Human Developement

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Human Developement

• Prenatal to postnatal

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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

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The first trimester

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

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Embryonic stages

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

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Embryonic stages

• Blastocyte - 5th day through 2nd 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)

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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

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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

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

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

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2nd trimester

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

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2nd trimester continue

• 6th month
• Picks up lots of weight
• Eyebrows and eyelashes appear
• Skin translucent and wrinkly

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3rd trimester

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

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8th month
7th month
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Postnatal

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

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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

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Infancy

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

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Childhood

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

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Adolescence

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

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Adulthood

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

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Senescence

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

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