Golgi Apparatus

The Golgi apparatus is an organelle mainly devoted to processing the proteins synthesized in the endoplasmic reticulum. It is found in most eukaryotic cells and was discovered in 1898 by the Italian physcian Camillo Golgi.

The Golgi apparatus, also called Golgi complex, consists of a series of five to eight cup-shaped, membrane-covered sacs called cisternae that look something like a stack of deflated balloons. In some unicellular flagellates, however, as many as 60 cisternae may combine to make up the Golgi apparatus.

The number of Golgi complexes in a cell varies according to its function. Animal cells generally contain between ten and twenty Golgi stacks per cell, which are linked into a single complex by tubular connections between cisternae. This complex is usually located close to the cell nucleus.

The Golgi apparatus functions as the processing and distribution department for the cell's chemical products. It modifies proteins and lipids that have been built in the endoplasmic reticulum and prepares them for export outside of the cell or for transport to other locations in the cell. Proteins and lipids built in the smooth and rough endoplasmic reticulum bud off in tiny bubble-like vesicles that move through the cytoplasm until they reach the Golgi complex.

Organelle

An organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane. The name organelle means little organ and comes from the idea that these structures are to cells what an organ is to the body.

There are many types of organelles, particularly in the eukaryotic cells of higher organisms. Some of them are separated from the rest of the cell by lipid layers similar in structure to the cell membrane. Major eukaryotic organelles are the Golgi apparatus, mitochondrion, chloroplast, endoplasmatic reticulum, vacuole, and nucleus.

Prokaryotic Cell

A prokaryotic cell is a cell which lacks a membrane-bound nucleus or any other membrane-bound organelles. A prokaryotic cell has few internal structures that are distinguishable under a microscope. Cells in the monera kingdom such as bacteria and cyanobacteria are prokaryotes.

Prokaryotic cells differ significantly from eukaryotic cells. They don't have a membrane-bound nucleus and instead of having chromosomal DNA, their genetic information is in a circular loop called a plasmid. Prokaryotic cells feature three major shapes: rod shaped, spherical, and spiral. Instead of going through elaborate replication processes, they divide by binary fission.

Eukaryotic Cell

An Eurkaryotic cell is a cell whose cytoplasm is bound by a plasma membrane and contains a nucleus. In its membrane-bound compartments specific metabolic activities take place. Most important among these compartments is the nucleus, which houses the eukaryotic cell’s DNA. It is this nucleus that gives the eukaryote its name, which literally means "true nucleus." Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi apparatus.

Eukaryotic cells are typically 10 to 100 micrometers across, or about 10 times the size of prokaryotic cells. Cell division in eukaryotes is different from organisms without a nucleus (prokaryotes). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes.

Eukaryotic cells are typically much larger than prokaryotes. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments, and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division.

Cell

A cell is a small, usually microscopic, mass of protoplasm which is bounded externally by a semipermeable membrane, including one or more nuclei and various non-living products, capable of performing the fundamental functions of life, forming the least structural unit of living matter.

The are two type of cells: a Eukaryote, and a Prokaryote cell. Prokaryotes differ from eukaryotes since they lack a nuclear envelope and a cell nucleus. Prokaryotes also lack most of the intracellular organelles and structures that are seen in eukaryotic cells.

A cell consists of a plasma membrane, which surrounds the body of the cell, a cytoplasm, and at the center a nucleus, which is surrounded by the nuclear membrane. The cytoplasm contains the Golgi apparatus, mitochondria, endoplasmatic reticuli, vesicules, etc. The chromosomes are contained in the nucleus of the cell.

Messier 22

Messier 22, or M22, is an elliptical globular cluster in the constellation Sagittarius near the Galactic bulge region. It is one of the brightest globulars that is visible in the night sky.

M22 is one of the nearer globular clusters to Earth at a distance of about 10,600 light-years away. It spans a spatial diameter of 99 ± 9 light-years. 32 variable stars have been recorded in M22. It is projected in front of the galactic bulge and is therefore useful for its microlensing effect on the background stars in the bulge. Despite its relative proximity to us, this metal-poor cluster's light is limited by dust extinction, giving it an apparent magnitude of 5.5 making it the brightest globular cluster in the norther hemisphere.

Messier 22 was one of the first globulars to be discovered in 1665 by Abraham Ihle and it was included in Charles Messier's catalog of comet-like objects on June 5, 1764. It was one of the first globular clusters to be carefully studied in 1930 first by Harlow Shapley, who discovered roughly 70,000 stars and found it had a dense core. Then Halton Arp and William G. Melbourne continued to study the M22 in 1959.

M87

Messier 87, or M87, is a giant elliptical galaxy. The galaxy is the largest and brightest galaxy within the northern Virgo Cluster, located about 55 million light years away. The galaxy also contains a notable active galactic nucleus that is a strong source of multiwavelength radiation, particularly radio waves. Since this is the largest giant elliptical galaxy near Earth and since it is one of the brightest radio sources in the sky, it is a popular target for both amateur astronomy observations and professional astronomy study. M87 is estimated to have a mass, within 32 kpc of its center, of 2.4 ± 0.6 ×1012 M.

H II Region

An H II region is a cloud of glowing gas and plasma, sometimes several hundred light-years across, in which star formation is taking place. Young, hot, blue stars which have formed from the gas emit copious amounts of ultraviolet light, ionizing the nebula surrounding them.
H II regions may give birth to thousands of stars over a period of several million years.

H II regions are named for the large amount of ionized atomic hydrogen they contain, referred to as H II by astronomers.

Open Cluster

An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud, and are still loosely gravitationally bound to each other. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring. They are usually less than a few hundred million years old: they become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center, as well as losing cluster members through internal close encounters.

Globular Cluster

A globular cluster is a spherical collection of stars which consists of ten thousand to one million stars. Orbiting a galactic core as a satellite, globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. They populate the halo of the Milky Way and other galaxies with a significant concentration toward the Galactic Center. The name of this category of globular cluster is derived from the Latin globulus—a small sphere.

Our galaxy has about 200 globular clusters, most in highly eccentric orbits that take them far outside the Milky Way. Most other galaxies have globular cluster systems as well, in some cases, such as the M87, containing several thousands of globulars.

Star Clusters

Star clusters are groups of stars which are gravitationally bound. There are two types of star clusters: globular clusters, which are tight groups of hundreds of thousands of very old stars, and open clusters which generally contain less than a few hundred members, and are often very young. Star clusters visible to the naked eye include Pleiades, Hyades and the Beehive Cluster.

Sirius

Sirius is the brightest star in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star. What the naked eye perceives as a single star is actually a binary star system, which consists of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B.

Sirius is also known colloquially as the "Dog Star", reflecting its prominence in its constellation, Canis Major (Big Dog). It is the subject of more myth and folklore than any other star apart from the sun. The heliacal rising of Sirius marked the flooding of the Nile in Ancient Egypt and the 'Dog Days' of summer for the Ancient Greeks, while to the Polynesians it marked winter and was an important star for navigation around the Pacific Ocean.

Cygnus X-1

Cygnus X-1 is a well known galactic X-ray source in the constellation Cygnus. It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth, producing a peak X-ray flux of 2.3×10−23 Wm−2Hz-1. Cygnus X-1 was the first X-ray source widely accepted to be a black hole candidate and it remains among the most studied astronomical objects in its class. It is estimated to have a mass about 8.7 times the mass of the Sun and has been shown to be too compact to be any known kind of normal star or other likely object besides a black hole. If so, the radius of its event horizon is probably about 26 km.

Cygnus X-1 belongs to a high-mass X-ray binary system about 6000 light years from the Sun that includes a blue supergiant variable star designated HDE 226868 which it orbits at about 0.2 AU, or 20% of the distance from the Earth to the Sun. A stellar wind from the star provides material for an accretion disk around the X-ray source. Matter in the inner disk is heated to millions of kelvin (K), generating the observed X-rays.

Binary Star

A binary star is a star system which consists of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is the secondary. Research between the early 1800s and today suggests that many stars are part of either binary star systems or star systems with more than two stars, called multiple star systems. The term double star may be used synonymously with binary star, but more generally, a double star may be either a binary star or an optical double star which consists of two stars with no physical connection but which appear close together in the sky as seen from the Earth.

In the science of astronomy, the term binary star is generally restricted to pairs of stars which revolve around a common centre of mass. Binary stars which can be resolved with a telescope or interferometric methods are known as visual binaries. Most of the known visual binary stars have not completed one whole revolution, but are observed to have travelled along a curved path or a partial arc. Binary stars are often detected optically, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy.

If the orbits of components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. Examples of binaries are Algol (an eclipsing binary), Sirius, and Cygnus X-1. Binary stars are also common as the nuclei of many planetary nebulae, and are the progenitors of both novae and type Ia supernovae.

John Michell was the first to suggest that double stars might be physically attached to each other when he argued in 1767 that the probability that a double star was due to a chance alignment was small. William Herschel began observing double stars in 1779 and soon thereafter published catalogs of about 700 double stars. By 1803, he had observed changes in the relative positions in a number of double stars over the course of 25 years, and concluded that they must be binary systems.

Large Magellanic Cloud

The Large Magellanic Cloud is a satellite galaxy of the Milky Way galaxy. It is located 160,000 light-years from Earth and is one of a handful of dwarf galaxies that orbit the Milky Way. The Large Magellanic Cloud is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy and the fourth largest of the Local Group.

The Large Magellanic Cloud is an irregular galaxy, rich in gas and dust, and it is currently undergoing star formation activity. It has a mass equivalent to approximately 10 billion times the mass of our Sun and a wide range of galactic objects and phenomena. It contains roughly 60 globular clusters, 400 planetary nebulae, and 700 open clusters, along with hundreds of thousands of giant and supergiant stars. On his voyage to find a direct way to the Pacific in 1519, Ferdinand Magellan was the first to bring the Large Magellanic Cloud into common knowledge, as it can be viewed from the Southern Hemisphere.

Dwarf Galaxy

A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars. The Large Magellanic Cloud, containing over 30 billion stars, is sometimes classified as a dwarf galaxy while others consider it a full-fledged galaxy going around the Milky Way galaxy.

Redshift

A redshift is a shift in the frequency of a photon toward lower energy, or longer wavelength. The redshift is defined as the change in the wavelength of the light divided by the rest wavelength of the light, as z = (Observed wavelength - Rest wavelength)/(Rest wavelength)

Redshift occurs when electromagnetic radiation emitted or reflected by an object is shifted towards the (less energetic) red end of the electromagnetic spectrum due to the Doppler effect. The Doppler Redshift results from the relative motion of the light emitting object and the observer. If the source of light is moving away from you then the wavelength of the light is stretched out, i.e., the light is shifted towards the red. These effects, individually called the blueshift, and the redshift are together known as doppler shifts. The shift in the wavelength is given by a simple formula: (Observed wavelength - Rest wavelength)/(Rest wavelength) = (v/c) so long as the velocity v is much less than the speed of light. A relativistic doppler formula is required when velocity is comparable to the speed of light.

