Periodontal scalers are dental instruments used in the prophylactic and periodontal care of teeth, including scaling and root planing. The working ends come in a variety of shapes and sizes, but they are always narrow at the tip, so as to allow for access to narrow embrasure spaces between teeth, they differ from periodontal curettes. Together with periodontal curettes, periodontal scalers are used to remove calculus from teeth. While curettes are universal in that they can be used on both supra- and sub-gingival calculus removals, scalers are restricted to supra-gingival use. Use of a scaler below the gum line is to damage the gingiva. Scalers have scraping edges on both sides of their blades and thus are fit for both mesial and distal surfaces of any tooth in the area in which they are being used. Scalers are best used when their terminal shank, the last portion of the functional shank closest to the working end, is angled toward the surface of the tooth; the composition of hand instruments are continuously evolving, why it may be a challenge to find the proper instrument for the right clinical situation.
With the broad variation of instrument designs and materials, it allows dental professionals to implement periodontal therapy with reduced strain and increased comfort levels for both the clinician and the patient. The following are some factors to consider with the design of periodontal scalers: Balance – when the working ends are aligned properly to the long axis of the instrument handle, finger pressure can be applied more to reduce muscle fatigue on the clinician’s hands and/or forearm. Diameter – the handles with larger diameters allow the instrument to be held easier and reduces muscle stress of the clinician’s fingers. Texture – the texture of the instrument handle increases control, such as finger grip, reduces hand fatigue. Weight – the handle’s hollowness allows the instrument to be more lightweight and increases the clinician's tactile sensitivity. With the continuous, evolving technology of hand instruments, it gives dental professionals the opportunity to implement dental treatment more for the patient while improving their work surroundings simultaneously.
There are two cutting edges per working end: the outer cutting edge and the inner cutting edge. This way, both edges can adapt to both the interproximal surfaces of any tooth, to which they are being used. Periodontal scalers have pointed backs, but some new scaler designs have working ends with rounded backs as well. Additionally, they have triangular cross sections. Periodontal scalers have pointed tips and faces perpendicular to the lower shank. There are two types of periodontal scaler designs: Anterior sickle scalers are designed to be used on anterior teeth, they are constructed with one working-end and are categorized as single-ended instruments. As well, they may be combined to produce a double-ended instrument with two working ends on both sides. Posterior sickle scalers may be used on both posterior teeth; the working ends are designed to be opposite images of one another, two posterior sickle scalers are combined to produce a double-ended instrument. When it comes to periodontal therapy, there are multiple steps that are required prior to activating a proper working stroke on the teeth.
First, a modified pen grasp position must be achieved before starting periodontal instrumentation. By holding periodontal instruments in this manner, it allows for precise control of the instrument, effective detection of rough areas on the tooth structure, reduces musculoskeletal stress on the clinician. In addition, there are several characteristics of a calculus removal stroke that are vital to the effectiveness of periodontal instrumentation. Stabilization is the pressure applied to the handle with the index finger and the thumb while maintaining the fulcrum finger against the tooth surface. Adaptation requires placing the tip third of the lateral face of the working end, in contact with the tooth structure. Angulation is the relationship between the face of the instrument and the tooth surface, ideally 70º-80º when using periodontal scalers. Lateral pressure is moderate to firm, the characteristics are short, controlled strokes; the stroke directions include vertical and horizontal strokes, all leading away from the soft tissue to avoid tissue trauma.
Stroke number is limited to the minimum number of strokes necessary, applied only when and where there is calculus present on a tooth surface. Once all these characteristics are understood, the clinician will activate the periodontal debridement strokes using the periodontal scalers; when performing periodontal debridement, the instrumentation of anterior teeth and posterior teeth are applied with the following steps. First, the fulcrum finger rests on a tooth to support the clinician’s hand at the initiation of a stroke, the clinician will press down on the fulcrum finger to further gain control, it is crucial to tilt the lower sh
Death is the permanent cessation of all biological functions that sustain a living organism. Phenomena which bring about death include aging, malnutrition, suicide, starvation and accidents or major trauma resulting in terminal injury. In most cases, bodies of living organisms begin to decompose shortly after death. Death – the death of humans – has been considered a sad or unpleasant occasion, due to the affection for the being that has died and the termination of social and familial bonds with the deceased. Other concerns include fear of death, anxiety, grief, emotional pain, sympathy, solitude, or saudade. Many cultures and religions have the idea of an afterlife, hold the idea of reward or judgement and punishment for past sin; the word death comes from Old English dēaþ. This comes from the Proto-Indo-European stem *dheu- meaning the "process, condition of dying"; the concept and symptoms of death, varying degrees of delicacy used in discussion in public forums, have generated numerous scientific and acceptable terms or euphemisms for death.
