fetal development - instruction2.mtsac.edu physio lecture… · stages of development pre-embryonic...
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Fetal development
Dr. Carmen Rexach
Physiology
Mt San Antonio College
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We all start as one fertilized oocyte!
Gestation lasts ≈266 days
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Trimesters: Clinical Approach
8 weeks 5 months
Full term
2nd trimester = 13-24 weeks
3rd trimester = 25 weeks to birth
1st trimester = 1st 12 weeks
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Stages of Development
Pre-embryonic
Zygote 0-30 hr A single diploid cell
Cleavage 30-72 hr Identical blastomeres
Morula 3-4d Ball of 16+ blastomeres
Blastocyst 4-16d Trophoblast + inner mass
Embryonic 16d-8wks Differentiation of 1o germ layers
Fetal 8-40wks Growth and maturation
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First trimester
8 weeks
12 weeks
7 weeks
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30 days post fertilization (3 weeks)
• Four limb buds are visible
• Lens disc & optic vesicle are formed and you can tell future eye color
• body is covered with first thin skin layer
• brain differentiates into forebrain, midbrain, hindbrain
• thyroid development in progress
• Lymphatic system forms
• hearing development begins
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30 days post fertilization
• Primitive mouth and tongue have formed • heart chambers are full of plasma and
blood cells • liver has formed and receives blood from
the umbilicus • blood circulation has established • gall bladder, stomach, intestines,
pancreas and stomach form
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7 to 8 weeks • First detectable brain waves
• head begins to become erect
• semicircular canals form
• gonads form – sex is visibly detectable by 8 weeks
• Legs formed with recognizable knees and ankles
• Toes are notched and toe nails begin to appear
• trunk elongates
• muscles continue to develop and grow strong
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12 weeks (2nd trimester begins)
• Fetus begins to move around
• Neck and shoulders are well-defined
• salivary glands function and sucking muscles of mouth are present
• tooth buds still developing
• hair pattern can be detected on the scalp
• heartbeat can be detected externally
3 months
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12 weeks (2nd trimester begins)
• fetus inhales and exhales amniotic fluid which aids in lung development
• 25 quarts of blood are pumped by heart each day
• Fully functional spleen under the direction of the liver
• Limbs are more proportional – Hands and thumbs show increased function
• sweat glands appear • body hair begins to grow • muscle and nerves continue to advance
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Second trimester
4 months
5 months
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Second trimester
• 14 weeks – increased flexibility
– eyes move forward in the face and ears are in correct position
– torso grows rapidly
12 weeks
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22 weeks – fetus occupies more space in uterus -- becomes
crowded
– fetus recognizes maternal sounds -- mother’s voice, heartbeat, breath, digestion
• auditory ossicles have hardened
– continued development of respiratory system
– continued growth of bones, muscles and organs
– skin is pink, wrinkled, with blood vessels, bones, and organs visible through the transparent surface
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3rd trimester
6 months
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Third trimester
• 28 weeks – brain waves function like full term baby
– forebrain enlarges
– eyelashes present and eyes partially opened
– improved sucking and swallowing
– lungs can breathe air
– 2-3% body fat
– testes descend in male
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40 weeks = Full term
– 15% of body is fat (80% under skin, 20% holding organs in place)
– 300 bones -- some will fuse postpartum to make 206 in adult
– over 70 reflex apparent
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Amniocentesis • Diagnostic test used to:
– Chromosomal abnormalities • Down’s syndrome
• Spina bifida
• anencephaly
– Rh abnormalities
– Lung maturity
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