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Connective Tissue

Connective tissue

Connective tissue is any type of biological tissue with an extensive extracellular matrix and often serves to support, bind together, and protect organs. There are four basic types:
- Bone contains specialized cells called osteocytes embedded in a mineralized extracellular matrix, and functions for general support.
- Blood functions in transport. Its extracellular matrix is the blood plasma, which transports dissolved nutrients, hormones, and carbon dioxide in the form of bicarbonate. The main cellular component is red blood cells.
- Cartilage makes up virtually the entire skeleton in the osteichthyes. In most other vertebrates, it is found primarily in joints, where it provides cushioning. The extracellular matrix of cartilage is composed primarily of collagen.
- Connective tissue proper
- Dense connective tissue or Fibrous connective tissue forms ligaments and tendons. Its densely packed collagen fibers have great tensile strength.
- Loose connective tissue or Areolar connective tissue holds organs and epithelia in place, and has a variety of proteinaceous fibers, including collagen and elastin. It is also important in inflammation.
- Reticular connective tissue is a network of reticular fibers (fine collagen) that form a soft skeleton to support the lymphoid organs (lymph nodes, bone marrow, and spleen.)
- Adipose tissue contains adipocytes, used for cushioning, insulation, lubrication (primarily in the pericardium) and energy storage.
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Disorders of connective tissue

Various connective tissue conditions have been described, these can be both inherited and environmental.
- Marfan syndrome - a genetic disease causing abnormal fibrillin.
- Scurvy - caused by a dietary deficiency in vitamin C, leading to abnormal collagen.
- Ehlers-Danlos syndrome - a genetic disease causing progressive deterioration of collagens, with different EDS types affecting different sites in the body, such as joints, heart valves, organ walls, arterial walls, etc.
- Osteogenesis imperfecta (brittle bone disease) - caused by insufficient production of good quality collagen to produce healthy, strong bones. See aalso: zootomy Category:Tissues

Biological tissue

Biological tissue is a substance made up of cells that perform a similar function. The study of tissues is known as histology, or, in connection with disease, histopathology. The classical tools for studying the tissues are the wax block, the tissue stain, and the optical microscope, though developments in electron microscopy, immunofluorescence, and frozen sections have all added to the sum of knowledge in the last couple of decades. With these tools, the classical appearances of the tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

Animal Tissues

There are four basic types of tissue in the body of all animals, including the human body and lowar multicellular organisms such as insects. These compose all the organs, structures and other contents.
- Epithelium - Tissues composed of layers of cells that cover organ surfaces such as surface of the skin and inner lining of digestive tract. The tissues serve for protection, secretion, and absorption.
- Connective tissue - As the name suggests, connective tissue holds everything together. Blood is considered a connective tissue.
- Muscle tissue - Muscle cells contain contractile filaments that move past each other and change the size of the cell.
- Nervous tissue - Cells forming the brain, spinal cord and peripheral nervous system.

Plant Tissues

Examples of tissue in other multicellular organisms are vascular tissue in plants, such as xylem and phloem. Plant tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and the vascular tissue.
- Epidermis - Cells forming the outer surface of the leaves and of the young plant body.
- Vascular tissue - The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally.
- Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients.

References

- Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (1986). Biology of Plants (4th ed.). New York: Worth Publishers. ISBN 0-87901-315-X. Category:Anatomy Category:Tissues ms:Tisu biologi ja:組織 (生物学) simple:Tissue (biological)

Organ (anatomy)

In biology, an organ (Latin: organum, "instrument, tool") is a group of tissues, which perform a specific function or group of functions. Common animal organs include the heart, lungs, brain, eye, stomach, spleen, pancreas, kidneys, liver, intestines, skin, uterus, bladder, bone, etc. A group of related organs is an organ system. Organelles are analogous sub-cellular structures.

Organ systems

Organ system – a system composed of organs working together to carry out a function.
- Circulatory system
- Digestive system
- Endocrine system
- Immune system
- Integumentary system
- Lymphatic system
- Muscular system
- Nervous system
- Reproductive system
- Respiratory system
- Skeletal system
- Urinary system Category:Anatomy
- ko:기관 (생물) ja:器官

Osteocyte

An osteocyte, a star-shaped cell, is the most abundant cell found in bone. Once osteoblasts become trapped in the matrix they secrete, they become osteocytes. Osteocytes are networked to each other via long processes that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste. The space that an osteocyte occupies is called a lacunae (Latin for a pit). Their main function involves maintaining the bone tissue. Calcium hydroxyapatite, calcium carbonate and calcium phosphate is deposited around the cell. Category:Skeletal system Category:Secretory cells

Extracellular matrix

In biology, extracellular matrix (ECM) is any material part of a tissue that is not part of any cell. Extracellular matrix is the defining feature of connective tissue. ECM's main component is various glycoproteins. In most animals, the most abundant glycoprotein in the ECM is collagen. ECM also contains many other components: proteins such as fibrin and elastin, minerals such as hydroxylapatite, or fluids such as blood plasma or serum with secreted free flowing antigens. Given this diversity, it can serve any number of functions, such as providing support and anchorage for the cells, providing a way of separating the tissues, and regulating intercellular communication. The ECM functions in a cell's dynamic behavior. The integrins transmit mechanical stimuli from the ECM to the cytoskeleton. Many cells bind to components of the extracellular matrix. This cell-to-ECM adhesion is due to specific cell surface cellular adhesion molecules (CAM) known as integrins. Category:Tissues ja:細胞外マトリックス

Nutrient

Nutrients and the body

A nutrient is any element or compound necessary for or contributing to an organism's metabolism, growth, or other functioning. Six nutrient groups exist, classifiable as those that provide energy, and as those that otherwise support metabolic processes in the body: Some of them are essential because they cannot be synthesized in the body and must be obtained from a food source. Substances that provide energy
- Carbohydrates: compounds made up of sugars used or stored as energy Carbohydrates have three different types of simple sugars, which provide short-term energy that are mostly found in fruits. These are monosaccharide, disaccharide, and polysaccharide. There are also complex carbohydrates, which provide sustained energy, for example, starches and fibers. Complex carbohydrates are stored in the body as glycogen.
- Proteins: nitrogenous organic compounds, including amino acids, that provide the building blocks (amino acids) for enzymes and other proteins within the body. The body does not manufacture certain amino acids (termed essential amino acids): the diet must supply these. Proteins are the most abundant component in the human body. Complete proteins include all nine of the required amino acids in adequate amounts. Incomplete proteins are proteins that lack at least one or two of the essential amino acids.
- Fats: fats can be defined as the basic nutrients composed of carbon and hydrogen atoms and oxygen; they are needed for the proper functioning of cells, insulation of body organs against shock, maintenance of body temperature, and needed for healthy skin and hair. including fatty acids (a fat consists of an assemblage of three fatty acids linked to a central glycerine molecule). The body does not manufacture certain fatty acids (termed essential fatty acids): the diet must supply these. Triglycerides make up 95% of our total body fat. The remaining 5% is composed of cholesterol. Fat has an energy content of 9 kcal/g; proteins and carbohydrates 4 kcal/g. Ethanol (grain alcohol) has an energy content of 7 kcal/g. Substances that support metabolism
- Minerals: generally trace elements, salts, or ions such as copper and iron; essential to normal metabolism
- Vitamins: organic compounds essential to the body's functioning, usually acting as coenzymes
- Water: absolute requirement for normal growth and metabolism directly involved in all the chemical reactions of life — sometimes referred to as the forgotten nutrient. Any classification of "nutrients" is likely to be arbitrary given the status of nutrition as a developing science. Researchers are becoming more aware of a wider range of nutrients esential for health. An organism will metabolise any organic compound to use for its energy content, for structural purposes (growth or replacement of living structures), or for participation in chemical reactions necessary for life. Any particular substance can play more than one role in the body, though researchers lack a good understanding of these roles. The discovery of the group of nutrients called phytonutrients reinforces the provisional nature of our knowledge. We know little about phytonutrients, organic compounds from plants, which play an essential role in the normal functioning of a body and have complex hormonal effects on health, or play an active role in the amelioration of disease. They do not fit readily into the scheme of the traditional nutrition categories.

