In this article we will discuss about the characteristics of metabolism during gastrulation period in animals.
Throughout gastrulation, the volume of the embryo does not change appreciably. Every expansion in one direction occurs at the expense of a contraction in another direction or directions. What has been said about the absence of growth during cleavage applies in the same way to the period of gastrulation.
Division of cells by mitosis continues, however, throughout gastrulation, and thus there is an increase of nuclear material at the expense of the cytoplasmic substances. Breakdown and assimilation of reserve materials are also proceeding, but here a new feature is observed that makes the metabolism of the gastrula different from the metabolism of a blastula.
The morphogenetic movements during gastrulation could be expected to cause an increased expenditure of energy and consequently increased oxidation. This is what is actually found; the oxygen consumption during gastrulation shows a further increase as compared with the cleavage stages and with the blastula. A similar sharp increase in total oxygen consumption is also observed in sea urchin eggs.
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One of the substances particularly involved in the supply of energy during gastrulation in amphibians is glycogen. It has been discovered that the amount of glycogen becomes considerably diminished in the invaginating cells of the dorsal lip of the blastopore. This was first discovered by histochemical methods, by using a specific stain for glycogen on sections of gastrulating embryos.
Later, by methods of chemical analysis, the exact amounts of glycogen consumed were determined; it was found that in the dorsal lip of the blastopore 31 per cent of the glycogen is lost during gastrulation, whereas in other parts of the embryo only from 1 per cent to 9 per cent is lost during the same time.
Rapid breakdown of glycogen in the dorsal lip suggests particularly active respiration in this area. Direct measurements of respiration, however, showed that the dorsal lip region is by no means the part of the gastrula which respires at the highest rate. In order to compare respiration in different parts of the embryo, frog gastrulae were cut into several regions.
Two big pieces were made of the vegetal hemisphere (a dorsal and a ventral one) and four pieces of the marginal zone and the animal hemisphere (pieces 1 to 4), starting with the dorsal lip of the blastopore. The oxygen consumption was determined for each piece as well as the dry weight, total nitrogen, and extractable nitrogen—the latter, is equivalent to the nitrogen of the active cytoplasm (total nitrogen less the nitrogen contained in the yolk).
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When the oxygen consumption is related to dry weight of the fragments, it is seen t