3Placental Structure Purple and pancake shaped 6 inch diameter, 1 inch thick13-16 square meter surface areaAttaches to upper 1/3 of uterusMaternal side: Decidua BasalisFetal side: Chorion (attaches to amniotic membrane)
4Placental FunctionsPrimary function is to act as organ of respiration and to be the pathway for exchange of nutrients and waste products between mother and fetusPhysical protectionHormone synthesisIron and Glycogen storageSome metabolic functionsAntibodies
5Maternal-Fetal Circulation Note: Maternal and fetal blood do not come into direct contact!
6Maternal-Fetal Circulation Blood comes to IV spaces (maternal side) from uterine arteriesBlood in villi (fetal side) comes from umbilical arteriesAfter exchange of O2 and CO2, the “fresh blood” returns to the fetus via the umbilical vein
7Umbilical Cord2 arteries1 veinSurrounded by Wharton’s jelly
8Amniotic SacThe outer layer of the umbilical cord forms the amniotic sac around the fetusFetus is in amniotic sac containing amniotic fluidAmniotic fluid made up of maternal serum and fetal urine and fetal lung fluid3 Functions of amniotic fluid:Shock absorption, temperature stability, sterile environment
10Why is fetal PO2 low? Placental O2 consumption Admixture and shunting Like the lung, the IV space and the villi are not perfectly matchedFetal hemoglobin (HbF)More of it (when compared to adult blood) and has greater affinity for O2Concentration is grams%Made up of alpha and gamma chains of amino acidsHbF is present for up to two months after birthFetal O2 consumption is about twice what an adults is
11Fetal CirculationOOOPS! This is fecal circulation!
13Fetal Circulation UV goes into liver and portal circulation Most of blood shunts across the Ductus Venosus into the inferior vena cavaAs inferior vena cava empties into right atrium, most blood shunts across the Foramen Ovale into the left atrium where it enters the systemic circulation from the left ventricleThe heart and brain get the best blood first!Blood from superior vena cava goes into right ventricle and then to pulmonary arteryMost of this blood flow shunts across the Ductus Arteriosus into the aortaDA is in the descending aorta after the archPre-ductal blood may have a higher PO2!Hence, only 3-10% of fetal cardiac out put perfuses the fetal lings
14Summary: Fetal Circulation 3 Shunts: Ductus Venosus, Foramen Ovale, and Ductus ArteriosusPlacental CirculationOnly 3-10% of fetal cardiac output actually perfuses the fetal lungs
15Fetal Lung Development Lung buds appear at 3.5 weeksTracheo-bronchial tree formed by 16 weeksAlveoli start forming at weeksSurfactant also starts to formCapillary networks starts forming and approaching alveoli at weeksLungs and surfactant mature at 35 weeksNormal term is 40 weeks
16SurfactantReduces surface tension so alveoli don’t collapse with each exhalationIs a phospolipid made up of dipalmityl-lecithin and sphingomyelinProduced through two enzymatic pathways:Methyl transferasePhosphocholine transferaseThis is the major pathway and has a longer half-lifeMatures last
17Respiratory Problems at Birth! Immature lung architecture if born prematureAnd/or:Surfactant levels may not be adequate if:Premature birthProduction inhibited if significant hypoxia, hypothermia, or hypoglycemia