An arthropod is an invertebrate animal having an exoskeleton, a segmented body, paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids and crustaceans; the term Arthropoda as proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora. Arthropods are characterized by their jointed limbs and cuticle made of chitin mineralised with calcium carbonate; the arthropod body plan consists of each with a pair of appendages. The rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Arthopods are bilaterally symmetrical and their body possesses an external skeleton; some species have wings. Their versatility has enabled them to become the most species-rich members of all ecological guilds in most environments, they have over a million described species, making up more than 80 per cent of all described living animal species, some of which, unlike most other animals, are successful in dry environments. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab.
Arthropods' primary internal cavity is a haemocoel, which accommodates their internal organs, through which their haemolymph – analogue of blood – circulates. Like their exteriors, the internal organs of arthropods are built of repeated segments, their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, their brains are formed by fusion of the ganglia of these segments and encircle the esophagus; the respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong. Their vision relies on various combinations of compound eyes and pigment-pit ocelli: in most species the ocelli can only detect the direction from which light is coming, the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey.
Arthropods have a wide range of chemical and mechanical sensors based on modifications of the many setae that project through their cuticles. Arthropods' methods of reproduction and development are diverse; the evolutionary ancestry of arthropods dates back to the Cambrian period. The group is regarded as monophyletic, many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall, the basal relationships of Metazoa are not yet well resolved; the relationships between various arthropod groups are still debated. Aquatic species use either external fertilization. All arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and undergo a total metamorphosis to produce the adult form; the level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. Arthropods contribute to the human food supply both directly as food, more indirectly as pollinators of crops.
Some species are known to spread severe disease to humans and crops. The word arthropod comes from the Greek ἄρθρον árthron, "joint", πούς pous, i.e. "foot" or "leg", which together mean "jointed leg". Arthropods are invertebrates with jointed limbs; the exoskeleton or cuticles consists of a polymer of glucosamine. The cuticle of many crustaceans, beetle mites, millipedes is biomineralized with calcium carbonate. Calcification of the endosternite, an internal structure used for muscle attachments occur in some opiliones. Estimates of the number of arthropod species vary between 1,170,000 and 5 to 10 million and account for over 80 per cent of all known living animal species; the number of species remains difficult to determine. This is due to the census modeling assumptions projected onto other regions in order to scale up from counts at specific locations applied to the whole world. A study in 1992 estimated that there were 500,000 species of animals and plants in Costa Rica alone, of which 365,000 were arthropods.
They are important members of marine, freshwater and air ecosystems, are one of only two major animal groups that have adapted to life in dry environments. One arthropod sub-group, insects, is the most species-rich member of all ecological guilds in land and freshwater environments; the lightest insects weigh less than 25 micrograms. Some living crustaceans are much larger; the embryos of all arthropods are segmented, built from a series of repeated modules. The last common ancestor of living arthropods consisted of a series of undifferentiated segments, each with a pair of appendages that functioned as limbs. However, all known living and fossil arthropods have grouped segments into tagmata in which segments and their limbs are specialized in various ways; the three-
Endothelium refers to cells that line the interior surface of blood vessels and lymphatic vessels, forming an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. It is a thin layer of single-layered, squamous cells called endothelial cells. 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 in vascular biology. These functions include fluid filtration, such as in the glomerulus of the kidney, blood vessel tone, neutrophil recruitment, hormone trafficking. Endothelium of the interior surfaces of the heart chambers is called endocardium. Endothelium is mesodermal in origin. Both blood and lymphatic capillaries are composed of a single layer of endothelial cells called a monolayer. In straight sections of a blood vessel, vascular endothelial cells align and elongate in the direction of fluid flow.
The foundational model of anatomy makes a distinction between endothelial cells and epithelial cells on the basis of which tissues they develop from, states that the presence of vimentin rather than keratin filaments separate these from epithelial cells. Many considered the endothelium a specialized epithelial tissue. Endothelial cells are involved in many aspects of vascular biology, including: Barrier function - the endothelium acts as a semi-selective barrier between the vessel lumen and surrounding tissue, controlling the passage of materials and the transit of white blood cells into and out of the bloodstream. Excessive or prolonged increases in permeability of the endothelial monolayer, as in cases of chronic inflammation, may lead to tissue edema/swelling. Blood clotting; the endothelium provides a non-thrombogenic surface because it contains, for example, heparan sulfate which acts as a cofactor for activating antithrombin, a protease that inactivates several factors in the coagulation cascade.
