Lecture 4 - Prenatal Development Flashcards
Germinal Stage
- occurs before body knows its pregnant
- fertilization - 2 weeks
- methodical cell division and specialization begins w/n 12 hours of fert
- fertilized egg called a blastocyst
Implantation
- 6-12 days after ovulation
- trophoblast cells penetrate uterine lining by mimicking blood vessels, and egg is pulled into endometrium
- hormonal changes occur that prevent menstruation (hCG levels increase)
Embryonic stage
- 3-8 weeks
- development of major body structures and organs - heart has started beating
What is gastrulation? What is the result of this?
- folding of the neural tube on itself, creates the 3 distinct germ layers
What are the three germ layers?
- ectoderm - nervous system and skin
- mesoderm - muscle, skeleton, kidneys, reproductive system
- endoderm - endocrine glands, lungs, digestive tract, liver
Organogenesis
simultaneous formation of organs that occurs after gastrulation
- high chance of miscarriage during this period bc lots of things are being developed at the same time
What are the chorioamniotic membranes?
- make up amniotic sac
- amnion - thin and tough inner fetal membrane, contains amniotic fluid and the embryo
- chorion - outer fetal membrane, part of placenta
Amniocentesis
- screening test of genetic or chromosomal abnormality using baby’s skin cells in amniotic fluid
- very small (0.06%) miscarriage risk
Placenta
- organ that connects the developing embryo to the uterine wall
- genetically ID to baby
- umbilical cord (attaches placenta to baby) and corresponding vein do not intersect, which i
Placental abruption
- placenta pulled partially/completely away from uterus
- deprivation of nutrients and O2
- c-section is only option
Placenta previa
- placenta grows across and blocks cervix
- more common in mothers who’ve had C-sections, scar tissue causes lower implantation
- c-section is only option
Placenta accreta
- blood vessels of placenta growing too deeply into uterus
- can cause internal hemorrhage when delivered
Thalidomide
- sedative that alleviated morning sickness used in 50s and 60s
- neg impact only during 2 weeks of pregnancy, window when arms and legs are developing
- about 10,000 babies were born w/ arm or leg birth defects
Teratogen
any environmental agent that can cause a birth defect or negatively alter cog and behavioral outcomes
What are the 3 categories of teratogens?
- Drugs - legal and illegal; alcohol, cigarettes, etc
- Illness/Disease - can be transmitted to baby; measles or syphilis
- other - radiation (x-ray), air pollution, water pollution, industrial cleaners
Congenital physical anomaly & Congenital malformation
- Congenital physical anomaly - atypical, but not problematic physical anomaly at birth
- congenital malformation - “birth defect”, problematic structural anomalies
Severity of teratogen depends on?
1) dosage
2) genetic susceptibility
3) timing of exposure - stronger impact during embryonic period
Neurulation
- formation of neural tube
- 18-24 days
- most susceptible to teratogens
NTDs
- neural tube defects
- occur when NT is disrupted
Spina Bifida
- most common of live births
- occurs when seam of NT does not seal all the way
- severity depends on where and how much spine is exposed
Anencephaly
- most common defect in utero, usually results in miscarriage
- occurs when top of NT does not close
- 95% die if born
Neurogenesis
- creation of new neurons
- begins @ 5 weeks gestation
- formation of major brain structures occur during first two trimesters
- refinement occurs during third trimester and infancy
Neural migration
- neurons move from neural plate to final position in brain
- occurs even after birth
What are some changes that can be seen by the end of the embryonic stage?
- all major organs and structures have been created
- 1” long
- head is 50% of length
- weak brain waves observed at 5 weeks
- development of nervous system at 3 weeks
Fetal stage
- 9 weeks to birth
- begins when major organs differentiated
- rapid physical growth - 1” to 7.5 lbs
- embryo -> fetus
Sex Differentiation
- completed 8-12 weeks
- determined at fert; XX = female, XY = male
Explain the importance of SRY, MIS and DHT in determining sex
- SRY gene causes production of DHT and MIS
- MIS (Mullerian-inhibiting substance) - inhibits development of Muller ducts in XY fetuses
- DHT (Dihydrotestosterone) - develops wolff ducts in XY fetuses
Physical development of fetus
- heart rate variability indicate taht the CNS and CV systems are working
- circadian rhythms
- vernix
- lanugo - fine, soft hair that covers body
Vernix
moisturizes skin, facilitates passage through birth canal, helps conserve heat
- clings to lanugo
Observable fetal behavior
- fetus is said to be an active contributor to own development in that they:
- swallow - digest and excrete amniotic fluid to ensure GI tract is functional
- breathe - prepare and develop lungs and associated muscles for breathing after birth
- moving - allows muscles to lengthen and bones to form
How do fetuses react to external stimuli? What is prenatal perception?
- Covers eyes when shown light
- avoids vibrations
- become familiarized w/ mom’s voice, auditory system becomes most developed
Prenatal pain, what is required to feel pain?
- Anterior Cingulate cortex (ACC) - acute pain perception, develops at 26 weeks
- Thalamocortical connection - transmit sensory information to cerebral cortex, develops at 29 weeks
