9.7.10 - Prenatal Development Timelines, Cognitive Anomalies

Front 1

What is the length of pregnancy?

Back 1

280 days (40 weeks) after last normal menstrual period (gestational age)

266 days (38 weeks) after fertilization

Front 2

How do you measure size and probable age of fetus?

What is this used for?

Back 2

ultrasound measurements of crown-rump length, fetal head measurements, femur length
weight of mother
to predict expected date of delivery

Front 3

Why would you use gestational age instead of time since fertilization?

Back 3

Because you don't always know when fertilization occurred.

Front 4

What happens in the 3 trimesters of pregnancy?

Back 4

First trimester: 0-3 months - all major systems develop
2nd: (4-6 months) fetus grows sufficiently. Anatomic detail can be visualized during ultrasonography.
3rd trimester: (7-9 months) fetus may survive if born prematurely

Front 5

What is the most critical period in organ development?

Back 5

when cell division, cell differentiation, and morphogenesis are at their peak

Front 6

What are the earliest organ systems to develop?

Back 6

heart, nervous system

Front 7

What is the critical period for brain development?

Back 7

3-16 wks

(but still can be disrupted afterwards b/c continues to grow)

Front 8

Are the development periods for eyes/ears short or long?

Back 8

long

Front 9

how long is palatal development?

Back 9

6-8 weeks

Front 10

When do external genitalia define themselves?

Back 10

in later weeks of embryonic period

Front 11

Summarize the order of development.

Back 11

Stuff at top starts working first, then works its way down.

Front 12

What is the embryonic period?

Back 12

0-8 weeks after fertilization

Front 13

What is the period of maximal susceptibility?

Back 13

Embryonic period (0-8 wks)

Front 14

What happens in Weeks 1-2

Back 14

fertilization
implantation on uterine wall
proliferation and differentiation of trophoblast as blastocyst completes implantation into endometrium
embryoblast differentiates into bilaminar embryonic disk (hypoblast, epiblast)

Front 15

What happens in week 3?

Back 15

- development of primitive streak
- gastrulation, differentiation of 3 germ layers
- neurulation, development of notochord
- embryonic blood vessels and heart develop (same time as need for blood vessels to bring oxygen and nutrients thru placenta)

Front 16

What happens in week 4?

Back 16

Neural tube formation across from somites. Cranial and caudal neuropores close.

body changes: folding of embryo, forebrain growth give embryo a C-shaped curvature. pharyngeal arches appear in head and neck. rudiments of organ systems established. heart begins to beat and pump blood. limb buds begin. Otic pits (ears) and lens placode (eyes) are visible.

Front 17

What happens in week 5?

Back 17

minor changes in body form
growth of head (rapid development of brain, facial)
Mesonephric ridges (--> kidneys)

Front 18

What happens in week 6?

Back 18

Upper limbs show differentiation (ie. elbows, fingers)
devel of lower limbs
spontaneous movements (twitching of trunk and limbs)
intestines enter extraembryonic coelom
umbilical herniation

Front 19

What happens in week 7?

Back 19

limbs undergo lots of change
fingers
ossification of bones
omphaloenteric duct (yolk stalk) - communication btw primordial gut and umbilical vesicle (yolk sac)

Front 20

What happens in week 8?

Back 20

limbs
digits separate
purposeful limb movements
intestines
sexual differences (but not enough to distinguish gender)
distinct human characteristics

Front 21

What is the fetal period?

Back 21

9-38 weeks
period of proliferation, differentiation, increase in siize.

primordia of all major organ systems have developed.
rapid body growth (measured by crown-rump length or crown-heel length)

Front 22

What happens in weeks 9-12?

Back 22

Rapid growth in body length (before, head was really big)
intestines go into abdomen
upper limbs finished developing, lower limbs still developing
erythropoiesis in liver, then spleen
urine produced by developing kidneys
primary ossification centers

Front 23

When can gender be distinguished externally?

Back 23

12 weeks

Front 24

What happens in weeks 13-16?

Back 24

coordination of limb movements
active ossification of skeleton
fetal ovaries are differentiated..with oogonia
eyes and ears have shifted to their places

Front 25

When are eggs produced in the fetus?

Back 25

month 4 (weeks 13-16)

Front 26

What happens in weeks 17-20?

Back 26

growth slows down
fetal movements (quickening) felt by mother
fetal skin becomes covered w/ vernix caseosa (mix of dead epidermal cells and fatty secretions from sebaceous gland) to protect skin from exposure to amniotic fluid
eyebrows, head hair, lanugo
uterus, vagina
testes descend

Front 27

What happens in weeks 21-26?

Back 27

substantial weight gain
secretory epithelial cells secrete surfactant onto lungs (lipid to maintain the patency of the developing alveoli of the lungs)

Front 28

At what point can a fetus be born and survive? What risks does it face?

Back 28

22 weeks

respiratory system is still immature though

Front 29

What happens in weeks 27-29?

Back 29

lungs and pulmonary vasculature have developed sufficiently to provide adequate gas exchange
CNS can direct rhythmic breathing movements, control body temp
bone marrow becomes site of erythropoiesis

Front 30

What happens in weeks 30-34?

Back 30

- skin is pink and smooth
- upper and lower limbs are chubby

Front 31

what age fetuses usually survive if born?

Back 31

32 weeks and older

Front 32

What happens in weeks 35-38?

Back 32

body growth slows during "finishing period"
nervous system is mature
adds a lot of fat during last weeks of gestation
testes are in scrotum (but often undescended in premature males)
head is still rly big

Front 33

What percent of human infants are born with an anomaly?

