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Lichenification
A CUTANEOUS CONDITION is any medical condition that affects the integumentary system —the organ system that encloses the body and includes skin , hair , nails , and related muscle and glands . The major function of this system is as a barrier against the external environment. Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails ). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying causes and pathogenetics are often not known
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Stratum Lucidum
The STRATUM LUCIDUM (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope . It is readily visible by light microscopy only in areas of thick skin , which are found on the palms of the hands and the soles of the feet. Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes . The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin , an intermediate form of keratin . They are surrounded by an oily substance that is the result of the exocytosis of lamellar bodies accumulated while the keratinocytes are moving through the stratum spinosum and stratum granulosum. The thickness of the lucidum is controlled by the rate of mitosis (division) of the epidermal cells. In addition, melanosomes determine the darkness of the stratum lucidum
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Stratum Corneum
The STRATUM CORNEUM ( Latin
Latin
for 'horny layer') is the outermost layer of the epidermis , consisting of dead cells (corneocytes ). This layer is composed of 15–20 layers of flattened cells with no nuclei and cell organelles. Their cytoplasm shows filamentous keratin . These corneocytes are embedded in a lipid matrix composed of ceramides , cholesterol , and fatty acids . The stratum corneum functions to form a barrier to protect underlying tissue from infection , dehydration , chemicals and mechanical stress. Desquamation
Desquamation
, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale . These cells migrate through the epidermis towards the surface in a journey that takes approximately fourteen days
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Stratum Granulosum
The STRATUM GRANULOSUM (or GRANULAR LAYER) is a thin layer of cells in the epidermis . Keratinocytes
Keratinocytes
migrating from the underlying stratum spinosum become known as granular cells in this layer. These cells contain keratohyalin granules, which are filled with histidine- and cysteine-rich proteins that appear to bind the keratin filaments together. Therefore, the main function of keratohyalin granules is to bind intermediate keratin filaments together. At the transition between this layer and the stratum corneum , cells secrete lamellar bodies (containing lipids and proteins ) into the extracellular space. This results in the formation of the hydrophobic lipid envelope responsible for the skin's barrier properties. Concomitantly, cells lose their nuclei and organelles causing the granular cells to become non-viable corneocytes in the stratum corneum
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Stratum Spinosum
The STRATUM SPINOSUM (or SPINOUS LAYER/PRICKLE CELL LAYER) is a layer of the epidermis found between the stratum granulosum and stratum basale . Their spiny (Latin, spinosum) appearance is due to shrinking of the microfilaments between desmosomes that occurs when stained with H"> Epidermis and dermis of human skin * Section of epidermis SEE ALSO Spinous cell REFERENCES * ^ McGrath, J.A.; Eady, R.A.; Pope, F.M. (2004). Rook's Textbook of Dermatology (Seventh Edition). Blackwell Publishing. Pages 3.7-3.8. ISBN 978-0-632-06429-8 . * ^ James, William; Berger, Timothy; Elston, Dirk (2005) Andrews' Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 2. ISBN 0-7216-2921-0 . * ^ Marks, James G; Miller, Jeffery (2006). Lookingbill and Marks' Principles of Dermatology (4th ed.). Elsevier Inc. Page 6
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Stratum Germinativum
The STRATUM BASALE (BASAL LAYER, sometimes referred to as STRATUM GERMINATIVUM) is the deepest layer of the five layers of the epidermis , the outer covering of skin in mammals . The stratum basale is a continuous layer of cells. It is often described as one cell thick, though it may in fact be two to three cells thick in glabrous skin (hairless), and hyperproliferative epidermis (from a skin disease). The stratum basale is primarily made up of basal keratinocyte stem cells, which can be considered the stem cells of the epidermis. They divide to form the keratinocytes of the stratum spinosum , which migrate superficially. Other types of cells found within the stratum basale are melanocytes (pigment-producing cells), Langerhans cells (immune cells), and Merkel cells (touch receptors)
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Stratum
In geology and related fields, a STRATUM (plural: STRATA) is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers. The "stratum" is the fundamental unit in a stratigraphic column and forms the basis of the study of stratigraphy . CONTENTS * 1 Characteristics * 2 Naming * 3 Gallery * 4 See also * 5 References * 6 External links CHARACTERISTICS The Permian
Permian
through Jurassic
Jurassic
strata in the Colorado Plateau
Colorado Plateau
area of southeastern Utah
Utah
demonstrates the principles of stratigraphy . These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park
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Epithelium
EPITHELIUM (epi- + thele + -ium ) is one of the four basic types of animal tissue , along with connective tissue , muscle tissue and nervous tissue . Epithelial tissues line the cavities and surfaces of blood vessels and organs throughout the body. There are three principal shapes of epithelial cell: squamous, columnar, and cuboidal. These can be arranged in a single layer of cells as simple epithelium, either squamous, columnar, cuboidal, pseudo-stratified columnar or in layers of two or more cells deep as stratified (layered), either squamous, columnar or cuboidal. All glands are made up of epithelial cells. Functions of epithelial cells include secretion , selective absorption , protection, transcellular transport , and sensing . Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane . Cell junctions are well-employed in epithelial tissues
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Arrector Pili
