Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin MUC5AC. The goblet cells use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions, when under stress; the term goblet refers to the cell's goblet-like shape. The apical portion is shaped like a cup; the goblet cell is polarized with the nucleus and other organelles concentrated at the base of the cell and secretory granules containing mucin, at the apical surface. The apical plasma membrane projects microvilli to give an increased surface area for secretion. Goblet cells are found in the respiratory and gastrointestinal tracts and are surrounded by stratified squamous cells. Differentiation of epithelial cells into goblet cells plays a key role in the excessive mucus production seen in many diseases, such as asthma and cancer. Goblet cells are found scattered among the epithelial lining of organs, such as the intestinal and respiratory tracts.
They are found inside the trachea and larger bronchioles in the respiratory tract, small intestines, the large intestine, conjunctiva in the upper eyelid. In the conjunctiva goblet cells are a source of mucin in tears and they secrete different types of mucins onto the ocular surface. In the lacrimal glands, mucus is synthesized by acinar cells instead. Goblet cells are simple columnar epithelial cells, having a height of four times that of their width; the cytoplasm of goblet cells tends to be displaced toward the basal end of the cell body by the large mucin granules, which accumulate near the apical surface of the cell along the Golgi apparatus, which lies between the granules and the nucleus. This gives the basal part of the cell a basophilic staining because of nucleic acids within the nucleus and rough endoplasmic reticulum staining with hematoxylin. Mucin within the granules stains pale in routine histology sections because these carbohydrate-rich proteins are washed out in the preparation of microscopy samples.
However, they stain with the PAS staining method, which colours them magenta. In mucicarmine stains, deep red mucin is found within goblet cell bodies. Goblet cells can be seen in the examples below as the more pale cells; the main role of goblet cells is to secrete mucus in order to protect the mucous membranes where they are found. Goblet cells accomplish this by secreting mucins, large glycoproteins formed by carbohydrates; the gel-like properties of mucins are given by its glycans attracting large quantities of water. On the inner surface of the human intestine, it forms a 200 µm thick layer that lubricates and protects the wall of the organ. Distinct forms of mucin are produced in different organs: while MUC2 is prevalent in the intestine, MUC5AC and MUC5B are the main forms found in the human airway. In the airway, mucus is swept by the cilia of epithelial cells, propelled out of the lungs and into the pharynx, which results in the removal of debris and pathogens from the airway. MUC5AC is overexpressed in allergic lung inflammation.
Mucins are continuously made and secreted by goblet cells in order to repair and replace the existing mucus layer. Mucins are stored in granules inside the goblet cells before being released to the lumen of the organ. Mucin secretion in the airway may occur via regulated secretion. Secretion may be stimulated by irritants such as dust and smoke in the airway. Other stimuli are microbes such as bacteria. Anomalies in the number of goblet cell are associated with changes in the secretion of mucins, which can result in many of the abnormalities seen in asthma patients, such as clogged airways due to mucus production, eventual loss of lung function. Overexpression of MUC5AC alone does not result in the pathophysiology seen in asthma patients. This, in addition to airway narrowing leads to the clogging of the airways, which can be detrimental to health if not treated. There are other cells that secrete mucus but these are distinguished histologically from goblet cells. Oral tolerance is the process by which the immune system is prevented from responding to antigen derived from food products, as peptides from food may pass into the bloodstream via the gut, which would in theory lead to an immune response.
