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Type I Hypersensitivity
Type I hypersensitivity (or immediate hypersensitivity), in the Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type I is distinct from type II, type III and type IV hypersensitivities. The relevance of the Gell and Coombs classification of allergic reactions has been questioned in the modern-day understanding of allergy, and it has limited utility in clinical practice. Exposure may be by ingestion, inhalation, injection, or direct contact. Pathophysiology In type I hypersensitivity, B cells are stimulated (by CD4+ Th2 cells) to produce IgE antibodies specific to an antigen. The difference between a normal infectious immune response and a type 1 hypersensitivity response is that in type 1 hypersensitivity, the antibody is IgE instead of IgA, IgG, or IgM. During sensitization, the IgE antibodies bind to FcεRI receptors on the surface of tissue mast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FcεRI
The high-affinity IgE receptor, also known as FcεRI, or Fc epsilon RI, is the high-affinity receptor for the Fc region of immunoglobulin E (IgE), an antibody isotype involved in the allergy disorder and parasites immunity. FcεRI is a tetrameric receptor complex that binds Fc portion of the ε heavy chain of IgE. It consists of one alpha (FcεRIα – antibody binding site), one beta (FcεRIβ – which amplifies the downstream signal), and two gamma chains (FcεRIγ – the site where the downstream signal initiates) connected by two disulfide bridges on mast cells and basophils. It lacks the beta subunit on other cells. It is constitutively expressed on mast cells and basophils and is inducible in eosinophils. Tissue distribution FcεRI is found on epidermal Langerhans cells, eosinophils, mast cells, and basophils. As a result of its cellular distribution, this receptor plays a major role in controlling allergic responses. FcεRI is also expressed on antigen-presenting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Smooth Muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit muscle, the whole bundle or sheet of smooth muscle cells contracts as a syncytium. Smooth muscle is found in the walls of hollow organs, including the stomach, intestines, bladder and uterus; in the walls of passageways, such as blood, and lymph vessels, and in the tracts of the respiratory, urinary, and reproductive systems. In the eyes, the ciliary muscles, a type of smooth muscle, dilate and contract the iris and alter the shape of the lens. In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature or fear. Structure Gross anatomy Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vasodilation
Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction, which is the narrowing of blood vessels. When blood vessels dilate, the flow of blood is increased due to a decrease in vascular resistance and increase in cardiac output. Therefore, dilation of arterial blood vessels (mainly the arterioles) decreases blood pressure. The response may be intrinsic (due to local processes in the surrounding tissue) or extrinsic (due to hormones or the nervous system). In addition, the response may be localized to a specific organ (depending on the metabolic needs of a particular tissue, as during strenuous exercise), or it may be systemic (seen throughout the entire systemic circulation). Endogenous substances and drugs that cause vasodilation are termed vasodilators. Such vasoactivity is necessary for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G-protein Coupled Receptor
G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of protein family, evolutionarily-related proteins that are cell surface receptors that detect molecules outside the cell (biology), cell and activate cellular responses. Coupling with G proteins, they are called seven-transmembrane receptors because they pass through the cell membrane seven times. Text was copied from this source, which is available under Attribution 2.5 Generic (CC BY 2.5) license. Ligands can bind either to extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices (Rhodopsin-like family). They are all activated by agonists although a spontaneous auto-activation of an empty receptor can also be observed. G protein-coupled receptors are found only in eukaryotes, including y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residue ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prostaglandin
The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derived enzymatically from the fatty acid arachidonic acid. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. They are a subclass of eicosanoids and of the prostanoid class of fatty acid derivatives. The structural differences between prostaglandins account for their different biological activities. A given prostaglandin may have different and even opposite effects in different tissues in some cases. The ability of the same prostaglandin to stimulate a reaction in one tissue and inhibit the same reaction in another tissue is determined by the type of receptor to which the prostaglandin binds. They act as autocrine or paracrine factors with their target cells present in the immediate vicinity of the site of their secret ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leukotriene
Leukotrienes are a family of eicosanoid inflammatory mediators produced in leukocytes by the oxidation of arachidonic acid (AA) and the essential fatty acid eicosapentaenoic acid (EPA) by the enzyme arachidonate 5-lipoxygenase. Leukotrienes use lipid signaling to convey information to either the cell producing them (autocrine signaling) or neighboring cells (paracrine signaling) in order to regulate immune responses. The production of leukotrienes is usually accompanied by the production of histamine and prostaglandins, which also act as inflammatory mediators. One of their roles (specifically, leukotriene D4) is to trigger contractions in the smooth muscles lining the bronchioles; their overproduction is a major cause of inflammation in asthma and allergic rhinitis. Leukotriene antagonists are used to treat these disorders by inhibiting the production or activity of leukotrienes. History and name The name ''leukotriene'', introduced by Swedish biochemist Bengt Samuelsso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histamine
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in 1910, it has been considered a local hormone (autocoid) because it lacks the classic endocrine glands to secrete it; however, in recent years, histamine has been recognized as a central neurotransmitter. Histamine is involved in the inflammatory response and has a central role as a mediator of itching. As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. It consists of an imidazole ring attached to an ethylamine chain; under physiological conditions, the amino group of the side-chain is protonate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arachidonic Acid
Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''arachis'' (peanut), but peanut oil does not contain any arachidonic acid. Chemistry In chemical structure, arachidonic acid is a carboxylic acid with a 20-carbon chain and four ''cis''-double bonds; the first double bond is located at the sixth carbon from the omega end. Some chemistry sources define 'arachidonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine, and nutrition limit the term to ''all cis''-5,8,11,14-eicosatetraenoic acid. Biology Arachidonic acid is a polyunsaturated fatty acid present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositides) of membranes of the body's cells, and is abundant in the brain, muscles, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Granule (cell Biology)
In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle. In leukocytes A group of leukocytes, called granulocytes, contain granules and play an important role in the immune system. The granules of certain cells, such as natural killer cells, contain components which can lead to the lysis of neighboring cells. The granules of leukocytes are classified as azurophilic granules or specific granules. Leukocyte granules are released in response to immunological stimuli during a process known as degranulation. In platelets The granules of platelets are classified as dense granules and alpha granules. α-Granules are unique to platelets and are the most abundant of the platelet granules, numbering 50–80 per platelet 2. These granules measure 200–500 nm in diameter and account for about 10% of platelet volume. They contain mainly proteins, both membrane-associated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mast Cell
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a part of the immune and neuroimmune systems. Mast cells were discovered by Paul Ehrlich in 1877. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing, angiogenesis, immune tolerance, defense against pathogens, and vascular permeability in brain tumours. The mast cell is very similar in both appearance and function to the basophil, another type of white blood cell. Although mast cells were once thought to be tissue-resident basophils, it has been shown that the two cells develop from different hematopoietic lineages and thus cannot be the same cells. Structure Mast cells are very similar to basophil granulocytes (a class of white ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
