Prenatal Development
- Created by: Meg Fraser
- Created on: 02-01-17 11:57
What are the three stages in prenatal development?
- Germinal
- Embryonic
- Fetal
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
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
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
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
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
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
What are the stages of brain development?
- Neurogenesis
- Neuronal migration
- Synaptogensis
- Myelination
- Synapse pruning
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
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
What are the prenatal abilities and behaviours?
- Touch
- Taste
- Smell
- Hearing
- Vision
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
Name some teratogens.
- Alcohol
- Smoking
- Medication
- Illegal drugs
- Air pollutants
- Radiation
- Mother's age
- Mother's diet
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
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
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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