development and circulation of the fetal

8/8/2019 Development and Circulation of the Fetal

1/38

Y O L A N D A C H A N D L E R , M S N , R N

Fetal Development andCirculation


2/38

Fetal Development

Cephalocaudal

Central to peripheral

Simple to complex

General to specific


3/38

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


4/38

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


5/38

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


6/38

Embryonic Period

Week4 continued

- Lower respiratory tract begins growth as a branch ofupper digestive tract

- Gradually esophagus & trachea separate completely


7/38

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


8/38

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


9/38

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


10/38

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


11/38


12/38

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


13/38

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


14/38

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


15/38

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


16/38

Fetal Period

Weeks 17-20

- Fetal movements feel like butterflies

- Vernix caseosa

- Lanugo

- Eyebrows/ head hair appear

- Brown fat


17/38

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


18/38

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


19/38

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


20/38

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)


21/38


22/38


23/38

Fetal Circulation

Fetus can thrive in a low oxygen environment


24/38

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


25/38


26/38

Fetal Circulation

3 shunts divert most of circulating blood away fromlungs/ liver:

Ductus venosus

Foramen Ovale Ductus arteriosus


27/38

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


28/38

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


29/38

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


30/38


31/38

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


32/38

Fetal Circulation

Changes After Birth-Foramen Ovale

Infant breathes

Blood flow to lungs increase

Pressure in right heart falls

Foramen ovale closes


33/38

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


34/38

Fetal Circulation

Changes After Birth- Ductus Venosus

Ductus venosus constricts when blood flow fromumbilical cord ceases


35/38


36/38

Factors Affecting Fetal Development

Exposure to teratogens (anything that adverselyaffects normal cellular development in embryo/fetus)


37/38

Factors Affecting Fetal Development

Maternal Health Habits/ Lifestyle

Can expose fetus to teratogens

Can limit amount of beneficial nutrients needed foroptimal growth and development


38/38

development and circulation of the fetal

Documents