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Septate Junctions
Septate junctions are intercellular junctions found in invertebrate epithelial cells, appearing as ladder-like structures under electron microscopy. They are thought to provide structural strength and a barrier to solute diffusion through the intercellular space. They are considered somewhat analogous to the (vertebrate) tight junctions; however, tight and septate junctions are different in many ways. Known insect homologues of tight junction components are components of conserved signalling pathways that localize to either adherens junctions, the subapical complex, or the marginal zone. Recent studies show that septate junctions are also identified in the myelinated nerve fibers of the vertebrates. Structure The main trait of septate junctions structure is that cross-bridges or septa are in the ladder-like shape and cover the 15–20 nm intermembrane space of cell–cell contacts. Septate junctions are in a tight arrangement which is parallel to each other. For the septate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drosophila Melanogaster
''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Charles W. Woodworth's 1901 proposal of the use of this species as a model organism, ''D. melanogaster'' continues to be widely used for biological research in genetics, physiology, microbial pathogenesis, and life history evolution. As of 2017, five Nobel Prizes have been awarded to drosophilists for their work using the insect. ''D. melanogaster'' is typically used in research owing to its rapid life cycle, relatively simple genetics with only four pairs of chromosomes, and large number of offspring per generation. It was originally an African species, with all non-African lineages having a common origin. Its geographic range includes all continents, including islands. ''D. melanogaster'' is a common pest in homes, restaurants, and othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gap Junction
Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells. One gap junction channel is composed of two protein hexamers (or hemichannels) called connexons in vertebrates and innexons in invertebrates. The hemichannel pair connect across the intercellular space bridging the gap between two cells. Gap junctions are analogous to the plasmodesmata that join plant cells. Gap junctions occur in virtually all tissues of the body, with the exception of adult fully developed skeletal muscle and mobile cell types such as sperm or erythrocytes. Gap junctions are not found in simpler organisms such as sponges and slime molds. A gap junction may also be called a ''nexus'' or ''macula communicans''. While an ephapse has some similarities to a gap junction, by modern definition the two a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemidesmosome
Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy, however, desmosomes attach to adjacent cells. Hemidesmosomes are also comparable to focal adhesions, as they both attach cells to the extracellular matrix. Instead of desmogleins and desmocollins in the extracellular space, hemidesmosomes utilize integrins. Hemidesmosomes are found in epithelial cells connecting the basal epithelial cells to the lamina lucida, which is part of the basal lamina. Hemidesmosomes are also involved in signaling pathways, such as keratinocyte migration or carcinoma cell intrusion. Structure Hemidesmosomes can be categorized into two types based on their protein constituents. Type 1 hemidesmosomes are found in stratified and pseudo-stratified epithelium. Type 1 hemidesmosomes have five main elements: integrin α6 β4, plectin in its isof ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desmosome
A desmosome (; "binding body"), also known as a macula adherens (plural: maculae adherentes) (Latin for ''adhering spot''), is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes. Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress, such as cardiac muscle tissue, bladder tissue, gastrointestinal mucosa, and epithelia. Structure Desmosomes are composed of desmosome-intermediate filament complexes (DIFC), which is a network of cadherin proteins, linker proteins and intermediate filaments. The DIFCs can be broken into three regions: the extracellular core region, or desmoglea, the outer dense plaque, or ODP, and the inner dense plaque, or IDP. The extracellular core region, approximately 34 nm in length, contains desmoglein and desmocollin, which are in the cadherin famil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adherens Junction
Adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome") are protein complexes that occur at cell–cell junctions, cell–matrix junctions in epithelial and endothelial tissues, usually more basal than tight junctions. An adherens junction is defined as a cell junction whose cytoplasmic face is linked to the actin cytoskeleton. They can appear as bands encircling the cell (zonula adherens) or as spots of attachment to the extracellular matrix (focal adhesion). Adherens junctions uniquely disassemble in uterine epithelial cells to allow the blastocyst to penetrate between epithelial cells. A similar cell junction in non-epithelial, non-endothelial cells is the fascia adherens. It is structurally the same, but appears in ribbonlike patterns that do not completely encircle the cells. One example is in cardiomyocytes. Proteins Adherens junctions are composed of the following proteins: * cadherins. The cadherins are a family of transmembrane proteins tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tight Junction
Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epithelial cells. They also play a critical role maintaining the structure and permeability of endothelial cells. Tight junctions may also serve as leaky pathways by forming selective channels for small cations, anions, or water. The corresponding junctions that occur in invertebrates are septate junctions. Structure Tight junctions are composed of a branching network of sealing strands, each strand acting independently from the others. Therefore, the efficiency of the junction in preventing ion passage increases exponentially with the number of strands. Each strand is formed from a row of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly. There are at least 40 different protei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malpighian Tubule System
The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids and tardigrades. The system consists of branching tubules extending from the alimentary canal that absorbs solutes, water, and wastes from the surrounding hemolymph. The wastes then are released from the organism in the form of solid nitrogenous compounds and calcium oxalate. The system is named after Marcello Malpighi, a seventeenth-century anatomist. Structure Malpighian tubules are slender tubes normally found in the posterior regions of arthropod alimentary canals. Each tubule consists of a single layer of cells that is closed off at the distal end with the proximal end joining the alimentary canal at the junction between the midgut and hindgut. Most tubules are normally highly convoluted. The number of tubules varies between species although most occur in multiples of two. Tubules are usually bathed in hemolymph and are in proximity to fat body tissue. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endoderm
Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems. In plant biology, endoderm corresponds to the innermost part of the cortex ( bark) in young shoots and young roots often consisting of a single cell layer. As the plant becomes older, more endoderm will lignify. Production The following chart shows the tissues produced by the endoderm. The embryonic endoderm develops into the interior linings of two tubes in the body, the digestive and respiratory tube. Liver and pancreas cells are believed to derive from a common precursor. In humans, the endoderm can differentiate into distinguishable organs after 5 week ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Na+/K+-ATPase
NA, N.A., Na, nA or n/a may refer to: Chemistry and physics * Sodium, symbol Na, a chemical element * Avogadro constant (''N''A) * Nucleophilic addition, a type of reaction in organic chemistry * Numerical aperture, a number that characterizes a range of angles in an optical system * nA, the symbol for nanoampere * Naturally aspirated engine Biology and medicine * Na (tree) or ''Mesua ferrea'', a species of tree native to Sri Lanka * Neuroacanthocytosis, a neurological condition * ''Nomina Anatomica'', a former international standard for human anatomical nomenclature * Noradrenaline, a hormone * Nucleic acid analogue, compounds analogous to naturally occurring RNA and DNA Places Current * Namibia (ISO country code) * Naples (car number plate code: NA), Italy * North America, a continent * North Africa, a subcontinent Historical * Netherlands Antilles (former international vehicle registration code: NA) * Na (Chinese state), a small state of the Chinese Zhou dynasty from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Microscope
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a higher resolving power than light microscopes and can reveal the structure of smaller objects. A scanning transmission electron microscope has achieved better than 50 pm resolution in annular dark-field imaging mode and magnifications of up to about 10,000,000× whereas most light microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000×. Electron microscopes use shaped magnetic fields to form electron optical lens systems that are analogous to the glass lenses of an optical light microscope. Electron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens including microorganisms, cells, large molecules, biopsy samples, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Testicle
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosterone. Testosterone release is controlled by the anterior pituitary luteinizing hormone, whereas sperm production is controlled both by the anterior pituitary follicle-stimulating hormone and gonadal testosterone. Structure Appearance Males have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. Scrotal asymmetry, in which one testicle extends farther down into the scrotum than the other, is common. This is because of the differences in the vasculature's anatomy. For 85% of men, the right testis hangs lower than the left one. Measurement and volume The volume of the testicle can be estimated by palpating it and comparing it to ellipsoids of known sizes. Another method is to use caliper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
