Gastrula is the stage that the embryo of a multicellular animal goes through during its development. Blastula transforms into gastrula. This is the earliest stage in the development of the embryo. The process of formation and growth of the gastrula is called gastrulation. Then comes the neurula stage.
The structure of the embryo during this period
As you know, the cells of the gastrula form the so-called petals. They correspond to three layers. The outer is called the exoderm, and in the future it turns into the epidermis - nails, hair and the nervous system of an adult organism.
The middle lobe of the gastrula is called the mesoderm. Muscles, skeleton, endocrine and circulatory systems grow out of it. But not all living organisms have a middle layer of cells. Some simple invertebrates develop from a bilayer gastrula.
The endoderm is the inner layer of the embryo. It forms the lungs, liver and intestines. The human fetus also has a gastrula stage. It is formed in a form resembling a disk, already on the 8th - 9th day of fertilization. But, nevertheless, it is a gastrula, like in amphibians with reptiles.
Waysgastrulation
Modern biology knows several of them:
Invagination. Occurs in coelenterates and even higher animals. Scyphoid jellyfish and corals in the embryonic phase develop precisely by invagination. This method leads to the retraction of the wall inward, and the formation of a hole, which in the future often becomes a mouth in protostomes, and an anus or cloaca in deuterostomes. Protostomes are simple animals of small size. Some are not even visible to the human eye. These are arthropods, mollusks, nematodes, annelids, tardigrades, etc. Deuterostomes include higher creatures: echinoderms and chordates. Including human
- Immigration. Indicates that the cells invade the blastula and form from the inside a special important tissue called the parenchyma. It is usually observed in sponges and coelenterates, on the example of which the great Russian scientist I. I. Mechnikov established that the gastrula is not a simple stage of the embryo, but an unusual discovery in world embryology.
- Delamination. Translated from Latin as "dividing into layers." This method of gastrulation is possible due to the splitting of blastula cells into two layers, from which the ectoderm and endoderm are later formed. This simple type of organogenesis is inherent in higher mammals.
- Epiboly. In some fish and amphibians, the gastrula develops in this way. In this case, small, yolk-poor cells grow around one large one, in which the yolkenough. The result is a gastrula, similar in composition to a bird's egg.
These four ways of gastrulation are rarely found in nature in their pure form. Their combinations are more often observed.
Name history
Russian biologist G. Kovalevsky in 1865 believed that the gastrula is an "intestinal larva", because of the similarity of the gastrula with the larva and its location in the area close to the intestines. Less than one decade later, in 1874, the German philosopher and naturalist E. Haeckel introduced the term "gastrula" itself, which is translated from ancient Greek as "womb", "stomach", which is also explained by the location of the embryo.
Independent organism
As a rule, a gastrula is an embryo that does not exist by itself. It is located in the egg or uterus. But in nature there are also animals that develop from free-swimming gastrulae. Most often - it is intestinal. This group of creatures is interesting for its simple structure, which in an adult is similar to the composition of the gastrula. From this it follows that it is the same independent organism as the animal that eventually grows out of it. It can perform all the functions necessary to maintain life in the embryonic state.