When a person has died, it is said they have passed away, passed on, expired, or are gone, among numerous other accepted, religiously specific and irreverent terms. Bereft of life, the dead person is a corpse, cadaver, a body, a set of remains, when all flesh has rotted away, a skeleton; the terms carrion and carcass can be used, though these more connote the remains of non-human animals. As a polite reference to a dead person, it has become common practice to use the participle form of "decease", as in the deceased; the ashes left after a cremation are sometimes referred to by the neologism cremains, a portmanteau of "cremation" and "remains". Senescence refers to a scenario when a living being is able to survive all calamities, but dies due to causes relating to old age. Animal and plant cells reproduce and function during the whole period of natural existence, but the aging process derives from deterioration of cellular activity and ruination of regular functioning. Aptitude of cells for gradual deterioration and mortality means that cells are sentenced to stable and long-term loss of living capacities despite continuing metabolic reactions and viability.
In the United Kingdom, for example, nine out of ten of all the deaths that occur on a daily basis relates to senescence, while around the world it accounts for two-thirds of 150,000 deaths that take place daily. All animals who survive external hazards to their biological functioning die from biological aging, known in life sciences as "senescence"; some organisms experience negligible senescence exhibiting biological immortality. These include the jellyfish Turritopsis dohrnii, the hydra, the planarian. Unnatural causes of death include homicide. From all causes 150,000 people die around the world each day. Of these, two thirds die directly or indirectly due to senescence, but in industrialized countries – such as the United States, the United Kingdom, Germany – the rate approaches 90%. Physiological death is now seen as a process, more than an event: conditions once considered indicative of death are now reversible. Where in the process a dividing line is drawn between life and death depends on factors beyond the presence or absence of vital signs.
In general, clinical death is neither sufficient for a determination of legal death. A patient with working heart and lungs determined to be brain dead can be pronounced dead without clinical death occurring; as scientific knowledge and medicine advance, formulating a precise medical definition of death becomes more difficult. Signs of death or strong indications that a warm-blooded animal is no longer alive are: Respiratory arrest Cardiac arrest Brain death Pallor mortis, paleness which happens in the 15–120 minutes after death Algor mortis, the reduction in body temperature following death; this is a steady decline until matching ambient temperature Rigor mortis, the limbs of the corpse become stiff and difficult to move or manipulate Livor mortis, a settling of the blood in the lower portion of the body Decomposition, the reduction into simpler forms of matter, accompanied by a strong, unpleasant odor. The concept of death is a key to human understanding of the phenomenon. There are many scientific approaches to the concept.
For example, brain death, as practiced in medical science, defines death as a point in time at which brain activity ceases. One of the challenges in defining death is in distinguishing it from life; as a point in time, death would seem to refer to the moment. Determining when death has occurred is difficult, as cessation of life functions is not simultaneous across organ systems; such determination therefore requires drawing precise conceptual boundaries between death. This is due to there being little consensus on how to define life; this general problem applies to the particular challenge of defining death in the context of medicine. It is possible to define life in terms of consciousness; when consciousness ceases, a living organism can be said to have died. One of the flaws in this approach is that there are many organisms which are alive but not conscious. Another problem is in defining consciousness, which has many different d
A gel is a solid jelly-like soft material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a dilute cross-linked system, which exhibits no flow when in the steady-state. By weight, gels are liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid, it is the crosslinking within the fluid that gives a gel its structure and contributes to the adhesive stick. In this way gels are a dispersion of molecules of a liquid within a solid in which liquid particles are dispersed in the solid medium; the word gel was coined by 19th-century Scottish chemist Thomas Graham by clipping from gelatine. Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects; this internal network structure may result from physical bonds or chemical bonds, as well as crystallites or other junctions that remain intact within the extending fluid. Any fluid can be used as an extender including water and air.
