Galvanic cell

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Galvanic_cell

Galvanic cell with no cation flow

A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous oxidation–reduction reactions. An example of a galvanic cell consists of two different metals, each immersed in separate beakers containing their respective metal ions in solution that are connected by a salt bridge or separated by a porous membrane.

Volta was the inventor of the voltaic pile, the first electrical battery. Common usage of the word battery has evolved to include a single Galvanic cell, but the first batteries had many Galvanic cells.

History

In 1780, Luigi Galvani discovered that when two different metals (e.g., copper and zinc) are in contact and then both are touched at the same time to two different parts of a muscle of a frog leg, to close the circuit, the frog's leg contracts. He called this "animal electricity". The frog's leg, as well as being a detector of electrical current, was also the electrolyte (to use the language of modern chemistry).

A year after Galvani published his work (1790), Alessandro Volta showed that the frog was not necessary, using instead a force-based detector and brine-soaked paper (as electrolyte). (Earlier Volta had established the law of capacitance C = ⁠Q/V⁠ with force-based detectors). In 1799 Volta invented the voltaic pile, which is a stack of galvanic cells each consisting of a metal disk, an electrolyte layer, and a disk of a different metal. He built it entirely out of non-biological material to challenge Galvani's (and the later experimenter Leopoldo Nobili)'s animal electricity theory in favor of his own metal-metal contact electricity theory. Carlo Matteucci in his turn constructed a battery entirely out of biological material in answer to Volta. Volta's contact electricity view characterized each electrode with a number that we would now call the work function of the electrode. This view ignored the chemical reactions at the electrode-electrolyte interfaces, which include H₂ formation on the more noble metal in Volta's pile.

Although Volta did not understand the operation of the battery or the galvanic cell, these discoveries paved the way for electrical batteries; Volta's cell was named an IEEE Milestone in 1999.

Some forty years later, Faraday (see Faraday's laws of electrolysis) showed that the galvanic cell—now often called a voltaic cell—was chemical in nature. Faraday introduced new terminology to the language of chemistry: electrode (cathode and anode), electrolyte, and ion (cation and anion). Thus Galvani incorrectly thought the source of electricity (or source of electromotive force (emf), or seat of emf) was in the animal, Volta incorrectly thought it was in the physical properties of the isolated electrodes, but Faraday correctly identified the source of emf as the chemical reactions at the two electrode-electrolyte interfaces. The authoritative work on the intellectual history of the voltaic cell remains that by Ostwald.

It was suggested by Wilhelm König in 1940 that the object known as the Baghdad battery might represent galvanic cell technology from ancient Parthia. Replicas filled with citric acid or grape juice have been shown to produce a voltage. However, it is far from certain that this was its purpose—other scholars have pointed out that it is very similar to vessels known to have been used for storing parchment scrolls.

Principles

Schematic of Zn–Cu galvanic cell

Galvanic cells are extensions of spontaneous redox reactions, but have been merely designed to harness the energy produced from said reaction. For example, when one immerses a strip of zinc metal (Zn) in an aqueous solution of copper sulfate (CuSO₄), dark-colored solid deposits will collect on the surface of the zinc metal and the blue color characteristic of the Cu⁺⁺ ion disappears from the solution. The depositions on the surface of the zinc metal consist of copper metal, and the solution now contains zinc ions. This reaction is represented by

Zn_(s) + Cu⁺⁺
_(aq) ⟶ Zn⁺⁺
_(aq) + Cu_(s)

In this redox reaction, Zn is oxidized to Zn⁺⁺ and Cu⁺⁺ is reduced to Cu. When electrons are transferred directly from Zn to Cu⁺⁺, the enthalpy of reaction is lost to the surroundings as heat. However, the same reaction can be carried out in a galvanic cell, allowing some of the chemical energy released to be converted into electrical energy. In its simplest form, a half-cell consists of a solid metal (called an electrode) that is submerged in a solution; the solution contains cations (+) of the electrode metal and anions (−) to balance the charge of the cations. The full cell consists of two half-cells, usually connected by a semi-permeable membrane or by a salt bridge that prevents the ions of the more noble metal from plating out at the other electrode.

A specific example is the Daniell cell (see figure), with a zinc (Zn) half-cell containing a solution of ZnSO₄ (zinc sulfate) and a copper (Cu) half-cell containing a solution of CuSO₄ (copper sulfate). A salt bridge is used here to complete the electric circuit.

If an external electrical conductor connects the copper and zinc electrodes, zinc from the zinc electrode dissolves into the solution as Zn⁺⁺ ions (oxidation), releasing electrons that enter the external conductor. To compensate for the increased zinc ion concentration, via the salt bridge zinc ions (cations) leave and sulfate ions (anions) enter the zinc half-cell. In the copper half-cell, the copper ions plate onto the copper electrode (reduction), taking up electrons that leave the external conductor. Since the Cu⁺⁺ ions (cations) plate onto the copper electrode, the latter is called the cathode. Correspondingly the zinc electrode is the anode. The electrochemical reaction is

${\displaystyle {\text{Zn}}_{\mathsf{(}\mathsf{\text{s}}\mathsf{)}}^{}+{\text{Cu}}_{\mathsf{(}\mathsf{\text{aq}}\mathsf{)}}^{++}⟶{\text{Zn}}_{\mathsf{(}\mathsf{\text{aq}}\mathsf{)}}^{++}+{\text{Cu}}_{\mathsf{(}\mathsf{\text{s}}\mathsf{)}}^{}}$

This is the same reaction as given in the previous example. In addition, electrons flow through the external conductor, which is the primary application of the galvanic cell.

As discussed under cell voltage, the electromotive force of the cell is the difference of the half-cell potentials, a measure of the relative ease of dissolution of the two electrodes into the electrolyte. The emf depends on both the electrodes and on the electrolyte, an indication that the emf is chemical in nature.