Inflammation Formation of new blood vessels Vasoconstriction and vasodilation, hence the control of blood pressure Repair of damaged or diseased organs via an injection of blood vessel cells Angiopoietin-2 works with VEGF to facilitate cell proliferation and migration of endothelial cells Endothelial dysfunction, or the loss of proper endothelial function, is a hallmark for vascular diseases, is regarded as a key early event in the development of atherosclerosis. Impaired endothelial function, causing hypertension and thrombosis, is seen in patients with coronary artery disease, diabetes mellitus, hypercholesterolemia, as well as in smokers. Endothelial dysfunction has been shown to be predictive of future adverse cardiovascular events, is present in inflammatory disease such as rheumatoid arthritis and systemic lupus erythematosus. One of the main mechanisms of endothelial dysfunction is the diminishing of nitric oxide due to high levels of asymmetric dimethylarginine, which interfere with the normal L-arginine-stimulated nitric oxide synthesis and so leads to hypertension.
The most prevailing mechanism of endothelial dysfunction is an increase in reactive oxygen species, which can impair nitric oxide production and activity via several mechanisms. The signalling protein ERK5 is essential for maintaining normal endothelial cell function. A further consequence of damage to the endothelium is the release of pathological quantities of von Willebrand factor, which promote platelet aggregation and adhesion to the subendothelium, thus the formation of fatal thrombi. Anatomy photo: Circulatory/vessels/capillaries1/capillaries3 - Comparative Organology at University of California, Davis, "Capillaries, non-fenestrated" Histology image: 21402ooa – Histology Learning System at Boston University Endothelium Journal of Endothelial Cell Research, Informa Healthcare Endothelium and inflammation Platelet Activation, University of Washington
A capillary is a small blood vessel from 5 to 10 micrometres in diameter, having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules; these microvessels are the site of exchange of many substances with the interstitial fluid surrounding them. Substances which exit include water and glucose. Lymph capillaries connect with larger lymph vessels to drain lymphatic fluid collected in the microcirculation. During early embryonic development new capillaries are formed through vasculogenesis, the process of blood vessel formation that occurs through a de novo production of endothelial cells which form vascular tubes; the term angiogenesis denotes the formation of new capillaries from pre-existing blood vessels and present endothelium which divides. Blood flows from the heart through arteries, which branch and narrow into arterioles, branch further into capillaries where nutrients and wastes are exchanged; the capillaries join and widen to become venules, which in turn widen and converge to become veins, which return blood back to the heart through the venae cavae.
Individual capillaries are part of the capillary bed, an interweaving network of capillaries supplying tissues and organs. The more metabolically active a tissue is, the more capillaries are required to supply nutrients and carry away waste products. There are two types of capillaries: true capillaries, which branch from arterioles and provide exchange between tissue and the capillary blood, metarterioles, found only in the mesenteric circulation, they are short vessels that directly connect the arterioles and venules at opposite ends of the beds. Metarterioles are found in the mesenteric microcirculation; the physiological mechanisms underlying precapillary resistance is no longer considered to be a result of precapillary sphincters outside of the mesentery organ. Lymphatic capillaries are larger in diameter than blood capillaries, have closed ends; this structure permits interstitial fluid to flow into them but not out. Lymph capillaries have a greater internal oncotic pressure than blood capillaries, due to the greater concentration of plasma proteins in the lymph.
There are three types of blood capillaries: Continuous capillaries are continuous in the sense that the endothelial cells provide an uninterrupted lining, they only allow smaller molecules, such as water and ions to pass through their intercellular clefts. Lipid-soluble molecules can passively diffuse through the endothelial cell membranes along concentration gradients. Continuous capillaries can be further divided into two subtypes: Those with numerous transport vesicles, which are found in skeletal muscles, fingers and skin; those with few vesicles, which are found in the central nervous system. These capillaries are a constituent of the blood–brain barrier. Fenestrated capillaries have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse. In the renal glomerulus there are cells with no diaphragms, called podocyte foot processes or pedicels, which have slit pores with a function analogous to the diaphragm of the capillaries.