Nutrients and the environment

phytonutrients While in essence true to the definition above, the term nutrients has a more limited meaning within the specialised fields of water quality and water pollution, referring specifically to plant fertilizers. In this context, certain mineral compounds can have an adverse impact on water quality because of their ability to promote plant and algae growth. An excessive growth of aquatic plants can clog waterways (see giant salvinia for example), and over-stimulation of algae and microbes leads to an ecological process called eutrophication. A surprisingly small number of elements provide interest or concern in this context: really just nitrogen and phosphorus in most aquatic systems. Mineral compounds involved are ammonia, nitrites, nitrates, and orthophosphates. Organic compounds also may contribute, in as much as they also contain nitrogen and phosphorus. The reason only a few chemicals are of concern has to do with the fact that plants are made up mostly of compounds of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P), and lesser amounts of sulfur (S), potassium (K), magnesium (Mg), and calcium (Ca). These elements constitute the macronutrients. Many other elements, though necessary for growth, classify as micronutrients due to the very small quantities required. Plants obtain carbon, hydrogen, and oxygen (elements most needed for growth) from the air and water, where all three elements occur in great abundance as water and as carbon dioxide. Nutrients having greatest potential to influence plant growth in aquatic environments is those elements needed for plant growth in proportionately large amounts (that is, macronutrients) but likely to become limiting—that is, present in amounts that could be depleted by continued growth. Once used up, further growth will not be possible. Of the nine macronutrients, nitrogen and phosphorus are most likely to become limiting. The others always remain present in great abundance (C, H, O) or usually in amounts that exceed the requirements of aquatic plants or algae. Farmers apply fertilizer nutrients in the form of nitrogen, phosphorus, and potassium (N, P, and K with perhaps micronutrients) to prevent these elements from becoming limiting in the soil. These elements become concentrated in wastewaters from animal pens and septic or sewage systems. And these elements (especially N and P) in runoff or wastewater discharges reaching streams, lakes, or seas will promote aquatic plant growth. Abundant plant growth itself gives cause for concern in assessing water quality. The most abundant "plants" in most aquatic environments are algae. When essential nutrients are plentiful, algae multiply. If these algae are microscopic phytoplankton, their growth increases the turbidity of the water. The water then becomes cloudy, colored a shade of green, yellow, or brown (sometimes red; see algal bloom). A super abundance of algae, or of higher plants, in an aquatic system can signal excessive inputs of nutrients.

References

- Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005. ISBN 0805328521

External links

- [http://www.sankey.ws/dietref.html recommendations for human diet] Category:Chemical oceanography Category:Ecology Category:Nutrients Category:Nutrition Category:Soil science ko:영양소 ja:栄養素

Carbon dioxide

Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. A very widely known chemical compound, it is frequently called by its formula CO₂. In its solid state, it is commonly known as dry ice. Carbon dioxide derives from multiple sources including volcanic outgassing, the combustion of organic matter and respiration processes of living aerobic organisms. It is also produced by various microorganisms from fermentation and cellular respiration. Plants utilize carbon dioxide during photosynthesis, using both the carbon and the oxygen to construct carbohydrates. In addition, plants also release oxygen to the atmosphere, which is subsequently used for respiration by heterotrophic organisms, forming a cycle. It is present in the Earth's atmosphere at a low concentration and acts as a greenhouse gas. It is a major component of the carbon cycle.

Chemical and physical properties

Carbon dioxide is a colorless gas which, when inhaled at high concentrations (a dangerous activity because of the associated asphyxiation risk), produces a sour taste in the mouth and a stinging sensation in the nose and throat. These effects result from the gas dissolving in the mucous membranes and saliva, forming a weak solution of carbonic acid. Its density at 25 °C is 1.98 kg m⁻³, about 1.5 times that of air. The carbon dioxide molecule (O=C=O) contains two double bonds and has a linear shape. It has no electrical dipole. As it is fully oxidized, it is not very reactive and, in particular, not flammable. At temperatures below −78 °C, carbon dioxide condenses into a white solid called dry ice. Liquid carbon dioxide forms only at pressures above 5.1 atm; at atmospheric pressure, it passes directly between the gaseous and solid phases in a process called sublimation. Water will absorb its own volume of carbon dioxide, and more than this under pressure. About 1% of the dissolved carbon dioxide turns into carbonic acid. The carbonic acid in turn dissociates partly to form bicarbonate and carbonate ions. Test For Carbon Dioxide. When a lighted splint is inserted into a test tube containing carbon dioxide, the flame is immediately extinguished, as carbon dioxide does not support combustion. (Certain fire extinguishers contain carbon dioxide to extinguish the flame). To further confirm that the gas is carbon dioxide, the gas may be bubbled into calcium hydroxide solution. The calcium hydroxide turns milky because of the formation of calcium carbonate.

Uses

Liquid and solid carbon dioxide are important refrigerants, especially in the food industry, where they are employed during the transportation and storage of ice cream and other frozen foods. Carbon dioxide is used to produce carbonated soft drinks and soda water. Traditionally, the carbonation in beer and sparkling wine comes about through natural fermentation, but some manufacturers carbonate these beverages artificially. The leavening agents used in baking produce carbon dioxide to cause dough to rise. Baker's yeast produces carbon dioxide by fermentation within the dough, while chemical leaveners such as baking powder and baking soda release carbon dioxide when heated or exposed to acids. Carbon dioxide is often used as an inexpensive, nonflammable pressurized gas. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Steel capsules are also sold as supplies of compressed gas for airguns, paintball markers, for inflating bicycle tires, and for making seltzer. Rapid vaporization of liquid CO₂ is used for blasting in coal mines. Carbon dioxide extinguishes flames, and some fire extinguishers, especially those designed for electrical fires, contain liquid carbon dioxide under pressure. Carbon dioxide also finds use as an atmosphere for welding, although in the welding arc, it reacts to oxidize most metals. Use in the automotive industry is common despite significant evidence that welds made in carbon dioxide are brittler than those made in more inert atmospheres, and that such weld joints deteriorate over time because of the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more inert gases such as argon or helium. Liquid carbon dioxide is a good solvent for many organic compounds, and is used to remove caffeine from coffee. It has begun to attract attention in the pharmaceutical and other chemical processing industries as a less toxic alternative to more traditional solvents such as organochlorides. (See green chemistry.) Plants require carbon dioxide to conduct photosynthesis, and greenhouses may enrich their atmospheres with additional CO₂ to boost plant growth. It has been proposed that carbon dioxide from power generation be bubbled into ponds to grow algae that could then be converted into biodiesel fuel. High levels of carbon dioxide in the atmosphere effectively exterminate many pests. Greenhouses will raise the level of CO₂ to 10,000 ppm (1%) for several hours to eliminate pests such as whitefly, spider mites, and others. In medicine, up to 5% carbon dioxide is added to pure oxygen for stimulation of breathing after apnea and to stabilize the O₂/CO₂ balance in blood. A common type of industrial gas laser, the carbon dioxide laser, uses carbon dioxide as a medium. Carbon dioxide is commonly injected into or adjacent to producing oil wells. It will act as both a pressurizing agent and, when dissolved into the underground crude oil, will significantly reduce its viscosity, enabling the oil to flow more rapidly through the earth to the removal well. In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection points.

Dry Ice

Dry ice is a genericized trademark for solid ("frozen") carbon dioxide. The term was coined in 1925 by Prest Air Devices, a company formed in Long Island City, New York in 1923. Dry ice at normal pressures does not melt into liquid carbon dioxide but rather sublimates directly into carbon dioxide gas at −78.5 °C (−109.3 °F). Hence it is called "dry ice" as opposed to normal "wet" ice (frozen water). Dry ice is produced by compressing carbon dioxide gas to a liquid form, removing the heat produced by the compression (see Charles' law), and then letting the liquid carbon dioxide expand quickly. This expansion causes a drop in temperature so that some of the CO₂ freezes into "snow", which is then compressed into pellets or blocks.

Uses

temperature, New York, USA)]]
- Cooling foodstuffs, biological samples, and other perishable items.
- Producing "dry ice fog" for special effects. When dry ice is put into contact with water, the frozen carbon dioxide sublimates into a mixture of cold carbon dioxide gas and cold humid air. This causes condensation and the formation of fog; see fog machine. The effect of fog by the mixture of dry ice with water, is best formed when the water is warm, rather than cold.
- Tiny pellets of dry ice (instead of sand) are shot at a surface to be cleaned. Dry ice is not as hard as sand, but it speeds processing by sublimating to nothing and does not produce nearly as much lung-damaging dust.
- Increasing precipitation from existing clouds or decreasing cloud thickness by cloud seeding.
- Producing carbon dioxide gas as needed in such systems as the fuel tank inerting system in the B-47 aircraft.
- Brass or other metallic bushings are buried in dry ice to shrink their size so they will fit inside a machined hole. When the bushing warms back up, it expands and makes an extremely tight fit.

Handling

Because of its particular characteristics, dry ice requires special precautions when handling. It is extremely cold and there should be no direct contact with skin (i.e., wear proper insulating gloves). It is constantly sublimating to carbon dioxide gas, so it cannot be stored in a sealed container as the pressure buildup will quickly cause the container to explode. The sublimated gas must be ventilated; otherwise, it may fill the enclosed space and create a suffocation hazard. Special care for ventilating vehicles is needed as well because of the small space. People who handle dry ice should also be aware that carbon dioxide is heavier than air and will sink to the floor. Some markets require those purchasing dry ice to be of 18 years of age or older.

Biology

Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars or fats with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all plants, animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to the lungs where it is exhaled. Carbon dioxide content in fresh air is approximately 0.04%, and in exhaled air approximately 4.5%. When inhaled in high concentrations (about 5% by volume), it is toxic to humans and other animals. Hemoglobin, the main oxygen-carrying molecule in red blood cells, can carry both oxygen and carbon dioxide, although in quite different ways. The decreased binding to oxygen in the blood due to increased carbon dioxide levels is known as the Haldane Effect, and is important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of CO₂ or a lower pH will cause offloading of oxygen from hemoglobin. This is known as the Bohr Effect. According to a study by the USDA [http://itest.slu.edu/articles/90s/hannan.html], an average person's respiration generates approximately 450 liters (roughly 900 grams) of carbon dioxide per day. CO₂ is carried in blood in three different ways. Most of it (about 80%–90%) is converted to bicarbonate ions HCO₃⁻ by the enzyme carbonic anhydrase in the red blood cells. 5%–10% is dissolved in the plasma and 5%–10% is bound to hemoglobin as carbamino compounds. The exact percentages vary depending whether it is arterial or venous blood. The CO₂ bound to hemoglobin does not bind to the same site as oxygen; rather it combines with the N-terminal groups on the four globin chains. However, because of allosteric effects on the hemoglobin molecule, the binding of CO₂ does decrease the amount of oxygen that is bound for a given partial pressure of oxygen. Carbon dioxide may be one of the mediators of local autoregulation of blood supply. If it is high, the capillaries expand to allow a greater blood flow to that tissue. Bicarbonate ions are crucial for regulating blood pH. As breathing rate influences the level of CO₂ in blood, too slow or shallow breathing causes respiratory acidosis, while too rapid breathing, hyperventilation, leads to respiratory alkalosis. It is interesting to note that although it is oxygen that the body requires for metabolism, it is not low oxygen levels that stimulate breathing, but is instead higher carbon dioxide levels. As a result, breathing low-pressure air or a gas mixture with no oxygen at all (e.g., pure nitrogen) leads to loss of consciousness without subjective breathing problems. This is especially perilous for high-altitude fighter pilots, and is also the reason why the instructions in commercial airplanes for case of loss of cabin pressure stress that one should apply the oxygen mask to oneself before helping others—otherwise one risks going unconscious without being aware of the imminent peril. Plants remove carbon dioxide from the atmosphere by photosynthesis, which uses light energy to produce organic plant materials by combining carbon dioxide and water. This releases free oxygen gas. Sometimes carbon dioxide gas is pumped into greenhouses to promote plant growth. Plants also emit CO₂ during respiration, but on balance they are net sinks of CO₂. OSHA limits carbon dioxide concentration in the workplace to 0.5% for prolonged periods, or to 3% for brief exposures (up to ten minutes). OSHA considers concentrations exceeding 4% as "immediately dangerous to life and health." People who breathe 5% carbon dioxide for more than half an hour show signs of acute hypercapnia, while breathing 7%–10% carbon dioxide can produce unconsciousness in only a few minutes. Carbon dioxide, either as a gas or as dry ice, should be handled only in well-ventilated areas. See also: Arterial blood gas.

Atmosphere

Arterial blood gas As of 2004, the earth's atmosphere is about 0.038% by volume (380 µL/L or ppmv) or 0.053% by weight CO₂. This represents about 2.7 × 10¹² tonnes of CO₂. Because of the greater land area, and therefore greater plant life, in the northern hemisphere as compared to the southern hemisphere, there is an annual fluctuation of about 5 µL/L, peaking in May and reaching a minimum in October at the end of the northern hemisphere growing season, when the quantity of biomass on the planet is greatest. Despite its small concentration, CO₂ is a very important component of Earth's atmosphere, because it absorbs infrared radiation and enhances the greenhouse effect. The initial carbon dioxide in the atmosphere of the young Earth was produced by volcanic activity; this was essential for a warm and stable climate conducive to life. Volcanic activity now releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year. Volcanic releases are about 1% of the amount which is released by human activities. short tons–2000.]] Since the start of the Industrial Revolution, the atmospheric CO₂ concentration has increased by approximately 110 µL/L or about 40%, most of it released since 1945. Monthly measurements taken at Mauna Loa [http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm] since 1958 show an increase from 316 µL/L in that year to 376 µL/L in 2003, an overall increase of 60 µL/L during the 44-year history of the measurements. Burning fossil fuels such as coal and petroleum is the leading cause of increased man-made CO₂; deforestation is the second major cause. In 1997, Indonesian peat fires may have released 13%–40% as much carbon as fossil fuel burning does [http://en.wikipedia.org/wiki/Peat#Peat_fires]. Various techniques have been proposed for removing excess carbon dioxide from the atmosphere in carbon dioxide sinks. Not all the emitted CO₂ remains in the atmosphere; some is absorbed in the oceans or biosphere. The ratio of the emitted CO₂ to the increase is atmospheric CO₂ is known as the airborne fraction (Keeling et al., 1995); this varies for short-term averages but is typically 57% over longer (5 year) periods.

carbon dioxide sink The Global Warming Theory (GWT) predicts that increased amounts of CO₂ in the atmosphere tend to enhance the greenhouse effect and thus contribute to global warming. The effect of combustion-produced carbon dioxide on climate is called the Callendar effect.