The Cosmological Redshift is a redshift caused by the expansion of space. The wavelength of light increases as it traverses the expanding universe between its point of emission and its point of detection by the same amount that space has expanded during the crossing time. The Gravitational Redshift is a shift in the frequency of a photon to lower energy as it climbs out of a gravitational field.

Quasar

A quasar is an extremely intense and active galactic nucleus and is considered to be the most distant object yet detected in the universe. Quasars were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies.

The word quasar is short for "quasi-stellar radio source". This name, which means star-like emitters of radio waves, was given in the 1960s when quasars were first detected. Despite their brightness, due to their great distance from Earth, no quasars can be seen with an unaided eye. Energy from quasars takes billions of years to reach the Earth's atmosphere.

There is now a scientific consensus that a quasar is a compact region 10-10,000 Schwarzschild radii across surrounding the central supermassive black hole of a galaxy, powered by its accretion disc. Quasars show a very high redshift, which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. The most luminous quasars radiate at a rate that can exceed the output of average galaxies, equivalent to one trillion (1012) suns.

The first quasars were discovered as radio loud sources in the late 1950's & early 1960's. The first optical discovery to accompany a radio source came in 1960 when radio source 3C 48 was tied to an optical object. The optical spectrum was difficult to interpret with many before unseen emission and absorbtion lines. In 1963 another source was tied with an optical component and it too exhibited these strange emission /absorbtion lines. It was soon discovered that these weren't so strange as they were just redshifted.

Parallel Universe

Parallel universe is a self-contained separate universe coexisting with one's own. In the science of physics, parallel universes hypothetically exist exactly like our ­universe. These universes are all related to ours; indeed, they branch off from ours, and our universe is branched off of others. Within these parallel universes, our wars have had different outcomes than the ones we know. Species that are extinct in our universe have evolved and adapted in others. In other universes, we humans may have become extinct.

In 1954, a young Princeton University doctoral candidate named Hugh Everett III came up with this radical idea of parallel universes. With his Many-Worlds hypothesis, Everett was attempting to answer a rather sticky question related to quantum physics: Why does quantum matter behave erratically? The quantum level is the smallest one science has detected so far. The study of quantum physics began in 1900, when the physicist Max Planck first introduced the concept to the scientific world. Planck's study of radiation yielded some unusual findings that contradicted classical physical laws. These findings suggested that there are other laws at work in the universe, operating on a deeper level than the one we know.

Parallel Universe

Spacetime

In the science of physics, spacetime is a mathematical model that combines space and time into a single construct called the spacetime continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of a fourth dimension that is of a different sort than the spatial dimensions.

The concept of spacetime combines space and time within a single coordinate system, typically with three spatial dimensions: length, width, height, and one temporal dimension: time. Dimensions are components of a coordinate grid typically used to locate a point in a certain defined "space" as, for example, on the globe by latitude and longitude. In spacetime, a coordinate grid that spans the 3+1 dimensions locates "events", so time is added as another dimension to the grid.

According to certain Euclidean space perceptions, the universe has three dimensions of space and one dimension of time. By combining space and time into a single manifold, scientists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.

In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space, because the rate at which time passes depends on an object's velocity relative to the speed of light and also on the strength of intense gravitational fields which can slow the passage of time.

Wormhole

A wormhole is hypothetical tunnel that connects two points in spacetime. This tunnel would be a shortcut through space and time in such a way that a trip through the wormhole could take much less time than a journey between the same starting and ending points in normal space. The ends of a wormhole could be intra-universe, that is to say that both exist in the same universe, or inter-universe, existing in different universes, and thus serve as a connecting passage between the two. Spacetime can be viewed as a 2D surface, and when 'folded' over, a wormhole bridge can be formed.

A wormhole has at least two mouths which are connected to a single throat or tube. If the wormhole is traversable, matter can 'travel' from one mouth to the other by passing through the throat. While there is no observational evidence for wormholes, spacetimes-containing wormholes are known to be valid solutions in general relativity.

The term wormhole was coined by the American theoretical physicist John Wheeler in 1957. However, the idea of wormholes had already been theorized in 1921 by the German mathematician Hermann Weyl in connection with his analysis of mass in terms of electromagnetic field energy.

Wormholes arise as solutions to the equations of Einstein's general theory of relativity. In fact, they crop up so readily in this context that some theorists are encouraged to think that real counterparts may eventually be found or fabricated and, perhaps, used for high-speed space travel and/or time travel. However, a known property of wormholes is that they are highly unstable and would probably collapse instantly if even the tiniest amount of matter, such as a single photon, attempted to pass through them.

Cooling Tower

A Cooling tower is a heat removal device used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in power platn, oil refineries, and chemical plants.

Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semi-conductor plants, and other industrial facilities. The circulation rate of cooling water in a typical 700 MW coal-fired power plant with a cooling tower amounts to about 315,000 U.S. gallons per minute (71,600 cubic metres an hour) and the circulating water requires a supply water make-up rate of perhaps 5 percent (i.e., 3,600 cubic metres an hour).

Chiller

A chiller is a machine that removes heat from a liquid via a vapor-compression. A vapor-compression water chiller comprises the 4 major components of the vapor-compression refrigeration cycle (compressor, evaporator, condenser, and some form of metering device). These machines can implement a variety of refrigerants. Absorption chillers utilize water as the refrigerant and rely on the strong affinity between the water and a lithium bromide solution to achieve a refrigeration effect. Most often, pure water is chilled, but this water may also contain a percentage of glycol and/or corrosion inhibitors; other fluids such as thin oils can be chilled as well.

Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional (CII) facilities. Water chillers can be either water cooled, air-cooled, or evaporatively cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Evaporatively cooled chillers offer efficiencies better than air cooled, but lower than water cooled. Water cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.

