prenatal development

Question 1

what are the 3 stages of prenatal development?

Answer 1

1. germinal stage
2. embryonic stage
3. fetal stage

Question 2

describe the germinal stage “zygote period”
1. start
2. end
3. duration
4. major achievements

Answer 2

1. start: conception (formation of a single-cell zygote through the fusion of a sperm cell and an egg cell)

process:

• zygote undergoes rapid cell division (mitosis), resulting in the formation of a cluster of cells (blastocyst). (1st major milestone)
• blastocyst consists of:
  *an outer layer of cells (trophoblast), which will eventually develop into the placenta
  *an inner cell mass, which will develop into the embryo

-blastocyst travels down fallopian tube

2. end: attachment to lining of uterine wall (implantation) (2nd major milestone)
3. duration: 2 wks
4. major achievements:
   - rapid cell division (mitosis) to form blastocyst
   - implantation of blastocyst to uterine lining

During the germinal stage, the zygote is highly vulnerable to environmental influences, and any disruptions during this critical period can result in developmental abnormalities or pregnancy loss

Question 3

what happens in the germinal stage after the blastocyst attaches to the lining of the uterus?

Answer 3

the trophoblast cells (blastocyst’s outer layer of cells) differentiate and form structures for the support and nourishment of the developing embryo, such as:
1. amniotic sac
2. placenta

Question 4

describe the embryonic stage:
1. start
2. end
3. duration
4. major achievements

Answer 4

1. start: blastocysts attaches itself to uterus lining

process:

• during 3rd and 4th week, neural tube forms, which eventually develops into brain and spinal cord
• heart begins to beat and circulate blood starting the 3rd week and by the end of the 4th week
• Limb buds emerge, and basic features of the face, eyes, ears, and other organs start to form
• Organ systems such as the respiratory, circulatory, digestive, and urinary sysems begin to develop during this stage
• Structures like the lungs, liver, kidneys, and intestines start to take shape
• Cells within the embryo become specialized to perform specific functions, including cell migration, cell signaling, and the activation of specific genes that regulate development

2. end: formation of bone cells
3. duration: 3rd to 8th wk (~5wks)
4. major achievements:
   - growth (1/4 in. to 1 in.)
   - major organs formed (~6.5 wks)

developing embryo is vulnerable to environmental influences. exposure to teratogens (substances that can cause birth defects), maternal nutrition, and maternal health can significantly impact the embryo’s development during this stage. risk of miscarriage is relatively high due to the complex processes occurring as the embryo develops.

Question 5

what is the neural tube?

Answer 5

• develops in embryonic stage, 3rd and 4th week after conception
• develops into brain and spinal cord
• if not closed after 4th week, risk of spinal bifida, paralysis, loss of sensation below the spinal cord (taking folic acid reduces this risk)

Question 6

(a) describe the fetal stage:
1. start
2. end
3. duration
4. major achievements

(b) when can mothers feel their babies moving?

(c) state what happens in the 17th, 18th, 20th, 22nd, and 28th week.

Answer 6

1. start: formation of bones

process:

• at 11 wks:
  *bones formed
  *can move
• at 16 wks:
  *lower body grows rapidly
  *more active; mother can feel
  *reflexes developed
• at 17 wks: brain lateralization
  *division of functions between the left and right hemispheres of the brain
  *left hemisphere specialized for language and analytical functions
  *right hemisphere specialized in spatial awareness, visual processing, and emotional expression
  *neurons in the fetal brain are rapidly proliferating and migrating to their appropriate locations within the cerebral cortex
  *as brain matures, connections between neurons strengthen through a process called synaptogenesis, allowing for more efficient communication within neural networks
  *brain lateralization continues throughout gestation and into early childhood
• at 18 wks:
  *skin vulnerable
  *sleeping and waking states
• at 20 wks: sex organs formed
  *begins at onset of fetal stage
  *all fetuses begin as female (if no testosterone produced, fetus develops female genitalia; if testosterone produced at 9 wks (for XY fetus), fetus develops male genitalia)
  *if XY fetus does not produce testosterone or XX fetus is exposed to testosterone, they may have genitalia of the opp sex, or both
• at 22 wks: vernix
  *fetus’s skin covered with waxy substance called vernix caseosa
  *protects delicate skin from the amniotic fluid and scratching
  *still present after birth, that’s why newborns are slimy
• at 28 wks (7th mth):
  *growth slows down
  *viable (able to survive if born) due to fully functioning digestive and respiratory systems

2. end: birth
   *avg length = 20 inches / 51cm
   *avg weight = 7 lbs / 3.2kg
   *heavy babies cause longer births -> oxygen deprivation/insufficiency
3. duration: 9th to 38th wk (~7 mths)
4. major achievements:
   - growth (3 in. to 20 in. / 7.62cm to 50.8cm)
   - movement felt by mother
   - sex (~12 wks)
   - hearing (~5 mths)
   - sensitivity to light

Question 7

what is the difference between cephalocaudal and proximal-distal?

Answer 7

cephalocaudal: develop in top-down direction

proximal distal: develop from center outwards

Question 8

what happens to fetuses when apoptosis is inhibited?

Answer 8

• excessive cell proliferation
• tumors and cancer
• malformations
• organ dysfunction
• autism, depression, schizo

Question 9

what are the 3 major aspects of changes in brain cells during the prenatal period?

Answer 9

1. cell proliferation
2. cell migration
3. cell differentiation (cells become heterogeneous and specialise to serve different functions)

Question 10

what are the 2 factors affecting fetus development?

Answer 10

1. teratogens (any envt agents causing damage during prenatal period)
2. critical periods (timeframe of greater vulnerability to damage from teratogens)

Question 11

a fetus is exposed to teratogens during its prenatal period. what does the extent of harm to the fetus depend on?

Answer 11

extent of harm is influenced by:

1. dose
2. heredity - some may better withstand negative influences
3. timing - sensitive periods (most influential)

Question 12

which of the 3 stages of prenatal period is most susceptible to teratogens?

Answer 12

embryonic stage. (3rd to 8th wk)

• major organs and systems form and begin to function
• each organ has a unique sensitive period influenced by different teratogens

Question 13

what are some features of fetal alcohol syndrome (fas)?

Answer 13

• small head
• low nasal bridge
• flat midface
• small eye openings
• smooth philtrum
• underdeveloped jaw
• thin upperlip
• short nose
• epicanthal folds

Question 14

what can exposure to alcohol during prenatal development lead to?

Answer 14

• small and underdeveloped brain
• facial and limb defects
• emotional and cognitive disorders

*leading non-genetic cause of mental retardation in the US

Question 15

what does exposure to smoking during prenatal development cause?

Answer 15

• underdeveloped lungs caused by lack of O2
• cognitive problems
• increased risks of:
• SIDS
• lower IQ
• cancer

Question 16

what are 3 other teratogens beside alcohol and smoke?

Answer 16

1. maternal diseases: HIV, Syphilis, toxoplasmosis
2. legal drugs: thalidomine (limbless), aspirin
3. illegal drugs: cocaine, heroin
4. envt pollutants: lead, mercury
5. radiation: x-rays
6. extreme exercise
7. poor nutrition
8. severe emotional stress