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Paraxial Mesoderm
Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube. The cells of this region give rise to somites, blocks of tissue running along both sides of the neural tube, which form muscle and the tissues of the back, including connective tissue and the dermis. Formation and somitogenesis The paraxial and other regions of the mesoderm are thought to be specified by bone morphogenetic proteins, or BMPs, along an axis spanning from the center to the sides of the body. Members of the FGF family also play an important role, as does the WNT pathway. In particular, Noggin, a downstream target of the Wnt pathway, antagonizes BMP signaling, forming boundaries where antagonists meet and limiting this signaling to a particular region of the mesoderm. Together, these pathways provide the initial specification of the paraxial mesoderm and maintain this identity. This specifi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chordamesoderm
Axial mesoderm, or chordamesoderm, is the mesoderm in the embryo that lies along the central axis under the neural tube. * will give rise to notochord * starts as the notochordal process, whose formation finishes at day 20 in humans. * important not only in forming the notochord itself but also in inducing development of the overlying ectoderm into the neural tube * will eventually induce the formation of vertebral bodies. * ventral floor of the notochordal process fuses with endoderm. * The notochord will form the nucleus pulposus of intervertebral discs. There is some discussion as to whether these cells contributed from the notochord are replaced by others from the adjacent mesoderm. It gives rise to the notochordal process, which later becomes the notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wnt Signalling Pathway
The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling pathways use either nearby cell-cell communication (paracrine) or same-cell communication (autocrine). They are highly evolutionarily conserved in animals, which means they are similar across animal species from fruit flies to humans. Three Wnt signaling pathways have been characterized: the canonical Wnt pathway, the noncanonical planar cell polarity pathway, and the noncanonical Wnt/calcium pathway. All three pathways are activated by the binding of a Wnt-protein ligand to a Frizzled family receptor, which passes the biological signal to the Dishevelled protein inside the cell. The canonical Wnt pathway leads to regulation of gene transcription, and is thought to be negatively regulated in part by the SPATS1 gene. The noncanonical plana ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triploblasty
Triploblasty is a condition of the gastrula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. Germ cells are set aside in the embryo at the blastula stage, which are incorporated into the gonads during organogenesis. The germ layers form during gastrulation of the blastula. The term ''triploblast'' may refer to any egg cell in which the blastoderm splits into three layers. All bilaterians, the animals with bilaterally symmetrical embryos, are triploblastic. Other animal taxa, the ctenophores, placozoans and cnidarians, are diploblastic, meaning their embryos contain only two germ layers. Sponges are even less developmentally specialized, lacking both true tissues and organs. The earliest triploblasts are thought to have evolved from the diploblasts some time in the Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesenchyme
Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every organ in the developing embryo. Vertebrates Structure Mesenchyme is characterized morphologically by a prominent ground substance matrix containing a loose aggregate of reticular fibers and unspecialized mesenchymal stem cells. Mesenchymal cells can migrate easily (in contrast to epithelial cells, which lack mobility), are organized into closely adherent sheets, and are polarized in an apical-basal orientation. Development The mesenchyme originates from the mesoderm. From the mesoderm, the mesenchyme appears as an embryologically primitive "soup". This "soup" exists as a combination of the mesenchymal cells plus serous fluid plus the many different tissue proteins. Serous fluid is typically stocked with the many serous elements, su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Somitomere
In the developing vertebrate embryo, the somitomeres (or somatomeres) are collections of cells that are derived from the loose masses of paraxial mesoderm that are found alongside the developing neural tube. In human embryogenesis they appear towards the end of the third gestational week. The approximately 50 pairs of somitomeres in the human embryo, begin developing in the cranial (head) region, continuing in a caudal (tail) direction until the end of week four. Development The first seven somitomeres give rise to the striated muscles of the face, jaws, and throat.Larsen W.J. Human Embryology. Churchill Livingstone.Third edition 2001.Page 62. The remaining somitomeres, likely driven by periodic expression of the '' hairy'' gene, begin expressing adhesion proteins such as N-cadherin and fibronectin, compact, and bud off forming somites. The somites give rise to the vertebral column ( sclerotome), associated muscles (myotome A myotome is the group of muscles that a single sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinoic Acid
