What are the 3 stages of Prenatal Development?
- pre-embryonic stage (zygote)
- embryonic stage (embryo)
- fetal stage (fetus)
What occurs in the pre-embryonic stage?
fertilisation of ovum by sperm
What days are the pre-embryonic stage from?
day 0 to 14
What occurs in the embryonic stage?
zygote implants in uterus
what days are the embryonic stage from?
day 15 to end of 8th week
what days are the fetal stage (fetus)
from end of 8th week until birth (38-42 weeks = full term)
what is developed in the embryonic stage?
all tissues/ organs formed
what 3 things happen to the cells in the embryonic stage?
- cell proliferation - division
- cell migration - movement
- cell differentiation (become more specialised)
what do the cells differentiate into in the embryonic stage?
- embryonic disk – 3 layers of cells
- neural tube formation: cephalic to caudal
what are the 3 layers of cells in the embryonic disk?
- endoderm
- mesoderm
- ectoderm
What does the endoderm (bottom layer) make up?
gut, liver, pancreas & respiratory systems
What does the mesoderm (middle layer) make up?
muscles, skeleton, excretory & circulatory systems
What does the ectoderm (top layer) make up?
sensory organs, hair, skin, nails & whole NS (CNS & PNS)
What are the different neural tube defects?
- ancephaly
- craniorachischisis
- open spina bifida
- closed spina bifida
- encephalocele
- iniencephaly
What are the different parts of the neural tube which can cause defects if injured?
- cranial neuropore
- middle
- caudal neuropore
- somite
- neural groove
- neural fold
What can disruptions during the pre-embryonic & the embryonic periods cause?
impact upon development of neural tube = neural tube defects (NTD)
What happens in weeks 13-24 of fetal development?
- neurogenesis
- most neurons by 24 week
- major regions of brain develop
- eyes sensitive to light, reacts to sound
What happens in weeks 25-38/40
- size increases, lungs mature, CNS matures
- rapid brain development
What is a teratogen?
substance / condition that can disturb the development of the embryo (toxic substance)
Why is the prenatal period a sensitive period?
limited time in which a part of the body / behaviour is biologically prepared to develop rapidly
- period of organ differentiation –> cells becoming specialised
what is a neonate?
first 4 weeks after birth
full term
from 37 weeks
what is still developing in neonates?
- myelination
- synpatogenesis
what is defined as ‘extremely premature’?
from 23-28 weeks
