Download FETAL PHYSIOLOGICAL DEVELOPMENT

FETAL PHYSIOLOGICAL
DEVELOPMENT
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
1st 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 bear 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
non-nucleated
• 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
antigen-specific 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)