Half reactions and conventions

A half-cell contains a metal in two oxidation states. Inside an isolated half-cell, there is an oxidation-reduction (redox) reaction that is in chemical equilibrium, a condition written symbolically as follows (here, "M" represents a metal cation, an atom that has a charge imbalance due to the loss of n electrons):

Mⁿ⁺
_{(oxidized species)} + n e⁻ ⇌ M_{(reduced species)}

A galvanic cell consists of two half-cells, such that the electrode of one half-cell is composed of metal A, and the electrode of the other half-cell is composed of metal B; the redox reactions for the two separate half-cells are thus:

A ⁿ⁺ + n e⁻ ⇌ A

B ^m+ + m e⁻ ⇌ B

The overall balanced reaction is:

m A + n B ^m+ ⇌ n B + m A ⁿ⁺

In other words, the metal atoms of one half-cell are oxidized while the metal cations of the other half-cell are reduced. By separating the metals in two half-cells, their reaction can be controlled in a way that forces transfer of electrons through the external circuit where they can do useful work.

• The electrodes are connected with a metal wire in order to conduct the electrons that participate in the reaction.

In one half-cell, dissolved metal B cations combine with the free electrons that are available at the interface between the solution and the metal B electrode; these cations are thereby neutralized, causing them to precipitate from solution as deposits on the metal B electrode, a process known as plating.

This reduction reaction causes the free electrons throughout the metal B electrode, the wire, and the metal A electrode to be pulled into the metal B electrode. Consequently, electrons are wrestled away from some of the atoms of the metal A electrode, as though the metal B cations were reacting directly with them; those metal A atoms become cations that dissolve into the surrounding solution.

As this reaction continues, the half-cell with the metal A electrode develops a positively charged solution (because the metal A cations dissolve into it), while the other half-cell develops a negatively charged solution (because the metal B cations precipitate out of it, leaving behind the anions); unabated, this imbalance in charge would stop the reaction. The solutions of the half-cells are connected by a salt bridge or a porous plate that allows ions to pass from one solution to the other, which balances the charges of the solutions and allows the reaction to continue.

By definition:

• The anode is the electrode where oxidation (loss of electrons) takes place (metal A electrode); in a galvanic cell, it is the negative electrode, because when oxidation occurs, electrons are left behind on the electrode. These electrons then flow through the external circuit to the cathode (positive electrode) (while in electrolysis, an electric current drives electron flow in the opposite direction and the anode is the positive electrode).

• The cathode is the electrode where reduction (gain of electrons) takes place (metal B electrode); in a galvanic cell, it is the positive electrode, as ions get reduced by taking up electrons from the electrode and plate out (while in electrolysis, the cathode is the negative terminal and attracts positive ions from the solution). In both cases, the statement 'the cathode attracts cations' is true.

By their nature, galvanic cells produce direct current.

The Weston cell has an anode composed of cadmium mercury amalgam, and a cathode composed of pure mercury. The electrolyte is a (saturated) solution of cadmium sulfate. The depolarizer is a paste of mercurous sulfate. When the electrolyte solution is saturated, the voltage of the cell is very reproducible; hence, in 1911, it was adopted as an international standard for voltage.

• In the strictest sense, a battery is a set of two or more galvanic cells that are connected in series to form a single source of voltage.

For instance, a typical 12 V lead–acid battery has six galvanic cells connected in series, with the anodes composed of lead and cathodes composed of lead dioxide, both immersed in sulfuric acid.

Large central office battery rooms – in a telephone exchange to provide power for subscribers' land-line telephones, for instance – may have many cells, connected both in series and parallel: Individual cells are connected in series as a battery of cells with some standard voltage (c. 40 V), and banks of such serial batteries, themselves connected in parallel, to provide adequate amperage to supply a typical peak demand for telephone connections.

Cell voltage

The voltage (electromotive force E^o) produced by a galvanic cell can be estimated from the standard Gibbs free energy change in the electrochemical reaction according to:

$${\displaystyle E_{\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}^{\mathsf{o}}=-\frac{{\mathrm{\Delta }}_r{G}^{\mathsf{o}}}{{\nu }_{\mathsf{e}}F}}$$

where ν_e is the number of electrons transferred in the balanced half reactions, and F is Faraday's constant. However, it can be determined more conveniently by the use of a standard potential table for the two half cells involved. The first step is to identify the two metals and their ions reacting in the cell. Then one looks up the standard electrode potential, E^o, in volts, for each of the two half reactions. The standard potential of the cell is equal to the more positive E^o value minus the more negative E^o value.

For example, in the figure above the solutions are CuSO₄ and ZnSO₄. Each solution has a corresponding metal strip in it, and a salt bridge or porous disk connecting the two solutions and allowing SO²⁻
₄ ions to flow freely between the copper and zinc solutions. To calculate the standard potential one looks up copper and zinc's half reactions and finds:

Cu⁺⁺ + 2
e⁻
⇌ Cu   :   E^o = +0.34 V

Zn⁺⁺ + 2
e⁻
⇌ Zn   :   E^o = −0.76 V

Thus the overall reaction is:

Cu⁺⁺ + Zn ⇌ Cu + Zn⁺⁺

The standard potential for the reaction is then +0.34 V − (−0.76 V) = +1.10 V . The polarity of the cell is determined as follows. Zinc metal is more strongly reducing than copper metal because the standard (reduction) potential for zinc is more negative than that of copper. Thus, zinc metal will lose electrons to copper ions and develop a positive electrical charge. The equilibrium constant, K, for the cell is given by:

$${\displaystyle {\log }_{e}K=\frac{{\nu }_{\mathsf{e}}F{E}_{\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}^{\mathsf{o}}}{RT}}$$

where

F is the Faraday constant,

R is the gas constant, and

T is the absolute temperature in Kelvins.

For the Daniell cell K ≈ 1.5×10³⁷ . Thus, at equilibrium, a few electrons are transferred, enough to cause the electrodes to be charged.