Both of these types of blood vessels have continuous basal laminae and are located in the endocrine glands, intestines and the glomeruli of the kidney. Sinusoid capillaries are a special type of open-pore capillary, that have larger openings in the endothelium; these types of blood vessels allow red and white blood cells and various serum proteins to pass, aided by a discontinuous basal lamina. These capillaries lack pinocytotic vesicles, therefore utilize gaps present in cell junctions to permit transfer between endothelial cells, hence across the membrane. Sinusoid blood vessels are located in the bone marrow, lymph nodes, adrenal glands; some sinusoids are distinctive in. They are called discontinuous sinusoidal capillaries, are present in the liver and spleen, where greater movement of cells and materials is necessary. A capillary wall is simple squamous epithelium; the capillary wall performs an important function by allowing nutrients and waste substances to pass across it. Molecules larger than 3 nm such as albumin and other large proteins pass through transcellular transport carried inside vesicles, a process which requires them to go through the cells that form the wall.
Molecules smaller than 3 nm such as water and gases cross the capillary wall through the space between cells in a process known as paracellular transport. These transport mechanisms allow bidirectional exchange of substances depending on osmotic gradients and can be further quantified by the Starling equation. Capillaries that form part of the blood–brain barrier however only allow for transcellular transport as tight junctions between endothelial cells seal the paracellular space. Capillary beds may control their blood flow via autoregulation; this allows an organ to maintain constant flow despite a change in central blood pressure. This is achieved by myogenic response, in the kidney by tubuloglomerular feedback; when blood pressure increases, arterioles are stretched and subsequently constrict to counteract the
The phylum Negarnaviricota includes all negative-sense single-stranded RNA viruses except Hepatitis delta virus. It is divided into Polyploviricotina; the name comes from the Latin RNA and - viricota, the suffix for a virus phylum. The taxonomy of the Negarnaviricota down to the rank of order is as follows: Subphylum Haploviricotina Class Chunqiuviricetes Order Muvirales Class Milneviricetes Order Serpentovirales Class Monjiviricetes Order Jingchuvirales Order Mononegavirales Class Yunchangviricetes Order Goujianvirales Subphylum Polyploviricotina Class Ellioviricetes Order Bunyavirales Class Insthoviricetes Order Articulavirales Ward, C. W.. "Progress towards a higher taxonomy of viruses". Research in Virology. 144: 419–53. Doi:10.1016/S0923-251680059-2. PMID 8140287
The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells. There are four choroid plexuses in one in each of the ventricles. Choroid plexus is present in all parts of the ventricular system except for the cerebral aqueduct, the frontal horn and the occipital horn of the lateral ventricles. Choroid plexus is located in the inferior horn of the lateral ventricle, passes into the interventricular foramen to the third ventricle. There is choroid plexus in the fourth ventricle beneath the cerebellum; the choroid plexus consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue. The epithelium of the choroid plexus is continuous with the ependymal cell layer that lines the ventricles; the cells of the choroid plexus are non ciliated but, unlike the ependyma, the choroid plexus epithelial layer has tight junctions between the cells on the side facing the ventricle.
These tight junctions prevent the majority of substances from crossing the cell layer into the cerebrospinal fluid. The choroid plexus folds into many villi around each capillary, creating frond-like processes that project into the ventricles; the villi, along with a brush border of microvilli increases the surface area of the choroid plexus. CSF is formed. Choroid plexus epithelial cells transport sodium ions into the ventricles and water follows the resulting osmotic gradient; the choroid plexus consists of many capillaries, separated from the ventricles by choroid epithelial cells. Fluid filters through these cells from blood to become cerebrospinal fluid. There is much active transport of substances into, out of, the CSF as it is made; the choroid plexus mediates the production of cerebrospinal fluid. CSF acts as a medium for filtration system that facilitates the removal of metabolic waste from the brain and exchange of biomolecules and xenobiotics into and out of the brain. In this way the choroid plexus has a important role in helping to maintain the delicate extracellular environment required by the brain to function optimally.
The choroid plexus is a major source of transferrin secretion that plays a part in iron homeostasis in the brain. The blood–cerebrospinal fluid barrier is a fluid–brain barrier, composed of a pair of membranes that separate blood from CSF and CSF from brain tissue; the blood–CSF boundary at the choroid plexus is a membrane composed of epithelial cells and tight junctions that link them. The brain–CSF boundary is the arachnoid membrane, which envelops the surface of the brain. Similar to the blood–brain barrier, the blood–CSF barrier functions to prevent the passage of most blood-borne substances into the brain, while selectively permitting the passage specific substances into the brain and facilitating the removal of brain metabolites and metabolic waste into the blood. Despite the similar function between the BBB and BCSFB, each facilitates the transport of different substances into the brain due to the distinct structural characteristics between the two barrier systems. For a number of substances, the BCSFB is the primary site of entry into brain tissue.
