development and circulation of the fetal
TRANSCRIPT
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Y O L A N D A C H A N D L E R , M S N , R N
Fetal Development andCirculation
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Fetal Development
Cephalocaudal
Central to peripheral
Simple to complex
General to specific
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Embryonic Period
From beginning of 3rd wk through 8thwk afterconception
Critical stage for organ development- by end of 8th
wk all major organ systems in placeOrgans developing rapidly / highly vulnerable to
teratogens such as specific drugs & diagnosticprocedures, as well as inadequate intake of beneficial
substances such as folic acid
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Embryonic Period
WEEK 3
- May miss first menstrual period
- Embryonic disk develops 3 layers (germ layers) that
give rise to major organ systems Ectoderm
Mesoderm
Endoderm
- Central nervous system begins developing includingneural plate (will become head)
- Early heart begins beating at 21-22 days
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Embryonic Period
Week4
- Embryo folds at head & tail end-resembles c-shapedcylinder by end of 4thwk
- Tail apparent as brain & spinal cord develop morerapidly than other systems
- Neural tube closes
- Formation of face /upper respiratory tract begins
(beginnings of internal ear and eye are apparent)- Upper extremities appear as buds
- Partitioning of heart into 4 chambers begins during4thwk /completed by end of 6thwk
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Embryonic Period
Week4 continued
- Lower respiratory tract begins growth as a branch ofupper digestive tract
- Gradually esophagus & trachea separate completely
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Embryonic Period
Week5
- Head large b/c brain grows rapidly this wk
- Heart beating /developing 4 chambers
- Upper limb buds paddle shaped w/ notches b/tfingers
- Lower limbs paddle shaped, but w/ less definitionbetween toes
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Embryonic Period
Week6
- Head prominent /bent over chest
- Heart reaches final four chambered form
- Upper/lower extremities continue to be moredefined
- Eye continues to develop
- Beginning of external ear is apparent as 6 smallbumps to each side of neck
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Embryonic Period
Week7
- Face human looking
- Eyelids grow
- Extremities longer/better defined
- Trunk elongates & straightens, although c-shapespinal curve remains at birth
- Intestines grow faster than abdominal cavity , somost of the intestines contained in umbilical cordwhile abdominal cavity grows to accommodate
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Embryonic Period
Week8
- Embryo has definite human form
- Ears low-set, but approaching final location
- Eyes pigmented, but not fully covered by eyelids
- Fingers/toes stubby but well defined
- External genitalia begin to differentiate, but
male/female characteristics not distinct until after10thwk
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Fetal Period
Begins 9 wks after conception & ends w/birth
Period of growth & refinement in structure /functionof organ systems
Less vulnerable to teratogens
Central nervous system vulnerable to damagingagents throughout pregnancy
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Fetal Period
Weeks 9-12
- Head half total length of fetus
- Body begins growing faster than head
- Extremities approach final relative length, but legsstill proportionally shorter than arms
- 1st movement begins, but too slight for maternaldetection
- Face broad w/ wide nose & widely spaced eyes- Eyes close at 9 wks- reopen at 26 wks
- Ears appear low set b/c mandible still small
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Fetal Period
Weeks 9-12 cont
- Intestinal contents enter abdominal cavity
- Blood formation occurs primarily in liver during 9th
wk but shifts to spleen by end of 12thwk
- Begins producing urine excreted into amniotic sacas part of amniotic fluid
- Internal differences in male/female apparent 7thwk
- Sex can be determined by end of 12thwk byappearance of external genitalia
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Fetal Period
Weeks 13-16
- Grows rapidly in length so head becomes smaller inproportion to total length
- Movements strengthen & some women may feelquickening
- Face looks human b/c eyes face forward & externalears approach final position
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Fetal Period
Weeks 17-20
- Fetal movements feel like butterflies
- Vernix caseosa
- Lanugo
- Eyebrows/ head hair appear
- Brown fat
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Fetal Period