Actual half-cell potentials must be calculated by using the Nernst equation as the solutes are unlikely to be in their standard states:

$${\displaystyle E_{\mathsf{h}\mathsf{a}\mathsf{l}\mathsf{f}\mathsf{-}\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}=E^{\mathsf{o}}-\frac{RT}{{\nu }_{\mathsf{e}}F}{\log }_{e}Q}$$

where Q is the reaction quotient. When the charges of the ions in the reaction are equal, this simplifies to:

$${\displaystyle E_{\mathsf{h}\mathsf{a}\mathsf{l}\mathsf{f}\mathsf{-}\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}=E^{\mathsf{o}}-2.303\frac{RT}{{\nu }_{\mathsf{e}}F}{\log }_{10}\left\{{\mathsf{M}}^{n+}\right\}}$$

where M ⁿ⁺ is the activity of the metal ion in solution. In practice concentration in ⁠ mol / L ⁠ is used in place of activity. The metal electrode is in its standard state so by definition has unit activity. The potential of the whole cell is obtained as the difference between the potentials for the two half-cells, so it depends on the concentrations of both dissolved metal ions. If the concentrations are the same the Nernst equation is not needed, and ${\displaystyle E_{\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}=E_{\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}^{\mathsf{o}}}$ under the conditions assumed here.

The value of 2.303 ⁠ R / F ⁠ is 1.9845×10⁻⁴ ⁠ V / K ⁠ , so at   T = 25 °C (298.15 K) the half-cell potential will change by only ⁠0.05918 V/ ν_e ⁠ if the concentration of a metal ion is increased or decreased by a factor of 10 .

$${\displaystyle E_{\mathsf{h}\mathsf{a}\mathsf{l}\mathsf{f}\mathsf{-}\mathsf{c}\mathsf{e}\mathsf{l}\mathsf{l}}=E^{\mathsf{o}}-\frac{0.05918\mathsf{V}}{{\nu }_{\mathsf{e}}}{\log }_{10}\left\{{\mathsf{M}}^{n+}\right\}}$$

These calculations are based on the assumption that all chemical reactions are in equilibrium. When a current flows in the circuit, equilibrium conditions are not achieved and the cell voltage will usually be reduced by various mechanisms, such as the development of overpotentials. Also, since chemical reactions occur when the cell is producing power, the electrolyte concentrations change and the cell voltage is reduced. A consequence of the temperature dependency of standard potentials is that the voltage produced by a galvanic cell is also temperature dependent.

Galvanic corrosion

Main article: Galvanic corrosion

Galvanic corrosion is the electrochemical erosion of metals. Corrosion occurs when two dissimilar metals are in contact with each other in the presence of an electrolyte, such as salt water. This forms a galvanic cell, with hydrogen gas forming on the more noble (less active) metal. The resulting electrochemical potential then develops an electric current that electrolytically dissolves the less noble material. A concentration cell can be formed if the same metal is exposed to two different concentrations of electrolyte.

Communication disorder

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Communication_disorder

A communication disorder is any disorder that affects an individual's ability to comprehend, detect, or apply language and speech to engage in dialogue effectively with others. This also encompasses deficiencies in verbal and non-verbal communication styles. The delays and disorders can range from simple sound substitution to the inability to understand or use one's native language. This article covers subjects such as diagnosis, the DSM-IV, the DSM-V, and examples like sensory impairments, aphasia, learning disabilities, and speech disorders.

Diagnosis

Disorders and tendencies included and excluded under the category of communication disorders may vary by source. For example, the definitions offered by the American Speech–Language–Hearing Association differ from those of the Diagnostic Statistical Manual 4th edition (DSM-IV).

Gleason (2001) defines a communication disorder as a speech and language disorder which refers to problems in communication and in related areas such as oral motor function. The delays and disorders can range from simple sound substitution to the inability to understand or use one's native language. In general, communication disorders commonly refer to problems in speech (comprehension and/or expression) that significantly interfere with an individual's achievement and/or quality of life. Knowing the operational definition of the agency performing an assessment or giving a diagnosis may help.

Persons who speak more than one language or are considered to have an accent in their location of residence do not have a speech disorder if they are speaking in a manner consistent with their home environment or that is a blending of their home and foreign environment.

Other conditions, as specified in the Cincinnati Children's Health Library (2019), that may increase the risk of developing a communication disorder include:

• Cleft lip or cleft palate – a disorder that is caused by the failure of the parts of the mouth and palate to form together while a fetus is developing in the womb, which then creates a deformity. This is often corrected by surgery.
• Craniofacial anomalies – a deformity of a child's facial bone structure and head bones that is caused by early or delayed fusion of the bones.
• Velopharyngeal insufficiency – when the soft palate does not make a tight enough seal against the pharynx and creates a nasally sound while speaking.
• Dental malocclusion – when the top and bottom teeth do not align when the mouth is closed.
• Oral-motor dysfunction – a disconnection between the brain and the mouth that results in the inability to perform tasks such as chewing, blowing, talking, among others.
• Neurological disease/dysfunction – a blanket term that encompasses multiple neurological disorders like dementia, Alzheimer's, epilepsy, and multiple sclerosis.
• Brain injury – when the brain is damaged in a traumatic event that makes the brain move around in the skull.
• Respirator dependency – the inability to breathe without the use of a ventilator machine.
• Respiratory compromise – the declination of respiratory function that can lead to failure or even death if it is left untreated.
• Tracheostomy – a surgical hole created in the trachea to assist in breathing.
• Vocal fold pathology – an abnormality of the cartilage on the vocal folds.
• Developmental delay – when a child fails to develop (whether that be mentally or physically) at the normal rate for children at the same age.
• Autism – a term that includes neurological disorders that inhibit social functioning, communication, sensory processing, and other challenges.
• Prematurity or traumatic birth – an early (before full term) birth, or one with complications.
• Hearing loss or deafness – when the auditory system does not function as it normally should, and there is a decrease in hearing.