The ARRECTOR PILI MUSCLES are small muscles attached to hair follicles in mammals . Contraction of these muscles causes the hairs to stand on end, known colloquially as goose bumps . Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit), and is innervated by the sympathetic branch of the autonomic nervous system . The contraction of the muscle is then involuntary–stresses such as cold, fear etc. may stimulate the sympathetic nervous system , and thus cause contraction. Contraction of the muscles has a number of different purposes. Its principal function in the majority of mammals is to provide insulation: air becomes trapped between the erect hairs, helping the animal retain heat
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Embryology
EMBRYOLOGY (from Greek ἔμβρυον, embryon, "the unborn, embryo "; and -λογία, -logia ) is the branch of biology that studies the prenatal development of gametes (sex cells), fertilization , and development of embryos and fetuses . Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology . CONTENTS* 1 Embryonic development of animals * 1.1 Bilateria
Bilateria
* 1.1.1 Drosophila melanogaster
Drosophila melanogaster
(fruit fly) * 1.1.2 Humans * 2 History * 2.1 After 1827 and Before 1950 * 2.2 After 1950 * 3 Vertebrate and invertebrate embryology * 4 Modern embryology research * 5 See also * 6 References * 6.1 Citations * 6.2 Sources * 7 Further reading * 8 External links EMBRYONIC DEVELOPMENT OF ANIMALSAfter cleavage , the dividing cells, or morula , becomes a hollow ball, or blastula , which develops a hole or pore at one end
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Ectoderm
ECTODERM is one of the three primary germ layers in the very early embryo . The other two layers are the mesoderm (middle layer) and endoderm (most proximal layer), with the ectoderm as the most exterior (or distal) layer. It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma, meaning "skin." Generally speaking, the ectoderm differentiates to form the nervous system (spine, peripheral nerves and brain), tooth enamel and the epidermis (the outer part of integument ). It also forms the lining of mouth, anus, nostrils, sweat glands, hair and nails. In vertebrates , the ectoderm has three parts: external ectoderm (also known as surface ectoderm ), the neural crest , and neural tube . The latter two are known as neuroectoderm
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Mesoderm
In all bilaterian animals, the MESODERM is one of the three primary germ layers in the very early embryo . The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them. The mesoderm forms mesenchyme , mesothelium , non-epithelial blood cells and coelomocytes . Mesothelium
Mesothelium
lines coeloms . Mesoderm
Mesoderm
forms the muscles in a process known as myogenesis , septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes ). Myogenesis is specifically a function of Mesenchyme
Mesenchyme
. The mesoderm differentiates from the rest of the embryo through intercellular signaling , after which the mesoderm is polarized by an organizing center
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Diffusion
Diffusion
Diffusion
is the net movement of molecules or atoms from a region of high concentration (or high chemical potential) to a region of low concentration (or low chemical potential). This is also referred to as the movement of a substance down a concentration gradient . A gradient is the change in the value of a quantity (e.g., concentration, pressure , temperature ) with the change in another variable (usually distance ). For example, a change in concentration over a distance is called a concentration gradient, a change in pressure over a distance is called a pressure gradient , and a change in temperature over a distance is a called a temperature gradient . The word DIFFUSION derives from the Latin
Latin
word, diffundere, which means "to spread out" (a substance that “spreads out” is moving from an area of high concentration to an area of low concentration)
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Keratinocyte
A KERATINOCYTE is the predominant cell type in the epidermis , the outermost layer of the skin , constituting 90% of the cells found there. Those keratinocytes found in the basal layer (stratum basale ) of the skin are sometimes referred to as "basal cells" or "basal keratinocytes". CONTENTS * 1 Function * 2 Structure * 3 Cell differentiation
Cell differentiation
* 4 Interaction with other cells * 5 Role in wound healing * 6 Sunburn cells * 7 See also * 8 References * 9 External links FUNCTIONThe primary function of keratinocytes is the formation of a barrier against environmental damage by pathogenic bacteria , fungi , parasites , and viruses , heat , UV radiation and water loss
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Elastic Fiber
ELASTIC FIBERS (or YELLOW FIBERS) are bundles of proteins (elastin ) found in extracellular matrix of connective tissue and produced by fibroblasts and smooth muscle cells in arteries . These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. Elastic fibers include elastin , elaunin and oxytalan . Elastic tissue is classified as "connective tissue proper". The elastic fiber is formed from the elastic microfibril (consisting of numerous proteins such as microfibrillar-associated glycoproteins , fibrillin , fibullin , and the elastin receptor ) and amorphous elastin . The microfibril scaffolds and organizes the deposition of amorphous elastin. Amorphous elastin forms from monomers of soluble tropoelastin which is insolubilized and crosslinked into amorphous elastin by lysyl oxidase . Lysyl oxidase reacts with specific lysine residues and by oxidative deamination generates reactive aldehydes and allysine
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Collagen
COLLAGEN /ˈkɒlədʒɪn/ is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen
Collagen
consists of amino acids wound together to form triple-helices to form of elongated fibrils . It is mostly found in fibrous tissues such as tendons , ligaments and skin . Depending upon the degree of mineralization, collagen tissues may be rigid (bone), compliant (tendon), or have a gradient from rigid to compliant (cartilage). It is also abundant in corneas , cartilage , bones , blood vessels , the gut , intervertebral discs , and the dentin in teeth. In muscle tissue , it serves as a major component of the endomysium
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