Variation in the past

Callendar effect The most direct method for measuring atmospheric carbon dioxide concentrations for periods before direct sampling is to measure bubbles of air (fluid or gas inclusions) trapped in the Antarctic or Greenland ice caps. The most widely accepted of such studies come from a variety of Antarctic cores and indicate that atmospheric CO₂ levels were about 260–280µL/L immediately before industrial emissions began and did not vary much from this level during the preceding 10,000 years. The longest ice core record comes from East Antarctica, where ice has been sampled to an age of 650,000 years before the present. [http://pubs.acs.org/cen/news/83/i48/8348notw1.html] During this time, the atmospheric carbon dioxide concentration has varied between 180–210 µL/L during ice ages, increasing to 280–300 µL/L during warmer interglacials. Some studies have disputed the claim of stable CO₂ levels during the present interglacial (the last 10 kyr). Based on an analysis of fossil leaves, Wagner et al. argued that CO₂ levels during the period 7–10 kyr ago were significantly higher (~300 µL/L) and contained substantial variations that may be correlated to climate variations. Others have disputed such claims, suggesting they are more likely to reflect calibration problems than actual changes in CO₂. Relevant to this dispute is the observation that Greenland ice cores often report higher and more variable CO₂ values than similar measurements in Antarctica. However, the groups responsible for such measurements (e.g., Smith et al.) believe the variations in Greenland cores result from in situ decomposition of calcium carbonate dust found in the ice. When dust levels in Greenland cores are low, as they nearly always are in Antarctic cores, the researchers report good agreement between Antarctic and Greenland CO₂ measurements. calcium carbonate On longer timescales, various proxy measurements have been used to attempt to determine atmospheric carbon dioxide levels millions of years in the past. These include boron and carbon isotope ratios in certain types of marine sediments, and the number of stomata observed on fossil plant leaves. While these measurements give much less precise estimates of carbon dioxide concentration than ice cores, there is evidence for very high CO₂ concentrations (>3,000 µL/L) between 600 and 400 Myr BP and between 200 and 150 Myr BP.[http://www.grida.no/climate/ipcc_tar/wg1/fig3-2.htm] On long timescales, atmospheric CO₂ content is determined by the balance among geochemical processes including organic carbon burial in sediments, silicate rock weathering, and vulcanism. The net effect of slight imbalances in the carbon cycle over tens to hundreds of millions of years has been to reduce atmospheric CO₂. The rates of these processes are extremely slow; hence they are of limited relevance to the atmospheric CO₂ response to emissions over the next hundred years. In more recent times, atmospheric CO₂ concentration continued to fall after about 60 Myr BP, and there is geochemical evidence that concentrations were <300 µL/L by about 20 Myr BP. Low CO₂ concentrations may have been the stimulus that favored the evolution of C4 plants, which increased greatly in abundance between 7 and 5 Myr BP. Although contemporary CO₂ concentrations were exceeded during earlier geological epochs, present carbon dioxide levels are likely higher now than at any time during the past 20 million years [http://www.grida.no/climate/ipcc_tar/wg1/107.htm#331] and at the same time lower than at any time in history if we look at time scales longer than 50 million years.

Oceans

The Earth's oceans contain a huge amount of carbon dioxide in the form of bicarbonate and carbonate ions—much more than the amount in the atmosphere. The bicarbonate is produced in reactions between rock, water, and carbon dioxide. One example is the dissolution of calcium carbonate: CaCO₃ + CO₂ + H₂O ⇌ Ca²⁺ + 2 HCO₃^- Reactions like this tend to buffer changes in atmospheric CO₂. Reactions between carbon dioxide and non-carbonate rocks also add bicarbonate to the seas, which can later undergo the reverse of the above reaction to form carbonate rocks, releasing half of the bicarbonate as CO₂. Over hundreds of millions of years this has produced huge quantities of carbonate rocks. If all the carbonate rocks in the earth's crust were to be converted back into carbon dioxide, the resulting carbon dioxide would weigh 40 times as much as the rest of the atmosphere. The vast majority of CO₂ added to the atmosphere will eventually be absorbed by the oceans and become bicarbonate ion, but the process takes on the order of a hundred years because most seawater rarely comes near the surface.

History

Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the 17th century, the Flemish chemist Jan Baptist van Helmont observed that when he burned charcoal in a closed vessel, the mass of the resulting ash was much less than that of the original charcoal. His interpretation was that the rest of the charcoal had been transmuted into an invisible substance he termed a "gas" or "wild spirit" (spiritus sylvestre). Carbon dioxide's properties were studied more thoroughly in the 1750s by the Scottish physician Joseph Black. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he termed "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. He also found that it would, when bubbled through an aqueous solution of lime (calcium hydroxide), precipitate calcium carbonate, and used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, Joseph Priestley used carbon dioxide produced from the action of sulfuric acid on limestone to prepare soda water, the first known instance of an artificially carbonated beverage. Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphrey Davy and Michael Faraday. The earliest description of solid carbon dioxide was given by Charles Thilorier, who in 1834 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO₂.

References

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External links

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- [http://www.dryiceinfo.com/science.htm Dry Ice information]
- Bassam Z. Shakhashiri: [http://scifun.chem.wisc.edu/chemweek/CO2/CO2.html Chemical of the Week: Carbon Dioxide]
- Keeling, C.D. and T.P. Whorf: [http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm Atmospheric carbon dioxide record from Mauna Loa], 2002
- [http://www.usatoday.com/weather/news/2004-03-21-co2-buildup_x.htm Mauna Loa 2004 update]
- [http://www.uigi.com/carbondioxide.html CO2 Carbon Dioxide Properties, Uses, Applications]
- [http://www.compchemwiki.org/index.php?title=Carbon_dioxide Computational Chemistry Wiki]
- [http://scifun.chem.wisc.edu/chemweek/CO2/CO2_phase_diagram.gif Pressure-Temperature phase diagram for carbon dioxide] Category:Inorganic carbon compounds Category:Oxides Category:Greenhouse gases Category:Propellants Category:Household chemicals Category:Solvents Category:Refrigerants Category:Fire suppression agents ko:이산화 탄소 ms:Karbon dioksida ja:二酸化炭素 simple:Carbon dioxide th:คาร์บอนไดออกไซด์

Red blood cell

Red blood cells are the most common type of blood cell and are the vertebrate body's principal means of delivering oxygen from the lungs or gills to body tissues via the blood. Red blood cells are also known as RBCs or erythrocytes (from Greek erythros for "red" and kytos for "hollow," nowadays translated as "cell"). A schistocyte is a red blood cell undergoing fragmentation, or a fragmented part of a red blood cell.

Vertebrate erythrocytes

Erythrocytes consist mainly of hemoglobin, a complex molecule containing heme groups whose iron molecules temporarily link to oxygen molecules in the lungs or gills and release them throughout the body. Hemoglobin also carries some of the waste product carbon dioxide back from the tissues. (In humans, less than 2% of the total oxygen, and most of the carbon dioxide, are held in solution in the blood plasma). A related compound, myoglobin, acts to store oxygen in muscle cells. The color of erythrocytes is due to the heme group of hemoglobin. The blood plasma is straw-colored alone, but the red blood cells change colors due to the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet and when oxygen has been released, the resulting deoxyhemogloben is darker, appearing bluish through the blood vessel walls. The keeping of oxygen-binding proteins in cells (rather than having them dissolved in body fluid) was an important step in the evolution of vertebrates; it allows for less viscous blood and longer transport ways of oxygen.

