blastocyst

Examples of blastocyst in the following topics:

• Blastocyst Formation

  • The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta.
  • In humans, the blastocyst is formed approximatelyy five days after fertilization.
  • 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 surrounds the inner cell mass and a fluid-filled, blastocyst cavity known as the blastocoele or the blastocystic cavity.
  • 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.

• Cleavage, the Blastula Stage, and Gastrulation

  • A zygote undergoes rapid cell divisions (cleavage) to form a spherical ball of cells: the blastula; this will further develop into a blastocyst.
  • Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula.
  • In mammals, the blastula forms the blastocyst in the next stage of development.
  • The rearrangement of the cells in the mammalian blastula to two layers, the inner cell mass and the trophoblast, results in the formation of the blastocyst.

• Implantation

  • At this stage of prenatal development, the embryo is a blastocyst.
  • In humans, implantation of a blastocyst occurs between 6 to 12 days after ovulation.
  • In preparation for implantation, the blastocyst sheds its outside layer, the zona pellucida, which binds sperm during fertilization.
  • The syncytiotrophoblast then implants the blastocyst into the endometrium of the uterus by forming finger-like projections into the uterine wall called chorionic villi.

• Bilaminar Embryonic Disc Development

  • By the blastocyst stage, the embryo has become a hollow ball of cells with the inner cell mass (embryoblast) off to one side, while the blastocystic cavity completes the remainder of the sphere.

• 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 outer layer of the blastocyst becomes the trophoblast, which forms the outer layer of the placenta.

• Cellular Differentiation

  • In humans, approximately four days after fertilization and after several cycles of cell division, these cells begin to specialize, forming a hollow sphere of cells, called a blastocyst.
  • The blastocyst has an outer layer of cells, and inside this hollow sphere, there is a cluster of cells called the inner cell mass.

• Uterine (Menstrual) Cycle

  • During the menstrual cycle, the endometrium grows to a thick, blood vessel-rich tissue lining, representing an optimal environment for the implantation of a blastocyst upon its arrival in the uterus.
  • If a blastocyst implants, then the lining remains as the decidua.

• Trophoblast Development

  • Trophoblasts (from the Greek words trephein, to feed, and blastos, germinator) are cells that form the outer layer of a blastocyst.
  • A blastocyst embedded in the uterine decidua.

• Human Gestation

  • The outer layers of the zygote (blastocyst) grow into the endometrium by digesting the endometrial cells.
  • Wound healing of the endometrium closes up the blastocyst into the tissue.
  • Another layer of the blastocyst, the chorion, begins releasing a hormone called human chorionic gonadotropin (hCG) which makes its way to the corpus luteum, keeping it active.

• Fertilization

  • The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy.