In animal anatomy, the mouth known as the oral cavity, buccal cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is the cavity lying at the upper end of the alimentary canal, bounded on the outside by the lips and inside by the pharynx and containing in higher vertebrates the tongue and teeth; this cavity is known as the buccal cavity, from the Latin bucca. Some animal phyla, including vertebrates, have a complete digestive system, with a mouth at one end and an anus at the other. Which end forms first in ontogeny is a criterion used to classify animals into protostomes and deuterostomes. In the first multicellular animals, there was no mouth or gut and food particles were engulfed by the cells on the exterior surface by a process known as endocytosis; the particles became enclosed in vacuoles into which enzymes were secreted and digestion took place intracellularly. The digestive products were diffused into other cells; this form of digestion is used nowadays by simple organisms such as Amoeba and Paramecium and by sponges which, despite their large size, have no mouth or gut and capture their food by endocytosis.
The vast majority of other multicellular organisms have a mouth and a gut, the lining of, continuous with the epithelial cells on the surface of the body. A few animals which live parasitically had guts but have secondarily lost these structures; the original gut of multicellular organisms consisted of a simple sac with a single opening, the mouth. Many modern invertebrates have such a system, food being ingested through the mouth broken down by enzymes secreted in the gut, the resulting particles engulfed by the other cells in the gut lining. Indigestible waste is ejected through the mouth. In animals at least as complex as an earthworm, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the formation of the gut. In deuterostomes, the blastopore becomes the anus while the gut tunnels through to make another opening, which forms the mouth. In the protostomes, it used to be thought that the blastopore formed the mouth while the anus formed as an opening made by the other end of the gut.
More recent research, shows that in protostomes the edges of the slit-like blastopore close up in the middle, leaving openings at both ends that become the mouth and anus. Apart from sponges and placozoans all animals have an internal gut cavity, lined with gastrodermal cells. In less advanced invertebrates such as the sea anemone, the mouth acts as an anus. Circular muscles around the mouth are able to contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape enough to accommodate large prey items. Food passes first into a pharynx and digestion occurs extracellularly in the gastrovascular cavity. Annelids have simple tube-like gets and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients. Many molluscs have a radula, used to scrape microscopic particles off surfaces. In invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have a range of mouthparts suited to their mode of feeding.
These include mandibles and labium and can be modified into suitable appendages for chewing, piercing and sucking. Decapods have six pairs of mouth appendages, one pair of mandibles, two pairs of maxillae and three of maxillipeds. Sea urchins have a set of five sharp calcareous plates which are used as jaws and are known as Aristotle's lantern. In vertebrates, the first part of the digestive system is the buccal cavity known as the mouth; the buccal cavity of a fish is separated from the opercular cavity by the gills. Water flows in through passes over the gills and exits via the operculum or gill slits. Nearly all fish have jaws and may seize food with them but most feed by opening their jaws, expanding their pharynx and sucking in food items; the food may be held or chewed by teeth located in the jaws, on the roof of the mouth, on the pharynx or on the gill arches. Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth where they hold the prey with their jaws.
They swallow their food whole without much chewing. They have many small hinged pedicellate teeth, the bases of which are attached to the jaws while the crowns break off at intervals and are replaced. Most amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians there are vomerine teeth attached to the bone in the roof of the mouth; the mouths of reptiles are similar to those of mammals. The crocodilians are the only reptiles to have teeth anchored in sockets in their jaws, they are able to replace each of their 80 teeth up to 50 times during their lives. Most reptiles are either carnivorous or insectivorous but turtles are herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles have gastroliths in their stomach to further grind the plant material. Snakes have a flexible lower jaw, the two halves of which are not rigidly attached, numerous other joints in their skull; these modifications allow them to open their mouths wide enough to swallow their prey whole if it is wider than they are.
Birds do not have teeth, macerating their food. Their beaks have a range of sizes and shapes according to their diet and are compose
Hydrogen peroxide is a chemical compound with the formula H2O2. In its pure form, it is a pale blue, clear liquid more viscous than water. Hydrogen peroxide is the simplest peroxide, it is used as bleaching agent and antiseptic. Concentrated hydrogen peroxide, or "high-test peroxide", is a reactive oxygen species and has been used as a propellant in rocketry, its chemistry is dominated by the nature of its unstable peroxide bond. Hydrogen peroxide is unstable and decomposes in the presence of light; because of its instability, hydrogen peroxide is stored with a stabilizer in a weakly acidic solution. Hydrogen peroxide is found in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as peroxidases; the boiling point of H2O2 has been extrapolated as being 150.2 °C 50 °C higher than water. In practice, hydrogen peroxide will undergo explosive thermal decomposition if heated to this temperature, it may be safely distilled at lower temperatures under reduced pressure.