Both by weight and volume, gels are fluid in composition and thus exhibit densities similar to those of their constituent liquids. Edible jelly is a common example of a hydrogel and has the density of water. Polyionic polymers are polymers with an ionic functional group; the ionic charges prevent the formation of coiled polymer chains. This allows them to contribute more to viscosity in their stretched state, because the stretched-out polymer takes up more space; this is the reason gel hardens. See polyelectrolyte for more information. A hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. A three-dimensional solid results from the hydrophilic polymer chains being held together by cross-links; because of the inherent cross-links, the structural integrity of the hydrogel network does not dissolve from the high concentration of water. Hydrogels are absorbent natural or synthetic polymeric networks. Hydrogels possess a degree of flexibility similar to natural tissue, due to their significant water content.
As responsive "smart materials," hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in most cases by a gel-sol transition to the liquid state. Chemomechanical polymers are also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors; the first appearance of the term'hydrogel' in the literature was in 1894. Common uses for hydrogels include: Scaffolds in tissue engineering; when used as scaffolds, hydrogels may contain human cells to repair tissue. They mimic 3D microenvironment of cells. Hydrogel-coated wells have been used for cell culture Environmentally sensitive hydrogels; these hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change. Sustained-release drug delivery systems Providing absorption and debriding of necrotic and fibrotic tissue Hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used as biosensors, as well as in DDS.
Disposable diapers where they absorb urine, or in sanitary napkins Contact lenses EEG and ECG medical electrodes using hydrogels composed of cross-linked polymers Water gel explosives Rectal drug delivery and diagnosis Encapsulation of quantum dots Breast implants Glue Granules for holding soil moisture in arid areas Dressings for healing of burn or other hard-to-heal wounds. Wound gels are excellent for helping to maintain a moist environment. Reservoirs in topical drug delivery. Materials mimicking animal mucosal tissues to be used for testing mucoadhesive properties of drug delivery systemsCommon ingredients include polyvinyl alcohol, sodium polyacrylate, acrylate polymers and copolymers with an abundance of hydrophilic groups. Natural hydrogel materials are being investigated for tissue engineering. Hydrogels show promise for use in agriculture, as they can release agrochemicals including pesticides and phosphate fertiliser increasing efficacy and reducing runoff, at the same time improve the water retention of drier soils such as sandy loams.
An organogel is a non-crystalline, non-glassy thermoreversible solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network. The liquid can be, for an organic solvent, mineral oil, or vegetable oil; the solubility and particle dimensions of the structurant are important characteristics for the elastic properties and firmness of the organogel. These systems are based on self-assembly of the structurant molecules. Organogels have potential for use in a number of applications, such as in pharmaceuticals, art conservation, food. A xerogel is a solid formed from a gel by drying with unhindered shrinkage. Xerogels retain high porosity and enormous surface area, along with small pore size; when solvent removal occurs under supercritical conditions, the network doe
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" sound in its physical properties, except that humans cannot hear it; this limit varies from person to person and is 20 kilohertz in healthy young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances. Ultrasound imaging or sonography is used in medicine. In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws. Industrially, ultrasound is used for cleaning and accelerating chemical processes. Animals such as bats and porpoises use ultrasound for locating prey and obstacles. Scientists are studying ultrasound using graphene diaphragms as a method of communication. Acoustics, the science of sound, starts as far back as Pythagoras in the 6th century BC, who wrote on the mathematical properties of stringed instruments.
Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound, not vision. Francis Galton in 1893 invented the Galton whistle, an adjustable whistle that produced ultrasound, which he used to measure the hearing range of humans and other animals, demonstrating that many animals could hear sounds above the hearing range of humans; the first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917. The piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water. Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. The upper frequency limit in humans is due to limitations of the middle ear. Auditory sensation can occur if high‐intensity ultrasound is fed directly into the human skull and reaches the cochlea through bone conduction, without passing through the middle ear.
Children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to decrease with age. An American cell phone company has used this to create ring signals that are only audible to younger humans, but many older people can hear the signals, which may be because of the considerable variation of age-related deterioration in the upper hearing threshold; the Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people. Bats use a variety of ultrasonic ranging techniques to detect their prey, they can detect frequencies beyond 100 kHz up to 200 kHz. Many insects have good ultrasonic hearing, most of these are nocturnal insects listening for echolocating bats; these include many groups of moths, praying mantids and lacewings. Upon hearing a bat, some insects will make evasive manoeuvres to escape being caught. Ultrasonic frequencies trigger a reflex action in the noctuid moth that causes it to drop in its flight to evade attack.
