FETAL PHYSIOLOGICAL
DEVELOPMENT
Prenatal development
 Ovular period / germinal period
 Embryonic period- CRL is 4mm
 Fetal period.
Principal events
 Day 14-21_ notochord
 Day 21-28_ neural fold fuse to form neural tube,
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heart beat
Week 4-6 post conception-face. Limb buds, optic
vesicle
Weeks 6-8_ all major structures form
Weeks 8-12 – external genital
Week 20 – skin is covered by lanugo
Week 28- testes descend to int inguinal ring
Week 36- one testes inti scrotum
Week 40 both testes descend, nail, post. fontonelle
CARDIOVASCULAR SYSTEM
Fetal Circulation
 Nutrients for growth and development are
delivered from the umbilical vein in the
umbilical cord → placenta → fetal heart
Fetal Circulation
Oxygenated blood from mother
↓ (via umbilical vein)
Liver
Portal sinus Ductus venosus
↓
Inferior vena cava (mixes with
deoxygenated blood)
↓
Right atrium
Right atrium
↓ (through Foramen ovale)
Left atrium
↓
Left ventricle
↓ (through Aorta)
Heart and Brain
Deoxygenated blood
from lower half of
fetal body
↓
Inferior vena cava
Deoxygenated blood
flowing through
Superior vena cava
Right atrium
↓
Right ventricle
Right ventricle
↓
Pulmonary artery
↓ (through Ductus arteriosus)
Descending aorta
↓
Hypogastric arteries
↓
Umbilical arteries
↓
Placenta
Fetal
Circulation
Source: http://images.google.com.ph
Differences in Fetal and
Adult
Circulation
st
1 difference:
 Presence of shunts which allow oxygenated blood
to bypass the right ventricle and pulmonary
circulation, flow directly to the left ventricle, and
for the aorta to supply the heart and brain
 3 shunts:
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
Differences in Fetal and
Adult Circulation
2nd difference:
 Ventricles of the fetal heart work in parallel
compared to the adult heart which works in
sequence.
Differences in Fetal and
Adult Circulation
 Fetal cardiac output per unit weight is 3 times
higher than that of an adult at rest.
 This compensated for low O2 content of fetal
blood.
 Is accomplished by ↑ heart rate and
↓
peripheral resistance
Changes After Birth
 Clamped cord + fetal lung expansion =
constricting and collapsing of umbilical
vessels, ductus arteriosus, foramen ovale,
ductus venosus
 Fetal circulation changes to that of an adult
Changes After Birth: Closing of
Shunts
Shunt
Ductus
arteriosus
Functional
closure
Anatomical
closure
Remnant
10 – 96 hrs after 2 – 3 wks after Ligamentum
birth
birth
arteriosum
Formamen Within several
ovale
mins after birth
One year after Fossa ovalis
birth
Ductus
venosus
3 – 7 days
after birth
Within several
mins after birth
Umbilical arteries → Umbilical ligaments
Umbilical vein → Ligamentum teres
Ligamentum
venosum
Changes After Birth
 Maintenance of ductus arteriosus depends
on:
- difference in blood pressure bet. Pulmonary
artery and aorta
- difference in O2 tension of blood passing
through ductus. ↑ p O2 = stops flow. Mediated
through prostaglandins.
Fetal Blood
Hematopoiesis
 First seen in the yolk sac during embryonic
period (mesoblastic period)
 Liver takes over up to term (hepatic period)
 Bone marrow: starts hematopoietic function
at around 4 months fetal age; major site of
blood formation in adults (myeloid period)
Fetal Blood
Hematopoiesis
 Erythrocytes progress from nulceated to nonnucleated
 Blood vol. and Hgb concentration increase
progressively
 Midpregnancy: Hgb 15 gms/dl
 Term: 18 gms/dl
Fetal Blood
Hematopoiesis
 Fetal erythrocytes: 2/3 that of adult’s (due to large
volume and more easily deformable)
 During states of fetal anemia: fetal liver synthesizes
erythropoietin and excretes it into the amniotic
fluid. (for erythropoiesis in utero)
Fetal Blood
Fetal Blood Volume
 Average volume of 80 ml/kg body wt. right
after cord clamping in normal term infants
 Placenta contains 45 ml/kg body weight
 Fetoplacental blood volume at term is
approx. 125 ml/kg of fetus
Fetal Blood
Fetal Hemoglobin
Type
Description
Hemoglobin F Fetal Hgb or alkalineresistant Hgb
Chains
2 alpha chains,
2 gamma chains
Hemoglobin A Adult Hgb. Formed starting 2 alpha chains,
at 32-34 wks gestation and 2 beta chains
results from methylation of
gamma globin chains
Hemoglobin
A2
Present in mature fetus in
small amounts that
increase after birth
2 alpha chains,
2 delta chains
Fetal Blood
Fetal Hemoglobin
 Fetal erythrocytes that contain mostly Hgb F bind
more O2 than Hgb A erythrocytes
 Hgb A binds more 2-3 BPG more tightly than Hgb F
(this lowers affinity of Hgb for O2)
 Increased O2 affinity of fetal erythrocytes results
from lower concentartion of 2-3 BPG in the fetus
 Affinity of fetal blood for O2 decreases at higher
temp. (maternal hyperthermia)
Oxygen dissociation curve of fetal and maternal blood
Source: http://www.colorado.edu/intphys/Class/IPHY3430-200/image/18-12.jpg