In aqueous solutions hydrogen peroxide differs from the pure substance due to the effects of hydrogen bonding between water and hydrogen peroxide molecules. Hydrogen peroxide and water form a eutectic mixture; the boiling point of the same mixtures is depressed in relation with the mean of both boiling points. It occurs at 114 °C; this boiling point is 14 °C greater than that of pure water and 36.2 °C less than that of pure hydrogen peroxide. Hydrogen peroxide is a nonplanar molecule as shown by Paul-Antoine Giguère in 1950 using infrared spectroscopy, with C2 symmetry. Although the O−O bond is a single bond, the molecule has a high rotational barrier of 2460 cm−1; the increased barrier is ascribed to repulsion between the lone pairs of the adjacent oxygen atoms and results in hydrogen peroxide displaying atropisomerism. The molecular structures of gaseous and crystalline H2O2 are different; this difference is attributed to the effects of hydrogen bonding, absent in the gaseous state. Crystals of H2O2 are tetragonal with the space group D44P4121.
Hydrogen peroxide has several structural analogues with Hm−X−X−Hn bonding arrangements. It has the highest boiling point of this series, its melting point is fairly high, being comparable to that of hydrazine and water, with only hydroxylamine crystallising more indicative of strong hydrogen bonding. Diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide. All of these analogues are thermodynamically unstable. Structurally, the analogues all adopt similar skewed structures, due to repulsion between adjacent lone pairs. Alexander von Humboldt synthesized one of the first synthetic peroxides, barium peroxide, in 1799 as a by-product of his attempts to decompose air. Nineteen years Louis Jacques Thénard recognized that this compound could be used for the preparation of a unknown compound, which he described as eau oxygénée – subsequently known as hydrogen peroxide. An improved version of Thénard's process used hydrochloric acid, followed by addition of sulfuric acid to precipitate the barium sulfate byproduct.
This process was used from the end of the 19th century until the middle of the 20th century. Thénard and Joseph Louis Gay-Lussac synthesized sodium peroxide in 1811; the bleaching effect of peroxides and their salts on natural dyes became known around that time, but early attempts of industrial production of peroxides failed, the first plant producing hydrogen peroxide was built in 1873 in Berlin. The discovery of the synthesis of hydrogen peroxide by electrolysis with sulfuric acid introduced the more efficient electrochemical method, it was first implemented into industry in 1908 in Weißenstein, Austria. The anthraquinone process, still used, was developed during the 1930s by the German chemical manufacturer IG Farben in Ludwigshafen; the increased demand and improvements in the synthesis methods resulted in the rise of the annual production of hydrogen peroxide from 35,000 tonnes in 1950, to over 100,000 tonnes in 1960, to 300,000 tonnes by 1970. Pure hydrogen peroxide was long believed to be unstable, as early attempts to separate it from the water, present during synthesis, all failed.
This instability was due to traces of impurities, which catalyze the decomposition of the hydrogen peroxide. Pure hydrogen peroxide was first obtained in 1894—almost 80 years after its discovery—by Richard Wolffenstein, who produced it by vacuum distillation. Determination of the molecular structure of hydrogen peroxide proved to be difficult. In 1892 the Italian physical chemist Giacomo Carrara determined its molecular mass by freezing-point depression, which confirmed that its molecular formula is H2O2. At least half a dozen hypothetical molecular structures seemed to be consistent with the available evidence. In 1934, the English mathematical physicist William Penney and the Scottish physicist Gordon Sutherland proposed a molecular structure for hydrogen peroxide, similar to the presently accepted one. Hydrogen peroxide was prepared industrially by hydrolysis of ammonium persulfate, itself obtained by the electrolysis of a solution
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of an amino sugar along with a uronic galactose. Glycosaminoglycans are polar and attract water, they are therefore useful to the body as a shock absorber. Mucopolysaccharidoses are a group of metabolic disorders in which abnormal accumulations of glycosaminoglycans occur because of enzyme deficiencies. Glycosaminoglycans have high degrees of heterogeneity with regards to molecular mass, disaccharide construction, sulfation due to the fact that GAG synthesis, unlike proteins or nucleic acids, is not template driven, dynamically modulated by processing enzymes. Based on core disaccharide structures, GAGs are classified into four groups. Heparin/heparan sulfate and chondroitin sulfate/dermatan sulfate are synthesized in the Golgi apparatus, where protein cores made in the rough endoplasmic reticulum are posttranslationally modified with O-linked glycosylations by glycosyltransferases forming proteoglycans.