Weeks 21-24
- Continues growing/ gaining weight, but thin w/little SQfat
- Skin translucent & red d/t capillaries close to its fragilesurface
- Lungs begin to produce surfactant
- Capillary network surrounding alveoli increasing, but
very immature, some gas exchange possible- Survival at end of this period is possible, but at high risk
for multiple complications r/t immaturity of all systems
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Fetal Period
Weeks 25-28
- More likely to survive if born after 24 wks
- Lungs, pulmonary capillaries, & CNS continue to
mature- Becomes plumper /smoother skinned as SQ fat is
deposited under the skin(skin less red)
- Eyes reopen
- Head hair abundant- Blood formation shifts from spleen to bone marrow
- Usually assumes head down position at this time
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Fetal Period
Weeks 29-32
- Skin smooth & pigmented according to race
- Larger vessels visible over abdomen, but capillaries
cannot be seen- Toenails present/fingernails extend to fingertips
- More SQ fat, rounding the body contours
- If born during this period, chances of survival good
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Fetal Period
Weeks 33-38
- Maturation of all body systems continue until birth, rateslows as full-term approaches
- Fetus mainly gaining weight- Pulmonary system matures to enable efficient/unlabored
breathing after birth
- Well nourished term fetus is rotund, w/ abundant SQ fat
- Lanugo may be present on forehead, upper back, upperarms
- Vernix may remain in major creases (groin and axillae)
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Fetal Circulation
Fetus can thrive in a low oxygen environment
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Fetal Circulation
Blood circulates from fetal heart to placenta forexchange of oxygen & waste products & back to fetusfor delivery to fetal tissues
Because fetus does not breath air or metabolizesubstances in the liver, the post-birth circulation isaltered during uterine life
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Fetal Circulation
3 shunts divert most of circulating blood away fromlungs/ liver:
Ductus venosus
Foramen Ovale Ductus arteriosus
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Fetal Circulation
Ductus Venosus-
Oxygenated blood from placenta enters fetal bodythrough umbilical vein
About 1/2 the blood goes through the liverThe rest bypasses the liver and enters the inferior
vena cava through the ductus venosus
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Fetal Circulation
Foramen Ovale-shunt between right and left atrium
From inferior vena cava, blood enters right atrium ofheart
Most of the blood passes directly into left atriumthrough the foramen ovale
Once in left atrium, blood mixes with small amt. ofblood returning from the lungs
Blood then enters the left ventricle and is pumpedinto the aorta to perfuse the body
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Fetal Circulation
Ductus Arteriosus- shunt between pulmonaryartery and aorta
Small amount of blood from right ventricle is
circulated to lungs to nourish lung tissueThe rest of blood from right ventricle is pumped into
the pulmonary artery where it joins oxygenatedblood in the aorta through the ductus arteriosus
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Fetal Circulation
Changes After Birth
Fetal circulatory shunts not needed after birth Oxygenates blood in lungs
Metabolizes substances in liver Stops circulating blood to placenta
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Fetal Circulation
Changes After Birth-Foramen Ovale
Infant breathes
Blood flow to lungs increase
Pressure in right heart falls
Foramen ovale closes
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Fetal Circulation
Changes After Birth- Ductus Arteriosus
Pressure in aorta rises as pressure in pulmonaryartery falls, causing direction of blood flow through
ductus arteriosus to reverse- from aorta intopulmonary artery
Ductus arteriosus constricts as arterial oxygen levelrises
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Fetal Circulation
Changes After Birth- Ductus Venosus
Ductus venosus constricts when blood flow fromumbilical cord ceases
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Factors Affecting Fetal Development
Exposure to teratogens (anything that adverselyaffects normal cellular development in embryo/fetus)
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Factors Affecting Fetal Development
Maternal Health Habits/ Lifestyle
Can expose fetus to teratogens
Can limit amount of beneficial nutrients needed foroptimal growth and development
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