Ectoderm is the outer germinal layer

Ectoderm is a part of any animal multicellular organism. Only in some, this structure is preserved only in the period of embryonic development, and in others - throughout life. What is ectoderm?

Types of embryonic leaflets

During ontogeny, the fertilized egg is divided many times, with the passage of time forming several layers of cells. In the course of their differentiation, several layers of the body are formed, from which tissues, organs and their systems are subsequently formed. Ectoderm is an external embryonic leaf. 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, respiratory and digestive systems develop from it. From the middle embryonic leaf - the mesoderm - organs are formed that seem to bind the whole body together. These are muscles and ligaments, the inner skeleton, the sex, blood and excretory systems.

Derived ectoderms

Ectoderm is an embryonic layer, from which cells integuments and organs of the nervous system are formed. Its formation takes place at the gastrula stage. 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 depart from them to all structures of the body. The sensory organs and sensory systems are also derived from the ectoderm. As this embryonic leaf develops from the outer layer of cells, it forms covers. First of all, it is the epithelial tissue of the skin and digestive system.

Ectoderm of Hydra

In coelenterates, the ectoderm is a layer of the body that persists throughout life. Consider its structure on the example of the freshwater hydra. This is a two-layered 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 functions. For the first time in the course of evolution, such specialized structures appear precisely in representatives of coelenterates.

The structure of the ectoderm includes dermal-muscular cells, which are capable of contraction. Thanks to them the hydra moves, like an acrobat, turning from the sole to the tentacles. When exposed to nerve cells, which are also located in the outer layer of the body, the animal shrinks. This is how their reflex activity manifests itself. In the outer layer, intermediate cells are also located, which can be converted into any other types. This determines the high level of regeneration of the 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 a means of hunting. This function is performed by stinging cells. They consist of a capsule with a thread stranded inside. When the victim swims by, she touches the sensitive hair. As a result, the stinging thread unwinds and bites into her body with force. Together with it, poisonous substances are introduced. The paralyzed victim with the help of tentacles is in the intestinal cavity, where it is digested. Many species 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 with deaths.

Thus, the ectoderm is an external embryonic leaf, from which, in the process of crushing, the veins of the body and organs of the nervous system form in vertebrates. In coelenterates, the ectoderm forms a number of specialized cells: skin-muscular, intermediate, nervous and stinging.