A paper published in Nature in 2012 has shed some light on the process and implicated goblet cells as having a role in the process. It was known that CD103-expressing dendritic cells of the lamina propria had a role to play in the induction of oral tolerance, this paper suggests that the goblet cells act to preferentially deliver antigen to these CD103+ dendritic cells; the excessive mucus production seen in allergic asthma patients is due to goblet cell metaplasia, the differentiation of airway epithelial cells into mucin producing goblet cells. These cells produce the thick mucins MUC5AC and MUC5B, which clog the airway, leading to the airflow obstruction characteristic of asthma. Goblet cell metaplasia in allergic asthma is due to the action of the cytokine IL-13. IL-13 initiates a STAT6 signalling response. Binding of IL-13 causes phosphorylation of tyrosine residues at the IL-4Rα; this results in docking of STAT6 monomers, which themselves are phosphorylated and subsequently leave the receptor and congregate form STAT6 homodimers in
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically similar to sodium, the previous element in group 1 of the periodic table, they have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, it is the most common radioisotope in the human body. Potassium ions are vital for the functioning of all living cells; the transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission. Fresh fruits and vegetables are good dietary sources of potassium; the body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s
Mucus is a polymer. It is a slippery aqueous secretion produced by, covering, mucous membranes, it is produced from cells found in mucous glands, although it may originate from mixed glands, which contain both serous and mucous cells. It is a viscous colloid containing inorganic salts, antiseptic enzymes and glycoproteins such as lactoferrin and mucins, which are produced by goblet cells in the mucous membranes and submucosal glands. Mucus serves to protect epithelial cells in the respiratory, urogenital and auditory systems. Most of the mucus produced is in the gastrointestinal tract. Bony fish, snails and some other invertebrates produce external mucus. In addition to serving a protective function against infectious agents, such mucus provides protection against toxins produced by predators, can facilitate movement and may play a role in communication. In the human respiratory system, mucus known as airway surface liquid, aids in the protection of the lungs by trapping foreign particles that enter them, in particular, through the nose, during normal breathing.
Further distinction exists between the superficial and cell-lining layers of ASL, which are known as mucus layer and pericilliary liquid layer, respectively. "Phlegm" is a specialized term for mucus, restricted to the respiratory tract, whereas the term "nasal mucus" describes secretions of the nasal passages. Nasal mucus is produced by the nasal mucosa. Small particles such as dust, particulate pollutants, allergens, as well as infectious agents and bacteria are caught in the viscous nasal or airway mucus and prevented from entering the system; this event along with the continual movement of the respiratory mucus layer toward the oropharynx, helps prevent foreign objects from entering the lungs during breathing. This explains why coughing occurs in those who smoke cigarettes; the body's natural reaction is to increase mucus production. In addition, mucus aids in moisturizing the inhaled air and prevents tissues such as the nasal and airway epithelia from drying out. Nasal and airway mucus is produced continuously, with most of it swallowed subconsciously when it is dried.
Increased mucus production in the respiratory tract is a symptom of many common illnesses, such as the common cold and influenza. Hypersecretion of mucus can occur in inflammatory respiratory diseases such as respiratory allergies and chronic bronchitis; the presence of mucus in the nose and throat is normal, but increased quantities can impede comfortable breathing and must be cleared by blowing the nose or expectorating phlegm from the throat. In general, nasal mucus is thin, serving to filter air during inhalation. During times of infection, mucus can change color to yellow or green either as a result of trapped bacteria or due to the body's reaction to viral infection; the green color of mucus comes from the heme group in the iron-containing enzyme myeloperoxidase secreted by white blood cells as a cytotoxic defense during a respiratory burst. In the case of bacterial infection, the bacterium becomes trapped in already-clogged sinuses, breeding in the moist, nutrient-rich environment. Sinusitis is an uncomfortable condition.
A bacterial infection in sinusitis will cause discolored mucus and would respond to antibiotic treatment. All sinusitis infections are viral and antibiotics are ineffective and not recommended for treating typical cases. In the case of a viral infection such as cold or flu, the first stage and the last stage of the infection cause the production of a clear, thin mucus in the nose or back of the throat; as the body begins to react to the virus, mucus may turn yellow or green. Viral infections cannot be treated with antibiotics, are a major avenue for their misuse. Treatment is symptom-based. Increased mucus production in the upper respiratory tract is a symptom of many common ailments, such as the common cold. Nasal mucus may be removed by using nasal irrigation. Excess nasal mucus, as with a cold or allergies, due to vascular engorgement associated with vasodilation and increased capillary permeability caused by histamines, may be treated cautiously with decongestant medications. Thickening of mucus as a "rebound" effect following overuse of decongestants may produce nasal or sinus drainage problems and circumstances that promote infection.
During cold, dry seasons, the mucus lining nasal passages tends to dry out, meaning that mucous membranes must work harder, producing more mucus to keep the cavity lined. As a result, the nasal cavity can fill up with mucus. At the same time, when air is exhaled, water vapor in breath condenses as the warm air meets the colder outside temperature near the nostrils; this causes an excess amount of water to build up inside nasal cavities. In these cases, the excess fluid spills out externally through the nostrils. Excess mucus production in the bronchi and bronchioles, as may occur in asthma, bronchitis or influenza, results from chronic airway inflammation, hence may be treated with anti-inflammatory medications. Impaired mucociliary clearance due to conditions such as primary ciliary dyskinesia may result in its accumulation in the bronchi; the dysregulation of
The orange is the fruit of the citrus species Citrus × sinensis in the family Rutaceae. It is called sweet orange, to distinguish it from the related Citrus × aurantium, referred to as bitter orange; the sweet orange reproduces asexually. The orange is a hybrid between mandarin; the chloroplast genome, therefore the maternal line, is that of pomelo. The sweet orange has had its full genome sequenced. Sweet orange originated in ancient China and the earliest mention of the sweet orange was in Chinese literature in 314 BC; as of 1987, orange trees were found to be the most cultivated fruit tree in the world. Orange trees are grown in tropical and subtropical climates for their sweet fruit; the fruit of the orange tree can be processed for its juice or fragrant peel. As of 2012, sweet oranges accounted for 70% of citrus production. In 2014, 70.9 million tonnes of oranges were grown worldwide, with Brazil producing 24% of the world total followed by China and India. All citrus trees belong to the single genus Citrus and remain entirely interfertile.
This includes grapefruits, limes and various other types and hybrids. As the interfertility of oranges and other citrus has produced numerous hybrids and cultivars, bud mutations have been selected, citrus taxonomy is controversial, confusing or inconsistent; the fruit of any citrus tree is considered a kind of modified berry. Different names have been given to the many varieties of the genus. Orange applies to the sweet orange – Citrus sinensis Osbeck; the orange tree is an evergreen, flowering tree, with an average height of 9 to 10 m, although some old specimens can reach 15 m. Its oval leaves, alternately arranged, have crenulate margins. Sweet oranges grow in a range of different sizes, shapes varying from spherical to oblong. Inside and attached to the rind is a porous white tissue, the white, bitter mesocarp or albedo; the orange contains a number of distinct carpels inside about ten, each delimited by a membrane, containing many juice-filled vesicles and a few seeds. When unripe, the fruit is green.
The grainy irregular rind of the ripe fruit can range from bright orange to yellow-orange, but retains green patches or, under warm climate conditions, remains green. Like all other citrus fruits, the sweet orange is non-climacteric; the Citrus sinensis group is subdivided into four classes with distinct characteristics: common oranges, blood or pigmented oranges, navel oranges, acidless oranges. Other citrus groups known as oranges are: Mandarin orange is an original species of citrus, is a progenitor of the common orange. Bitter orange known as Seville orange, sour orange, bigarade orange and marmalade orange. Like the sweet orange, it is a pomelo x mandarin hybrid, but arose from a distinct hybridization event. Bergamot orange, grown in Italy for its peel, producing a primary essence for perfumes used to flavor Earl Grey tea, it is a hybrid of bitter orange x lemon. Trifoliate orange, sometimes included in the genus, it serves as a rootstock for sweet orange trees and other Citrus cultivars.
An enormous number of cultivars have, like a mix of pomelo and mandarin ancestry. Some cultivars are mandarin-pomelo hybrids, bred from the same parents as the sweet orange. Other cultivars are sweet orange x mandarin hybrids. Mandarin traits include being smaller and oblate, easier to peel, less acidic. Pomelo traits include a thick white albedo, more attached to the segments. Orange trees are grafted; the bottom of the tree, including the roots and trunk, is called rootstock, while the fruit-bearing top has two different names: budwood and scion. The word orange derives from the Sanskrit word for "orange tree", which in turn derives from a Dravidian root word; the Sanskrit word reached European languages through Persian نارنگ and its Arabic derivative نارنج. The word entered Late Middle English in the fourteenth century via Old French orenge; the French word, in turn, comes from Old Provençal auranja, based on Arabic nāranj. In several languages, the initial n present in earlier forms of the word dropped off because it may have been mistaken as part of an indefinite article ending in an n sound—in French, for example, une norenge may have been heard as une orenge.