Fetal Blood
Fetal Coagulation Factors
 Contains lowers levels of coagulation factors II, VI, IX, X,
XI, XII, XIII and fibrinogen (vit. K dependent factors)
 Routine prophylaxis of vit. K injections to prevent
hemorrhagic disease of the newborn
 Platelet count is normal
 Thrombin time prolonged
 Factor XIII (fibrin stabilizing factor) & plasminogen lower
than adult
 Low level of factor VIII → hemophilia in male infants
Fetal Blood
Fetal Plasma Proteins and Blood Viscosity
 Mean total plasma protein, Plasma albumin
concentration, and Blood viscosity: similar in
maternal & fetal blood
 Increased viscosity in fetal blood: due to
higher Hct. Is offset by lower levels of
fibrinogen and IgM, and by more deformable
erythrocytes
Fetal Blood
Immunocompetence of Fetus
 IgG from mother begins at around 16 wks and is most
pronounce during last 4 wks or pregnancy
 Newborns produce IgG and adult values are reached at 3
years old
 IgM produced by fetus in response to congenital
infections (Rubella, CMV, Toxoplasmosis)
 Adult levels of IgM attained by 9 mos old
Fetal Blood
 B lymphocytes appear in liver by 9 wks gestation,
and seen in the blood and spleen by 12 wks
gestation
 T lymphocytes produced by thymus at 14 wks
 Monocytes of newborns able to process and
present antigen when tested w/ maternal antigenspecific T-cells
Fetal Blood
Ontogeny of the Immune Response
 Hemolytic disease of the newborn: maternal
antibodies to fetal erythrocyte antigen cross the
placenta to destroy fetal erythrocytes
 Fetus is immunologically competent at 13 wks AOG
 Synthesis of complement in late 1st trimester. At
term, complement levels are ½ of adults
Fetal Blood
Ontogeny of the Immune Response
 Newborn responds poorly to immunization (due to
deficient response of newborn B cells or lack of T
cells)
 Only IgA from colostrum may protect against
enteric infections
 IgM predominantly produced in response to
antigenic stimulation. Identification may help
diagnose intrauterine infections
NERVOUS SYSTEM and SENSORY
ORGANS
 Sufficient development of synaptic functions
are signified by flexion of fetal neck & trunk
 If fetus is removed from the uterus during the
10th wk, spontaneous movements may be
observed although movements in utero
aren’t felt by the mother until 18-20 wks
NERVOUS SYSTEM and SENSORY ORGANS
Gestational
age
10 wks
Fetal development
12 wks
Squinting, opening of mouth, incomplete finger
closure, plantar flexion of toes, swallowing and
respiration
Taste buds evident histologically
16 wks
Complete finger closure
24 – 26
wks
Ability to suck, hears some sounds
28 wks
Eyes sensitive to light, responsive to variations
in taste of ingested substances
DIGESTIVE SYSTEM
 11 wks gestation → peristalsis in small
intestine, transporting glucose actively
 16 wks gestation → able to swallow amniotic
fluid, absorb much water from it, and propel
unabsorbed matter to lowe colon
 Hydrochloric acid & other digestive enzymes
present in very small amounts
DIGESTIVE SYSTEM
 Term fetuses can swallow 450 ml amniotic fluid in 24
hours
 This regulates amniotic fluid volume:
- inhibition of swallowing (esophageal atresia) =
Polyhydramnios
 Amniotic fluid contributes little to caloric requirements of
fetus, but contributes essential nutrients: 0.8 gms of
soluble protein is ingested daily by the fetus from
amniotic fluids. Half is alubumin.
DIGESTIVE SYSTEM
 Meconium passed after birth
 Dark greenish black color of meconium caused by
bile pigments (esp. biliverdin)
 Meconium passage during labor due to hypoxia
(stimulates smooth muscle of colon to contract)
 Small bowel obstruction may lead to vomiting in
utero
 Fetuses with congenital chloride diarrhea may have
diarrhea in utero. Vomiting and diarrhea in utero
may lead to polyhydramnios and preterm delivery
DIGESTIVE SYSTEM
Liver and Pancreas
 Fetal liver enzymes reduced in amount compared to
adult
 Fetal liver has limited capacity to convert free bilirubin
to conjugated bilirubin
 Fetus produces more bilirubin due to shorter life span
of fetal erythrocytes. Small fraction is conjugated and
excreted and oxidized to biliverdin
 Much bilirubin is transferred to the placenta and to the
maternal liver for conjugation and excretion
DIGESTIVE SYSTEM
 Fetal pancreas responds to hyperglycemia by
↑ insulin
 Insulin containing granules identified in fetal
pancreas at 9-10 wks. Insulin in fetal plasma
detectable at 12 wks.
 Insulin levels: ↑ in newborns of diabetic
mothers and LGAs (large for gestational age);
↓in infants who are SGA (small for gestational
age)
endocrinology
 Growth hormone, ACTH, prolactin, TSH and
gonadotrophic hormones- pituitary -10 wk
 12 wk- vasopressin and oxytocin- post
pituitary
 Small amount of thyroxin- 11wk
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