Keratan sulfate may modify core proteins through N-linked glycosylation or O-linked glycosylation of the proteoglycan. The fourth class of GAG, hyaluronic acid, is not synthesized by the Golgi, but rather by integral membrane synthases which secrete the dynamically elongated disaccharide chain. HSGAG and CSGAG modified proteoglycans first begin with a consensus Ser-Gly/Ala-X-Gly motif in the core protein. Construction of a tetrasaccharide linker that consists of -GlcAβ1–3Galβ1–3Galβ1–4Xylβ1-O--, where xylosyltransferase, β4-galactosyl transferase,β3-galactosyl transferase, β3-GlcA transferase transfer the four monosaccharides, begins synthesis of the GAG modified protein; the first modification of the tetrasaccharide linker determines whether the HSGAGs or CSGAGs will be added. Addition of a GlcNAc promotes the addition of HSGAGs while addition of GalNAc to the tetrasaccharide linker promotes CSGAG development. GlcNAcT-I transfers GlcNAc to the tetrasaccahride linker, distinct from glycosyltransferase GlcNAcT-II, the enzyme, utilized to build HSGAGs.
EXTL2 and EXTL3, two genes in the EXT tumor suppressor family, have been shown to have GlcNAcT-I activity. Conversely, GalNAc is transferred to the linker by the enzyme GalNAcT to initiate synthesis of CSGAGs, an enzyme which may or may not have distinct activity compared to the GalNAc transferase activity of chondroitin synthase. With regard to HSGAGs, a multimeric enzyme encoded by EXT1 and EXT2 of the EXT family of genes, transfers both GlcNAc and GlcA for HSGAG chain elongation. While elongating, the HSGAG is dynamically modified, first by N-deacetylase, N-sulfotransferase, a bifunctional enzyme that cleaves the N-acetyl group from GlcNAc and subsequently sulfates the N-position. Next, C-5 uronyl epimerase coverts d-GlcA to l-IdoA followed by 2-O sulfation of the uronic acid sugar by 2-O sulfotransferase; the 6-O and 3-O positions of GlcNAc moities are sulfated by 6-O and 3-O sulfotransferases. Chondroitin sulfate and dermatan sulfate, which comprise CSGAGs, are differentiated from each other by the presence of GlcA and IdoA epimers respectively.
Similar to the production of HSGAGs, C-5 uronyl epimerase converts d-GlcA to l-IdoA to synthesize dermatan sulfate. Three sulfation events of the CSGAG chains occur: 4-O and/or 6-O sulfation of GalNAc and 2-O sulfation of uronic acid. Four isoforms of the 4-O GalNAc sulfotransferases and three isoforms of the GalNAc 6-O sulfotransferases are responsible for the sulfation of GalNAc. Unlike HSGAGs and CSGAGs, the third class of GAGs, those belonging to keratan sulfate types, are driven towards biosynthesis through particular protein sequence motifs. For example, in the cornea and cartilage, the keratan sulfate domain of aggrecan consists of a series of tandemly repeated hexapeptides with a consensus sequence of EPFPS. Additionally, for three other keratan sulfated proteoglycans, lumican and mimecan, the consensus sequence NX along with protein secondary structure was determined to be involved in N-linked oligosaccharide extension with keratan sulfate. Keratan sulfate elongation begins at the nonreducing ends of three linkage oligosaccharides, which define the three classes of keratan sulfate.
Keratan sulfate. Keratan sulfate II and keratan sulfate III are O-linked, with KSII linkages identical to that of mucin core structure, KSIII linked to a 2-O mannose. Elongation of the keratan sulfate polymer occurs through the glycosyltransferase addition of Gal and GlcNAc. Galactose addition occurs through the β-1,4-galactosyltransferase enzyme while the enzymes responsible for β-3-Nacetylglucosamine have not been identified. Sulfation of the polymer occurs at the 6-position of both sugar residues; the enzyme KS-Gal6ST transfers sulfate groups to galactose while N-acetylglucosaminyl-6-sulfotransferase transfers sulfate groups to terminal GlcNAc in keratan sulfate. The fourth class of GAG, hyaluronan, is not sulfated and is synthesized by three transmembrane synthase proteins HAS1, HAS2, HAS3. HA, a linear polysaccharide, is composed of repeating disaccharide units of →4)GlcAβGlcNAcβ(1→ and has a high molecular mass, ranging from 105 to 107 Da; each HAS enzyme is capable of transglycosylation when supplied with UDP-G
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA, or in chloroplasts as chloroplast DNA. In contrast, prokaryotes store their DNA only in circular chromosomes.
Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix. The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide.
A biopolymer comprising multiple linked nucleotides is called a polynucleotide. The backbone of the DNA strand is made from alternating sugar residues; the sugar in DNA is 2-deoxyribose, a pentose sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings; these are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. When imagining DNA, each phosphoryl is considered to "belong" to the nucleotide whose 5′ carbon forms a bond therewith. Any DNA strand therefore has one end at which there is a phosphoryl attached to the 5′ carbon of a ribose and another end a
Caterpillars are the larval stage of members of the order Lepidoptera. As with most common names, the application of the word is arbitrary and the larvae of sawflies are called caterpillars as well. Both lepidopteran and symphytan larvae have eruciform body shapes. Caterpillars of most species are herbivorous, but not all; some feed on other animal products. Caterpillars are voracious feeders and many of them are among the most serious of agricultural pests. In fact many moth species are best known in their caterpillar stages because of the damage they cause to fruits and other agricultural produce, whereas the moths are obscure and do no direct harm. Conversely, various species of caterpillar are valued as sources of silk, as human or animal food, or for biological control of pest plants; the origins of the word "caterpillar" date from the early 16th century. They derive from Middle English catirpel, catirpeller an alteration of Old North French catepelose: cate, cat + pelose, hairy; the inchworm, or looper caterpillars from the family Geometridae are so named because of the way they move, appearing to measure the earth.
Caterpillars have soft bodies that can grow between moults. Their size varies between instars from as small as 1 mm up to 14 cm; some larvae of the order Hymenoptera can appear like the caterpillars of the Lepidoptera. Such larvae are seen in the sawfly suborder; however while these larvae superficially resemble caterpillars, they can be distinguished by the presence of prolegs on every abdominal segment, an absence of crochets or hooks on the prolegs, one pair of prominent ocelli on the head capsule, an absence of the upside-down Y-shaped suture on the front of the head. Lepidopteran caterpillars can be differentiated from sawfly larvae by: the numbers of pairs of pro-legs; the number of stemmata. The presence of crochets on the prolegs. Sawfly larvae have an invariably smooth head capsule with no cleavage lines, while lepidopterous caterpillars bear an inverted "Y" or "V". Many animals feed on caterpillars; as a result, caterpillars have evolved various means of defense. Caterpillars have evolved defenses against physical conditions such as cold, hot or dry environmental conditions.
Some Arctic species like Gynaephora groenlandica have special basking and aggregation behaviours apart from physiological adaptations to remain in a dormant state. The appearance of a caterpillar can repel a predator: its markings and certain body parts can make it seem poisonous, or bigger in size and thus threatening, or non-edible; some types of caterpillars are indeed poisonous or distasteful and their bright coloring is aposematic. Others may mimic other animals while not being dangerous themselves. Many caterpillars are cryptically resemble the plants on which they feed. An example of caterpillars that use camouflage for defence is the species Nemoria arizonaria. If the caterpillars hatch in the spring and feed on oak catkins they appear green. If they hatch in the summer they appear dark colored, like oak twigs; the differential development is linked to the tannin content in the diet. Caterpillars may have spines or growths that resemble plant parts such as thorns; some look like objects in the environment such as bird droppings.
More aggressive self-defense measures are taken by some caterpillars. These measures include having spiny bristles or long fine hair-like setae with detachable tips that will irritate by lodging in the skin or mucous membranes; however some birds will swallow the hairiest of caterpillars. Other caterpillars acquire toxins from their host plants that render them unpalatable to most of their predators. For instance, ornate moth caterpillars utilize pyrrolizidine alkaloids that they obtain from their food plants to deter predators; the most aggressive caterpillar defenses are bristles associated with venom glands. These bristles are called urticating hairs. A venom, among the most potent defensive chemicals in any animal is produced by the South American silk moth genus Lonomia, its venom is an anticoagulant powerful enough to cause a human to hemorrhage to death. This chemical is being investigated for potential medical applications. Most urticating hairs range in effect from mild irritation to dermatitis.
Example: Brown-tail moth. Plants contain toxins which protect them from herbivores, but some caterpillars have evolved countermeasures which enable them to eat the leaves of such toxic plants. In addition to being unaffected by the poison, the caterpillars sequester it in their body, making them toxic to predators; the chemicals are carried on into the adult stages. These toxic species, such as the cinnabar moth and monarch caterpillars advertise themselves with the danger colors of red and black in bright stripes. Any predator that attempts to eat a caterpillar with an aggressive defense mechanism will learn and avoid future attempts; some caterpill
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
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