Ectoderm: what it is and how it develops during pregnancy

The largest system or organ that makes us up, both human beings and animals, is the skin. Said organ fulfills the protective barrier function of the whole organism and is made up of three main layers: the epidermis, the hypodermis and the hypodermis. The first of them, the epidermis (the outermost layer of the skin), begins its development from the embryonic period, from an earlier set of tissues called 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.

• Related article: "The 3 phases of intrauterine or prenatal development: from the zygote to the fetus"

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 make up 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 that was later called ectoderm. Later, in 1825,

embryologist Martin Rathke discovered the same cell layers in invertebrate animals.

Around the 19th century, it was Karl Ernst von Baer from 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 developed later.

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 in the latter when the embryo organizes three different germ layers.

One of these layers is the ectoderm. The others are the mesoderm and the endoderm. Together, the three layers that make up the tissues of the skin, nerves, organs and muscles. They differ from one another by the depth at which they are found, as well as by their particular functions.

Once gastrulation is complete, the embryo enters another stage known as neurulation, at which point 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 foundations for both the development of the nervous system.

In other words, the central nervous system is formed from a first neural plate made up 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.

• You may be interested in: "Endoderm: parts and development in gestation"

Parts of the ectoderm

During the neurulation stage, the ectoderm is divided into two large parts: the superficial ectoderm and the neuroectoderm.

1. surface ectoderm

The superficial ectoderm gives rise to the tissues found on the outermost surface of the body, for example the epidermis, hair or nails.

2. neuroectoderm

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

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

In other species, the ectoderm performs similar functions. Specifically in fish, the neural crest shapes the backbone, and in turtles it helps to form the shell.

Its functions

As we have seen, the ectoderm It is the layer from which the skin and all sensory structures are derived.. Being a layer, it is made up of groups of cells that fuse with each other during the embryonic development of all animals. In vertebrate animals, the ectoderm is responsible for the development of the following tissues:

• Fur
• Nails
• eye lens
• Epithelium, that is, the tissue that covers the organs that regulate the senses.
• scalp and hair
• Nasal Cavity
• paranasal sinuses
• Mouth, including dental enamel
• anal canal
• Nervous tissue, including 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 "phyla"), 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 in https://www.britannica.com/science/ectoderm.
• McCord, K. (2013). ectoderm. The Embryo Project Encyclopedia. Retrieved August 22, 2018. Available in https://embryo.asu.edu/pages/ectoderm.
• Martos, C. (2018). Ectoderm: Parts, Derivatives and Alterations. Lifeder.com. Retrieved August 22, 2018. Available in https://www.lifeder.com/ectodermo/.
• Poch, M. L. (2001). Neurobiology of early development. Educational Contexts, 4: 79-94.