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

The first trimester

  • This is week 1-12 (the first three months of the pregnancy)
  • lasts until the 8th week

◦at this time it is recognizable human typically 30mm long and weighs 5 g

  • The starts at the 8th week and lasts until the baby is born

Embryonic stages

  • Zygote – the egg is fertilized
  • – 30 hours to third day

◦Mitosis increase the number of cells (doubling each time)

  • Morula – 3rd -4th day- is a

Embryonic stages

  • Blastocyte - 5th day through 2nd week

◦A

◦Begins to attach to the endometrium layer

◦forms the trophoblast which helps to protect and provide nutrients

◦inner mass cells – become (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

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

◦The is formed from the chorion and the allantois

Fetal Development

  • During the third month

◦Body lengthens

◦ begins

◦By the twelfth week (end of the 1st trimester) external reproductive organs are distinguishable

2nd trimester

  • 4th month -

◦Grows rapidly reaches up to 20 cm skeleton continues ossification

  • 5th month

◦Growth slows

◦

◦Hair appears on head

2nd trimester continue

  • 6th month

◦

◦

◦Skin translucent and wrinkly

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

◦

◦Testis drop

◦Respiratory and digestive system

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

  • Major events

◦Respire (breath)

◦Eat and digest nutrients

◦Excrete waste

◦Regulate body temp

◦Control cardiovascular and changes it

Infancy

  • End of
  • Major events

◦High growth rate

◦

◦Muscular and nervous system mature allowing coordinated activities

◦Communication begins

Childhood

  • Major events

◦Rapid growth rate

◦Teeth finish erupting and are replaced by 2nd set

◦Bladder and bowel control

◦Intellectual abilities mature

◦Fine muscle control

Adolescence

  • Major events

◦

◦

◦Growth spurts

◦Higher levels of motor skills

◦Intellectual abilities continue to improve

Adulthood

  • Major events

◦Remains pretty much unchanged anatomically and physiologically

◦Eventually degenerative changes begin to occur

Senescence

  • Major events

◦Degenerative changes continue

◦Body unable to cope with demands slowly