Human Developement Prenatal to postnatal Prenatal Starts as

Human Developement Prenatal to postnatal

Prenatal • Starts as soon as the egg meets up with the sperm and fertilization occurs. (hopefully this is in the oviduct) – This union creates a zygote

The first trimester • This is week 1 -12 (the first three months of the pregnancy) • Embryonic stage lasts until the 8 th week – at this time it is recognizable human typically 30 mm long and weighs 5 g • The Fetal stage starts at the 8 th week and lasts until the baby is born

Embryonic stages • Zygote – the egg is fertilized • Cleavage – 30 hours to third day – Mitosis increase the number of cells (doubling each time) • Morula – 3 rd -4 th day- is a solid ball of cells

Embryonic stages • Blastocyte - 5 th day through 2 nd week – A hollow ball of cells – Begins to attach to the endometrium layer – forms the trophoblast which helps to protect and provide nutrients – inner mass cells – become the offspring (true beginning of the embryonic stages)

Last Stage • Gastrula – end of second week – Primary germ layers form • Ectodermal layer • Mesodermal layer • Endodermal layer – The trophoblast is lined with another layer of cells – together they are called the Chorion which eventually becomes the placenta

A few other developments • The amnion forms around the embryo as the chorion that is surrounding it dissolves (except that which becomes the placenta) – It fills with a fluid called amniotic fluid – The umbilical cord is formed from the chorion and the allantois

End of the 8 th week About to be called a fetus Beginning of the 8 th week

Fetal Development • During the third month – Body lengthens – Ossification begins – By the twelfth week (end of the 1 st trimester) external reproductive organs are distinguishable

2 nd trimester • 4 th month – Grows rapidly reaches up to 20 cm skeleton continues ossification • 5 th month – Growth slows – Skeletal muscles contract – Hair appears on head

2 nd trimester continue • 6 th month – Picks up lots of weight – Eyebrows and eyelashes appear – Skin translucent and wrinkly

3 trimester rd • 7 th month – now 40 cm long – Fat deposited in the subcutaneous layer – smooths skin – Eyelids reopen • 8 th and 9 th month end up about 50 cm – Brain cells network – Testis drop – Respiratory and digestive system mature

7 th month 8 th month

Postnatal • From birth to death • Lost of changes are in store for the little on that has already morphed quite a bit since conception

Neonatal • Birth to end of the fourth week • Major events – Respire (breath) – Eat and digest nutrients – Excrete waste – Regulate body temp – Control cardiovascular and changes it

Infancy • End of week four until year one • Major events – High growth rate – Teeth – Muscular and nervous system mature allowing coordinated activities – Communication begins

Childhood • One year to puberty • Major events – Rapid growth rate – Teeth finish erupting and are replaced by 2 nd set – Bladder and bowel control – Intellectual abilities mature – Fine muscle control

Adolescence • Puberty to adulthood • Major events – Reproductively functioning – Emotionally more mature – Growth spurts – Higher levels of motor skills – Intellectual abilities continue to improve

Adulthood • Adolescence to old age • Major events – Remains pretty much unchanged anatomically and physiologically – Eventually degenerative changes begin to occur

Senescence • Old age to death • Major events – Degenerative changes continue – Body unable to cope with demands slowly