DSM-IV

According to the DSM-IV-TR (no longer used), communication disorders were usually first diagnosed in childhood or adolescence, though they are not limited as childhood disorders and may persist into adulthood. They may also occur with other disorders.

Diagnosis involved testing and evaluation during which it is determined if the scores/performance are "substantially below" developmental expectations and if they "significantly" interfere with academic achievement, social interactions, and daily living. This assessment might have also determined if the characteristic is deviant or delayed. Therefore, it may have been possible for an individual to have communication challenges but not meet the criteria of being "substantially below" criteria of the DSM IV-TR. The DSM diagnoses did not comprise a complete list of all communication disorders, for example, auditory processing disorder is not classified under the DSM or ICD-10. The following diagnoses were included as communication disorders:

• Expressive language disorder – characterized by difficulty expressing oneself beyond simple sentences and a limited vocabulary. Individuals can better understand than use language; they may have a lot to say, but have more difficulty organizing and retrieving the words than expected for their developmental stage.
• Mixed receptive-expressive language disorder – problems comprehending the commands of others.
• Stuttering – a speech disorder characterized by a break in fluency, where sounds, syllables, or words may be repeated or prolonged.
• Phonological disorder – a speech sound disorder characterized by problems in making patterns of sound errors (e.g., "dat" for "that").
• Communication disorder NOS (not otherwise specified) – the DSM-IV diagnosis in which disorders that do not meet the specific criteria for the disorder listed above may be classified.

DSM-5

The DSM-5 diagnoses for communication disorders completely rework the ones stated above. The diagnoses are made more general in order to capture the various aspects of communications disorders in a way that emphasizes their childhood onset and differentiate these communications disorders from those associated with other disorders (e.g. autism spectrum disorders).

• Language disorder – the important characteristics of a language disorder are difficulties in learning and using language, which is caused by problems with vocabulary, with grammar, and with putting sentences together in a proper manner. Problems can both be receptive (understanding language) and expressive (producing language).
• Speech sound disorder – previously called phonological disorder, for those with problems with pronunciation and articulation of their native language.
• Childhood-Onset Fluency Disorder (Stuttering) – standard fluency and rhythm of speech is interrupted, often causing the repetition of whole words and syllables. May also include the prolongation of words and syllables; pauses within a word; and/or the avoidance of pronouncing difficult words and replacing them with easier words that the individual is better able to pronounce. This disorder causes many communication problems for the individual and may interfere with social communication and performance in work and/or school settings where communication is essential.
• Social (pragmatic) communication disorder – this diagnosis described difficulties in the social uses of verbal and nonverbal communication in naturalistic contexts, which affects the development of social relationships and dialogue comprehension. The difference between this diagnosis and autism spectrum disorder is that in the latter there is also a restricted or repetitive pattern of behavior.
• Unspecified communication disorder – for those who have symptoms of a communication disorder but who do not meet all criteria, and whose symptoms cause distress or impairment.

Examples

Examples of disorders that may include or create challenges in language and communication and/or may co-occur with the above disorders:

• autism spectrum disorders - autistic disorder, pervasive developmental disorder not otherwise specified (PDDNOS), and Asperger disorder – developmental disorders that affect the brain's normal development of social and communication skills.
• expressive language disorder – affects speaking and understanding where there is no delay in non-verbal intelligence.
• mixed receptive-expressive language disorder – affects speaking, understanding, reading and writing where there is no delay in non-verbal intelligence.
• specific language impairment – a language disorder that delays the mastery of language skills in children who have no hearing loss or other developmental delays. SLI is also called developmental language disorder, language delay, or developmental dysphasia.

Sensory impairments

• Blindness – A link between communication skills and visual impairment with children who are blind is currently being investigated.
• Deafness/frequent ear infections – Hearing impairments during language acquisition may lead to spoken language problems. Children with frequent ear infections may temporarily develop problems pronouncing words correctly. The inability to hear is not in itself a communication disorder.

Aphasia

Aphasia is loss of the ability to produce or comprehend language. There are acute aphasias which result from stroke or brain injury, and primary progressive aphasias caused by progressive illnesses such as dementia.

• Acute aphasias
  • Expressive aphasia also known as Broca's aphasia, expressive aphasia is a non-fluent aphasia that is characterized by damage to the frontal lobe region of the brain. A person with expressive aphasia usually speaks in short sentences that make sense but take great effort to produce. Also, a person with expressive aphasia understands another person's speech but has trouble responding quickly.
  • Receptive aphasia also known as Wernicke's aphasia, receptive aphasia is a fluent aphasia that is categorized by damage to the temporal lobe region of the brain. A person with receptive aphasia usually speaks in long sentences that have no meaning or content. People with this type of aphasia often have trouble understanding other's speech and generally do not realize that they are not making any sense.
  • Conduction aphasia also known as association aphasia, is when there is a difficulty repeating words or phrases. Comprehension and spontaneous speech are usually not limited, just repetition.
  • Anomic aphasia is when one has difficulty retrieving words and may take long pauses when trying to recall certain verbs or nouns. This is a mild form of aphasia as comprehension is not limited.
  • Global aphasia is the most severe form of aphasia as there is difficulty with speech comprehension, as well as difficulty in responding in meaningful ways. This is caused by several brain injuries in more than one spot.
• Primary progressive aphasias (PPA)
  • Progressive nonfluent aphasia also known as PNFA, is a form of PPA that involves a reduction of speech fluency, syntax and grammar impairment, difficulty of articulation and word finding, and long-term comprehension.
  • Semantic dementia is a condition in which words and phrases slowly begin to lose meaning, and comprehension is lost because of a deterioration in the semantic memory. This is usually characterized by behavior changes, fluent speech but with no meaning, preserved syntax and grammar, and the impaired ability to recognize objects.
  • Logopenic progressive aphasia also known as LPA, is associated with Alzheimer's disease. This is characterized by difficulty in word retrieval and repetition, phonological errors, anomia, and the preservation of single-word comprehension.

