placenta

(noun)

a vascular organ in mammals that supplies food and oxygen from the mother to the fetus, while passing back waste; it is implanted in the wall of the uterus

Related Terms

Examples of placenta in the following topics:

  • 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.

  • 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.

  • Human Gestation

    • As the trimester progresses, the outer layer of the embryo begins to merge with the endometrium and the placenta forms.
    • This organ takes over the nutrient and waste requirements of the embryo and fetus, with the mother's blood passing nutrients to the placenta and removing waste from it.
    • Some of the mother's immunoglobulins will pass through the placenta, providing passive immunity against some potential infections.
    • The placenta will continue functioning up through the delivery of the fetus.
    • This fetus is just entering the second trimester, when the placenta takes over more of the functions performed as the baby develops.

  • Characteristics of Amniotes

    • In mammals, membranes that are homologous to the extra-embryonic membranes in eggs are present in the placenta.

  • Gene Expression in Stem Cells

    • These stem cells can become any tissue in the body, excluding a placenta.
    • Only cells from an earlier stage of the embryo, known as the morula, are totipotent, able to become all tissues in the body and the extraembryonic placenta.

  • External and Internal Fertilization

    • In viviparity, the young develop within the female, receiving nourishment from the mother's blood through a placenta.

  • Cleavage, the Blastula Stage, and Gastrulation

    • The trophoblast will contribute to the placenta and nourish the embryo.

  • Humoral Immune Response

    • For example, antibodies circulating in a pregnant woman's body move across the placenta into the developing fetus.