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.

• 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.

• 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.

• Tissue Development

  • This then becomes a blastocyst, consisting of an outer layer called a trophoblast, and an inner cell mass called the embryoblast.
  • Filled with uterine fluid, the blastocyst breaks out of the egg coating and undergoes implantation.

• Early Pregnancy Tests

  • The first of these markers to be discovered, human chorionic gonadotropin (hCG), is produced by the trophoblast cells of the fertilized ovum (blastocyst).

• Cleavage of the Zygote

  • Fluid collects between the trophoblast and the greater part of the inner cell mass, and thus the morula, is converted into the blastodermic vesicle (also called the blastocyst or blastula).

• Hormonal Regulation of the Female Reproductive Cycle

  • Progesterone plays a vital role in making the endometrium receptive to implantation of the blastocyst and supportive of the early pregnancy.