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0-2 weeks

shortest of the stages of the human lifespan

begins with fertilization and ending with implantation

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union of sperm cell and egg cell

contains 23 chromosomes from sperm and 23 chromosomes from ova

begins as a single cell but divides rapidly

takes on spherical shape known as morula

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morula has 64 cells

turns into blastocyst

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inner mass becomes embryo

outer cell becomes placenta

implants itself in endometrium

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3-8 weeks

period after implantation

all of the major organs and structures are formed

once fully formed, it expands, grows, and continues to develop

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embryo is only around 2cm long by the end of this stage

many of the internal and external organs and systems are formed

brain and spinal cord are almost complete by the end of it

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during this stage internal sex organs will begin to form

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occurs from center of body in an outward direction

evident in 32 and 52 days old embryo

spine is predominate

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head to foot development

development progressing from head through the trunk of the body to feet

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9-40 weeks

significant change and growth

the early body systems and structures established in the embryonic stage continue to develop.

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foetus measures 2.5 centimetres in length

weighs about 2 grams at the beginning of this stage

about 50 centimetres and 3500 grams by the end

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systems including the lungs, digestive system, liver and kidneys are formed

these are functioning in the early stages of foetal development

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start taking shape and by around the 15th week

female foetus will have produced millions of ova, number will be reduced by the time she is born

the testes of a male foetus will be producing testosterone

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movement occurs in almost all parts of the foetal body and becomes more noticeable

reflexes such as sucking and grasping are highly responsive

foetus displays a breathing movement

lungs are filled with amniotic fluid, not air

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during the second half of the foetal stage, tooth buds form in the gums

the bones, which mainly consist of cartilage, also start to harden or ossify around this time

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the senses also begin to function around 25 weeks after fertilisation

the foetus may respond to light, sound and touch

these senses become more sensitive throughout the remainder of the foetal stage

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organ connects developing foetus to uterine wall to allow nutrient uptake, waste elimination and gas exchange via mothers blood supply

expelled in third stage of labour, after baby is born