Mammalian erythrocytes

Erythrocytes in mammals are anucleate when mature, meaning that they don't have a cell nucleus and thus no DNA. (The erythrocytes of nearly all other vertebrates have nuclei; the only known exception is salamanders of the Batrachoseps genus.) Erythrocytes also lose their other organelles including their mitochondria and produce energy by fermentation, via glycolysis of glucose followed by lactic acid production. Like most cell types, red cells do not have an insulin receptor and thus glucose uptake is not regulated by insulin. Mammalian erythrocytes have a biconcave shape: flattened and depressed in the center. This shape (as well as the loss of organelles) optimizes the cell for the exchange of oxygen with its surroundings. The cells are flexible so as to fit through tiny capillaries, where they release their oxygen load. Erythrocytes are circular, except in the camel family Camelidae, where they are oval. In large blood vessels, red blood cells sometimes occur as a stack, flat side next to flat side. This is known as rouleaux formation, and it occurs more often if the levels of certain serum proteins are elevated, as for instance during inflammation. The spleen acts as a reservoir of red blood cells, but this effect is somewhat limited in humans. In some other mammals such as dogs and horses, the spleen sequesters large numbers of red blood cells that are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity.

Human erythrocytes

The diameter of a typical human erythrocyte is 6–8 µm; they are thus much smaller than most other human cells. A typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups. Adult humans have roughly 2–3 × 10¹³ red blood cells at any given time (women have about 4 million to 5 million erythrocytes per cubic millimeter (microliter) of blood and men about 5 million to 6 million; people living at high altitudes with low oxygen concentration will have more). Red blood cells are thus much more common than the other blood particles: There are about 4,000–11,000 white blood cells and about 150,000–400,000 platelets in a cubic millimeter of human blood. The red blood cells store collectively about 3.5 grams of iron; that's more than five times the iron stored by all the other tissues combined. The process by which red blood cells are produced is called erythropoiesis. Erythrocytes are continuously being produced in the red bone marrow of large bones. (In the embryo, the liver is the main site of red blood cell production.) The production can be stimulated by the hormone erythropoietin (EPO), which is used for doping in sports. Erythrocytes develop in about 7 days and live a total of about 120 days. The aging cells swell up to a sphere-like shape and are engulfed by phagocytes, destroyed and their materials are released into the blood. The main sites of destruction are the liver and the spleen. The heme constituent of hemoglobin is eventually excreted as bilirubin. The blood types of humans are due to variations in surface glycoproteins of erythrocytes. Red blood cells can be separated from blood plasma by centrifugation. During plasma donation, the red blood cells are pumped back into the body right away, and the plasma is collected. Some athletes have tried to improve their performance by doping their blood: First about 1 liter of their blood is extracted, then the red blood cells are isolated, frozen and stored, to be reinjected shortly before the competition. (Red blood cells can be conserved for 5 weeks at −78 °C.) This practice is hard to detect but may endanger the human cardiovascular system which is not equipped to deal with blood of the resulting higher viscosity.

Diseases and diagnostic tools

viscosity Blood diseases involving the red blood cells include:
- Anemias (or anaemias) are diseases characterized by low oxygen transport capacity of the blood, because of low red cell count or some abnormality of the red blood cells or the hemoglobin.
- Iron deficiency anemia is the most common anemia; it occurs when the dietary intake or absorption of iron is insufficient, and hemoglobin, which contains iron, cannot be formed
- Sickle-cell disease is a genetic disease which leads to mis-shaped red blood cells.
- Thalassemia is a genetic disease that results in the production of abnormal hemoglobin molecules.
- Spherocytosis is a genetic disease that causes a defect in the red blood cell's cytoskeleton, causing the RBCs to be small, sphere-shaped, and fragile instead of donut-shaped and flexible.
- Pernicious anemia is an autoimmune disease wherein the body lacks intrinsic factor, required to absorb vitamin B12 from food. Vitamin B12 is needed for the production of hemoglobin.
- Aplastic anemia is caused by the inability of the bone marrow to produce blood cells.
- Hemolysis is the general term for excessive breakdown of red blood cells. It can have several causes.
- The malaria parasite spends part of its life-cycle in red blood cells, feeds on their hemoglobin and then breaks them apart, causing fever. Both sickle-cell disease and thalassemia are more common in malaria areas, because these mutations convey some protection against the parasite.
- Polycythemias (or erythrocytoses) are diseases characterized by a surplus of red blood cells. The increased viscosity of the blood can cause a number of symptoms.
- In polycythemia vera the increased number of red blood cells results from an abnormality in the bone marrow. Several blood tests involve red blood cells, including the RBC count (the number of red blood cells per volume of blood) and the hematocrit (percentage of blood volume occupied by red blood cells). The blood type needs to be determined to prepare for a blood transfusion or an organ transplantation.

History

In 1658, the Dutch Jan Swammerdam was the first to describe red blood cells; he had used an early microscope.

External links

- [http://www.genomesize.com/cellsize/ Database of vertebrate erythrocyte sizes] Category:Blood cells Category:Hematology ko:적혈구 ja:赤血球

Cartilage

Cartilage is a type of dense connective tissue. Cartilage is composed of cells called chondrocytes which are dispersed in a firm gel-like ground substance, called the matrix. Cartilage is avascular (contains no blood vessels) and nutrients are diffused through the matrix. Cartilage is found in the joints, the rib cage, the ear, the nose, in the throat and between intervertebral disks. There are three main types of cartilage: hyaline, elastic and fibrocartilage.

Composition

Much like other connective tissue, cartilage is composed of cells, fibers and a matrix.

Cells

Chondrocytes and the precusor forms of chondrocytes known as chondroblasts are the only cells found in cartilage. They are responsible for the secretion and maintenance of the matrix. The matrix immediately surrounding the chondrocytes is referred to as the territorial matrix and stains darker than the interstitial matrix. Chondrocytes lie in a cavity called a lacuna. During slide preparations, chondrocytes often shrink and appear smaller than the lacunae but in live tissue, they occupy the entire area.

Fibers

Cartilage is composed of collagen and elastic fibers. In hyaline cartilage, Type II collagen makes up 40% of its dry weight and is arranged in cross-striated fibers, 15-45nm in diameter that do not assemble into large bundles. Elastic cartilage also contains elastic fibers and fibrocartilage contains more collagen than hyaline cartilage.

Matrix

The matrix is mainly composed of proteoglycans, a special type of glycosaminoglycans. The most common type is chondroitin sulfate and keratan sulfate.

Types of cartilage

There are three different types of cartilage, each with special characteristics adapted to local needs.

Hyaline cartilage

This is the most abundant type of cartilage. The name hyaline is derived from the greek word hyalos, meaning glass. This refers to the translucent matrix or ground substance. Hyaline cartilage is found lining bones in joints (articular cartilage) . It is also present inside bones, serving as a center of ossification or bone growth...

Elastic cartilage

Elastic cartilage (also called yellow cartilage) is found in the pinna of the ear and several tubes, such as the walls of the auditory and eustachian canals and larynx. Cartilage is present to keep the tubes permanently open. Elastic cartilage is similar to hyaline cartilage but contains elastic bundles (elastin) scattered throughout the matrix. This provides a tissue which is stiff yet elastic.

Fibrocartilage

Fibrocartilage (also called white cartilage) is a specialised type of cartilage found in areas requiring tough support or great tensile strength, such as between intervertebral disks, the pubic and other symphyses, and at sites connecting tendons or ligaments to bones. There is rarely any clear line of demarcation between fibrocartilage and the neighboring hyaline cartilage or connective tissue. The fibrocartilage found in intervertebral disks contains more collagen compared to hyaline. Fibrocartilage lacks a perichondrium.

Growth and development

Chondrification

Most of the skeletal system is derived from mesoderm tissue. Chondrification is the process in which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondrocytes and begins secreting the materials that form the matrix.

Mineralisation

Adult hyaline articular cartilage is progressively mineralised at the junction between cartilage and bone. It is then termed articular calcified cartilage. A mineralisation front advances through the base of the hyaline articular cartilage at a rate dependent on cartilage load and shear stress. Intermittent variations in the rate of advance and mineral deposition density of the mineralising front lead to multiple tidemarks in the articular calcified cartilage. Adult articular calcified cartilage is penetrated by vascular buds, and new bone produced in the vascular space in a process similar to endochondral ossification at the physis. A cement line demarcates articular calcified cartilage from subchondral bone. Two types of growth can occur in cartilage: appositional and interstitial.