Air Cooled and Evaporatively Cooled chillers are usually intended for outdoor installation and operation. Air cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Evaporatively cooled machines are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air cooled machine. No remote cooling tower is typically required with either of these types of packaged air cooled or evaporatively cooled chillers.

Zeeman Effect

The Zeeman effect is the splitting of a spectral line into several components in the presence of a static magnetic field. It is analogous to the Stark effect, the splitting of a spectral line into several components in the presence of an electric field. The Zeeman effect is very important in applications such as nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, magnetic resonance imaging and Mössbauer spectroscopy. It may also be utilized to improve accuracy in Atomic absorption spectroscopy. When the spectral lines are absorption lines, the effect is called Inverse Zeeman effect. The Zeeman effect is named after the Dutch physicist Pieter Zeeman.

In most atoms, there exist several electronic configurations that have the same energy, so that transitions between different pairs of configurations correspond to a single spectral line. The presence of a magnetic field breaks the degeneracy, since it interacts in a different way with electrons with different quantum numbers, slightly modifying their energies. The result is that, where there were several configurations with the same energy, now there are different energies, which give rise to several very close spectral lines.

Lever

A lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to lift another object. This leverage is also termed mechanical advantage, and is one example of the principle of moments. A lever is one of the six simple machines.

A lever is a simple machine consisting of a bar supported at some stationary point along its length and used to overcome resistance at a second point by application of force at a third point. The stationary point of a lever is known as its fulcrum. The term lever is also applied to a projecting piece that is moved to operate or adjust inner machinery, such as a lever moved to the right or left to switch electric current on or off or to adjust the size of the opening of a shutter in a camera.

The lever is used for prying, as in the case of the crowbar, or for lifting. For example, the fulcrum is the point upon which a crowbar rests when used to lift or to pry loose some object; the effort is applied at the end farther from the fulcrum and is relatively small. The distance from the operator's hands to the fulcrum is known as the lever arm, or effort arm; the object being pried loose is the resisting force, or resistance; the object's distance from the fulcrum is the resistance arm. Levers in which the fulcrum is located between the effort and the resistance, as in the crowbar and the beam balance, are known as first-class levers. The fulcrum may also be located at one end of the lever, with the effort applied at the other end and the resistance in between; this type of lever, illustrated by the wheelbarrow and the nutcracker, is known as a second-class lever. The final possibility, known as a third-class lever, has the effort applied between the fulcrum and the resistance and is illustrated by various types of tongs.

Ampermeter

An ampermeter (or ammeter) is an instrument that measures electric current in amperes through a conductor. The ammeter is placed in series with the component through which current is to be measured, and is constructed with a low internal resistance in order to prevent the reduction of that current as it flows through the instrument itself. Ampere is the amount of electric charge per unit time. So, an ampermeter is an instrument for measuring electric current whose unit is the ampere.

An ampermeter uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The voltage drop across the coil is kept to a minimum to minimize resistance across the ammeter in any circuit into which it is inserted.

Electrode

An electrode is a conductor to establish electrical contact with a non-metalic part of a circuit. The word was coined by the scientist Michael Faraday from the Greek words elektron.

Transistor

A transistor is a three-terminal, semiconductor device commonly used to amplify electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much larger than the controlling (input) power, the transistor provides amplification of a signal.

This three terminal character of the transistor is what allows us to make an amplifier for electrical signals, like the one in our radio. With the three-terminal transistor we can also make an electric switch, which can be controlled by another electrical switch. By cascading these switches, switches that control switches that control switches, etc., we can build up very complicated logic circuits. These logic circuits can be built very compact on a silicon chip with 1,000,000 transistors per square centimeter. We can turn them on and off very rapidly by switching every 0.000000001 seconds. Such logic chips are at the heart of your personal computer and many other gadgets you use today.

In 1947, John Bardeen and Walter Brattain observed that when electrical contacts were applied to a crystal of germanium, the output power was larger than the input. William Shockley saw the potential in this and worked over the next few months greatly expanding the knowledge of semiconductors and is considered by many to be the 'father' of the transistor. The term was coined by John R. Pierce. They quickly made a few of these transistors and connected them with some other components to make an audio amplifier. This audio amplifier was shown to chief executives at Bell Telephone Company, who were very impressed that it didn't need time to warm up like the heaters in vacuum tube circuits. They immediately realized the power of this new technology.

Thermionic Emission

Thermionic emission is the flow of electrons from heated materials through a barrier into a vacuum. Emission of electrons or ions by substances that are highly heated, the charged particles being called thermions. The number of thermions emitted increases rapidly as the temperature of the substance rises. The heated material may be in the form of a metal filament or of some compound that coats and is heated by the filament. If the heated body carries a positive or negative charge, the thermions will be of the same charge. At temperatures below red heat, thermionic emission from uncharged bodies is chiefly positive; at higher temperatures it is negative. The thermionic phenomenon was discovered by Thomas A. Edison in 1883 when he was working on filaments for the electric light. Thermionic emission's most important practical application in electronics is in the electron tube, since it is the mechanism by which electrons are emitted from the cathode.

Diode

A diode is a two-terminal, semiconductor device which allows current to move through it in one direction, blocking current in the opposite direction. The most common kind of diode in modern circuit design is the semiconductor diode. It has two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property.

Vacuum Tube

A vacuum tube is a device used to amplify, switch, modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space. A vacuum tube is also called thermionic valve. Some special function vacuum tubes are filled with low-pressure gas: these are so-called soft valves (or tubes), as distinct from the hard vacuum type which have the internal gas pressure reduced as far as possible. Almost all depend on the thermal emission of electrons, hence thermionic.

