Back
ditki Logo
medical & biological sciences
All Access Pass - 1 FREE Month!
Institutional email required, no credit card necessary.
Cleavage & Implantation
Cleavage
Zygote divides and develops to form the blastocyst* during passage through the uterine tube.
  • Involves multiple rounds of mitotic division without growth in size.
Key Steps:
  • Zygote, single cell, produced by fusion of the male and female gametes in fertilization.
    • Has zona pellucida, which is the acellular protective coat.
After a single round of mitosis, the zygote gives rise to two cells, aka, blastomeres.*
  • By the four-cell stage, the blastomeres are loosely organized, with incomplete contact between the cells.
This changes at the 8-cell stage, when compaction* reorganizes the cells and forms:
    • An inner cell mass, which is held together by tight junctions.
    • An outer cell mass, which is covered by the zona pellucida.
In the histological sample, notice the tightly packed cells and thick outer zona pellucida.
In the next stage the morula* comprises approximately 16 cells.
    • Sodium-potassium pumps are responsible for pulling water into the morula cell mass.
    • As a result, cavitation occurs
Morula gives rise to the blastocyst, with a blastocyst cavity (blastocoel*)
  • Blastocyst:
    • Zona pellucida surrounds two cell populations:
Outer cell population is now called the trophoblast. Inner cell mass, which has become concentrated to one side, is now called the embryoblast.
As we learn elsewhere, the trophoblast plays an essential role in implantation and formation of the placenta, and the embryoblast gives rise to the tissues of the embryo proper.
  • Cavitation establishes embryonic polarity:
    • Embryonic pole at the side of the embryoblast.
    • Abembryonic pole at the opposite side.
FREE ONE-MONTH ACCESS
Institutional (.edu or .org) Email Required
Register Now!
No institutional email? Start your 1-week free trial, now!
- or -
Access through your institution

Cleavage & Implantation

Cleavage
Mitotic division that occurs in the uterine tube.
Implantation
Endometrial encapsulation that occurs within the uterus.
    • Endometrium comprises multiple layers, and, under direction from the ovarian hormones, cyclically prepares for implantation of an embryo. In the absence of implantation, the endometrial lining is shed during menstruation.
We show implantation in 4 key steps:
1. Pre-implantation events, which include "hatching" of the blastocyst from the zona pellucida. 2. Blastocyst apposition to the uterine wall. 3. Early adhesion to uterine epithelia. 4. Uterine stroma – embryo contact, which ultimately connects the maternal vascular supply to the embryo.

Related Tutorials