Appositional

Appositional growth results in the increase of the diameter or thickness of the cartilage. The new cells derive from the perichondrium and occur on the surface of the cartilage model.

Interstitial

Interstitial growth results in an increase of cartilage mass and occurs from within. Chondrocytes undergo mitosis within their lacuna but remain imprisoned in the matrix, which results in clusters of cells called isogenous groups.

Cartilage in fetal development

In the fetus, at an early period, the greater part of the skeleton is cartilaginous; as this cartilage is afterward replaced by bone, it is called temporary, in contradistinction to that which remains unossified during the whole of life, and is called permanent. It has been said that the cartilage in ears and noses continues to grow in size throughout adult life; however, this seems to be an urban myth which is not substantiated by research.

Diseases / Medicine

There are several diseases which can affect the cartilage. Chondrodystrophies are a group of diseases characterized by disturbance of growth and subsequent ossification of cartilage. Some common diseases affecting/involving the cartilage are listed below.
- Arthritis: The cartilage covering bones in joints (articular cartilage) is degraded, resulting in limitation of movement and pain.
- Achondroplasia: Reduced proliferation of chondrocytes in the epiphyseal plate of long bones results in a form of dwarfism.
- Costochondritis: Inflammation of cartilage in the ribs which causes chest pain
- Herniated disk: Asymmetrical compression of a disk ruptures the cartilage ring, causing tissue to herniate into the spinal canal. The matrix of cartilage acts as a barrier, preventing the entry of lymphocytes or diffusion of immunoglobulins. This property allows for the transplantation of cartilage from one individual to another without fear of tissue rejection. Bioengineering techniques are being developed to generate new cartilage, using a cellular "scaffolding" material and cultured cells to grow artificial cartilage.

Fibrocartilage

Fibrocartilage, as its name implies, is a type of cartilage arranged in a fibrous matrix that is similar to fibrous connective tissies. It is found in areas that require tensile strength, such as invertebral disks. Chondrocytes are separated by dense bundles of collagenous fibers. Chondrocytes are usually arranged in short rows of 3 or 4. When hyaline cartilage, the shiny white gristle at the end of long bones, is damaged, it is often replaced with fibrocartilage, though it remains a poorer substitue.

Invertebrate cartilage

Cartilage tissue can also be found among invertebrates, for instance Limulus (horse-shoe crab), marine snails and cephalopods.

External links

- University of Kansas Medical Center [http://www.kumc.edu/instruction/medicine/anatomy/histoweb/cart/cart.htm Cartilage tutorial]
- public domain [http://www.bartleby.com/107/pages/page279.html text from Gray's anatomy] dated 1918, so probably needs updating
- [http://www.madsci.org/posts/archives/Mar2003/1048719208.Dv.r.html I've heard 'Ears and nose do not ever stop growing.' Is this true?] Category:Skeletal system Category:Tissues

Osteichthyes

See under classes: Actinopterygii and Sarcopterygii Class Osteichthyes are the bony fish, a group paraphyletic to the land vertebrates, which are sometimes included. Most belong to the Actinopterygii. The others are called lobe-finned fish, and include lungfish and coelacanths. They are traditionally treated as a class of vertebrates, with subclasses Actinopterygii and Sarcopterygii, but newer schemes may divide them into several separate classes. The vast majority of fish are bony fish, and therefore belong to class Osteichthyes. Osteichthians are characterized by a relatively stable pattern of cranial bones, rooted teeth, medial insertion of mandibular muscle in lower jaw. The head and pectoral girdles are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, although this characteristic has been lost or modified in many modern species. The labyrinth in the inner ear contains large otoliths. The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by fissure. Osteichthyans possess a lung or swim bladder. They do not have fin spines, but instead support the fin with lepidotrichia (bone fin rays). One of the best-known innovations of the osteichthians is endochondral or "replacement" bone, i.e. bone ossified internally, by replacement of cartilage, as well as perichondrally, as "spongy bone." In the more general vertebrates there are various types of calcified tissues: dentine, enamel (or "enameloids") and bone, plus variants, characterized by their ontogeny, chemistry, form and location. However, endochondral bone is unique because it begins life as cartilage. In more basal vertebrates, cartilaginous structures can become superficially calcified. However, in osteichthians, the circulatory system actually invades the cartilaginous matrix. This permits the local osteoblasts (bone-forming cells) to continue bone formation within the cartilage and also recruits additional, circulating osteoblasts. Other cells gradually eat away at the surrounding cartilage. The net result is that the cartilage is replaced from within by a somewhat irregular vascularized network of bone. Structurally, the effect is to create a relatively lightweight, flexible, "spongy" bone interior, surrounded by an outline of dense, lamellar periostial bone (since this bone now surrounds other bone, rather than cartilage, it is referred to as periostial rather than perichondral). This is the unique endochondral bone from which the osteichthians derived their name, as well as countless structural advantages. However useful endochondral bone may be, it is also much heavier and less flexible than cartilage. Thus, many modern osteichian groups, including the extremely successful teleosts, have evolved away from extensive use of endochondral bone. The question of the largest bony fish or osteichthian is an interesting one. Contenders for the title include the Blue Marlin, that have been relatively reliably recorded to weights in excess of 820 kilograms, and several sturgeon species.

Vertebrate

Conodonta
Hyperoartia
:Petromyzontidae (lampreys)
Pteraspidomorphi (early jawless fish)
Thelodonti
Anaspida
Cephalaspidomorphi (early jawless fish)
:Galeaspida
:Pituriaspida
:Osteostraci
Gnathostomata (jawed vertebrates)
:Placodermi
:Chondrichthyes (cartilaginous fish)
:Acanthodii
:Osteichthyes (bony fish)
::Actinopterygii (ray-finned fish)
::Sarcopterygii (lobe-finned fish)
:::Actinistia (coelacanths)
:::Dipnoi (lungfish)
:::Tetrapoda ::::Amphibia
::::Amniota
:::::Sauropsida/(Reptiles)
::::::Aves (Birds)
:::::Synapsida
::::::Mammalia Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. Vertebrates started to evolve about 530 million years ago during the Cambrian explosion, which is part of the Cambrian period (first known vertebrate is Myllokunmingia). The bones of the spinal column (or vertebral column) are called vertebrae. Vertebrata is the largest subphylum of chordates, and contains most animals with which people are generally familiar (except insects). Fish (including lampreys, but traditionally not hagfish, though this is now disputed), amphibians, reptiles, birds, and mammals (including humans) are vertebrates. Additional characteristics of the subphylum are a muscular system that mostly consists of paired masses, as well as a central nervous system which is partly located inside the backbone. The internal skeleton which defines vertebrates consists of cartilage or bone, or in some cases both. The skeleton provides support to the organism during the period of growth. For this reason vertebrates can achieve larger sizes than invertebrates, and on average vertebrates are in fact larger. The skeleton of most vertebrates, that is excluding the most primitive ones, consists of a skull, the vertebral column and two pairs of limbs. In some forms of vertebrates, one or both of these pairs of limbs may be absent, such as in snakes or whales. These limbs have been lost in the course of evolution. The skull is thought to have facilitated the development of intelligence as it protects vital organs such as the brain, the eyes and the ears. The protection of these organs is also thought to have positively influenced the development of high responsiveness to the environment often found in vertebrates. Both the vertebral column and the limbs support the body of the vertebrate overall. This support facilitates movement. Movement is normally achieved with muscles that are attached directly to the bones or cartilages. The contour of the body of a vertebrate is formed by the muscles. A skin covers the inner parts of a vertebrate's body. The skin sometimes acts as a structure for protective features, such as horny scales or fur. Feathers are also attached to the skin. The trunk of a vertebrate is hollow and houses the internal organs. The heart and the respiratory organs are protected in the trunk. The heart is located behind the gills, or where there are lungs, in between the lungs. The central nervous system of a vertebrate consists of the brain and the spinal cord. Both of these are characterized by being hollow. In lower vertebrates the brain mostly controls the functioning of the sense organs. In higher vertebrates the size of the brain relative to the size of the body is larger. This larger brain enables more intensive exchange of information between the different parts of the brain. The nerves from the spinal cord, which lies behind the brain, extend to the skin, the inner organs and the muscles. Some nerves are directly connected to the brain, linking the brain with the ears and lungs. Vertebrates have been traced back to the ostracoderms of the Silurian Period (444 million to 409 million years ago) and the conodonts, a group of eel-like vertebrates characterized by multiple pairs of bony toothplates. All vertebrates have: the ability to form bones; paired, specialised sensory organs and a brain.

