placenta

Examples of placenta in the following topics:

• Placenta Previa

  • Placenta previa is an obstetric complication in which the placenta is attached to the uterine wall close to or covering the cervix.
  • Placenta previa is an obstetric complication in which the placenta is attached to the uterine wall close to or covering the cervix .
  • In a normal pregnancy, the placenta does not overlie it, so there is no bleeding.
  • If the placenta does overlie the lower segment, as is the case with placenta previa, it may shear off and a small section may bleed.
  • The following have been identified as risk factors for placenta previa:

• Placenta

  • The placenta is an organ that connects the developing fetus to the mother's blood supply.
  • The fetal placenta, which develops from the same sperm and egg cells that form the fetus.
  • The umbilical cord inserts into the chorionic plate of the placenta.
  • IgG antibodies can pass through the human placenta, thereby providing protection to the fetus in utero.
  • The placenta also secretes hormones that are important during pregnancy.

• Chorionic Villi and Placental Development

  • The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium.
  • The placenta functions as a fetomaternal organ with two components: the fetal placenta (chorion frondosum), which develops from the same blastocyst that forms the fetus; and the maternal placenta (decidua basalis), which develops from the maternal uterine tissue.
  • The latter is a multinucleated, continuous cell layer that covers the surface of the placenta.
  • Image illustrating the placenta and chorionic villi.
  • The umbilical cord is seen connected to the fetus and the placenta.

• Fetal Circulation

  • The fetal circulation includes the blood vessels within the placenta and the umbilical cord that carry fetal blood.
  • The fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord.
  • Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen.
  • The uterine arteries carry oxygenated blood to the placenta, which then permeates the sponge-like placenta.
  • Blood from the placenta is carried to the fetus by the umbilical vein.

• Blastocyst Formation

  • The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta.
  • The blastocyst possesses an inner cell mass (ICM), or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast, which later forms the placenta.
  • The trophoblast combines with the maternal endometrium to form the placenta in eutherian mammals.
  • As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta.
  • The blastocyst possesses an inner cell mass from which the embryo will develop, and an outer layer of cells, called the trophoblast, which will eventually form the placenta.

• Living Mammals

  • Eutherian mammals are sometimes called placental mammals because all species possess a complex placenta that connects a fetus to the mother, allowing for gas, fluid, and nutrient exchange.
  • While other mammals possess a less complex placenta or briefly have a placenta, all eutherians possess a complex placenta during gestation.
  • Red foxes are eutherian (placental) mammals because the mothers nourish their young via a placenta during fetal development.
  • The placenta enables a mother to exchange gases, fluids, and nutrients with the growing embryos.

• Labor and Birth

  • Labor and birth are divided into three stages: the dilation of the cervix, the delivery of the baby, and the expulsion of the placenta.
  • Labor is the physical effort of expulsion of the fetus and the placenta from the uterus during birth (parturition).
  • At the same time, the placenta releases prostaglandins into the uterus, increasing the contractions.
  • This is necessary for the baby and placenta to be expelled during birth.
  • The last stage is the passage of the placenta after the baby has been born and the organ has completely disengaged from the uterine wall, usually within a few minutes.

• Trophoblast Development

  • Trophoblasts are the outer layer of cells that provide nutrients to the embryo and form part of the placenta.
  • These cells provide nutrients to the embryo and develop into a large part of the placenta.
  • Extravillous trophoblasts grow out from the placenta and penetrate into the decidualized uterus.
  • This process is essential not only for physically attaching the placenta to the mother, but also for altering the vasculature in the uterus to allow it to provide an adequate blood supply to the growing fetus as pregnancy progresses.
  • This ensures the fetus receives a steady supply of blood, and the placenta is not sensitive to fluctuations in oxygen that could cause it damage.

• Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)

  • Hemolytic disease of the newborn occurs when IgG produced by the mother transfers through the placenta and attacks fetal red blood cells.
  • Also known as erythroblastosis fetalis, this an alloimmune condition that develops in a fetus when the IgG molecules (one of the five main types of antibodies) produced by the mother pass through the placenta.
  • After delivery, bilirubin is no longer cleared (via the placenta) from the neonate's blood and the symptoms of jaundice (yellowish skin and yellow discoloration of the whites of the eyes) increase within 24 hours after birth.
  • Fetal-maternal hemorrhage can occur due to trauma, abortion, childbirth, ruptures in the placenta during pregnancy, or medical procedures carried out during pregnancy that breach the uterine wall.
  • In subsequent pregnancies, if there is a similar incompatibility in the fetus, these antibodies are then able to cross the placenta into the fetal bloodstream to attach to the red blood cells and cause hemolysis.

• Stages of Labor

  • Vaginal delivery childbirth has three distinct phases: dilation of the cervix, delivery of the infant, and delivery of the placenta.
  • The third stage of labor is the period from just after the fetus is expelled until just after the placenta is expelled. 
  • The average time from delivery of the baby until complete expulsion of the placenta is estimated to be 10–12 minutes.
  • Alternatively, it can be managed expectantly, allowing the placenta to be expelled without medical assistance.
  • It can refer to the immediate puerperium, or the hours immediately after delivery of the placenta.