Vacuum tubes played a key role in the development of electronic technology that drove the expansion and commercialization of radio broadcasting, television, radar, sound reproduction, large telephone networks, analog and digital computers, and industrial process control. For most purposes, the vacuum tube has been replaced by solid-state devices such as transistors and solid-state diodes. Solid-state devices last much longer, are smaller, more efficient, more reliable, and cheaper than equivalent vacuum tube devices. However, tubes are still used in specialized applications: for engineering reasons, as in high-power radio frequency transmitters.

A vacuum tube consists of electrodes in a vacuum in a insulating heat-resistant envelope. Many tubes have glass envelopes, though some types such as power tubes may have ceramic or metal envelopes. The electrodes are attached to leads which pass through the envelope via an airtight seal. On most tubes, the leads are designed to plug into a tube socket for easy replacement. The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air. When hot, the filament releases electrons into the vacuum: a process called thermionic emission. The resulting negatively charged cloud of electrons is called a space charge. These electrons will be drawn to a metal plate inside the envelope, if the plate is positively charged relative to the filament. The result is a flow of electrons from filament to plate.

Resistor

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. This device restricts the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

The primary characteristics of resistors are their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Practical resistors can be made of resistive wire, and various compounds and films, and they can be integrated into hybrid and printed circuits. Size, and position of leads are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power.

Oscilloscope

An oscilloscope is a type of electronic test equipment that allows signal voltages to be viewed, usually as a two-dimensional graph plotted as a function of time or of some other voltage. The oscilloscope is one of the most versatile and widely-used electronic instruments. An oscilloscope can measure the frequency, show distortion, and show the relative timing of two related signals. Oscilloscopes are used in the sciences, medicine, engineering, telecommunications, and industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as adjusting an automotive ignition system, or to display the waveform of the heartbeat.

The oscilloscope is basically a graph-displaying device - it draws a graph of an electrical signal. In most applications the graph shows how signals change over time: the vertical axis represents voltage and the horizontal axis represents time. The intensity or brightness of the display is sometimes called the Z axis. This simple graph can tell you many things about a signal.

Cathode Ray Tube

The cathode ray tube is a vacuum tube containing an electron gun, as a source of electrons, and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms, television pictures, radar targets and others. The cathode ray tube uses an evacuated glass envelope which is large, deep, heavy, and relatively fragile. Display technologies without these disadvantages, such as flat plasma screens, liquid crystal displays, DLP, OLED displays have replaced cathode ray tube in many applications and are becoming increasingly common as costs decline.

The earliest version of the cathode ray tube was invented by the German physicist Ferdinand Braun in 1897 and is also known as the 'Braun tube'. It was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen. The first version to use a hot cathode was developed by John B. Johnson, who gave his name to the term Johnson noise, and Harry Weiner Weinhart of Western Electric, and became a commercial product in 1922.

Electronic Circuit

An electronic circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. The electronic circuits may be physically constructed using any number of methods. Breadboards, perfboards or stripboards are common for testing new designs. Mass-produced circuits are typically built using a printed circuit board (PCB) that is used to mechanically support and electrically connect electronic components. Electronic circuits can display highly complex behaviors, even though they are governed by the same laws of physics as simpler circuits.

Oscillator

An electronic oscillator is an electronic device that produces a repetitive electronic signal, often a sine wave or a square wave. It works on the principles of oscillation, which is a periodic fluctuation between two things based on changes in energy. Computers, clocks, watches, radios, and metal detectors are among the many devices that use oscillators. A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform at a frequency below ≈200 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.

There are many types of electronic oscillators, but they all operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.

Relay

A relay is a simple electromechanical switch made of an electromagnet and a set of contacts that opens and closes under the control of another electrical circuit. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.

A simple electromagnetic relay is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a moveable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energised there is an air gap in the magnetic circuit.

Joule

a) A joule is a unit of electrical energy equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second.

b) A unit of energy equal to the work done when a force of one newton acts through a distance of one meter.

Gastric Juice

Gastric juice is a strong acidic liquid which is produced by the gastric glands in the lining of the stomach. It has a pH 1 to 3 in humans, which is close to being colourless. The hormone gastrin is released into the bloodstream and causes gastric glands to secrete gastric juice. The gastric juice main components are digestive enzymes pepsin and rennin (rennin found in babies), hydrochloric acid, and mucus.

Gastric juice secretion is stimulated by a number of hormones and chemical substances, by the presence of food in the stomach, and by a number of psychological factors, such as the smell of a favorite food. A decrease or total absence of gastric juice secretion may be a congenital abnormality or a concomitant of advanced age. Certain cells of the stomach lining secrete a substance known as intrinsic factor, which is necessary for the absorption of vitamin B 12 ; absence of this substance results in pernicious anemia, or B 12 deficiency.

Cardiac Sphincter

The cardiac sphincter is the junction orifice between the stomach and the esophagus. The cadiac sphincter has a muscular structure that relaxes to allow food to pass into the stomach but usually not letting it move back up into the Esophagus. This therefore prevents gastroesophageal reflux.

Esophagus

The esophagus is an organ that is part of the digestive tract and consists of a muscular tube through which food passes from the pharynx to the stomach. In humans the esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. The esophagus passes through a hole in the thoracic diaphragm called the esophageal hiatus. It is usually 25-30 cm long and is divided into three parts; the cervical, thoracic, and abdominal parts.

Food is pushed down the esophagus through a process called peristalsis. The esophagus is deeply lined with muscle that acts with peristaltic action to move swallowed food down to the stomach. Due to the fact that the esophagus lacks the mucus lining like that of the stomach, it can get irritated by stomach acid that passes the cardiac sphincter, which is the junction between the esophagus and the stomach.