Learning disability

• Dyscalculia – an impairment in the systems used in communicating numbers
• Dyslexia – an impairment in systems used in reading
• Dysgraphia – an impairment in the systems used in writing

Speech disorders

• cluttering - a syndrome characterized by a speech delivery rate which is either abnormally fast, irregular, or both.
• dysarthria - a condition that occurs when problems with the muscles that helps a person to talk make it difficult to pronounce words.
• esophageal voice - involves the patient injecting or swallowing air into the esophagus. Usually learnt and used by patients who cannot use their larynges to speak. Once the patient has forced the air into their esophagus, the air vibrates a muscle and creates esophageal voice. Esophageal voice tends to be difficult to learn and patients are often only able to talk in short phrases with a quiet voice.
• lisp - a speech impairment that is also known as sigmatism.
• speech sound disorder - Speech-sound disorders (SSD) involve impairments in speech-sound production and range from mild articulation issues involving a limited number of speech sounds to more severe phonologic disorders involving multiple errors in speech-sound production and reduced intelligibility.
• stuttering - a speech disorder in which sounds, syllables, or words are repeated or last longer than normal. These problems cause a break in the flow of speech (called disfluency).

Cancer research

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Cancer_research

Cancer research is research into cancer to identify causes and develop strategies for prevention, diagnosis, treatment, and cure.

Cancer research ranges from epidemiology, molecular bioscience to the performance of clinical trials to evaluate and compare applications of the various cancer treatments. These applications include surgery, radiation therapy, chemotherapy, hormone therapy, immunotherapy and combined treatment modalities such as chemo-radiotherapy. Starting in the mid-1990s, the emphasis in clinical cancer research shifted towards therapies derived from biotechnology research, such as cancer immunotherapy and gene therapy.

Cancer research is done in academia, research institutes, and corporate environments, and is largely government funded.

History

Sidney Farber is regarded as the father of modern chemotherapy.

Cancer research has been ongoing for centuries. Early research focused on the causes of cancer. Percivall Pott identified the first environmental trigger (chimney soot) for cancer in 1775 and cigarette smoking was identified as a cause of lung cancer in 1950. Early cancer treatment focused on improving surgical techniques for removing tumors. Radiation therapy took hold in the 1900s. Chemotherapeutics were developed and refined throughout the 20th century.

The U.S. declared a "War on Cancer" in the 1970s, and increased the funding and support for cancer research.

Seminal papers

Some of the most highly cited and most influential research reports include:

• The Hallmarks of Cancer, published in 2000, and Hallmarks of Cancer: The Next Generation, published in 2011, by Douglas Hanahan and Robert Weinberg. Together, these articles have been cited in over 30,000 published papers.

Types of research

Cancer research encompasses a variety of types and interdisciplinary areas of research. Scientists involved in cancer research may be trained in areas such as chemistry, biochemistry, molecular biology, physiology, medical physics, epidemiology, and biomedical engineering. Research performed on a foundational level is referred to as basic research and is intended to clarify scientific principles and mechanisms. Translational research aims to elucidate mechanisms of cancer development and progression and transform basic scientific findings into concepts that can be applicable to the treatment and prevention of cancer. Clinical research is devoted to the development of pharmaceuticals, surgical procedures, and medical technologies for the eventual treatment of patients.

Prevention and epidemiology

Epidemiologic analysis indicates that at least 35% of all cancer deaths in the world could now be avoided by primary prevention. According to a newer GBD systematic analysis, in 2019, ~44% of all cancer deaths — or ~4.5 million deaths or ~105 million lost disability-adjusted life years — were due to known clearly preventable risk factors, led by smoking, alcohol use and high BMI.

However, one 2015 study suggested that between ~70% and ~90% of cancers are due to environmental factors and therefore potentially preventable. Furthermore, it is estimated that with further research cancer death rates could be reduced by 70% around the world even without the development of any new therapies. Cancer prevention research receives only 2–9% of global cancer research funding, albeit many of the options for prevention are already well-known without further cancer-specific research but are not reflected in economics and policy. Mutational signatures of various cancers, for example, could reveal further causes of cancer and support causal attribution.

Detection

Further information: Cancer screening

See also: Biomarker

Prompt detection of cancer is important, since it is usually more difficult to treat in later stages. Accurate detection of cancer is also important because false positives can cause harm from unnecessary medical procedures. Some screening protocols are currently not accurate (such as prostate-specific antigen testing). Others such as a colonoscopy or mammogram are unpleasant and as a result some patients may opt out. Active research is underway to address all these problems, to develop novel ways of cancer screening and to increase detection rates.

For example:

• Multimodal learning AI systems are being developed to help detect many cancer types via integrating different types of data.
• Scientists work on identifying and measurability of novel biomarkers or sets of such to detect cancer early, such as tumor-associated mycobiomes and bacterial microbiomes
• Researchers investigate whether ants could be used as biosensors to detect cancer via urine

Treatment

Main article: Treatment of cancer

Emerging topics of cancer treatment research include:

• Anti-cancer vaccines
  • Oncophage
  • Sipuleucel-T (Provenge) is a prostate cancer vaccine
  • Inactivated tumor cells are investigated as potential bifunctional cancer vaccines
• Newer forms of chemotherapy
• Gene therapy
• Photodynamic therapy
• Radiation therapy
• Reoviridae (Reolysin drug therapy)
• Targeted therapy
• Medical microbots (including bacterial), nanobots and bacterial 'cyborg cells'
• Virotherapy
• Antibodies
• Photoimmunotherapy (for brain cancer)
• Natural killer cells can induce immunological memory. Research is being developed to modify their action against cancer.
• How treatments can best be combined (in combination therapies)

Cause and development of cancer

Numerous cell signaling pathways are disrupted in the development of cancer.