Back 33

2-5%

Front 34

What are the 3 classes of congenital anomalies?

Back 34

1. Malformation: morphological defect from intrinsically abnormal dev process (ie. chromosome abnormality)
2. disruption - morphological defect from extrinsic breakdown/interference w/ normal developmental process. Cannot be inherited. (FAS)
3. deformation - abnormal form/shape/position of a body part due to mechanical forces (ie. clubbed foot)

Front 35

What is a syndrome?

Back 35

group of anomalies occurring together, have common cause

Front 36

What is an association?

Back 36

nonrandom appearance of anomalies together at higher-than-chance frequency, but cause is unknown

Front 37

Give an example of association.

Back 37

VACTERL
vertebral
anal
cardiac
tracheoesophageal
renal
limb

Front 38

What are the 4 causes of congenital abnormalities?

Back 38

1. genetic factors
2. environmental factors
3. multifactorial (combination of genes, environment.)
4. other - 50-60%

Front 39

What is a teratogen?

Back 39

any agent that can produce a congenital anomaly/increase incidence of congenital anomaly in the population

Front 40

What is thalidomide?

Back 40

used to be used as sedative/tranquilizer/to treat nausea during pregnancy.
but resulted in lots of infants w/ severe limb deformities

meromelia - absence of part of the upper/lower limbs
phocomelia - seal hands
amelia - absense of limbs
micromelia - abnormally small or short limbs

anomalies in other organs as well

Front 41

When does thalidomide have to be taken to cause the birth defects?

Back 41

caused anomalies 24-36 days after fertilization (critiical period)

earlier it was taken, the worse the deformities

Front 42

why is there a renewed interest in thalidomide?

Back 42

potential use as tx for multiple myeloma, complications of HIV, skin lesions caused by leprosy

but cannot be taken by women of childbearing age!!

Front 43

What is accutane?

Back 43

a vitamin A analogue
was prescribed for severe cystic acne.
retinoic acid is a signaling molecule, synth from vitamin A, that controls gene expression at trsn level. can alter pattern of regulatory gene expression if it binds to Hox, pax.

so accutane somehow affects gene expression

results in cranial dysmorphism, cleft palate, cardiovascular anomalies, NT defects, mental retardation

Front 44

What is the critical period for exposure to accutane?

Back 44

3-5 wks after fertilization

Front 45

What are the symptoms of fetal alcohol syndrome?

Back 45

mental retardation
microcephaly
short palpebral fissures
epicanthal folds
maxilalry hypoplasia
short nose
thin upper lip
palmar creases
joint anomalies
congenital heart disease

Front 46

What causes the features of FAS?

Back 46

abnormal cell death in structures derived from neural crest cells

Front 47

What does maternal smoking result in?

Back 47

intrauterine growth restriction

premature delivery is 2x as frequent

low birth weight

Front 48

How does smoking affect the embryo?

Back 48

nicotine constricts uterine blood vessels --> decr in uterine blood flow
less oxygen/nutrients available to fetus
--> impaired cell growth
high levels of carboxyhemoglobin in maternal and fetal blood (so chorionic fetal hypoxia =- low oxygen levels)

Front 49

What can happen if the mother has rubella?

Back 49

Can cross the placenta, infect embryo/fetus
cause eye defects (glaucoma, cataracts), cardiac defects, deafness

Front 50

What can happen if the mother has cytomegalovirus?

Back 50

most common viral infection of the fetus
spontaneous abortion if it affects the embryo
if it happens later in pregnancy: many diff anomalies

even if it's an asymptomatic infection, can still have audiologic, neurobehavioral, neurologic disturbances during first few years of life.

Front 51

What can happen if the mother has toxoplasmosis?

Back 51

caused by intracellular parasite (protozoan) from eating raw meat, close contact with infected domestic animals (cats), infected soil
defects in brain and eyes
fetal death may follow infection, during early stages of pregnancy

Front 52

what plays the biggest role in neural tube defects?

Back 52

folic acid

Front 53

What causes spina bifida?

Back 53

nonfusion of embryonic neural arches

Front 54

What is spina bifida oculta?

Back 54

Spina bifida occulta – small separation or gap in one or more spinal vertebrae due
to failure of the vertebral arch to fuse. The spinal cord is covered by skin.

Front 55

What is spina bifida cystica

Back 55

Spina bifida cystica – a cyst-like sac protrudes through defect in vertebral arch

Front 56

What is meningomyelocele?

Back 56

meninges & spinal cord &/or nerve roots are exposed in
cyst-like sac

Front 57

what is meningocele?

Back 57

 Meningocele – only meninges are exposed in cyst-like sac

Front 58

What is encephalocele?

Back 58

Encephalocele – sac-like protrusions of brain & meninges through openings in skull

Front 59

What is anencephaly?

Back 59

Anencephaly – absence of a major portion of the brain, skull, & scalp caused by
failure of the anterior neuropore to close; infant dies soon after birth.

Front 60

Aside from NTDs, folic acid can also prevent what?

Back 60

cleft lips

Front 61

What if you have a positive family history of NTDs?

Back 61

Have to take higher dosage of folic acid

Front 62

How can radiation affect the embryo?
what is the solution?

Back 62

X-rays/high levels of radiation can result in birth defects: microencephaly, spina bifida, cleft palate, limb defects, anomalies of the CNS and eyes

Must shield pregnant females durring radiation