Block 7 BRS - Placenta And Amniotic Fluid

A placenta implanted in the lower part of the uterus near the internal os is called placenta
previa. The repeated episodes of bright red vaginal bleeding are caused by the gradual dilation of
the uterus in the later stages of pregnancy. As the uterus dilates, spiral arteries and veins supplying the placenta are ruptured. The mother may bleed to death, and the fetus is placed in jeopardy because of the compromised maternal blood flow.

The intervillous space contains only maternal blood as the spiral arteries of the
endometrium penetrate the outer cytotrophoblast shell.

The normal amount of amniotic fluid at term is 1000 mL. However, the amount of amniotic
fluid at various stages of pregnancy can be indicative of congenital malformations.
Oligohydramnios (400 mL in late pregnancy) may be indicative of renal agenesis.
Polyhydramnios (2000 mL in late pregnancy) may be indicative of either anencephaly or
esophageal atresia.

Insulin, like all protein hormones, does not cross the placental membrane in significant
amounts.

During the later stages of pregnancy, the placental membrane becomes very thin and consists of two layers, the syncytiotrophoblast and fetal endothelium.

The placenta is a unique organ in that it is a composite of tissue from two different sources,
the mother and the fetus. The maternal component is the decidua basalis, and the fetal component is the villous chorion

Dizygotic twins and 35% of monozygotic twins have two placentas, two amniotic sacs, and
two chorions (i.e., 222).

The syncytiotrophoblast produces hCG.

A velamentous placenta occurs when umbilical blood vessels abnormally travel through the
amniochorionic membrane before reaching the placenta proper. If the vessels cross the internal
os, a serious condition called vasa previa exists. As the fetus grows during pregnancy and the
amniochorionic membrane stretches, the umbilical vessels may rupture. When that happens, the
fetus will bleed to death. The mother is in no danger of bleeding to death in vasa previa because
only the umbilical vessels rupture.

Huntington disease demonstrates an autosomal dominant inheritance pattern.

The fetal heart rate is first audible in the first trimester at around week 12.

Cystic fibrosis is an autosomal recessive disease that involves a mutation in the CF gene that encodes for a Cl- channel.

The amnion does not pass through the primitive umbilical ring. As craniocaudal folding
occurs, the amnion becomes the outer covering of the umbilical cord.

The lungs become capable of respiration at weeks 25-27 in the second trimester

Duchenne muscular dystrophy demonstrates an X-linked recessive inheritance pattern

. Leber hereditary optic neuropathy demonstrates a mitochondrial inheritance pattern.

Leber hereditary optic neuropathy involves a mutation in the ND4 gene located on mitochondrial DNA. All mitochondrial DNA is inherited only from the mother because sperm (male) mitochondria do not pass into the ovum at fertilization

Maternal urinary levels of estriol have long been recognized as a reliable index of fetalplacental function because estriol production is dependent on a normal-functioning fetal adrenal cortex, fetal liver, and placenta.