Research into the cause of cancer involves many different disciplines including genetics, diet, environmental factors (i.e. chemical carcinogens). In regard to investigation of causes and potential targets for therapy, the route used starts with data obtained from clinical observations, enters basic research, and, once convincing and independently confirmed results are obtained, proceeds with clinical research, involving appropriately designed trials on consenting human subjects, with the aim to test safety and efficiency of the therapeutic intervention method. An important part of basic research is characterization of the potential mechanisms of carcinogenesis, in regard to the types of genetic and epigenetic changes that are associated with cancer development. The mouse is often used as a mammalian model for manipulation of the function of genes that play a role in tumor formation, while basic aspects of tumor initiation, such as mutagenesis, are assayed on cultures of bacteria and mammalian cells.

Genes involved in cancer

Main article: Oncogenomics

See also: Databases for oncogenomic research

The goal of oncogenomics is to identify new oncogenes or tumor suppressor genes that may provide new insights into cancer diagnosis, predicting clinical outcome of cancers, and new targets for cancer therapies. As the Cancer Genome Project stated in a 2004 review article, "a central aim of cancer research has been to identify the mutated genes that are causally implicated in oncogenesis (cancer genes)." The Cancer Genome Atlas project is a related effort investigating the genomic changes associated with cancer, while the COSMIC cancer database documents acquired genetic mutations from hundreds of thousands of human cancer samples.

These large scale projects, involving about 350 different types of cancer, have identified ~130,000 mutations in ~3000 genes that have been mutated in the tumors. The majority occurred in 319 genes, of which 286 were tumor suppressor genes and 33 oncogenes.

Several hereditary factors can increase the chance of cancer-causing mutations, including the activation of oncogenes or the inhibition of tumor suppressor genes. The functions of various onco- and tumor suppressor genes can be disrupted at different stages of tumor progression. Mutations in such genes can be used to classify the malignancy of a tumor.

In later stages, tumors can develop a resistance to cancer treatment. The identification of oncogenes and tumor suppressor genes is important to understand tumor progression and treatment success. The role of a given gene in cancer progression may vary tremendously, depending on the stage and type of cancer involved.

Cancer epigenetics

Cancer epigenetics is the study of epigenetic modifications to the DNA of cancer cells that do not involve a change in the nucleotide sequence, but instead involve a change in the way the genetic code is expressed. Epigenetic mechanisms are necessary to maintain normal sequences of tissue specific gene expression and are crucial for normal development. They may be just as important, if not even more important, than genetic mutations in a cell's transformation to cancer. The disturbance of epigenetic processes in cancers, can lead to a loss of expression of genes that occurs about 10 times more frequently by transcription silencing (caused by epigenetic promoter hypermethylation of CpG islands) than by mutations. As Vogelstein et al. points out, in a colorectal cancer there are usually about 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations. However, in colon tumors compared to adjacent normal-appearing colonic mucosa, there are about 600 to 800 heavily methylated CpG islands in the promoters of genes in the tumors while these CpG islands are not methylated in the adjacent mucosa. Manipulation of epigenetic alterations holds great promise for cancer prevention, detection, and therapy. In different types of cancer, a variety of epigenetic mechanisms can be perturbed, such as the silencing of tumor suppressor genes and activation of oncogenes by altered CpG island methylation patterns, histone modifications, and dysregulation of DNA binding proteins. There are several medications which have epigenetic impact, that are now used in a number of these diseases.

Diet and cancer

Advertisement suggesting that a healthy diet helps prevent cancer.

Many dietary recommendations have been proposed to reduce the risk of cancer, few have significant supporting scientific evidence. Obesity and drinking alcohol have been correlated with the incidence and progression of some cancers. Lowering the consumption of sweetened beverages is recommended as a measure to address obesity.

Some specific foods are linked to specific cancers. There is strong evidence that processed meat and red meat intake increases risk of colorectal cancer. Aflatoxin B₁, a frequent food contaminant, increases risk of liver cancer, while drinking coffee is associated with a reduced risk. Betel nut chewing causes oral cancer. Stomach cancer is more common in Japan due to its high-salt diet.

Dietary recommendations for cancer prevention typically include weight management and eating a healthy diet, consisting mainly of "vegetables, fruit, whole grains and fish, and a reduced intake of red meat, animal fat, and refined sugar." A healthy dietary pattern may lower cancer risk by 10–20%. There is no clinical evidence that diets or specific foods can cure cancer.

Periods of intermittent fasting (time-restricted feeding which may not include caloric restriction) is investigated for potential usefulness in cancer prevention and treatment and as of 2021 additional trials are needed to elucidate the risks and benefits. In some cases, "caloric restrictions could hinder both cancer growth and progression, besides enhancing the efficacy of chemotherapy and radiation therapy". Caloric restriction mimetics, including some present in foods like spermidine, are also investigated for these or similar reasons. Such and similar dietary supplements may contribute to prevention or treatment, with candidate substances including apigenin, berberine, jiaogulan, and rhodiola rosea.

Research funding

See also: Global health and Funding of science

Cancer research is funded by government grants, charitable foundations and pharmaceutical and biotechnology companies.

In the early 2000s, most funding for cancer research came from taxpayers and charities, rather than from corporations. In the US, less than 30% of all cancer research was funded by commercial researchers such as pharmaceutical companies. Per capita, public spending on cancer research by taxpayers and charities in the US was five times as much in 2002–03 as public spending by taxpayers and charities in the 15 countries that were full members of the European Union. As a percentage of GDP, the non-commercial funding of cancer research in the US was four times the amount dedicated to cancer research in Europe. Half of Europe's non-commercial cancer research is funded by charitable organizations.

The National Cancer Institute is the major funding institution in the United States. In the 2023 fiscal year, the NCI funded $7.1 billion in cancer research.

