fetal+physiological+development
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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
Right atrium ↓
Right ventricle
Deoxygenated blood flowing through
Superior vena cava
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 Functional closure
Anatomical closure
Remnant
Ductus arteriosus
10 – 96 hrs after birth
2 – 3 wks after birth
Ligamentum arteriosum
Formamen ovale
Within several mins after birth
One year after birth
Fossa ovalis
Ductus venosus
Within several mins after birth
3 – 7 days after birth
Ligamentum venosum
Umbilical arteries → Umbilical ligaments
Umbilical vein → Ligamentum teres
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
Type Description Chains
Hemoglobin F Fetal Hgb or alkaline-resistant Hgb
2 alpha chains, 2 gamma chains
Hemoglobin A Adult Hgb. Formed starting at 32-34 wks gestation and results from methylation of gamma globin chains
2 alpha chains, 2 beta chains
Hemoglobin A2
Present in mature fetus in small amounts that increase after birth
2 alpha chains,2 delta chains
Fetal Hemoglobin
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 BloodFetal 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 BloodImmunocompetence 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 ORGANSGestational
age Fetal development
10 wks Squinting, opening of mouth, incomplete finger closure, plantar flexion of toes, swallowing and respiration
12 wks 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)