What is the mesoderm?

The mesoderm is one of the three main layers in a developing embryo, known as the germ cell layers. Other germ cell layers are the endoderm and ectoderm. As the embryo develops, different organs and body parts develop from these germ cell layers. Muscles, bones, some skin tissues, connective tissues, the reproductive and urinary systems, and other internal organs develop from the mesoderm. The embryos of all complex animals, including humans, contain mesodermal layers early in development.

The functioning of the mesoderm in the development of an embryo is representative of the complex process by which humans and other vertebrates develop in utero. Each of the various layers in the early embryo start out as relatively simple structures, then change and grow to form the many interacting parts needed to create a functioning living creature. Each layer develops into organs and tissues that depend on the tissues and organs created in other layers, so the development of each layer must occur properly to become a viable fetus.

Within the mesoderm itself there are additional layers that differentiate into different organs and body parts during gestation. Each of these subdivisions develops into a different set of organs and other body tissues. The other two layers, the ectoderm and endoderm, eventually develop into outer tissue, such as the skin and teeth (ectoderm), and the inner tissue that lines most internal organs (endoderm). This development process is similar among most vertebrates.

One of the layers of the mesoderm is the lateral plate mesoderm. This portion of the embryonic tissue divides into layers that develop into the body wall, as well as the wall of the intestines and the circulatory system. Another layer, the intermediate mesoderm, becomes the urinary and reproductive systems. Paraxial mesoderm develops into facial muscles, vertebrae, skeletal muscles, and the dermis layer of the skin. Chordamesoderm, or axial mesoderm, develops in various parts of the spinal column.

Another benefit of this means of development is that a coelom, or body cavity, forms early in the process. Within this cavity, there is room for the various internal organs to develop. When the animal is mature, the body cavity, located in the abdomen, houses most of the vital organs, providing protection for such delicate and important body parts as the heart, lungs, and intestines. The lining of the abdominal cavity, called the peritoneum, is also derived from the mesoderm during early development.

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