping around
80 times a minute.
Lungs - Lungs appear at 4 weeks and have divided into segments by six. Around 4
months the blood vessels have formed. They get oxygen from the placenta so the air sacks stay closed but they practice breathing.
Digestive system - In week 4 they develop a basic digestive tract from the mouth to the
stomach. Then by week 8 it is fully developed.
Liver and kidneys - The first set of kidneys appear in week
4 but do not function, the second appear a few days later and filter blood for most of the second month. In the 5th week the
final set develop. By week nine the baby's kidneys produce urine and function fully. At this point the liver is creating
most of the red blood cells. By six months all of the organs are in place and they will continue to develop over the
next 3 months
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