mesoderm

Examples of mesoderm in the following topics:

• Somite Development

  • Somites develop from the paraxial mesoderm and participate in the facilitation of multiple developmental processes.
  • During the second week of development, the lateral mesoderm splits into a dorsal somatic mesoderm (somatopleure) and a ventral splanchnic mesoderm (splanchnopleure).
  • The mesoderm found lateral to the neural tube is called the paraxial mesoderm.
  • The paraxial mesoderm is initially called the unsegmented mesoderm in vertebrates (but segmented mesoderm in chick embryos).
  • The dermatome is the dorsal portion of the paraxial mesoderm somite.

• Development of the Urinary System

  • The urinary system develops from the intermediate mesoderm during prenatal development.
  • The urogenital system arises during the fourth week of development from urogenital ridges in the intermediate mesoderm on each side of the primitive aorta.
  • It develops from the uteric bud, an outgrowth of the mesonephric duct, and the metanephric mesoderm, derived from the caudal part of the nephrogenic ridge.
  • The connective tissue and smooth muscle surrounding the bladder are derived from adjacent splanchnic mesoderm.
  • Intermediate mesenchyme or intermediate mesoderm is a type of embryological tissue called "mesoderm" that is located between the paraxial mesoderm and the lateral plate.

• Development of the Extraembryonic Coelom

  • During formation of the primitive yolk sac, some of the migrating hypoblast cells transdifferentiate into mesenchymal cells that fill the space between Heuser's membrane and the trophoblast, forming the extraembryonic mesoderm.
  • As development progresses, small lacunae begin to form within the extraembryonic mesoderm which become larger and form the extraembryonic celom.
  • The extraembryonic mesoderm is divided into two layers: Extraembryonic splanchnopleuric mesoderm, which lies adjacent to Heuser's membrane around the outside of the primitive yolk sac, and extraembryonic somatopleuric mesoderm, which lies adjacent to the cytotrophoblast layer of the embryo.
  • The chorionic plate is composed of an inner layer of somatopleuric mesoderm and an outer layer of trophoblast cells.
  • It consists of extraembryonic mesoderm and two layers of trophoblast and surrounds the embryo and other membranes.

• Animal Characterization Based on Features of Embryological Development

  • The pseudocoelomates have a coelom derived partly from mesoderm and partly from endoderm.
  • These pouches eventually fuse to form the mesoderm, which then gives rise to the coelom.
  • Triploblasts develop a third layer, the mesoderm, between the endoderm and ectoderm
  • Eucoelomates have a body cavity within the mesoderm, called a coelom, which is lined with mesoderm.
  • In deuterostomes, the mesoderm pinches off to form the coelom in a process called enterocoely.

• Development of the Integumentary System

  • The integumentary system develops from all embryonic layers (ectoderm, mesoderm and neural crest cells).
  • Fetal skin forms from three layers: ectoderm, mesoderm, and neural crest cells.
  • During this same period, the mesoderm forms the blood vessels and connective tissues.

• Tissue Development

  • The epiblast keeps moving and forms a second layer, the mesoderm.
  • The mesoderm germ layer forms in the embryos of triploblastic animals.
  • The formation of a mesoderm leads to the development of a coelom, a fluid filled cavity.
  • Image illustrates the types of cells produced by the mesoderm (middle germ layer) of the developing embryo.
  • Compare the three embryonic germ layers (endoderm, mesoderm, and ectoderm) from which all body tissues develop

• Neurulation

  • Following gastrulation, the neurulation process develops the neural tube in the ectoderm, above the notochord of the mesoderm.
  • During gastrulation cells migrate to the interior of the embryo, forming the three germ layers the endoderm (the deepest layer), mesoderm (the middle layer), and ectoderm (the surface layer) from which all tissues and organs will arise.
  • In a simplified way, it can be said that the ectoderm gives rise to skin and nervous system, the endoderm to the intestinal organs, and the mesoderm to the rest of the organs.
  • After gastrulation the notochord, a flexible, rod-shaped body that runs along the back of the embryo, has been formed from the mesoderm.

• Gastrulation

  • During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm), which differentiate into distinct tissues.
  • These three germ layers are known as the ectoderm, mesoderm, and endoderm.
  • The mesoderm is found between the ectoderm and the endoderm, giving rise to somites.
  • However, some common features of gastrulation across triploblastic organisms include: (1) A change in the topological structure of the embryo, from a simply connected surface (sphere-like), to a non-simply connected surface (torus-like); (2) the differentiation of cells into one of three types (endodermal, mesodermal, or ectodermal); and (3) the digestive function of a large number of endodermal cells.

• Organogenesis

  • Organogenesis is the process by which the three germ tissue layers of the embryo, which are the ectoderm, endoderm, and mesoderm, develop into the internal organs of the organism.
  • The mesoderm that lies on either side of the vertebrate neural tube will develop into the various connective tissues of the animal body .
  • A spatial pattern of gene expression reorganizes the mesoderm into groups of cells called somites, with spaces between them.
  • The mesoderm also forms a structure called the notochord, which is rod-shaped and forms the central axis of the animal body.
  • The mesoderm aids in the production of cardiac muscles, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells.

• Chorionic Villi and Placental Development

  • During the secondary stage (fifth week), the villi increase in size and ramify, while the mesoderm grows into them, so that at this point the villi contain trophoblast and mesoderm.
  • During the tertiary stage (fifth to sixth week), the branches of the umbilical vessels grow into the mesoderm; in this way, the chorionic villi are vascularized.
  • At this point, the villi contain trophoblast, mesoderm, and blood vessels.