Fetal Physiology By Abdul Qahar


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Fetal physiology

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Fetal Physiology By Abdul Qahar

  1. 1. Fetal Circulation  Nutrients for growth and development are delivered from the umbilical vein in the umbilical cord → placenta → fetal heart
  2. 2. Oxygenated blood from mother ↓ (via umbilical vein) Liver Portal sinus Ductus venosus ↓ Inferior vena cava (mixes with deoxygenated blood) ↓ Right atrium
  3. 3. Right atrium ↓ (through Foramen ovale) Left atrium ↓ Left ventricle ↓ (through Aorta) Heart and Brain
  4. 4. Deoxygenated blood from lower half of fetal body ↓ Inferior vena cava Deoxygenated blood flowing through Superior vena cava Right atrium ↓ Right ventricle
  5. 5. Right ventricle ↓ Pulmonary artery ↓ (through Ductus arteriosus) Descending aorta ↓ Hypogastric arteries ↓ Umbilical arteries ↓ Placenta
  6. 6. 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.
  7. 7.  3 shunts: - Ductus venosus - Foramen ovale - Ductus arteriosus
  8. 8. 2nd difference:  Ventricles of the fetal heart work in parallel compared to the adult heart which works in sequence.
  9. 9.  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
  10. 10.  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
  11. 11. 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
  12. 12.  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.
  13. 13. 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)
  14. 14. Hematopoiesis  Erythrocytes progress from nulceated to non- nucleated  Blood vol. and Hgb concentration increase progressively  Midpregnancy: Hgb 15 gms/dl  Term: 18 gms/dl
  15. 15. 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)
  16. 16. 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
  17. 17. 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
  18. 18. 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)
  19. 19.  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)
  20. 20.  Sufficient development of synaptic functions are signified by flexion of fetal neck & trunk  If fetus is removed from the uterus during the 10 th wk, spontaneous movements may be observed although movements in utero aren’t felt by the mother until 18-20 wks
  21. 21. Gestational 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
  22. 22.  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
  23. 23.  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.
  24. 24.  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)
  25. 25.  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
  26. 26. 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
  27. 27.  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.
  28. 28.  Insulin levels: ↑ in newborns of diabetic mothers and LGAs (large for gestational age); ↓in infants who are SGA (small for gestational age)