External links

- [http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_vertebrates Tree of Life]
- [http://reference.allrefer.com/encyclopedia/categories/vertz.html Vertebrate Zoology] Category:Chordates ko:척추동물 ms:Vertebrata ja:脊椎動物 simple:Vertebrate th:สัตว์มีกระดูกสันหลัง

Joint

A joint is the location at which two bones make contact. Joints are constructed to both allow movement and provide mechanical support.

Classification

Structure and function of a joint are closely related.

Structural classification

Structurally, joints are classified as:
- fibrous - bones are connected by fibrous connective tissue.
- cartilaginous - bones are connected by cartilage.
- synovial - there is a space (synovial cavity) between the articulating bones.

Fibrous joints

In fibrous joints bones are joined by tight and inflexible layers of dense connective tissue, consisting mainly of collagen fibers. In adults, these are not designed to allow any movement; however, in children, fibrous joints have not solidified and are movable. Examples of fibrous joints are:
- Cranial sutures, joining the bones of the cranium.
- Gomphoses, the joints between the roots of the teeth and their sockets (or alveoli) in maxilla and mandible.

Cartilaginous joints

In cartilaginous joints (also known as synchondroses) bones are connected entirely by cartilage. In comparison to synovial joints, cartilaginous joints allow only slight movement. Examples of cartilaginous joints are the pubic symphysis, the joints between the ribs and the sternum, and the cartilage connecting the growth regions of immature long bones. Another example is in the spinal column - the cartilaginous region between adjacent vertebrae.

Synovial joints

The term "Synovial joint" and "Diarthrosis joint" are often used interchangably, although the first term refers to the structure and the second one to the function. For more details, see "Diarthrosis joints" below.

Functional classification

Functionally, they can be classified as:
- synarthrosis - permit no movement.
- amphiarthrosis - permit little movement.
- diarthrosis - permit a variety of movements (e.g. flexion, adduction, pronation). Only synovial joints are diarthrosis.

Synarthrosis joints

Synarthroses are joints with very little (if any) mobility. They can be categorised by how the two bones are joined together:
- Syndesmoses are joints where the two bones are joined by one of more ligaments.
- Synchondroses are joints where the two bones are joined by a piece of cartilage.
- Synostoses are the fusion of two bones, to the point that they are practically one bone. In humans, the plates of the cranium, initially separate, fuse together as the child approaches adulthood. Children whose craniums fuse too early may suffer deformities and brain damage, as the skull does not expand properly to accommodate the growing brain - a condition known as craniostenosis.
- Amphiarthroses are slightly moveable joints where the two bone surfaces at the joint - both covered in hyaline cartilage - are joined by strands of fibrocartilage.

Amphiarthrosis joints

Most amphiarthrosis joints are cartilaginous. See above for more details.

Diarthrosis joints

fibrocartilage Diarthroses (sometimes called synovial joints and also diarthroidal joints) are the most common and most moveable type of joint in the body. The whole of a diarthrosis is contained by a ligamentous sac called the articluar capsule. The surfaces of the two bones at the joint are covered in cartilage. The thickness of the cartilage varies with each joint, and sometimes may be of uneven thickness. Articular cartilage is multi-layered. A thin superficial layer provides a smooth surface for the two bones to slide against each other. Of all the layers, it has the highest concentration of collagen and the lowest concentration of proteoglycans, making it very resistant to shear stresses. Deeper than that is an intermediate layer, which is mechanically designed to absorb shocks and distribute the load efficiently. The deepest layer is highly calcified, and anchors the articular cartilage to the bone. In joints where the two surfaces do not fit snugly together, a meniscus or multiple folds of fibro-cartilage within the joint correct the fit, ensuring stability and the optimal distribution of load forces. The synovium is a membrane that covers all the non-cartilaginous surfaces within the articular capsule. It secretes synovial fluid into the joint, which nourishes and lubricates the articular cartilage. The synovium is separated from the capsule by a layer of celluar tissue that contains blood vessels and nerves. Synovial joints can be further grouped by their shape, which controls the movement they allow:
- Gliding joints, such as in the carpals of the wrist. These joints allow a wide variety of movement, but not much distance.
- Hinge joints, such as the elbow (between the humerus and the ulna). These joints act like a door hinge, allowing flexion and extension in just one plane.
- Pivot joints, such as the elbow (between the radius and the ulna). This is where one bone rotates about another.
- Condyloid (ellipsoid) joints, such as the knee. When the knee is extended there is no rotation, when it is flexed some rotation is possible. A condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. Some classifications make a distinction between condyloid and ellipsoid joints.
- Saddle joints, such as at the thumb (between the metacarpal and carpal). Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints.
- Ball and socket joints, such as the hip joint. These allow a wide arrange of movement.

External links

- [http://www.shockfamily.net/skeleton/JOINTS.HTML Illustration of synovial joints] Category:Skeletal system ja:関節

Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 1/4 of the total. It is one of the long, fibrous structural proteins whose functions are quite different from those of globular proteins such as enzymes. It is tough and inextensible, with great tensile strength, and is the main component of cartilage, ligaments and tendons, and the main protein component of bone and teeth. Along with soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging. It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form. It is also used in cosmetic surgery — for example lip enhancement — although hyaluronic acid is now often used instead.