Appendix

The human appendix is a blind ended narrow tube connected to the cecum, from which it develops embryologically. The cecum is a pouch-like structure located at the junction of the small intestine and the large intestine. The full name of this small tube that sticks out of the cecum is vermiform appendix. The term "vermiform" comes from Latin and means “worm-like in appearance.”

The appendix is located in the lower right quadrant of the abdomen, or more specifically, the right iliac fossa. It averages 10 cm in length, but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The human appendix is a vestigial structure which does absolutely nothing for the body. Given the appendix's propensity to cause death via infection, and the general good health of people who have had their appendix removed or who have a congenital absence of it, the appendix appears to have no function in the human body.

The Large Intestine

The large intestine is the last part of the digestive system. Its function is to absorb water from the remaining indigestible food matter, and then to pass this useless waste material from the body. It consists of the cecum and colon. The large intestine begins in the right iliac region of the pelvis, just at the right waist, where it is joined to the bottom end of the small intestine. From here it continues up the abdomen, then across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus. It is about 4.9 ft long, that is to say one-fifth of the whole length of the intestinal canal.

The large intestine takes 12–25 hours to finish up the remaining processes of the digestive system. Food is not broken down any further in this stage of digestion. The large intestine simply absorbs vitamins that are created by the bacteria inhabiting the colon. It is also very important in absorbing water and compacting the feces. It also stores fecal matter in the rectum until eliminated through the anus and thus is responsible for passing along solid waste.

Pyloric Stenosis

Pyloric stenosis is the narrowing of the pylorus, which is the passage between stomach and intestine. When an infant has pyloric stenosis, the muscles in the pylorus have become enlarged, choking in this passage, and preventing food from emptying out of the stomach. It causes severe vomiting in the first few months of life. It is uncertain whether there is a real congenital narrowing or whether there is a functional hypertrophy of the muscle which develops in the first few weeks of life.

Pyloric stenosis affects males more commonly than females, with firstborn males affected about four times as often, and there is a genetic predisposition for the disease. It is commonly associated with people of Jewish ancestry. Pyloric stenosis is more common in whites than Hispanics, African Americans, or Asians. The incidence is 2.4 per 1000 live births in whites, 1.8 in Hispanics, 0.7 in African Americans, and 0.6 in Asians. It is also less common amongst children of mixed race parents. Caucasian babies with blood type B or O are more likely than other types to be affected.

Some scientists believe that babies with pyloric stenosis lack receptors in the pyloric muscle that detect nitric oxide, a chemical in the body that tells the pylorus muscle to relax. As a result, the muscle is in a state of contraction almost continually, which causes it to become larger and thicker over time. It may take some time for this thickening to occur, which is why pyloric stenosis usually appears in babies a few weeks after birth.

Pyloric Sphincter

The pyloric sphincter, or valve, is a strong ring of smooth muscle at the end of the pyloric canal and lets food pass from the stomach to the duodenum. It receives sympathetic innervation from celiac ganglion. It is located at the base of the stomach.
.
The pyloric valve keeps the stomach shut at the far end so that it has a chance to digest proteins. Then it opens and allows the contents of the stomach, now called chyme, to pass through and enter the small intestine, whose first section is called duodenum and it does the majority of digestion and some absorption.

Pylorus

The pylorus is the cone-shaped opening between the stomach and the small intestine . It is divided into two parts: the pyloric antrum, which connects to the body of the stomach; and the pyloric canal, which connects to the duodenum (small intestine).

Peristalsis

Peristalsis is the rhythmic contraction of smooth muscles to push contents through the digestive tract. The word derives Greek peristaltikos, which means “to wrap around.” In much of the gastrointestinal tract, smooth muscles contract in sequence to produce a peristaltic wave which forces a ball of food along the gastrointestinal tract. This ball of food is called a bolus while in the esophagus and gastrointestinal tract, and chyme in the stomach. Peristaltic movement is initiated by circular smooth muscles contracting behind the chewed material to prevent it from moving back into the mouth, followed by a contraction of longitudinal smooth muscles which pushes the digested food forward.

Peristalsis begins just after food has been chewed into a bolus and swallowed down into the esophagus. Smooth muscles will contract behind the bolus to prevent it from being squeezed back onto the mouth, then rhythmic, unidirectional waves of contractions will work to rapidly force the food into the stomach. This process works in one direction only and its sole purpose is to move food from the mouth into the stomach.

In the esophagus, two types of peristalsis occur. First, there is a primary peristaltic wave. Once the bolus enters the esophagus during swallowing. The primary peristaltic wave forces the bolus down the esophagus and into the stomach in a wave lasting about 8-9 seconds. The wave travels down to the stomach even if the bolus of food descends at a greater rate than the wave itself, and will continue even if for some reason the bolus gets stuck further up the esophagus.

If the bolus gets stuck or moves slower than the primary peristaltic wave (as can happen when it is poorly lubricated), stretch receptors in the esophageal lining are stimulated and a local reflex response causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus, and these secondary waves will continue indefinitely until the bolus enters the stomach. During vomiting the propulsion of food up the esophagus and out the mouth comes from contraction of the abdominal muscles. Peristalsis does not reverse in the esophagus.

When the chyme has been processed and digested by the stomach, it is squeezed through the pyloric valve down into the small intestine. Once past the stomach a typical peristaltic wave will only last for a few seconds, traveling at only a few centimeters per second. Its primary purpose is to mix the chyme in the intestine rather than to move it forward in the intestine. Through this process of mixing and continued digestion and absorption of nutrients, the chyme gradually works its way through the small intestine to the large intestine.

