Ectoderm is part of any animal multicellular organism. Only in some this structure is preserved only during the period of embryonic development, and in others - throughout life. What is ectoderm?
Types of germ leaves
During ontogenesis, a fertilized egg repeatedly divides, forming several layers of cells over time. In the process of their differentiation, the formation of several layers of the body occurs, from which tissues, organs and their systems are subsequently formed. Ectoderm is the external germinal layer. During the development of the zygote, it is formed first from the outer layer of cells. The inner leaf of the embryo is called the endoderm. Subsequently, the respiratory and digestive systems develop from it. From the middle germinal leaf — the mesoderm — organs are formed that, as it were, bind the whole organism together. These are muscles and ligaments, the internal skeleton, reproductive, circulatory and excretory systems.
Derivatives of ectoderm
Ectoderm is an embryonic layer from which cells integument and organs of the nervous system are formed. Its formation occurs at the stage of gastrula. The nervous system of vertebrates is characterized by a high level of development. It consists of the brain and spinal cord, as well as individual fibers that extend from them to all body structures. Sensory organs and sensory systems are also derivatives of ectoderm. As this embryonic leaf develops from the outer layer of cells, it forms integument. First of all, it is the epithelial tissue of the skin and digestive system.
Ectoderm hydra
In enteric animals, ectoderm is a layer of the body that persists throughout life. Consider its structure on the example of freshwater hydra. This is a two-layer animal whose body is formed by ecto- and endoderm. Between them is a dense plate of intercellular substance. Ectoderm cells are diverse in structure and function. For the first time in the course of evolution, such specialized structures appear precisely in representatives of the intestinal cavity.
The composition of the ectoderm includes skin and muscle cells, which are capable of contracting. Thanks to them, the hydra moves like an acrobat, turning over from the sole to the tentacles. When exposed to nerve cells, which are also located in the outer layer of the body, the animal contracts. So their reflex activity is shown. In the outer layer intermediate cells are also located that can turn into any other types. This determines a high level of regeneration of freshwater hydra. She can completely restore her body even from a mushy state.
What are stinging cells
Ectoderm is the outer layer, which serves as a reliable protection and means of hunting. This function is performed by stinging cells. They consist of a capsule with a thread twisted inside. When the victim swims past, she touches a sensitive hair. As a result, the stinging thread unwinds and forces itself into her body. Poisonous substances are introduced along with it. A paralyzed victim with the help of tentacles is in the intestinal cavity, where it is digested. Many types of jellyfish are dangerous to humans. The action of their stinging cells causes severe burns, disruption of the heart and respiratory system, and sometimes even ends in deaths.
So, the ectoderm is the external germinal sheet from which, in the process of crushing, vertebrates form the integument of the body and organs of the nervous system. In the intestinal cavity, the ectoderm forms a number of specialized cells: skin-muscle, intermediate, nervous and stinging.