placental

Examples of placental in the following topics:

• Living Mammals

  • The eutherians, or placental mammals, and the metatherians, or marsupials, together comprise the clade of therian mammals.
  • Marsupials differ from eutherians in that there is a less complex placental connection.
  • There are 18 to 20 orders of placental 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.
  • Red foxes are eutherian (placental) mammals because the mothers nourish their young via a placenta during fetal development.

• Chorionic Villi and Placental Development

  • It forms as a result of differentiation and fusion of the underlying cytotrophoblast cells, a process that continues throughout placental development.

• Placenta

  • "True" placentas are a defining characteristic of eutherian or "placental" mammals .
  • Active transport systems allow significantly different plasma concentrations of various large molecules to be maintained on the maternal and fetal sides of the placental barrier.
  • Human Chorionic Gonadotropin (hCG): The first placental hormone produced is hCG, which can be found in maternal blood and urine as early as the first missed menstrual period (shortly after implantation has occurred) through about the 100th day of pregnancy.
  • Women's blood serum will be completely negative for hCG by one to two weeks after birth. hCG testing is proof that all placental tissue is delivered. hCG is present only during pregnancy because it is secreted by the placenta, which is present only during pregnancy. hCG also ensures that the corpus luteum continues to secrete progesterone and estrogen.
  • Human Placental Lactogen (hPL [Human Chorionic Somatomammotropin]): This hormone is lactogenic and has growth-promoting properties.

• Evolution of Mammals

  • Synapsids from this period include Dryolestes (more closely related to extant placentals and marsupials than to monotremes) as well as Ambondro (more closely related to monotremes).
  • Metatherians are the animals more closely related to the marsupials, while eutherians are those more closely related to the placentals.
  • One of the major differences between placental and nonplacental eutherians is that placentals lack epipubic bones, which are present in all other fossil and living mammals (marsupials and monotremes).
  • After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds are generally regarded as the surviving dinosaurs) and several other mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Paleogene and Neogene, by the end of which all modern orders had appeared.

• Adjustments of the Infant at Birth

  • Perfusing its body by breathing independently instead of utilizing placental oxygen is the first challenge of a newborn.
  • Oxygenated blood now stimulates constriction of the umbilical arteries resulting in a reduction in placental blood flow.
  • As the pulmonary circulation increases, there is an equivalent reduction in the placental blood flow which normally ceases completely after about three minutes.
  • Energy metabolism in the fetus must be converted from a continuous placental supply of glucose to intermittent feeding.

• Trophoblast Development

  • The syncytiotrophoblast are the cells in direct contact with the maternal blood that reaches the placental surface, and thus facilitates the exchange of nutrients, wastes, and gases between the maternal and fetal systems.
  • The primary factor in IUGR is placental dysfunction caused by failure of the extravillous trophoblasts to penetrate and modify the uterine spiral arteries.

• Physiology of Lactation

  • In most species, milk comes out of the mother's nipples ; however, the platypus (a non-placental mammal) releases milk through ducts in its abdomen.
  • At birth, prolactin levels remain high, while the delivery of the placenta results in a sudden drop in progesterone, estrogen, and human placental lactogen levels.

• Other Hormone-Producing Structures

  • The first placental hormone produced is hCG, which can be found in maternal blood and urine as early as the first missed menstrual period (shortly after implantation has occurred) through about the 100th day of pregnancy.
  • Women's blood serum will be completely negative for hCG by one to two weeks after birth. hCG testing is proof that all placental tissue is delivered. hCG is present only during pregnancy because it is secreted by the placenta, which is present only during pregnancy. hCG also ensures that the corpus luteum continues to secrete progesterone and estrogen.
  • Human Placental Lactogen: this hormone is lactogenic and growth-promoting properties.

• Metabolic Changes

  • This is likely due to pregnancy related factors such as the presence of human placental lactogen that interferes with susceptible insulin receptors.

• Fertilization

  • In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane .