blastocisto

The blastocisto, commonly called the blastocyst, is a defining pre-implantation stage of mammalian development that follows fertilization. In humans it typically forms about five to six days after conception and consists of a fluid-filled cavity (the blastocoel), an outer layer of trophoblast cells, and an inner cell mass containing the cells that will give rise to the embryo.

During blastulation, the morula develops a fluid-filled cavity, forming the blastocyst. The blastocyst is initially enclosed by the zona pellucida and, as implantation nears, hatches from the zona to expose the trophoblast to the uterine lining; the outer trophoblast forms the interface with the maternal tissues, while the inner cell mass becomes the embryo.

Implantation into the uterine wall occurs as the blastocyst reaches the endometrium, typically around days 6 to 10 after ovulation. The trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast, which invade the endometrium and establish the placenta, while the embryoblast yields the developing embryo.

In clinical practice, blastocysts are often cultured for several days in assisted reproductive technology and transferred at the blastocyst stage to improve implantation rates. Procedures such as preimplantation genetic testing may be performed on trophectoderm cells, and blastocysts are frequently cryopreserved for later use.

The blastocyst represents a critical juncture between totipotency and the subsequent specialization of tissues. While the general structure is conserved across mammals, species-specific timing and regulatory mechanisms vary, and research continues to illuminate early human development and implantation biology.