Composition and structure

Collagen has an unusual amino acid composition and sequence. Glycine (Gly) is found at almost every third residue, and collagen contains large amounts of proline, (Pro) — as well as two uncommon derivative amino acids not directly inserted during translation of mRNA: hydroxyproline (Hypro) and hydroxylysine. Prolines and lysines at specific locations relative to glycine are modified post-translationally by different enzymes, both of which require vitamin C as a cofactor. Vitamin C deficiency causes scurvy, a serious and painful disease in which defective collagen prevents the formation of strong connective tissue. Gums deteriorate and bleed, with loss of teeth; skin discolors, and wounds do not heal. This was notorious in the British Royal Navy, where sailors were deprived of fresh fruits and vegetables during long voyages. Depending on the type of collagen, varying numbers of hydroxylysines have disaccharides attached to them. The tropocollagen subunit is a rod about 300 nm long and 1.5 nm in diameter, made up of three polypeptide strands, each of which is a left-handed helix. They are twisted together into a right-handed coiled coil, a triple helix, a cooperative quaternary structure stabilized by numerous hydrogen bonds. Tropocollagen subunits spontaneously self-assemble, with regularly staggered ends, into even larger arrays in the extracellular spaces of tissues. There is some covalent crosslinking within the triple helices, and a variable amount of covalent crosslinking between tropocollagen helices, to form the different types of collagen found in different mature tissues — similar to the situation found with the α-keratins in hair. Collagen's insolubility was a barrier to study until it was found that tropocollagen from young animals can be extracted because it is not yet fully crosslinked. A distinctive feature of collagen is the regular arrangement of amino acids in each of the three chains of these collagen subunits. The sequence often follows the pattern Gly-X-Pro or Gly-X-Hypro, where X may be any of various other amino acid residues. Gly-Pro-Hypro occurs frequently. This kind of regular repetition and high glycine content is found in only a few other fibrous proteins, such as silk fibroin. 75-80% of silk is (approximately) -Gly-Ala-Gly-Ala- with 10% serine — and elastin is rich in glycine, proline, and alanine (Ala), whose side group is a small, inert methyl. Such high glycine and regular repetitions are never found in globular proteins. Chemically-reactive side groups are not needed in structural proteins as they are in enzymes and transport proteins. The high content of Pro and Hypro rings, with their geometrically constrained carboxyl and (secondary) amino groups, accounts for the tendency of the individual polypeptide strands to form left-handed helices spontaneously, without any intrachain hydrogen bonding. The triple helix tightens under tension, resisting stretching, making collagen inextensible. Because glycine is the smallest amino acid, it plays a unique role in fibrous structural proteins. In collagen, Gly is required at every third position because the assembly of the triple helix puts this residue at the interior (axis) of the helix, where there is no space for a larger side group than glycine’s single hydrogen atom. For the same reason, the rings of the Pro and Hypro must point outward. These two imino acids thermally stabilize the triple helix — Hypro even more so than Pro — and less of them is required in animals such as fish, whose body temperatures are low. In bone, entire collagen triple helices lie in a parallel, staggered array. 40 nm gaps between the ends of the tropocollagen subunits probably serve as nucleation sites for the deposition of long, hard, fine crystals of the mineral component, which is (approximately) hydroxyapatite, Ca₅(PO₄)₃(OH), with some phosphate. It is in this way that certain kinds of cartilage turn into bone. Collagen gives bone its elasticity and contributes to fracture resistance.

Human Uses

If collagen is solubilized and heated, the three tropocollagen strands separate into globular, random coils, producing gelatin, which is used in many foods, including flavored desserts. It is not a good dietary source for synthesizing bodily proteins in general because it lacks adequate amounts of most of the essential amino acids. Collagen means "glue producer" (kolla is Greek for glue), derived from the early process of boiling the skin, hooves and sinews of horses and other animals to obtain glue. Collagen adhesive was used by Egyptians about 4,000 years ago, and Native Americans used it in bows about 1,500 years ago. [http://www.archaeology.org/online/news/glue.html] The oldest glue in the world, carbon dated as more than 8,000 years old, was found to be collagen — used as a protective lining on rope baskets and embroidered fabrics, and to hold utensils together; also in crisscross decorations on human skulls. Collagen normally converts to gelatin, but survived due to the dry conditions. Animal glues are thermoplastic, softening again upon reheating, and so they are still used in making musical instruments such as fine violins and guitars, which may have to be reopened for repairs — an application incompatible with tough, synthetic plastic adhesives, which are permanent. Animal sinews and skins, including leather, have been used to make useful articles for millennia. Gelatin-resorcinol-formaldehyde glue (and with formaldehyde replaced by less-toxic pentanedial and ethanedial) has been used to repair experimental incisions in rabbit lungs. (Ann Thorac Surg. 1994 Jun; 57(6): 1622-7)

Types of collagen

Collagen occurs in many places throughout the body, and occurs in different forms known as types, which include:
- Type I collagen - This is the most abundant collagen of the human body. It is present in scar tissue, the end product when tissue heals by repair. It is found in tendons and the organic part of bone.
- Type II collagen - Articular cartilage
- Type III collagen - This is the collagen of granulation tissue, and is produced quickly by young fibroblasts before the tougher type I collagen is synthesised.
- Type IV collagen - basal lamina; eye lens
- Type V collagen - most interstitial tissue, assoc. with type I, associated with placenta
- Type VI collagen - most interstitial tissue, assoc. with type I
- Type VII collagen - epithelia
- Type VIII collagen - some endothelial cells
- Type IX collagen - cartilage, assoc. with type II
- Type X collagen - hypertrophic and mineralizing cartilage
- Type XI collagen - cartilage
- Type XII collagen - interacts with types I and III
- Type XIII collagen - interacts with types I and II There are 8 other types of Collagen

Staining

In histology, the dye methyl violet is used to stain the collagen in tissue samples.

External links and references

- [http://web.indstate.edu/thcme/mwking/extracellularmatrix.html 12 types of collagen]
- [http://www.rcsb.org/pdb/molecules/pdb4_1.html Collagen structure and information (PDB)]
- [http://directscience.freespaces.com/articles/collagen.html Collagen Article (Direct Science)]
- [http://www.archaeology.org/online/news/glue.html] Category:Structural proteins Category:Edible thickening agents ja:コラーゲン

Dense connective tissue

Dense connective tissue, also called dense fibrous tissue, has collagen fibers as its main matrix element. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that manufacture the fibers. Dense connective tissue forms strong, rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers that tendons. Dense connective tissue also make up the lower layers of the skin (dermis), where it is arranged in sheets. Category:Tissues

Fibrous connective tissue

In zootomy, fibrous connective tissue (FCT) is a type of connective tissue which has relatively high tensile strength, due to a relatively high concentration of collagenous fibers. Such tissues form ligaments and tendons; the majority of the tissue does not contain living cells, the tissue is primary composed of polysaccharides, proteins, and water. The cells of fibrous connective tissue are mostly fibroblasts, irregular, branching cells that secrete strong fibrous proteins as an extracellular matrix. The most commonly secreted protein is collagen which represents one-fourth of all vertebrate protein. Collagen is tough and flexible and gives strength to tissue. Elastin fibers are thinner than collagen fibers and are also secreted by fibroblasts. These protein fibers have longer cross-links than collagen fibers, which gives elastin fibers great elasticity.

Types

There are several categories of fibrous connective tissue:
- Loose connective tissue supports most epithelia and many organs. It also surrounds blood vessels and nerves.
- Dense connective tissue
- Dense regular connective tissue provides strong connection between different tissues. The collagen fibers in dense regular connective tissue are bundled in a parallel fashion. Tendons, which connect muscle to bone, derive their strength from the regular, longitudinal arrangement of bundles of collagen fibers. Ligaments bind bone to bone and are similar in structure to tendons.
- Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue. This tissue comprises a large portion of the dermal layer of skin.
- Elastic connective tissue is primarily composed of elastin fibers, giving them great elasticity. It appears in the walls of the aorta.
- Reticular connective tissue is composed of interlacing fibers of collagen called reticular fibers. This tissue forms supporting structures for many organs, such as the spleen and thymus. Category:Tissues

Ligament

A ligament is a short band of tough fibrous connective tissue composed mainly of long, stringy collagen fibres. Ligaments connect bones to other bones to form a joint. (They do not connect muscles to bones; that is the function of tendons.) Some ligaments limit the mobility of articulations, or prevent certain movements altogether. Capsular ligaments are part of the articular capsule that surrounds synovial joints. They act as mechanical reinforments. Extra-capsular ligaments join bones together and provide joint stability. Ligaments are slightly elastic; under tension, they gradually lengthen. This is one reason why dislocated joints must be set as quickly as possible: if the ligaments lengthen too much, then the joint will be weakened, becoming prone to future dislocations. Athletes, gymnasts and martial artists perform stretching exercises to lengthen their ligaments, making their joints more supple. The term double-jointed refers to people who have more elastic ligaments, allowing their joints to stretch and contort further. The study of ligaments is called desmology.

List of major ligaments

External links

- [http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_l_09zPzhtm Exhaustive list of ligaments] Category:Skeletal system

Tendon

:Tendon is also the name of a commune in the Vosges