Ectoderm: what it is and how it develops during gestation.

A set of cells that, in a matter of weeks, transform into different organs.

The largest system or organ that shapes us, both humans and animals, is the skin. This organ serves as a protective barrier for the whole organism and is composed of three main layers: the epidermis, the hypodermis and the hypodermis. The first of these, the epidermis (the outermost layer of the skin), begins its development from the embryonic period, from an earlier set of tissues called the ectoderm..

In this article we will see what the ectoderm is and what it is responsible for, as well as the specific moment of development in which it originates.

What is ectoderm?

The ectoderm is the outer germ layer in the early embryo.. It is one of the three germ layers of embryonic origin, found in both vertebrate and invertebrate animals. Broadly speaking, it is a set of cells that form the large tissues of our body, and that arises from the first weeks of gestation.

The ectoderm has been studied since 1817, when Christian Pander, a doctoral student at the University of Würzburg, Germany, discovered two embryonic plates in vertebrates, which later led him to discover a third one that was subsequently called the ectoderm. Later, in 1825, embryologist Martin Rathke discovered the same cell layers in invertebrate animals..

Towards the 19th century it was Karl Ernst von Baer of the University of Konigsberg in Prussia, who extended these investigations and took them to different species. The same researcher is credited with the first description of the blastula stage, which we will see further developed below.

How does it develop in pregnancy?

During embryonic development, cells go through a multiple process of cell division. Eventually, the cells generated by this process reach a stage called gastrulation.. It is during gastrulation that the embryo organizes three distinct germ layers.

One of these layers is the ectoderm. The others are the mesoderm and the endoderm. Together, the three layers form the tissues of the skin, nerves, organs and muscles. They are differentiated from each other by the depth at which they are found, as well as by their particular functions.

Once gastrulation is completed, the embryo enters another stage known as neurulation, when the development of the nervous system begins. This stage is characterized by a thickening of the ectoderm, which allows the generation of "neural plates". In turn, the neural plates gradually thicken and lay the lay the foundations for the development of the nervous system..

In other words, the central nervous system is formed from a first neural plate composed of ectodermal cells found on the dorsal surface of the embryo. This generates a neural tube that will later form the ventricles and the cells necessary to consolidate the peripheral nervous system and the motor fibers that compose it. To better explain this process, the ectoderm has been divided into different parts.

Parts of the ectoderm

During the neurulation stage, the ectoderm is divided into two major partsThe superficial ectoderm and the neuroectoderm.

1. Superficial ectoderm

The superficial ectoderm gives rise to the tissues found on the tissues found on the outermost surface of the organism, e.g. the epidermis, hair or nails.e.g. epidermis, hair or nails.

2. Neuroectoderm

The neuroectoderm is further divided into two main elements, which will later shape the nervous system. One is the neural tube, precursor of the central nervous system in the embryo, as well as the brain and spinal cord.

The other is the neural crestwhich shapes many of the bones and connective tissues of the head and face, as well as some parts of the peripheral nervous system, such as some nerve ganglia, and also the adrenal glands and melanocytes (those that give rise to myelin).

In other species, the ectoderm serves similar functions. Specifically in fish, the neural crest shapes the spine, and in turtles it helps form the carapace.

Its functions

As we have seen, the ectoderm is the layer from which the skin and all sensory structures derive.. Being a layer, it is composed of groups of cells that fuse together during the embryonic development of all animals. In vertebrate animals, the ectoderm is responsible for the development of the following tissues:

• Skin
• Nails
• Lens of the eye
• EpitheliumEpithelium, i.e. the tissue that covers the organs that regulate the senses.
• Scalp and hair
• Nasal cavity
• Paranasal sinuses
• Mouth, including tooth enamel
• Anal canal
• Nervous tissueincluding endocrine cells such as the pituitary body and chromaffin tissue

On the other hand, in invertebrate animals such as cnidarians or ctenophores (relatively simple aquatic animals of the taxonomic category "phylum"), the ectoderm covers the entire body, so in these cases the epidermis and ectodermis is the same layer.

Bibliographic references:

• Ectoderm (2018). Encyclopedia Britannica. Retrieved August 22. Available at https://www.britannica.com/science/ectoderm.
• MacCord, K. (2013). Ectoderm. The Embryo Project Encyclopedia. Retrieved August 22, 2018. Available at https://embryo.asu.edu/pages/ectoderm.
• Martos, C. (2018). Ectoderm: Parts, Derivatives and Alterations. Lifeder.com. Retrieved August 22, 2018. Available at https://www.lifeder.com/ectodermo/.
• Poch, M.L. (2001). Neurobiology of early development. Contextos Educativos, 4: 79-94.