Retinoic acid (used simplified here for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''- retinol) that mediates the functions of vitamin A1 required for growth and development. All-''trans''-retinoic acid is required in chordate animals, which includes all higher animals from fish to humans. During early embryonic development, all-''trans''-retinoic acid generated in a specific region of the embryo helps determine position along the embryonic anterior/posterior axis by serving as an intercellular signaling molecule that guides development of the posterior portion of the embryo. It acts through Hox genes, which ultimately control anterior/posterior patterning in early developmental stages. All-''trans''-retinoic acid (ATRA) is the major occurring retinoic acid, while isomers like 13-''cis''- and 9-''cis''-retinoic acid are also present in much lower levels. The key role of all-''trans''-retinoic acid in embryonic development mediates the high teratoge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endothelium
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. Endothelial cells form the barrier between vessels and tissue and control the flow of substances and fluid into and out of a tissue. Endothelial cells in direct contact with blood are called vascular endothelial cells whereas those in direct contact with lymph are known as lymphatic endothelial cells. Vascular endothelial cells line the entire circulatory system, from the heart to the smallest capillaries. These cells have unique functions that include fluid filtration, such as in the glomerulus of the kidney, blood vessel tone, hemostasis, neutrophil recruitment, and hormone trafficking. Endothelium of the interior surfaces of the heart chambers is called endocardium. An impaired function can lead to serious health i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dermatomal Mesenchyme
The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide into the dermatomes, myotomes, sclerotomes and syndetomes that give rise to the vertebrae of the vertebral column, rib cage, part of the occipital bone, skeletal muscle, cartilage, tendons, and skin (of the back). The word ''somite'' is sometimes also used in place of the word '' metamere''. In this definition, the somite is a homologously-paired structure in an animal body plan, such as is visible in annelids and arthropods. Development The mesoderm forms at the same time as the other two germ layers, the ectoderm and endoderm. The mesoderm at either side of the neural tube is called paraxial mesoderm. It is distinct from the mesoderm underneath the neural tube which is called the chordamesoderm that becomes the notochord. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myotome
A myotome is the group of muscles that a single spinal nerve innervates. Similarly a dermatome is an area of skin that a single nerve innervates with sensory fibers. Myotomes are separated by myosepta (singular: myoseptum). In vertebrate embryonic development, a myotome is the part of a somite that develops into muscle. Structure The anatomical term myotome which describes the muscles served by a spinal nerve root, is also used in embryology to describe that part of the somite which develops into the muscles. In anatomy the myotome is the motor equivalent of a dermatome. Function Each muscle in the body is supplied by one or more levels or segments of the spinal cord and by their corresponding spinal nerves. A group of muscles innervated by the motor fibres of a single nerve root is known as a myotome. List of myotomes Myotome distributions of the upper and lower extremity are as follows; * C1/ C2: neck flexion/extension * C3: Lateral Neck Flexion * C4: shoulder elev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sclerotome
The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide into the dermatomes, myotomes, sclerotomes and syndetomes that give rise to the vertebrae of the vertebral column, rib cage, part of the occipital bone, skeletal muscle, cartilage, tendons, and skin (of the back). The word ''somite'' is sometimes also used in place of the word '' metamere''. In this definition, the somite is a homologously-paired structure in an animal body plan, such as is visible in annelids and arthropods. Development The mesoderm forms at the same time as the other two germ layers, the ectoderm and endoderm. The mesoderm at either side of the neural tube is called paraxial mesoderm. It is distinct from the mesoderm underneath the neural tube which is called the chordamesoderm that becomes the notochord. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gastrulation
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst is reorganized into a multilayered structure known as the gastrula. Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body (e.g. dorsal-ventral, anterior-posterior), and internalized one or more cell types including the prospective gut. In triploblastic organisms, the gastrula is trilaminar (three-layered). These three germ layers are the ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer).Mundlos 2009p. 422/ref>McGeady, 2004: p. 34 In diploblastic organisms, such as Cnidaria and Ctenophora, the gastrula has only ectoderm and endoderm. The two layers are also sometimes referred to as the ''hypoblast'' and ''epiblast' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Primitive Streak
The primitive streak is a structure that forms in the early embryo in amniotes. In amphibians the equivalent structure is the blastopore. During early embryonic development, the embryonic disc becomes oval shaped, and then pear-shaped with the broad end towards the anterior, and the narrower region projected to the posterior. The primitive streak forms a longitudinal midline structure in the narrower posterior (caudal) region of the developing embryo on its dorsal side. At first formation the primitive streak extends for half the length of the embryo. In the human embryo this appears by stage 6, about 17 days. The primitive streak establishes bilateral symmetry, determines the site of gastrulation, and initiates germ layer formation. To form the primitive streak mesenchymal stem cells are arranged along the prospective midline, establishing the second embryonic axis, and the site where cells will ingress and migrate during the process of gastrulation and germ layer formation. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