Tiger moths emit clicks which may disturb bats' echolocation, in other cases may advertise the fact that they are poisonous by emitting sound. Dogs and cats' hearing range extends into the ultrasound; the wild ancestors of cats and dogs evolved this higher hearing range to hear high-frequency sounds made by their preferred prey, small rodents. A dog whistle is a whistle that emits ultrasound, used for calling dogs; the frequency of most dog whistles is within the range of 23 to 54 kHz. Toothed whales, including dolphins, can hear ultrasound and use such sounds in their navigational system to orient and to capture prey. Porpoises have the highest known upper hearing limit at around 160 kHz. Several types of fish can detect ultrasound. In the order Clupeiformes, members of the subfamily Alosinae have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies can hear only up to 4 kHz. Ultrasound generator/speaker systems are sold as electronic pest control devices, which are claimed to frighten away rodents and insects, but there is no scientific evidence that the devices work.
An ultrasonic level or sensing system requires no contact with the target. For many processes in the medical, pharmaceutical and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product. Both continuous wave and pulsed systems are used; the principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel. Only a signal received during this window will qualify for additional signal processing. A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a lightweight transducer system to focus the camera automatically. Polaroid licensed this ultrasound technology and it became the basis of a variety of ultrasonic products. A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door.
Ultrasonic sensors are used to detect intruders. The flow in pipes or open channels can be measured by ultrasonic flowmeters, which measure the average veloci
Bromelain is an enzyme extract derived from the stems of pineapples, although it exists in all parts of the fresh plant and fruit. The extract has a history of folk medicine use; as a culinary ingredient, it may be used as a meat tenderizer. The term "bromelain" may refer to either of two protease enzymes extracted from the plants of the family Bromeliaceae, or it may refer to a combination of those enzymes along with other compounds produced in an extract. Although tested in a variety of folk medicine and research models for its possible efficacy against diseases, the only approved clinical application for bromelain was issued in 2012 by the European Medicines Agency for a topical medication called NexoBrid used to remove dead tissue in severe skin burns. Bromelain extract is a mixture of protein-digesting enzymes and several other substances in smaller quantities; the proteolytic enzymes are sulfhydryl proteases. The two main enzymes are: Stem bromelain – EC 188.8.131.52 Fruit bromelain – EC 184.108.40.206 Pineapples have a long tradition as a medicinal plant among the natives of South and Central America.
The first isolation of bromelain was recorded by the Venezuelan chemist Vicente Marcano in 1891 by fermenting the fruit of pineapple. In 1892, Russell Henry Chittenden, assisted by Elliott P. Joslin and Frank Sherman Meara, investigated the matter more and called it'bromelin'; the term'bromelain' was introduced and applied to any protease from any member of the plant family Bromeliaceae. Bromelain is present in all parts of the pineapple plant, but the stem is the most common commercial source because usable quantities are extractable after the fruit has been harvested. Produced in parts of the world where pineapples are grown, such as Thailand or Malaysia, bromelain is extracted from the peel, leaves or waste of the pineapple plant after processing the fruit for juice or other purposes; the starting material is blended and pressed through a filter to obtain a supernatant liquid containing the soluble bromelain enzyme. Further processing includes concentration of the enzyme. After an hour at 50 °C, 83% of the enzyme remains active, while at 40 °C 100% remains active.
8 minutes at 80 °C is sufficient to completely inactivate the enzyme. The proteolytic activity of concentrated bromelain solutions remains stable for at least 1 week at room temperature, with minimal inactivation by multiple freeze-thaw cycles or exposure to the digestive enzyme trypsin. Along with papain, bromelain is one of the most popular proteases to use for meat tenderizing. Bromelain is sold in a powdered form, combined with a marinade, or directly sprinkled on the uncooked meat. Cooked or canned pineapple does not have a tenderizing effect, as the enzymes are heat-labile and denatured in the cooking process; some prepared meat products, such as meatballs and commercially available marinades, include pineapple and/or pineapple-derived ingredients. Although the quantity of bromelain in a typical serving of pineapple fruit is not significant, specific extraction can yield sufficient quantities for domestic and industrial processing, including uses in baking, anti-browning of cut fruit and cosmetics manufacturing.
