Ricci Chapter 10: Fetal Development and Genetics
Fetal Development, Fetal Circulation, and Genetics; Review Table 10.1; Figure 10.9
1. Define the three stages of fetal development during pregnancy:
Preembryonic 1st two weeks after fertilization.
Begins with fertilization/conception in the fallopian tube. It is
the union of the ovum and the sperm.
Once sperm reaches the plasma membrane, ovum resumes
meiosis and forms a nucleus with half the number of
chromosomes (23). when the ovum and the sperm makes
contact, they lose their nuclear membranes and combine their
maternal and paternal chromosomes.
Haploids (23) join and forms a diploid (46) = zygote.
Implantation occurs 7-10 days after conception in the
endometrium.
Free floating ball of cells making its way to the uterus.
Morula ball of specialized cells that will later form into fetal structures. Contains blastocyst and trophoblast
(turns into amnion and chorion, respectively, which forms the placenta).
Further differentiation of trophoblast:
o Ectoderm CNS, sense, skin and glands
o Mesoderm skeletal, urinary, circulatory, reproductive
o Endoderm respiratory, liver, pancreas, GI
This stage ends w/ implantation.
Embryonic 2 weeks – 8 weeks after conception
Basic structures of all major body organs and external features are completed (organogenesis)
Heartbeat present, circulation begins
Heartbeat seen on transvaginal U/S around 6 weeks
Bone begins to replace cartilage
Fetal 8 weeks - birth
Longest period of prenatal development. Embryo mature enough to be called a fetus.
Dramatic growth and refinement of all organ systems take place during this stage.
Heartbeat able to be heard on external U/S at around 12 weeks
Fetus able to hear at 18 weeks
Able to open and close eyes at 28 weeks
Lungs continue to develop and more alveoli form completed around 35 weeks (placenta does gas exchange).
2. Why is the embryonic stage a critical time in development? This is a critical period of differentiation because the rapidly
growing embryo is most susceptible to damage from external sources, including teratogens (alcohol and drugs), radiation,
infections (ex. Rub, CMV), radiation, and nutritional deficiencies.
3. What are the major milestones related to fetal development during each trimester?
First trimester: 0 – 12th week; look above for 0 – 8th week.
o Week 9 -12 sexual differentiation; GI activity; head half the fetus size; face and neck well formed; urogenital
tract complete; RBCs produced in liver; urine begins to produce; FETAL GENDER can be determined at week 12.
Fetus moves, kicks and swallows.
Second trimester: 13th – 28th week
o Week 13-16 hair develops; skin transparent; bones become harder; active movement; sucking motions;
external genitals; fingernails and toenails; weigh quadruples
o Week 17-20 rapid brain growth; eyebrows and hair appear; muscles well developed.
o Week 21-24 eyebrows, eyelashes; hand grasp and startle reflex; lungs start to develop and produce
surfactant.
o Week 25-28 15 inches; fingerprints; blood formation from spleen to bone marrow; head down position;
responds to light and sounds; suck thumb
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, Antepartum
Third trimester: 29th week – 40th week
o Week 29-32 rapid in body fat; CNS control; rhythmic breathing movements; pupillary light reflex present;
stores iron, calcium and phosphorus
o Week 33-38 testes; hand grasp reflex; earlobes; small breast buds; mom supplies ANTIBODIES against disease;
FULL TERM at 38 weeks.
4. How is fetal circulation different from that of a child or adult? Closed circulatory system. Fetal circulation involves the
circulation of blood from the placenta to and through the fetus, and back to the placenta. Blood flow from mother goes to
the placenta and nutrients are absorbed and O2 diffused through fetal circulation via the umbilical cord to the fetus.
What is the function of the placenta in fetal circulation? Placenta essentially takes over the functions of the lungs and
liver during fetal life. Also plays a role in nutrient exchange.
What is the function of the shunts in fetal circulation? Lungs and liver are not fully functional. Bypasses/shunts are
needed to ensure adequate oxygenation.
3 shunts/bypasses present during fetal life:
1. Ductus venosus shunts blood from the umbilical cord vein into the
inferior vena cava bypasses the liver.
Critical for quickly shunting oxygenated blood to the fetal brain.
2. Ductus arteriosus connects pulmonary artery and aorta, bypasses
lungs.
3. Foramen ovale connects L and R atrium, bypasses lungs. Blood
shunts R L.
Blood to placenta
Oxygenated blood from placenta to body; Mixes w/
deoxygenated blood from tissues
Shunt to bypass liver; Fetal alcohol syndrome
Shunt from R atrium to L atrium; Blood bypasses lungs
Shunt from pulmonary a. to aorta; Blood bypasses lungs
Umbilical vein carries oxygen rich blood from the placenta to the liver and
through the DV. From there it is carried to tin inferior vena cava to the R.atrium
of the heart. Some of the blood is shunted through the FO to the L.side of the
heart, where it is routed to the brain and upper extremities.
The rest of the blood travels down to the R.ventricle and through the
pulmonary artery. A small portion of the blood travels to the
nonfunctioning lungs, while the remaining blood is shunted through the DA
into the aorta to supply the rest of the body.
5.
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