This linguistic change is called juncture loss. The color was named after the fruit, the first recorded use of orange as a color name in English was in 1512; as Portuguese merchants were the first to introduce the sweet orange to some regions of Europe, in several modern Indo-European languages the fruit has been named after them. Some examples are Albanian portokall, Bulgarian портокал, Greek πορτοκάλι, Macedonian portokal, Persian پرتقال, Turkish portakal and Romanian portocală. Related names can be found in other languages, such as Arabic البرتقال, Georgian ფორთოხალი and Amharic birtukan. In
Basil called great basil or Saint-Joseph's-wort, is a culinary herb of the family Lamiaceae. Basil is native to tropical regions from central Africa to Southeast Asia, it is a tender plant, is used in cuisines worldwide. Depending on the species and cultivar, the leaves may taste somewhat like anise, with a strong, pungent sweet smell. There are many varieties of basil, as well as several related species or hybrids called basil; the type used as a flavor is called sweet basil, as opposed to Thai basil, lemon basil, holy basil. While most common varieties of basil are treated as annuals, some are perennial in warm, tropical climates, including holy basil and a cultivar known as "African blue basil". Basil is sometimes perennial, herb used for its leaves. Depending on the variety, plants can reach between 150 cm, its leaves are richly green and ovate, but otherwise come in a wide variety of sizes and shapes depending on cultivar. Leaf sizes range from 3 cm to 11 cm long, between 1 cm and 6 cm wide.
Basil grows a central taproot. Its flowers are small and white, grow from a central inflorescence that emerges from the central stem atop the plant; the various basils have such different scents because the herb has a number of different essential oils in different proportions for various cultivars. The essential oil from European basil contains high concentrations of linalool and methyl chavicol, in a ratio of about 3:1. Other constituents include: 1,8-cineole and myrcene, among others; the clove scent of sweet basil is derived from eugenol. The aroma profile of basil includes 1,8-cineole and methyl eugenol; the exact taxonomy of basil is uncertain due to the immense number of cultivars, its ready polymorphy, frequent cross-pollination with other members of the Ocimum genus and within the species. Ocimum basilicum has at least 60 varieties. Most basils are cultivars of sweet basil. Anise basil, Licorice basil or Persian basil Cinnamon basil Dark opal basil Lettuce leaf basil Purple basil Rubin basil Globe basil, dwarf basil, French basil Thai basil African blue basil Spice basil, sometimes sold as holy basil) Lemon basil Camphor basil, African basil Clove basil African basil Holy basil Several other basils, including some other Ocimum species, are grown in many regions of Asia.
Most of the Asian basils have a clove-like flavor that is, in general, stronger than the Mediterranean basils. The most notable is a revered home-grown plant in India and Nepal. Lemon basil has a strong lemony smell and flavor different from those of other varieties because it contains a chemical called citral, it is used in Indonesia, where it is called kemangi, served raw together with raw cabbage, green beans, cucumber as an accompaniment to fried fish or duck. Its flowers, when broken up, are a zesty salad condiment; the name "basil" comes from Latin and Greek βασιλικόν φυτόν, "royal/kingly plant" because the plant was believed to have been used in production of royal perfumes. The Latin name has been confused with basilisk, as it was supposed to be an antidote to the basilisk's venom. Basil is native to India and other tropical regions stretching from Africa to Southeast Asia, but has now become globalized due to human cultivation. Most culinary and ornamental basils are cultivars of the species Ocimum basilicum, but other species are grown and there are many hybrids between species.
Traditionally a green plant, some varieties, such as ` Purple Delight' have leaves. Basil grows between 30–130 cm tall, with opposite, light green, silky leaves 3–11 cm long and 1–6 cm broad; the flowers white in color and arranged in a terminal spike. Unusual among Lamiaceae, the four stamens and the pistil are not pushed under the upper lip of the corolla, but lie over the inferior lip. After entomophilous pollination, the corolla falls off and four round achenes develop inside the bilabiate calyx. Basil is sensitive to cold, with best growth in dry conditions, it behaves as an annual. However, due to its popularity, basil is cultivated in many countries around the world. Production areas include countries in the Mediterranean area, those in the temperate zone, others in subtropical climates. In Northern Europe, the northern states of the U. S. and the South Island of New Zealand it will grow best if sown under glass in a peat pot planted out in late spring/early summer. Additionally, it may be sown in soil.