As opposed to the more continuous peristalsis of the small intestines, fecal contents are propelled into the large intestine by periodic mass movements. These mass movements occur one to three times per day in the large intestines and colon, and help propel the contents from the large intestine through the colon to the rectum.

Cecum

The cecum or caecum, which means “blind” in Latin, is a pouch that marks the beginning of the large intestine. It is connected to the ascending colon of the large intestine and the ileum. The cecum is separated from the ileum by the ileocecal valve or Bauhin's valve. It is also separated from the colon by the cecocolic junction.

The cecum, as well as all the organs at this 'traffic junction' for the flow of waste - caecum, ileocecal valve and appendix - must be cleared of waste on a daily basis. In the squatting position, the right thigh, pressing against the lower abdomen on the right side of the body, 'squeezes' the caecum to force wastes upwards into the ascending colon and away from the appendix, ileocecal valve and small intestines. As a result of waste being pushed away and out of the caecum, the appendix would never be clogged with waste.

Ileum

The ileum is the final section of the small intestine. It follows the duodenum and jejunum, and is separated from the cecum by the ileocecal valve (ICV). In humans, the ileum is about 2-4 m long. It is neutral or slightly alkaline with a pH between 7 and 8. It absorves any remaining nutrients from the breakdown of protein.

The main function of the ileum is to absorb vitamin B12 and bile salts and whatever products of digestion were not absorbed by the jejunum. The wall itself is made up of folds, each of which has many tiny finger-like projections known as villi on its surface. In turn, the epithelial cells which line these villi possess even larger numbers of microvilli. Therefore the ileum has an extremely large surface area both for the attachment of enzyme molecules and for the absorption of products of digestion.

Jejunum

The Jejunum is the central part of the small intestine between the the duodenum and the ileum. The change from the duodenum to the jejunum is usually defined as the ligament of Treitz. The adult small intestine is about 6 meter long, and the jejunum forms a little less than half of the small intestine. The jejunum and the ileum are suspended by an extensive mesentery giving the bowel great mobility within the abdomen.

The inner surface of the jejunum, its mucous membrane, is covered in projections called villi, which increase the surface area of tissue available to absorb nutrients from the gut contents. The epithelial cells which line these villi possess even larger numbers of microvilli. The transport of nutrients across epithelial cells through the jejunum and ileum includes the passive transport of sugar fructose and the active transport of amino acids, small peptides, vitamins, and most glucose. The villi in the jejunum are much longer than in the duodenum or ileum.

Gut Flora

The gut flora are the bacteria that normally live in the digestive tract and can perform a number of useful functions for their hosts. Also known as the intestinal microflora, the gut flora is made up of about 100 trillion bacteria, that is to say about ten times the number of cells the average human body consists of. There's an estimate of about 500 different bacterial species in the intestine. The metabolic activity performed by these bacteria is equal to that of a virtual organ making the gut bacteria termed as a forgotten organ.

The relationship between gut flora and humans is a mutualistic, symbiotic relationship. These microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host such as biotin and vitamin K, and producing hormones to direct the host to store fats. However, in certain conditions, some species are thought to be capable of causing disease or increasing cancer risk for the host.

Although the acid in the stomach, as well as bile and pancreatic secretions, hinder colonization of most bacteria in the stomach and proximal small intestine, most of the gut flora are found in the distal small intestine and in the cecum and ascending colon. In the small intestine there are Gram-positive cocci (bacteria), while those in the colon are mostly Gram-negative. The first part of the colon is mostly responsible for fermenting carbohydrates, while the latter part mostly breaks down proteins and amino acids. Bacterial growth is rapid.

Chyme

Gastric chyme is the semiliquid substance found in the stomach and resulting from the partial digestion of food by the salivary enzyme amylase, the gastric enzyme pepsin, and hydrochloric acid. Secretion of hydrochloric acid by the stomach makes the chyme strongly acidic. The rhythmic muscular action of the stomach wall releases the chyme into the duodenum through the pyloric valve. In the duodenum (small intestine) it stimulates the release of secretin, a hormone that increases the flow of pancreatic juice as well as bile and intestinal juices. Chyme also stimulates the release of cholecystokinin, a hormone that primarily increases the flow of bile but also increases the proportion of digestive enzymes in the pancreatic juice.

Chyme has a pH of around 2 and emerged from the stomach very acidic. To raise its pH, the duodenum secretes cholecystokinin (CCK), which causes the gall bladder to contract, releasing alkaline bile into the duodenum.

Duodenum

The duodenum is the first and shortest part of the small intestine. It is a hollow tube between 10 and 12 inches long connecting the stomach to the jejunum. This first section of the small intestine begins with the duodenal bulb and ends at the ligament of Treitz. Most of the chemical digestion and the absorption of vitamins, minerals, and other nutrients take place in the duodenum. After foods mix with stomach acid , they move into the duodenum, where they mix with bile from the gallbladder, and digestive juices from the pancreas.

The duodenum is largely responsible for the breakdown of food in the small intestine, using enzymes. Brunner's glands, which secrete mucus, are found in the duodenum. The duodenum wall is composed of a very thin layer of cells that form the muscularis mucosae. The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. Secretin and cholecystokinin are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pyloris opens and releases gastric chyme into the duodenum for further digestion. These cause the liver and gall bladder to release bile, and the pancreas to release bicarbonate and digestive enzymes such as trypsin, lipase and amylase into the duodenum as they are needed.

Intestinal Villus

Intestinal villi are small finger-like projections that extend from the wall of the small intestine and increase the absorptive area of the intestinal wall. The villi have additional extensions called microvilli which protrude from epithelial cells lining villi. Digested nutrients such as sugar and amino acids seep through into the villi and are carried away by circulating blood.

