Fetal Development (exam 1) Flashcards
First week of human development
transport of embryo down uterine tube and into uterus
- Mitotic cellular replication (cleavage) occurs as baby (zygote) is propelled toward uterus
Morula
16 cells
trophoblast
outer layer of cells
blastocyst
inner layer of cells (baby)
Ovum term
Conception to 14 days
Encompasses cellular replication -> zygote to blastocyst formation and differentiation into the three primary germ layers of cells (ectoderm, mesoderm, endoderm)
Ectoderm
Trophoblast (outer layer) develops into the placenta, integument, neural tissue, and glands
outer layer -> skin, nervous system, and other external parts of the body
Mesoderm
middler layer -> forms muscles, bones, connective tissue, circulatory system, reproductive organs, and gu system
Endoderm
inner layer -> thymus, thyroid, digestive, respiratory, and parts of the gu system
Embryo term
15 days to 8 weeks (organs are forming)
- Embryonic stage is the most critical time in the development of the organ systems and the external features
Teratogen
Environmental substances or exposures that result in functional or structural disability
- Developing areas with rapid cell division are the most vulnerable to malformation by environmental teratogens
folic acid
helps with fetal development (NTDs)
Viability
Capability to survive outside the uterus
Major criteria: CNS function and O2 capability of lungs
- Weight of 350g, 400g, or 500g
- 20 weeks past conception (22 weeks since LNMP)
(varies by state - TN is 500g, 20 weeks)
22-25 weeks still very concerning (threshold of viability)
Shunts
Allow most oxygenated blood to go to the brain
- maternal and fetal blood do not normally mix
- poorly oxygenated blood returns to the placenta for oxygen and nutrient through umbilical arteries
Ductus venosus
Foramen ovale
Ductus arteriosus
ductus venosus
shunts around liver
Placenta does the work of liver for fetus
foramen ovale
right to left shunt
Blood transfers from right atrium through foramen oval to left atria
ductus arteriosus
shunts around lung
just enough to keep viable
Hematopoietic
the formation of blood
- Starting in the yolk sac (3rd week)
- Stem cells seed the liver function 5th week
- Hematopoiesis begins the 6th week
- Stem cells seed the fetal bone marrow, spleen, thymus, and lymph nodes week 8 & 11
- Antigenic factors determine blood type and are present in the erythrocytes around 5 weeks
- Babies have their own blood type
- If woman should spontaneously abort the baby, a small bit of baby blood may get into her blood system
- If she happens to be Rh- and the baby is Rh+, her body immediately sets up a reaction to foreign substance (begins to develop antibodies to the Rh+ blood)
Circulatory system
Blood cells and heart functioning at 3 weeks
- Heart is fully developed at 8 weeks
- Hgb in fetus is about 50% greater than mother
- Normal fetal HR 110-160 = CO per fetal body weight higher than adults
The antigenic factors that determine blood type are present in erythrocytes after 6th week
- Places Rh- mom at risk for isoimmunization in any pregnancy that lasts longer than 6 weeks
(antigenic factors: Rh factor -> rbc’s are - or +)
Pulmonary Surfactant
Lecithin:Sphingomyelin (L:S) ration of 2:1 at maturity
Oxygenation
L:S ratio 2:1 at maturation
Lung movement can be seen by 11th week
Lungs fully mature about 34 weeks gestation (does not mean they know how to use them)
Breathing (swallowing AF) can be seen on US
Steroids can help build lung development
4 weeks external appearance
- Body flexed
- C shaped
- Arm and leg buds present
- Head at right angles to body
8 weeks external appearance
- Body fairly well formed
- Nose flat
- Eyes far apart
- Digits well formed
- Head elevating
- Tail almost disappeared
- Eyes, ears, nose, and mouth recognizable
12 weeks external appearance
- Nails appearing
- Resembles a human
- Head erect but disproportionately large
- Skin pink, delicate
16 weeks external appearance
- Head still dominant
- Face looks human
- Eyes, ears, and nose approach typical appearance on gross examination
- Arm/leg ratio proportionate
- Scalp hair appears
20 weeks external appearance
- Vernix Caseosa appears
- Lanugo appears
- Legs lengthen considerably
- Sebaceous glands appear
24 weeks external appearance
- Body lean but fairly well proportioned
- Skin red and wrinkled
- Vernix caseosa present
- Sweat glands forming
28 weeks external appearance
- Lean body
- Less wrinkled and red
- Nails appear
30-31 weeks external appearance
- Subcutaneous fat beginning to collect
- More rounded appearance
- Skin pink and smooth
- Has assumed birth position
36 weeks external appearance
- Skin pink
- Body rounded
- General lanugo disappearing
- Body usually plump
40 weeks external appearance
- Skin smooth and pink
- Scant vernix caseosa
- Moderate to profuse hair
- Lanugo on shoulders and upper body only
- Nasal and alar cartilage present
Dizygotic twins
Two separate pregnancies occurring simultaneously
- 2 embryos, 2 placentas, 2 chorions, and 2 amnions
Dichorionic/Diamniotic (di/di)
each embryo has their own amniotic sac (fraternal)
Monozygotic twins
Result from the division of a single fertilized ovum
- same sex, same physical traits
- shared placenta, 2 embryos, 2 amnions, 1 chorion, 1 placenta
Monochorionic/Diamniotic (mo/di):
Each embryo has their own amniotic sac (amnion) but share a placenta (chorion)
Monochorionic/Monoamniotic (mo/mo):
2 embryos, 1 sac, 1 placenta (always identical)
blood cells and blood vessels beginning to form, heart is beating
3rd week
fetal heartbeat heard with US doppler
10-12 weeks
sex is apparent at how many weeks
end of 12 gestation weeks
AF is adequate amount for amniocentesis
end of 16 gestation weeks
weight at the end of 24 weeks
600 gm
surfactant forming on alveolar surfaces by how many weeks
end of 28
L:S, 2:1 ration at ____ weeks
35