The blood–cerebrospinal fluid barrier has been shown to modulate the entry of leukocytes from the blood to the central nervous system. The choroid plexus cells secrete cytokines that recruit monocyte-derived macrophages, among other cells, to the brain; this cellular trafficking has implications both in normal brain homeostasis as in neuroinflammatory processes. During embryological development, some fetuses may form choroid plexus cysts; these fluid-filled cysts can be detected by a detailed second trimester ultrasound. The finding is common, with a prevalence of ~1%. Choroid plexus cysts are an isolated finding; the cysts disappear during pregnancy, are harmless. They have no effect on infant and early childhood development. Cysts confers a 1% risk of fetal aneuploidy; the risk of aneuploidy increases to 10.5-12 %. Size, disappearance or progression, whether the cysts are found on both sides or not do not affect the risk of aneuploidy. 44-50% of Edwards syndrome cases will present with choroid plexus cysts, as well 1.4% of Down syndrome cases.
~75% of abnormal karyotypes associated with choroid plexus cysts are trisomy 18, while the remainder are trisomy 21. There are three graded types of choroid plexus tumor that affect young children; these malignant neoplasms are rare. Choroid plexus translates from the Latin plexus chorioides, which mirrors Ancient Greek χοριοειδές πλέγμα; the word chorion was used by Galen to refer to the outer membrane enclosing the fetus. Both meanings of the word plexus are given as braiding; as happens language changes and the use of both choroid or chorioid is both accepted. Nomina Anatomica reflected this dual usage. Choroid plexus papilloma Tela choroidea 3-Dimensional images of choroid plexus "Anatomy diagram: 13048.000-3". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01. MedPix Images of Choroid Plexus More info at BrainInfo
Flaviviridae is a family of viruses. Humans and other mammals serve as natural hosts, they are spread through arthropod vectors. The family gets its name from the type virus of Flaviviridae. There are over 100 species in this family, divided among four genera. Diseases associated with this family include: hepatitis, hemorrhagic syndromes, fatal mucosal disease, hemorrhagic fever and the birth defect microcephaly; this family has a number of unclassified species. Genus Flavivirus. Genus Hepacivirus (type species Hepacivirus C includes Hepacivirus B Genus Pegivirus (includes Pegivirus A, Pegivirus C, Pegivirus B Genus Pestivirus (type species Bovine virus diarrhea virus 1, others include Classical swine fever virus —contains viruses infecting non-human mammalsGroup: ssRNA UnclassifiedOther flaviviruses are known that have yet to be classified; these include the Wenling shark virus. There are a number of viruses that may be related to the flaviviruses but have features that are atypical of the flaviviruses.
These include Citrus jingmen-like virus, Guaico Culex virus, Jingmen tick virus, Mogiana tick virus, Soybean cyst nematode virus 5, Toxocara canis larva agent, Wuhan cricket virus and Gentian Kobu-sho-associated virus. Flaviviridae have monopartite, single-stranded RNA genomes of positive polarity, 9.6 to 12.3 kilobase in length. The 5'-termini of flaviviruses carry a methylated nucleotide cap, while other members of this family are uncapped and encode an internal ribosome entry site; the genome encodes a single polyprotein with multiple transmembrane domains, cleaved, by both host and viral proteases, into structural and non-structural proteins. Among the non-structural protein products, the locations and sequences of NS3 and NS5, which contain motifs essential for polyprotein processing and RNA replication are well conserved across the family and may be useful for phylogenetic analysis. Virus particles are enveloped, with icosahedral and spherical geometries, about 40–60 nm in diameter. Viral replication is cytoplasmic.
Entry into the host cell is achieved by attachment of the viral envelope protein E to host receptors, which mediates clathrin-mediated endocytosis. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription is the method of transcription. Translation takes place by viral initiation; the virus exits the host cell by budding. Humans and mammals serve as the natural host; the virus is transmitted via a vector. Major diseases caused by the Flaviviridae family include: Dengue fever Hepatitis C Virus Infection Japanese encephalitis Kyasanur Forest disease Murray Valley encephalitis St. Louis encephalitis Tick-borne encephalitis West Nile encephalitis Yellow fever Zika fever ICTV Online Report. NCBI Taxonomy Browser. 11050