In all humans, the villi and microvilli together increase intestinal absorptive surface area 30-fold and 600-fold, respectively, providing exceptionally efficient absorption of nutrients in the lumen. There are also enzymes on the surface for digestion. Villus capillaries collects amino acids and simple sugars taken up by the villi into the blood stream. Lymph capillary collects absorbed fatty acids, which are reconstructed into triglycerides, combined with cholesterol and amphipathic proteins to form chylomicrons, and are taken to the rest of the body through the Lymph fluid.

Small Intestine

The small intestine is the part of the gastrointestinal tract following the stomach, and is where the majority of digestion takes place. Although the small intestine is much longer than the large intestine, it is referred to as such due to its comparatively smaller diameter. On average, the diameter of the small intestine of an adult human measures approximately 2.5-3 cm, and the large intestine measures about 7.6 cm in diameter. In humans over 5 years old it is approximately 23 ft. The small intestine is divided into three structural parts: Duodenum 9.8 inch in length, Jejunum 8.2 ft, Ileum 11.5 ft.

The small intestine is covered in wrinkles called plicae circulares. From the plicae circulares project microscopic finger-like pieces of tissue called villi (Latin for shaggy hair). Each villus is covered in microvilli, which increase the surface area manyfold. Each villus contains a lacteal and capillaries. The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for secretion of enzymes and absorption of nutrients.

Food from the stomach is allowed into the duodenum by a muscle called pyloric sphincter. It is then pushed through the small intestine by a process of muscular-wavelike contractions called peristalsis. Most of the chemical digestion takes place in the small intestine. Chemical breakdown begun in the stomach is further broken down in the small intestine. Thus proteins are degraded into peptides by proteolytic enzymes such as trypsin and chymotrypsin. Then peptides are further broken down into amino acids. Lipids (fats) are broken down into fatty acids and glycerol by the pancreatic lipase. And carbohydrates such as starch are degraded into glucose (a simple form of sugar) by the pancreatic amylase.

The digested food passes now into the blood vessels in the wall of the intestine. This process is called absorption. The thousands of finger-like outgrowths called villi (s. vellus) in the inner walls of the small intestine increase the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels close to its surface. The surface of the villi absorbs the digested food materials. The absorbed substances are transported via the blood vessels to different organs of the body. Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions. Iron is absorbed in the duodenum. Vitamin B12 and bile salts are absorbed in the terminal ileum. Water and lipids are absorbed by passive diffusion throughout. Sodium is absorbed by active transport and glucose and amino acid co-transport. Fructose is absorbed by facilitated diffusion.

Stomach

The stomach is a sac-like, muscular organ which is involved in the second phase of digestion, following mastication. It is part of the digestive tract as it is located between the esophagus and the intestines. The word stomach is derived from the Latin stomachus, which derives from the Greek word stomachos. The human stomach is a muscular, elastic, pear-shaped bag, lying crosswise in the abdominal cavity beneath the diaphragm. It changes size and shape according to the position of the body and the amount of food inside. The stomach's capacity is about 1 liter in an adult.

The stomach has two smooth muscle valves, or sphincters, which keep the contents of the stomach contained. They are the esophageal sphincter that is found in the cardiac region and divides the tract above, and the Pyloric sphincter which divides the stomach from the small intestine. Food enters the stomach from the esophagus through the esophageal sphincter, which prevents food from passing back to the esophagus.

The stomach consists of five layers. Starting from the inside, the innermost layer is called the mucosa. Stomach acid and digestive juices are secreted by the mucosa layer. The next layer is called the submucosa, which is surrounded by the muscularis, a layer of muscle that moves and mixes the stomach contents. The next two layers, the subserosa and the serosa are the wrapping for the stomach. The serosa is the outermost layer of the stomach. The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) nervous plexuses (anterior gastric, posterior, superior and inferior, celiac and myenteric). These plexuses regulate both the secretory activity and the motor activity of the muscles.

Four major types of secretory epithelial cells cover the inner surface of the stomach and extend down into gastric pits and glands. Mucous cells secrete an alkaline mucus that protects the epithelium against shear stress and acid. Parietal cells secrete hydrochloric acid. Chief cells produce pepsin, a proteolytic enzyme. G cells secrete the hormone gastrin.

Pancreatic Adenocarcinoma

Pancreatic Adenocarcinoma is a malignant tumor of the pancreas. Pancreatic cancer is sometimes called a "silent disease" because pancreatic adenocarcinoma often does not cause symptoms in its early stages, but the later symptoms include: pain in the upper abdomen that typically radiates to the back and is relieved by leaning forward (seen in carcinoma of the body or tail of the pancreas); loss of appetite (anorexia), and/or nausea and vomiting; significant weight loss; painless jaundice (yellow skin/eyes, dark urine) related to bile duct obstruction (carcinoma of the head of the pancreas). This may also cause acholic stool and steatorrhea.

All of these symptoms can have multiple other causes. Therefore, pancreatic cancer is often not diagnosed until it is advanced.

Each year about 37,680 individuals in the United States are diagnosed with this condition, and 34,290 die from the disease. In Europe more than 60,000 are diagnosed each year. Depending on the extent of the tumor at the time of diagnosis, the prognosis is generally regarded as poor, with less than 5 percent of those diagnosed still alive five years after diagnosis, and complete remission still extremely rare. About 95 percent of pancreatic tumors are adenocarcinomas. The remaining 5 percent include other tumors of the exocrine pancreas, acinar cell cancers, and pancreatic neuroendocrine tumors. These tumors have a completely different diagnostic and therapeutic profile, and generally a more favorable prognosis.