Difficulties

Difficulties inherent to cancer research are shared with many types of biomedical research.

Cancer research processes have been criticised. These include, especially in the US, for the financial resources and positions required to conduct research. Other consequences of competition for research resources appear to be a substantial number of research publications whose results cannot be replicated.

Replicability

Results from The Reproducibility Project: Cancer Biology suggest most studies of the cancer research sector may not be replicable.

In a 2012 paper, C. Glenn Begley, a biotech consultant working at Amgen, and Lee Ellis, a medical researcher at the University of Texas, found that only 11% of 53 pre-clinical cancer studies had replications that could confirm conclusions from the original studies. In late 2021, The Reproducibility Project: Cancer Biology examined 53 top papers about cancer published between 2010 and 2012 and showed that among studies that provided sufficient information to be redone, the effect sizes were 85% smaller on average than the original findings. A survey of cancer researchers found that half of them had been unable to reproduce a published result. Another report estimated that almost half of randomized controlled trials contained flawed data (based on the analysis of anonymized individual participant data (IPD) from more than 150 trials).

Public participation

Distributed computing

One can share computer time for distributed cancer research projects like Help Conquer Cancer. World Community Grid also had a project called Help Defeat Cancer. Other related projects include the Folding@home and Rosetta@home projects, which focus on groundbreaking protein folding and protein structure prediction research. Vodafone has also partnered with the Garvan Institute to create the DreamLab Project, which uses distributed computing via an app on cellphones to perform cancer research.

Clinical trials

MatchMiner overview of data flow and modes of use

Members of the public can also join clinical trials as healthy control subjects or for methods of cancer detection.

There could be software and data-related procedures that increase participation in trials and make them faster and less expensive. One open source platform matches genomically profiled cancer patients to precision medicine drug trials.

MD Anderson Cancer Center is ranked as one of the top cancer research institutions.

Organizations

Breast cancer awareness ribbon statue in Kentucky

Organizations exist as associations for scientists participating in cancer research, such as the American Association for Cancer Research and American Society of Clinical Oncology, and as foundations for public awareness or raising funds for cancer research, such as Relay For Life and the American Cancer Society.

Awareness campaigns

Supporters of different types of cancer have adopted different colored awareness ribbons and promote months of the year as being dedicated to the support of specific types of cancer. The American Cancer Society began promoting October as Breast Cancer Awareness Month in the United States in the 1980s. Pink products are sold to both generate awareness and raise money to be donated for research purposes. This has led to pinkwashing, or the selling of ordinary products turned pink as a promotion for the company.

Oncology

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Oncology 

A coronal CT scan showing a malignant mesothelioma, indicated by the asterisk and the arrows
Focus	Cancerous tumor
Subdivisions	Medical oncology, radiation oncology, surgical oncology
Significant tests	Tumor markers, TNM staging, CT scans, MRI

Oncologist

Occupation
Occupation type	Specialty
Activity sectors	Medicine
Description
Fields of employment	Hospitals, clinics, clinical research centers

Oncology is a branch of medicine that deals with the study, treatment, diagnosis, and prevention of cancer. A medical professional who practices oncology is an oncologist. The name's etymological origin is the Greek word ὄγκος (ónkos), meaning "tumor", "volume" or "mass".

Oncology is concerned with the diagnosis of any cancer in a person, therapy (e.g., surgery, chemotherapy, radiotherapy and other modalities), monitoring of people with cancer after treatment, palliative care of people with terminal malignancies, ethical questions surrounding cancer care, screening of people or populations with cancer, and the study of cancer treatments through clinical research.

An oncologist typically focuses on a specialty area for how cancer is treated, such as for surgery, radiation, gynecological, geriatrics, pediatrics, and numerous disciplines based on individual organ systems (breast, brain, liver, among others).

The expertise of an oncologist is obtained when a person suspects having cancer, is diagnosed with having cancer, or is being treated for cancer.

Diagnosis

Medical histories remain an important screening tool for an oncologist to assess the character of the concerns and nonspecific symptoms in the person with cancer (such as fatigue, weight loss, unexplained anemia, fever of unknown origin, paraneoplastic phenomena and other signs) may warrant further investigation for malignancy.

Diagnostic methods in oncology may involve a biopsy or resection; these are methods by which suspicious neoplastic growths can be removed in part or in whole, and evaluated by a pathologist to determine malignancy. This is currently the gold standard for the diagnosis of cancer and is crucial in guiding the next step in management (active surveillance, surgery, radiation therapy, chemotherapy, or a combination of these)

Other diagnostic procedures may include an endoscopy, either upper or lower gastrointestinal, cystoscopy, bronchoscopy, or nasendoscopy to localize tissues suspicious for malignancy and biopsy, mammograms, X-rays, CT scanning, MRI scanning, ultrasound and other radiological techniques to localize and guide biopsy. Scintigraphy, single photon emission computed tomography (SPECT), positron emission tomography (PET) and other methods of nuclear medicine are imaging technologies used to identify areas suspicious of malignancy. Blood tests, including tumor markers, can assist diagnosis of certain types of cancers.

Apart from diagnoses, these modalities (especially imaging by CT scanning) are often used to determine operability, i.e., whether it is surgically possible to remove a tumor in its entirety.

A tissue diagnosis (from a biopsy) by a pathologist is essential for the proper classification of cancer and to guide the next step of treatment. On extremely rare instances when this is not possible, "empirical therapy" (without an exact diagnosis) may be considered, based on the available evidence (e.g. history, x-rays and scans.)

Immunohistochemical markers often give a strong indication of the primary malignancy. This situation is referred to as "malignancy of unknown primary", and again, treatment is empirically based on past experience of the most likely origin.

Therapy

Depending upon the cancer identified, follow-up and palliative care will be administered at that time. Certain disorders (such as ALL or AML) will require immediate admission and chemotherapy, while others will be followed up with regular physical examination and blood tests.

