placental memberane

Placental Development and Circulation

• The placenta is a feto-maternal organ with two components: a fetal part derived from the chorionic sac and a maternal part derived from the endometrium.
• The placenta develops from the chorionic sac, which forms the villous chorion, and the decidua basalis, which forms the maternal part.
• The decidua is the endometrium of the uterus during pregnancy, consisting of three regions: decidua basalis, decidua capsularis, and decidua parietalis.
• The decidua separates from the remainder of the uterus after childbirth.

Fetal and Maternal Circulation

• Fetal circulation: poorly oxygenated blood passes through the umbilical arteries, placenta, and chorionic arteries, and then returns to the fetus through the umbilical vein.
• Maternal circulation: maternal blood enters the intervillous space through spiral endometrial arteries, and returns to the maternal circulation through endometrial veins.
• Reductions in uteroplacental circulation can result in fetal hypoxia and intrauterine growth restriction.

Placental Membrane and Functions

• The placental membrane separates fetal and maternal circulations, consisting of four layers: syncytiotrophoblast, cytotrophoblast, connective tissue, and endothelium of fetal capillaries.
• The placenta has several functions:
  • Metabolism (synthesizing glycogen, cholesterol, and fatty acids)
  • Transport of gases and nutrients
  • Endocrine secretion (hCG, human chorionic somatomammotropin, etc.)
  • Protection
  • Excretion (fetal waste products)
• The placenta allows for the transfer of substances between fetal and maternal blood through simple diffusion, facilitated diffusion, active transport, and pinocytosis.

Hormones and Tumorigenic Properties

• The placenta synthesizes protein hormones, including hCG, human chorionic somatomammotropin, and human chorionic thyrotropin.
• The placenta has tumorigenic properties, invading the uterus to establish a blood supply and facilitate exchange of molecules between the mother and embryo/fetus.

Umbilical Cord and Amniotic Fluid

• The umbilical cord is a tube-like structure connecting the placenta to the fetus, carrying fetal blood to the placenta and maternal blood to the fetus.
• The amniotic fluid is derived from maternal tissue and the fetus, serving as a protective environment for the developing embryo/fetus.
• The amniotic fluid allows for symmetric external growth, acts as a barrier to infection, and permits normal fetal lung development.

Fetal Development and Multiple Pregnancies

• The embryo is defined as the developing pregnancy from fertilization to the end of the 8th week, after which it is called a fetus.
• Multiple pregnancies increase the risks of chromosomal anomalies and fetal morbidity, with the frequency of dizygotic twinning showing racial differences.
• Dizygotic twins develop from two zygotes and may be of the same sex or different sexes, while monzygotic twins are genetically identical and develop from one zygote.