Morula
A morula (from Latin morum ' mulberry ' ), also known as a "mulberry germ", is a developmental stage in the early embryogenesis of multicellular organisms such as humans in biology .
The morula is a globular cluster of 16 to 32 cells ( blastomeres ), which emerges from the zygote after the first divisions . In humans, from the 16-cell stage and around four days after fertilization , one speaks of a morula. At this point, the cluster of cells is usually in the fallopian tube . The volume of the morula is unchanged from that of the zygote, as both are surrounded by the rigid zona pellucida , a layer of glycoproteins . The diameter is 150 µm . The zona pellucida is retained up to the 6th day ( blastocyst stage ) to stabilize the shape of the early seedling, to prevent implantation in the fallopian tubes and to protect against immunological reactions of the mother .
In the morula stage , the cells differentiate into an inner and an outer cell mass, which, however, do not yet differ externally. The outer cells form impermeable cell connections ( tight junctions ) with one another and thus separate the inner cell mass from the external fluid environment. With this step, the cells lose their totipotency and become pluripotent . This forms the basis for the formation of the blastocyst and differentiation into the trophoblast on the outside, from which the placenta and membranes emerge, as well as in the embryoblast on the inside, from which the actual embryo develops.
In artificial insemination , the embryos are usually inserted at an early stage of morula.
The morula becomes the blastula or, in non-egg-laying mammals, the blastocyst.