Often, surgery is attempted to remove a tumor entirely. This is only feasible when there is some degree of certainty that the tumor can in fact be removed. When it is certain that parts will remain, curative surgery is often impossible, e.g. when there are metastases, or when the tumor has invaded a structure that cannot be operated upon without risking the patient's life. Occasionally surgery can improve survival even if not all tumour tissue has been removed; the procedure is referred to as "debulking" (i.e. reducing the overall amount of tumour tissue). Surgery is also used for the palliative treatment of some cancers, e.g. to relieve biliary obstruction, or to relieve the problems associated with some cerebral tumors. The risks of surgery must be weighed against the benefits.

Chemotherapy and radiotherapy are used as a first-line radical therapy in several malignancies. They are also used for adjuvant therapy, i.e. when the macroscopic tumor has already been completely removed surgically but there is a reasonable statistical risk that it will recur. Chemotherapy and radiotherapy are commonly used for palliation, where disease is clearly incurable: in this situation the aim is to improve the quality of life and to prolong it.

Hormone manipulation is well established, particularly in the treatment of breast and prostate cancer.

There is currently a rapid expansion in the use of monoclonal antibody treatments, notably for lymphoma (Rituximab) and breast cancer (Trastuzumab).

Vaccines and other immunotherapies are the subject of intensive research.

Palliative care

Approximately 50% of all cancer cases in the Western world can be treated to remission with radical treatment. For pediatric patients, that number is much higher. A large number of cancer patients will die from the disease, and a significant proportion of patients with incurable cancer will die of other causes. There may be ongoing issues with symptom control associated with progressive cancer, and also with the treatment of the disease. These problems may include pain, nausea, anorexia, fatigue, immobility, and depression. Not all issues are strictly physical: personal dignity may be affected. Moral and spiritual issues are also important.

While many of these problems fall within the remit of the oncologist, palliative care has matured into a separate, closely allied specialty to address the problems associated with advanced disease. Palliative care is an essential part of the multidisciplinary cancer care team. Palliative care services may be less hospital-based than oncology, with nurses and doctors who are able to visit the patient at home.

Ethical issues

There are a number of recurring ethical questions and dilemmas in oncological practice. These include:

• What information to give the patient regarding disease extent/progression/prognosis.
• Entry into clinical trials, especially in the face of terminal illness.
• Withdrawal of active treatment.
• "Do Not Resuscitate" orders and other end-of-life issues.

These issues are closely related to the patient's personality, religion, culture, and family life. Though these issues are complex and emotional, the answers are often achieved by the patient seeking counsel from trusted personal friends and advisors. It requires a degree of sensitivity and very good communication on the part of the oncology team to address these problems properly.

Progress and research

There is a tremendous amount of research being conducted on all frontiers of oncology, ranging from cancer cell biology, and radiation therapy to chemotherapy treatment regimens and optimal palliative care and pain relief. Next-generation sequencing and whole-genome sequencing have completely changed the understanding of cancers. Identification of novel genetic/molecular markers will change the methods of diagnosis and treatment, paving the way for personalized medicine.

Therapeutic trials often involve patients from many different hospitals in a particular region. In the UK, patients are often enrolled in large studies coordinated by Cancer Research UK (CRUK), Medical Research Council (MRC), the European Organisation for Research and Treatment of Cancer (EORTC) or the National Cancer Research Network (NCRN).

The most valued companies worldwide whose leading products are in Oncology include Pfizer (United States), Roche (Switzerland), Merck (United States), AstraZeneca (United Kingdom), Novartis (Switzerland) and Bristol-Myers Squibb (United States) who are active in the treatment areas Kinase inhibitors, Antibodies, Immuno-oncology and Radiopharmaceuticals.

Specialties

The four main divisions:

• Medical oncology: focuses on the treatment of cancer with chemotherapy, targeted therapy, immunotherapy, and hormonal therapy.
• Surgical oncology: focuses on treatment of cancer with surgery.
• Radiation oncology: focuses on treatment of cancer with radiation.
• Clinical oncology: focuses on treatment of cancer with both systemic therapies and radiation.

Sub-specialties in Oncology:

• Neuro-oncology: focuses on cancers of brain.
• Ocular oncology: focuses on cancers of eye.
• Head & Neck oncology: focuses on cancers of oral cavity, nasal cavity, oropharynx, hypopharynx and larynx.
• Thoracic oncology: focuses on cancers of lung, mediastinum, oesophagus and pleura.
• Breast oncology: focuses on cancers of breast.
• Gastrointestinal oncology: focuses on cancers of the stomach, colon, rectum, anal canal, liver, gallbladder, pancreas.
• Bone & Musculoskeletal oncology: focuses on cancers of bones and soft tissue.
• Dermatological oncology: focuses on the medical and surgical treatment of skin, hair, sweat gland, and nail cancers
• Genitourinary oncology: focuses on cancers of genital and urinary system.
• Gynecologic oncology: focuses on cancers of the female reproductive system.
• Pediatric oncology: concerned with the treatment of cancer in children.
• Adolescent and young adult (AYA) oncology.
• Hemato oncology: focuses on cancers of blood and stem cell transplantation.
• Preventive oncology: focuses on epidemiology & prevention of cancer.
• Geriatric oncology: focuses on cancers in elderly population.
• Pain & Palliative oncology: focuses on treatment of end stage cancer to help alleviate pain and suffering.
• Molecular oncology: focuses on molecular diagnostic methods in oncology.
• Nuclear medicine oncology: focuses on diagnosis and treatment of cancer with radiopharmaceuticals.
• Psycho-oncology: focuses on psychosocial issues on diagnosis and treatment of cancer patients.
• Veterinary oncology: focuses on treatment of cancer in animals.

Emerging specialties:

• Cardiooncology is a branch of cardiology that addresses the cardiovascular impact of cancer and its treatments.