Prenatal Development

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What are the three stages in prenatal development?

  • Germinal
  • Embryonic 
  • Fetal
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Describe the germinal stage.

  • Once the egg is fertilised, it becomes a zygote
  • A zygote has half the genetic material from the mother and half from the father
  • Egg and sperm have only 23 chromosomes each
  • Zygote will have 46 chromosomes 
  • The blastocyst embeds itself in the uterus wall 
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Describe the blastocyst.

  • A bulging sphere of cells
  • It travels down the fallopian tube
  • Becomes embedded in the uterus wall 
  • It is dependent of the mother 
  • If the blastocyst divides, you will get MZ twins
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Describe the embryonic stage.

  • Beginning of 3rd week until end of 8th week
  • Huge increase in size 
  • Support systems (umbilical cord, amniotic sac, placenta) develop
  • Inner body differentiaties into 3 layers:

Endoderm - organs such as lungs

Mesoderm - muscles and skeleton 

Ectoderm - nervous system and skin 

  • Cells start to migrate and take on their particular functions 
  • Cephalocaudal is development from the head down
  • Proximal-distal is development from the inner core out 
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Describe the support systems.

  • Umbilical cord 

Connects the embryo and the placenta 

  • Placenta 

Semi-permeable membrane 

Nutrients come in and waste goes out

  • Amniotic sac

Contains clear watery fluid

Compensates for jolting and temperature change 

Allows the babies muscles to develop

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What are the four processes in the embryonic stage

  • Cell division

Each cell contains full and identical genetic material 

  • Cell migration

New cells move to different locations of the embryo

  • Cell differentiation

Stem cells start to specialise

  • Apoptosis

Selective death of some cells 

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Describe the fetal stage.

  • Beginning of the 9th week until birth
  • By the end of the 3rd month, all body parts are present 
  • By the end of the 4th month, mothers can feel movement 
  • At 5 months, reflexes, swallowing and sucking 
  • At 6 months, eyes can open and close
  • At 22-26 weeks, physical systems sufficiently advanced to survive a premature birth
  • Respiratory system continues to develop into 9th month 
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What are the stages of brain development?

  • Neurogenesis
  • Neuronal migration
  • Synaptogensis 
  • Myelination
  • Synapse pruning
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Describe the stages of brain development.

  • Neurogenesis - rapid production of neurons from week 3 to 16
  • Neuronal migration - from week 4, neurons travel to different parts of the brain and nervous system to form structures
  • Synaptogenesis - increase in potential connections (synapses) between neurons
  • Myelination - coating of the neural membrane and neurons to increase efficiency of signals
  • Synapse pruning - Synapses are elimated to make way for new connections 
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What is the formation of brain structures?

  • By 22 days, there are clear divisions between fore, mid and hind brain 
  • First synapses form in the spinal cord
  • By 6 months, the brain stem (between spinal cord and cerebral cortex) matures
  • Critical reflex behaviours appear e.g. swallowing
  • Cerebral cortex begins to function at time of birth
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What are the prenatal abilities and behaviours?

  • Touch
  • Taste 
  • Smell
  • Hearing 
  • Vision 
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Describe the prenatal abilities and behaviours?

  • Touch

Earliest to develop

By 8/9 weeks, the head moves if touched in the mouth region 

  • Taste and smell 

Responses when different substances are introduced in ultrasound

  • Hearing 

Begins with startle reflex then has preference for certain sounds

  • Vision 

The least developed due to lack of light in the womb

By 7 months are able to see main features of the world

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Name some teratogens.

  • Alcohol 
  • Smoking
  • Medication 
  • Illegal drugs
  • Air pollutants
  • Radiation 
  • Mother's age
  • Mother's diet
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What are the severity of teratogen effects dependi

  • No environmental impact in first 2 weeks
  • Next 6 weeks the most sensitive period during rapid development 
  • As development slows down, the effect of teratogens decreases
  • The central nervous in sensitive for the longest 
  • The upper and lower limbs are senstive for the shortest 
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What are possible genetic abnormalities and exampl

  • Down's syndrome - most common genetic abnormality which includes an extra chromosome, impaired cognitive abilities etc. 
  • Inherited diseases e.g. cystic fibrosis and muscular dystrophy
  • Sex-chromosome abnormalities e.g. klinefelter's syndrome and turner's syndrome 
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What are the functions of the birth experience?

  • Increases chance of survival (adaptive value)
  • Reduces size of the head to prevent damage
  • Stimulates production of hormones
  • Forces amniotic fluid out of the lungs
  • First cry allows large oxygen intake
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