Bromelain has not been scientifically proven to be effective in treating any diseases and has not been approved by the U. S. Food and Drug Administration for the treatment of any disorder. In the United States, the passage of the Dietary Supplement Health and Education Act allows the sale of bromelain-containing dietary supplements though efficacy has not been confirmed. Bromelain is a known allergen. While there have been studies which correlated the use of bromelain with reduction of symptom severity in osteoarthritis, "he majority of the studies have methodological issues that make it difficult to draw definite conclusions", as none definitively established efficacy, recommended dosage, long term safety, or adverse interaction with other medications. Bromelain has been studied as an antithrombotic and anti-inflammatory agent in the treatment of cardiovascular disease, a 2012 review suggests that it may have other properties for therapeutic treatment, but all of these possible effects remain unconfirmed and under preliminary research.
A concentrate of proteolytic enzymes enriched in bromelain is approved in Europe for the debridement of severe burn wounds under the trade name NexoBrid. Systemic enzyme therapy has been investigated in Europe to evaluate the efficacy in breast and plasmacytoma cancer patients. Bromelain may be effective as an adjunct therapy in relieving symptoms of acute rhinosinusitis in patients not treated with antibiotics. Bromelain is claimed as a tooth plaque removal enhancer in toothpastes. Phytochemicals Papain The MEROPS online database for peptidases and their inhibitors: C01.005 Stem Bromelain C01.028 Fruit Bromelain Bromelains at the US National Library of Medicine Medical Subject Headings
In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the English word "tissue" is derived from the French "tissu", meaning something, "woven", from the verb tisser, "to weave". The study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant anatomy; the classical tools for studying tissues are the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis.
Animal tissues are grouped into four basic types: connective, muscle and epithelial. Collections of tissues joined in structural units to serve a common function compose organs. While all eumetazoan animals can be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals; the epithelium in all birds and animals is derived from the ectoderm and endoderm, with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier; this tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, the digestive tract.
It serves functions of protection and absorption, is separated from other tissues below by a basal lamina. Connective tissues are fibrous tissues, they are made up of cells separated by non-living material, called an extracellular matrix. This matrix can be rigid. For example, blood contains plasma as its matrix and bone's matrix is rigid. Connective tissue holds them in place. Blood, tendon, ligament and areolar tissues are examples of connective tissues. One method of classifying connective tissues is to divide them into three types: fibrous connective tissue, skeletal connective tissue, fluid connective tissue. Muscle cells form the active contractile tissue of the body known as muscle tissue or muscular tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle, found in the inner linings of organs. Cells comprising the central nervous system and peripheral nervous system are classified as nervous tissue.
In the central nervous system, neural tissues form spinal cord. In the peripheral nervous system, neural tissues form the cranial nerves and spinal nerves, inclusive of the motor neurons; the epithelial tissues are formed by cells that cover the organ surfaces, such as the surface of skin, the airways, the reproductive tract, the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via tight junctions. In addition to this protective function, epithelial tissue may be specialized to function in secretion and absorption. Epithelial tissue helps to protect organs from microorganisms and fluid loss. Functions of epithelial tissue: The cells of the body's surface form the outer layer of skin. Inside the body, epithelial cells form the lining of the mouth and alimentary canal and protect these organs. Epithelial tissues help in absorption of water and nutrients. Epithelial tissues help in the elimination of waste. Epithelial tissues hormones in the form of glands; some epithelial tissue perform secretory functions.
They secrete a variety of substances such as sweat, enzymes, etc. There are many kinds of epithelium, nomenclature is somewhat variable. Most classification schemes combine a description of the cell-shape in the upper layer of the epithelium with a word denoting the number of layers: either simple or stratified. However, other cellular features, such as cilia may be described in the classification system; some common kinds of epithelium are listed below: Simple squamous epithelium Stratified squamous epithelium Simple cuboidal epithelium Transitional epithelium Pseudostratified columnar epithelium Columnar epithelium Glandular epithelium Ciliated columnar epithelium In plant anatomy, tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, 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 transport nutrients internally.
