A germ layer is a collection of cells, formed during animal embryogenesis. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Embryogenesis is the process by which the Embryo is formed and develops Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sponges (eumetazoans and agnotozoans) produce two or three primary tissue layers (sometimes called primary germ layers). Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals Eumetazoa is a Clade comprising all major Animal groups except sponges Characteristics of eumetazoans include true tissues organized into Animals with radial symmetry, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. "Bilateral symmetry" redirects here For bilateral symmetry in mathematics see Reflection symmetry. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments The ectoderm is the start of a tissue that covers the body surfaces Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. Diploblasty is a condition of the ovum in which there are two primary Germ layers the Ectoderm and Endoderm. Animals with bilateral symmetry produce a third layer between these two layers (appropriately called the mesoderm) making them triploblastic. "Bilateral symmetry" redirects here For bilateral symmetry in mathematics see Reflection symmetry. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. Germ layers eventually give rise to all of an animal’s tissues and organs through the process of organogenesis. Tissue is a cellular organizational level intermediate between cells and a complete organism In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument In animal development, organogenesis is the process by which the Ectoderm, Endoderm, and Mesoderm develop into the Internal organs
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Germ layers
Caspar Friedrich Wolff observed organization of the early embryo in leaf-like layers. Caspar Friedrich Wolff ( January 18, 1733 &ndash February 22, 1794) was a German Physiologist and one of the founders of Later, Heinz Christian Pander discovered germ layers while studying chick embryos. Heinz Christian Pander, name sometimes given as Christian Heinrich Pander (1794-1865 was a Russian Biologist and Embryologist who was born in Riga
Among animals, sponges show the simplest organization, having a single germ layer. The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals Although they have differentiated cells (e. g. collar cells), they lack true tissue coordination. Choanocytes (also known as "collar cells" are cells that line the interior of Asconoid sponges that contain a central Flagellum surrounded Diploblastic animals, Cnidaria and ctenophores, show an increase in complexity, having two germ layers, the endoderm and ectoderm. Diploblasty is a condition of the ovum in which there are two primary Germ layers the Ectoderm and Endoderm. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments The phylum Ctenophora (tɨˈnɒfərə commonly known as comb jellies, is a phylum that includes the Sea gooseberry ( Pleurobrachia pileus) and Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. The ectoderm is the start of a tissue that covers the body surfaces Diploblastic animals are organized into recognisable tissues. All higher animals (from flatworms to man) are triploblastic, possessing a mesoderm in additition to the germ layers found in Diploblasts. Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. Triploblastic animals develop recognisable organs.
Development
Fertilization leads to the formation of a zygote. For soil improvement see Fertilization (soil. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" During the next stage, cleavage, mitotic cell divisions transform the zygote into a tiny ball of cells, a blastula. In Embryology, cleavage is the division of cells in the early Embryo. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei The blastula is an early stage of Embryonic development in Animals It is also called blastosphere This early embryonic form undergoes gastrulation, forming a gastrula with either two or three layers (the germ layers). Gastrulation is a phase early in the development of animal Embryos during which the morphology of the embryo is dramatically restructured by Cell migration. Gastrulation is a phase early in the development of animal Embryos during which the morphology of the embryo is dramatically restructured by Cell migration. In all vertebrates, these are the forerunners of all adult tissues and organs. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes
The appearance of the archenteron marks the onset of gastrulation. The primitive gut that forms during Gastrulation in the developing Blastula is known as the archenteron.
In humans, after about three days, the zygote forms a solid mass of cells by mitotic division, called a morula. A morula ( Latin "morus" Mulberry) is an Embryo at an early stage of Embryonic development, consisting of approximately 12-32 This then changes to a blastocyst, consisting of an outer layer called a trophoblast, and an inner cell mass called the embryoblast. The blastocyst is the structure formed in early Embryogenesis, after the formation of the Blastocoel, but before Implantation. Trophoblasts (from Greek threphein: to feed and blastos: germinator are cells forming the outer layer of a Blastocyst, which provide nutrients In early Embryogenesis of most Eutherian mammals the inner cell mass (abbreviated ICM and also known as the embryoblast or Pluriblast Filled with uterine fluid, the blastocyst breaks out of the zona pellucida and undergoes implantation. Implantation is an event that occurs early in pregnancy in which the Embryo adheres to the wall of Uterus. The inner cell mass initially has two layers: the hypoblast and epiblast. At the end of the second week, a primitive streak appears. The primitive streak is a structure that forms during the early stages of Avian, Reptilian and Mammalian Embryonic development. The epiblast in this region moves towards the primitive streak, dives down into it, and forms a new layer, called the endoderm, pushing the hypoblast out of the way (this goes on to form the amnion. Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. For the alien race in Stephen Donaldson 's The Gap Cycle, see Amnion (Gap Cycle. ) The epiblast keeps moving and forms a second layer, the mesoderm. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. The top layer is now called the ectoderm. The ectoderm is the start of a tissue that covers the body surfaces
Endoderm
The endoderm is one of the germ layers formed during animal embryogenesis. Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis.
The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and air cells of the lungs; the urinary bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus.
The endoderm forms: the stomach, the colon, the liver, the pancreas, the urinary bladder, the lining of the urethra, the epithelial parts of trachea, the lungs, the pharynx, the thyroid, the parathyroid, and the intestines. Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis.
Mesoderm
The mesoderm germ layer forms in the embryos of triploblastic animals. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm. Gastrulation is a phase early in the development of animal Embryos during which the morphology of the embryo is dramatically restructured by Cell migration. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. The ectoderm is the start of a tissue that covers the body surfaces
This key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. The formation of a mesoderm led to the development of a coelom. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.
The mesoderm forms: skeletal muscle, the skeleton, the dermis of skin, the crystal lens of the eye, connective tissue, the urogenital system, the heart, blood (lymph cells), and the spleen. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. The lymphatic system in Vertebrates is a network of conduits that carry a clear fluid called Lymph.
Ectoderm
The ectoderm is the start of a tissue that covers the body surfaces. The ectoderm is the start of a tissue that covers the body surfaces It emerges first and forms from the outermost of the germ layers.
The ectoderm forms: the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands. The ectoderm is the start of a tissue that covers the body surfaces
Neural crest
Because of its great importance, the neural crest is sometimes considered a fourth germ layer. The neural crest, a transient component of the Ectoderm, is located in between the Neural tube and the epidermis (or the free margins of the Neural folds It is, however, derived from the ectoderm.
References
- Evers, Christine A. , Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.
See also
In Developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized Cell type. Embryogenesis is the process by which the Embryo is formed and develops Histogenesis is the formation of different tissues from undifferentiated cells. Neurulation is a part of Organogenesis in Vertebrate Embryos Steps of neurulation include the formation of the Dorsal nerve cord, and the eventual In animal development, organogenesis is the process by which the Ectoderm, Endoderm, and Mesoderm develop into the Internal organsDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic