The three primary germ layers, endoderm, ectoderm, and mesoderm , are formed and organized in proper locations in the embryo during gastrulation in triploblastic organisms. The inward movement of the surface cells is called invagination. The invaginated cells are juxtaposed to the opposite side, converting the embryo into a double-walled cup, which gives rise to the endoderm and mesoderm. The remaining exterior cup becomes the ectoderm.
In contrast, diploblastic organisms only contain two primary germ layers: endoderm and ectoderm. The blastocoel is eliminated by the invagination of cells. The opening of the archenteron is called blastopore. After gastrulation, cells in the embryo undergo rapid diversification into the rudimentary form of various organs in the embryo in a process called organogenesis. Gastrulation is shown in figure 2. Blastula: Blastula is an animal embryo at the early stage of development when it is a hollow ball of cells.
Gastrula: Gastrula is an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells. Blastula: Blastula is formed from the morula in the process called blastulation. Gastrula: Gastrula is formed from the blastula in the process called gastrulation. Blastula: Rapid mitotic cell divisions result in the blastula. Gastrula: Slow mitotic cell divisions result in the gastrula.
Blastula: Blastula is a single-layered, hollow structure. Gastrula: Gastrula is a three-layered, hollow structure. Blastula: Cells in the morula do not show any movement during the formation of the blastula.
Gastrula: Cell masses are migrated from the surface of the blastula during the formation of the gastrula. Gastrula: Gastrula contains more cells than blastula. Blastula: Blastula comprises of undifferentiated cells. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane.
The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte.
The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy.
Process of fertilization : a Fertilization is the process in which sperm and egg fuse to form a zygote. To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg membrane, the egg releases proteins in other locations to prevent other sperm from fusing with the egg.
If this mechanism fails, multiple sperm can fuse with the egg, resulting in polyspermy. The resulting embryo is not genetically viable and dies within a few days. A zygote undergoes rapid cell divisions cleavage to form a spherical ball of cells: the blastula; this will further develop into a blastocyst.
The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. After the cleavage has produced over cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells the blastoderm surrounding a fluid-filled or yolk-filled cavity the blastocoel.
Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula. During cleavage, the cells divide without an increase in mass; that is, one large single-celled zygote divides into multiple smaller cells. Each cell within the blastula is called a blastomere. Cleavage can take place in two ways: holoblastic total cleavage or meroblastic partial cleavage.
With the time, morula differentiates into blastula, which has a higher cell number and different structure. In this article, differences between morula and blastula will be outlined.
Morula is a ball-like mass of cells formed by the cleavage of the zygote. Morula usually consists of 16 — 32 cells.
The first cleavage in human zygote occurs in the fallopian tube, about 30 hours after fertilization. Second and third cleavage take place about 60 hours and 72 hours after fertilization respectively. Cleavage increases the number of cells, but not result in growth. Thus, morula has the same size as the zygote. As a result of subsequent cleavage division, morula forms into a centrally located inner cell mass and a surrounding layer, the outer cell mass.
During the embryonic development, the inner cell mass forms the tissues of the embryo while the outer cell mass gives rise the trophoblast , which lately develops into the placenta.
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