Ground tissue - Ground tissue is less differentiated than other tissues. Ground tis
Necrosis is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma which result in the unregulated digestion of cell components. In contrast, apoptosis is a occurring programmed and targeted cause of cellular death. While apoptosis provides beneficial effects to the organism, necrosis is always detrimental and can be fatal. Cellular death due to necrosis does not follow the apoptotic signal transduction pathway, but rather various receptors are activated, result in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space; this initiates in the surrounding tissue an inflammatory response which attracts leukocytes and nearby phagocytes which eliminate the dead cells by phagocytosis. However, microbial damaging substances released by leukocytes would create collateral damage to surrounding tissues.
This excess collateral damage inhibits the healing process. Thus, untreated necrosis results in a build-up of decomposing dead tissue and cell debris at or near the site of the cell death. A classic example is gangrene. For this reason, it is necessary to remove necrotic tissue surgically, a procedure known as debridement. Structural signs that indicate irreversible cell injury and the progression of necrosis include dense clumping and progressive disruption of genetic material, disruption to membranes of cells and organelles. There are six distinctive morphological patterns of necrosis: Coagulative necrosis is characterized by the formation of a gelatinous substance in dead tissues in which the architecture of the tissue is maintained, can be observed by light microscopy. Coagulation occurs as a result of protein denaturation, causing albumin to transform into a firm and opaque state; this pattern of necrosis is seen in hypoxic environments, such as infarction. Coagulative necrosis occurs in tissues such as the kidney and adrenal glands.
Severe ischemia most causes necrosis of this form. Liquefactive necrosis, in contrast to coagulative necrosis, is characterized by the digestion of dead cells to form a viscous liquid mass; this is typical of bacterial, or sometimes fungal, infections because of their ability to stimulate an inflammatory response. The necrotic liquid mass is creamy yellow due to the presence of dead leukocytes and is known as pus. Hypoxic infarcts in the brain presents as this type of necrosis, because the brain contains little connective tissue but high amounts of digestive enzymes and lipids, cells therefore can be digested by their own enzymes. Gangrenous necrosis can be considered a type of coagulative necrosis that resembles mummified tissue, it is characteristic of ischemia of the gastrointestinal tracts. If superimposed infection of dead tissues occurs liquefactive necrosis ensues Caseous necrosis can be considered a combination of coagulative and liquefactive necrosis caused by mycobacteria and some foreign substances.
The necrotic tissue appears as friable, like clumped cheese. Dead cells disintegrate but are not digested, leaving granular particles. Microscopic examination shows amorphous granular debris enclosed within a distinctive inflammatory border. Granuloma has this characteristic. Fat necrosis is specialized necrosis of fat tissue, resulting from the action of activated lipases on fatty tissues such as the pancreas. In the pancreas it leads to acute pancreatitis, a condition where the pancreatic enzymes leak out into the peritoneal cavity, liquefy the membrane by splitting the triglyceride esters into fatty acids through fat saponification. Calcium, magnesium or sodium may bind to these lesions to produce a chalky-white substance; the calcium deposits are microscopically distinctive and may be large enough to be visible on radiographic examinations. To the naked eye, calcium deposits appear as gritty white flecks. Fibrinoid necrosis is a special form of necrosis caused by immune-mediated vascular damage.
It is marked by complexes of antigen and antibodies, sometimes referred to as "immune complexes" deposited within arterial walls together with fibrin. There are very specific forms of necrosis such as gangrene, gummatous necrosis and hemorrhagic necrosis; some spider bites may lead to necrosis. In the United States, only spider bites from the brown recluse spider reliably progress to necrosis. In other countries, spiders of the same genus, such as the Chilean recluse in South America, are known to cause necrosis. Claims that yellow sac spiders and hobo spiders possess necrotic venom have not been substantiated. In blind mole rats, the process of necrosis replaces the role of the systematic apoptosis used in many organisms. Low oxygen conditions, such as those common in blind mole rats' burrows cause cells to undergo apoptosis. In adaptation to higher tendency of cell death, blind mole rats evolved a mutation in the tumor suppressor protein p53 to prevent cells from undergoing apoptosis. Human cancer patients have similar mutations, blind mole rats were thought to be more susceptible to cancer because their cells cannot undergo apoptosis.
However, after a specific amount of time (within 3 days according to a study conducted at the University of