It fares best in sunny exposure. Although basil grows best outdoors, it can be grown indoors in a pot and, like most herbs, will do best on a sun-facing windowsill, it should be kept away from cold drafts, grows best in strong sunlight, therefore a greenhouse or row cover is ideal if available. It can, however, be grown in a basement, under fluorescent lights. If its leaves have wilted from lack of water, it will recov
Cannabis is a genus of flowering plants in the family Cannabaceae. The number of species within the genus is disputed. Three species may be recognized: Cannabis sativa, Cannabis indica, Cannabis ruderalis; the genus is accepted as being indigenous to and originating from Central Asia, with some researchers including upper South Asia in its origin. The plant is known as hemp, although this term is used to refer only to varieties of Cannabis cultivated for non-drug use. Cannabis has long been used for hemp fibre, hemp seeds and their oils, hemp leaves for use as vegetables and as juice, medicinal purposes, as a recreational drug. Industrial hemp products are made from cannabis plants selected to produce an abundance of fiber. To satisfy the UN Narcotics Convention, some cannabis strains have been bred to produce minimal levels of tetrahydrocannabinol, the principal psychoactive constituent; some strains have been selectively bred to produce a maximum of THC, the strength of, enhanced by curing the flowers.
Various compounds, including hashish and hash oil, are extracted from the plant. Globally, in 2013, 60,400 kilograms of cannabis were produced legally. In 2014 there were an estimated 182.5 million cannabis users. This percentage has not changed between 1998 and 2014. Cannabis is an annual, flowering herb; the leaves are palmately digitate, with serrate leaflets. The first pair of leaves have a single leaflet, the number increasing up to a maximum of about thirteen leaflets per leaf, depending on variety and growing conditions. At the top of a flowering plant, this number again diminishes to a single leaflet per leaf; the lower leaf pairs occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant. The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a cannabis leaf from unrelated species that have confusingly similar leaves; as is common in serrated leaves, each serration has a central vein extending to its tip.
However, the serration vein originates from lower down the central vein of the leaflet opposite to the position of, not the first notch down, but the next notch. This means that on its way from the midrib of the leaflet to the point of the serration, the vein serving the tip of the serration passes close by the intervening notch. Sometimes the vein will pass tangent to the notch, but it will pass by at a small distance, when that happens a spur vein branches off and joins the leaf margin at the deepest point of the notch; this venation pattern varies among varieties, but in general it enables one to tell Cannabis leaves from superficially similar leaves without difficulty and without special equipment. Tiny samples of Cannabis plants can be identified with precision by microscopic examination of leaf cells and similar features, but that requires special expertise and equipment. All known strains of Cannabis are wind-pollinated and the fruit is an achene. Most strains of Cannabis are short day plants, with the possible exception of C. sativa subsp.
Sativa var. spontanea, described as "auto-flowering" and may be day-neutral. Cannabis is predominantly dioecious, having imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants. "At a early period the Chinese recognized the Cannabis plant as dioecious", the Erya dictionary defined xi 枲 "male Cannabis" and fu 莩 "female Cannabis". Male flowers are borne on loose panicles, female flowers are borne on racemes. Many monoecious varieties have been described, in which individual plants bear both male and female flowers. Subdioecy is widespread. Many populations have been described as sexually labile; as a result of intensive selection in cultivation, Cannabis exhibits many sexual phenotypes that can be described in terms of the ratio of female to male flowers occurring in the individual, or typical in the cultivar. Dioecious varieties are preferred for drug production. Dioecious varieties are preferred for textile fiber production, whereas monoecious varieties are preferred for pulp and paper production.
It has been suggested that the presence of monoecy can be used to differentiate licit crops of monoecious hemp from illicit drug crops. However, sativa strains produce monoecious individuals as a result of inbreeding. Cannabis has been described as having one of the most complicated mechanisms of sex determination among the dioecious plants. Many models have been proposed to explain sex determination in Cannabis. Based on studies of sex reversal in hemp, it was first reported by K. Hirata in 1924 that an XY sex-determination system is present. At the time, the XY system was the only known system of sex determination; the X:A system was first described in Drosophila spp in 1925. Soon thereafter, Schaffner disputed Hirata's interpretation, published results from his o
Flavonoids are a class of plant and fungus secondary metabolites. Chemically, flavonoids have the general structure of a 15-carbon skeleton, which consists of two phenyl rings and a heterocyclic ring; this carbon structure can be abbreviated C6-C3-C6. According to the IUPAC nomenclature, they can be classified into: flavonoids or bioflavonoids isoflavonoids, derived from 3-phenylchromen-4-one structure neoflavonoids, derived from 4-phenylcoumarine structureThe three flavonoid classes above are all ketone-containing compounds, as such, are anthoxanthins; this class was the first to be termed bioflavonoids. The terms flavonoid and bioflavonoid have been more loosely used to describe non-ketone polyhydroxy polyphenol compounds which are more termed flavanoids; the three cycle or heterocycles in the flavonoid backbone are called ring A, B and C. Ring A shows a phloroglucinol substitution pattern. Flavonoids are distributed in plants, fulfilling many functions. Flavonoids are the most important plant pigments for flower coloration, producing yellow or red/blue pigmentation in petals designed to attract pollinator animals.
