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Placenta
Structure, development, hormones
| Term | Definition |
|---|---|
| What makes up the fetal component of the placenta? | Cytotrophoblast, syncytiotrophoblast |
| What is the cytotrophoblast? | Inner layer of fetal placental chorionic villi -> makes cells |
| What is the syncytiotrophoblast? | Outer layer of fetal placental chorionic villi -> makes/secretes hormones (hCG) -> lacks MHC I expression to reduce maternal immune response |
| What is the parental component of the placenta? | Decidua basalis -> derived from uterine endometrium |
| What makes up the parental circulation of the placenta? | Endometrial vein -> removes fetal waste products, endometrial artery -> provides fetus w/ nutrients and O2 (pathway for drugs and viruses as well) |
| What makes up the fetal circulation? | 1 umbilical vein -> provides fetus w/ O2 -> drains into fetal IVC via liver/DV, 2 umbilical arteries -> spiral around vein -> take fetus waste products from fetal internal iliac arteries to placenta |
| How do the fetal and parental circulation meet? | Umbilical vessels create branch villus that are near parental blood in intervillous space -> separated by inner cytotrophoblast and outer syncytiotrophoblast of chorionic villi |
| Where are the fetal circulation derived from? | Allantois -> umbilical arteries and vein -> forms from hindgut extending into urogenital sinus |
| What is amniotic fluid derived from and how is it cleared? | Fetal urine and expelled fetal lung liquid -> cleared by fetal swallowing/intramembranous absorption |
| What is polyhydramnios? | Xcs amniotic fluid -> idiopathic/fetal malformations (oesophageal/duodenal atresia/anencephaly -> cannot swallow) caused by diabetes in pregnant patient/fetal anaemia |
| What is oligohydramnios? | Insufficient amniotic fluid -> placental insufficiency, bilateral renal agenesis -> inability to excrete urine |
| What are dizygotic twins? | Fraternal twins -> 2 eggs separately fertilised by 2 different sperm -> 2 separate amniotic sacs/placentas (chorion) -> dichorionic diamniotic |
| What are monozygotic twins? | Identical twins -> 1 egg and 1 sperm fertilisied -> splits in early pregnancy -> timing determines chorionicity/amnionicity |
| What results from monozygotic twins splitting 0-4 days? | 25% -> 2-cell stage -> separate chorions (placentas) and amnions -> dichorionic, diamniotic but identical |
| What results from monozygotic twins splitting 4-8 days? | 75% -> morula formed -> shared chorion (1 placenta) but separate amnions -> monochorionic, diamniotic but identical |
| What results from monozygotic twins splitting 8-12 days? | Rare -> blastocyst formed -> shared chorion (1 placenta) and shared amnion -> monochorionic, monoamniotic but identical |
| What results from monozygotic twins splitting 12-16 days? | Rare -> embryonic disc has formed -> splitting -> normal baby, axis duplication -> conjoined twins (monochorionic, monoamniotic) |
| What is twin-twin transfusion syndrome? | Monochorionic twin gestations -> unbalanced vascular connections btwn twins -> net blood flow from one twin to the other -> donor twin becomes hypovolaemic/oligohydramniotic -> recipient twin becomes hypervolaemic/polyhydramniotic |
Created by:
vykleung
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