In higher plants, flavonoids are involved in UV filtration, symbiotic nitrogen fixation and floral pigmentation. They may act as chemical messengers, physiological regulators, cell cycle inhibitors. Flavonoids secreted by the root of their host plant help Rhizobia in the infection stage of their symbiotic relationship with legumes like peas, beans and soy. Rhizobia living in soil are able to sense the flavonoids and this triggers the secretion of Nod factors, which in turn are recognized by the host plant and can lead to root hair deformation and several cellular responses such as ion fluxes and the formation of a root nodule. In addition, some flavonoids have inhibitory activity against organisms that cause plant diseases, e.g. Fusarium oxysporum. Over 5000 occurring flavonoids have been characterized from various plants, they have been classified according to their chemical structure, are subdivided into the following subgroups: Anthocyanidins are the aglycones of anthocyanins. Examples: Cyanidin, Malvidin, Peonidin, Petunidin Anthoxanthins are divided into two groups: Flavanones Flavanonols Include flavan-3-ols, flavan-4-ols and flavan-3,4-diols.
Flavan-3-ols Flavan-3-ols use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeletonExamples: Catechin, Catechin 3-gallate, Gallocatechin 3-gallate, Epigallocatechin, Epicatechin 3-gallate, Epigallocatechin 3-gallate TheaflavinExamples: Theaflavin-3-gallate, Theaflavin-3'-gallate, Theaflavin-3,3'-digallateThearubigin Proanthocyanidins are dimers, oligomers, or polymers of the flavanols Isoflavonoids Isoflavones use the 3-phenylchromen-4-one skeleton Examples: Genistein, GlyciteinIsoflavanes Isoflavandiols Isoflavenes Coumestans Pterocarpans Flavonoids are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants". Flavonols, the original bioflavonoids such as quercetin, are found ubiquitously, but in lesser quantities; the widespread distribution of flavonoids, their variety and their low toxicity compared to other active plant compounds mean that many animals, including humans, ingest significant quantities in their diet. Foods with a high flavonoid content include parsley, onions and other berries, black tea, green tea and oolong tea, all citrus fruits, Ginkgo biloba, red wine, sea-buckthorns and dark chocolate.
Further information on dietary sources of flavonoids can be obtained from the US Department of Agriculture flavonoid database. Parsley, both fresh and dried, contains flavones. Blueberries are a dietary source of anthocyanidins. Black tea is a rich source of dietary flavan-3-ols; the citrus flavonoids include hesperidin, quercitrin and the flavone tangeritin. Flavonoids exist in cocoa, but because they can be bitter, they are removed from chocolate dark chocolate. Although flavonoids are present in milk chocolate, milk may interfere with their absorption. Peanut skin contains significant polyphenol content, including flavonoids. Food composition data for flavonoids were provided by the USDA database on flavonoids. In the United States NHANES survey, mean flavonoid intake was 190 mg/d in adults, with flavan-3-ols as the main contributor. In the European Union, based on data from EFSA, mean flavonoid intake was 140 mg/d, although there were considerable differences between individual countries; the main type of flavonoids consumed in the EU and USA were flavan-3-ols from tea, while intake of other flavonoids was lower.
Though there is ongoing research into the potential health benefits of individual flavonoids, neither the Food and Drug Administration nor the European Food Safety Authority has approved any health claim for flavonoids or approved any flavonoids as pharmaceutical drugs. Moreover, several companies have been cautioned by the FDA over misleading health claims. Flavonoids have been shown to have a wide range of biological and pharmacological act