Home » Pharmaceutical Glossary » Glossary of Terms - A

Acclimatization
The biological process whereby an organism adapts to a new environment. One example is the process of developing microorganisms that degrade toxic wastes in the environment.

Accommodation Schedule
Defines all areas that can influence unit operations required for manufacturing, and relationships and flows between them.

Account Policy
Specifies how passwords must be defined and employed for all user accounts on a system. It specifically addresses the issues of password aging, password uniqueness, and locking a user account because of invalid logon attempts. CFR 21 Part 11 mandates technical controls in these areas specifically.

Acid
A compound of an electronegative element or radical with hydrogen; it form salts by replacing all or part of the hydrogen with an electropositive element or radical. Or, a hydrogen-containing substance that when dissolved in water dissociates to produce one or more hydrogen ions (H+).

Acid Feed
Injection of an acid into a liquid stream to make it less alkaline (pH adjustment).

Action Point
A value set to identify when a parameter has drifted outside the operating range (Acceptance Criteria). A documented response is usually required.

Activated Carbon
Material used to adsorb organic impurities from water. Derived from wood, lignite, pulp-mill char, blood, etc. The source material is initially charred at high temperature to convert it to carbon. The carbon is then "activated" by oxidation from exposure to high temperature steam. It comes in granular or powdered form.

Active Immunity
The formation of an antibody that can be stimulated by infection or vaccination.

Active Ingredient
Any component that is intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body of man or other animals. The term includes those components that may undergo chemical change in the manufacture of the drug product and are present in the drug product in a modified form intended to furnish the specified activity or effect.

Active Pharmaceutical Ingredient

Active Site
The region of a protein molecule that binds the specific substrate and chemically modifies it into the new product (in an enzyme) or interacts with it (in a receptor).

Active Transport
Energy-requiring transport of a solution across a membrane in the direction of increasing concentration.

Actual Yield
The quantity that is actually produced at any appropriate phase of manufacture, processing, or packaging of a particular drug product.

Adenine (A)
A purine base, 6-aminopurine, occurring in RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) and as a component of adenosine triphosphate.

ADR
see: Adverse Drug Reaction

Adsorption
Adhesion of the molecules of a gas, liquid or dissolved substance to a surface because of chemical or electrical attraction - typically accomplished with granular activated carbon to remove dissolved organics and chlorine. The attachment of charged particles to the chemically active groups on the surface and in the pores of an ion exchanger.

Adventitious Agents
Acquired, sporadic, accidental contaminants.

Adverse Agents
Undesired effects or toxicity due to exposure (often but not limited to a drug or medical device).

Adverse Drug Reaction (ADR)
An undesirable effect that may be caused by a study drug.

Advisory Alarm
An alarm indicating a drift of a monitored parameter toward an out-of-spec condition. It is advisory in that no GMP violation has occurred, and is used to advise corrective action before an action alarm can happen.

Aerobe
An organism that can live and grow only in the presence of oxygen.
1. Facultative aerobe: one which normally thrives in the absence of oxygen, but which may acquire the faculty of living in the presence of oxygen.
2. Obligate aerobe: one that cannot live without air.

Aerobia
The plural of aerobe.

Aerobic
Living in air.

Aerobic Bacteria
Bacteria capable of growing in the presence of Oxygen.

Aerobion
see: Aerobe

Aerosol
A product that is dispensed by a propellant from a metal can up to a maximum size of 33.8 fluid ounces (1000 mL) or a glass or plastic bottle up to a size of 4 fluid ounces (118.3 mL), other than a rim-vented container.

Aerosol
A gaseous suspension of fine (100µm or smaller in size) solid or liquid particles.

Aerosol Photometer
Light-scattering mass concentration indicating instrument with a threshold sensitivity of at least 10 to the negative third power microgram per liter for 0.3µm diameter DOP (Dioctyl Phthalate) concentrations over a range of 10 to the fifth power times the threshold sensitivity. Photometers may include hand-held remote meter probes that can scan for airborne contaminants in HEPA filters, in penetrations around frames, seals and plenums, and in hoods and work stations.

AES
see: Auger Electron Spectroscopy

Agar
A complex mixture of polysaccharides obtained from marine red algae, used as an emulsion stabilizer in foods, as a sizing in fabrics, as a gelling agent and as a solid substrate or media for the laboratory culture of microorganisms. Agar melts at 100ºC and when cooled below 44ºC forms a stiff and transparent gel. Microorganisms are seeded and grown on the surface of the gel.

Agarose
A highly purified form of agar.

Agarose Gel Electrophoresis
A method used to separate, identify, and purify molecules of different molecular weight and/or structure. It is specifically applied to the separation of protein or DNA fragments where it is rapid, simple, and accurate, and the separated molecules can be visualized directly by staining with dyes. The electrophoretic migration rate of molecules through agarose gel is dependent on the following parameters:
1. Molecular size: molecules pass through the gel at rates that are inversely proportional to the log of their molecular weight.
2. Agarose concentration: a molecule of a given size migrates at different rates through gels containing different concentrations of agarose.
3. Molecular conformation: a molecule of the same molecular weight but of a different conformation will migrate at different rates. Generally, closed circular or globular forms will migrate faster than linear forms.
4. Electric current: at low voltages the rate of migration is proportional to the voltage, but as the voltage is increased the rate of migration of high molecular weight fragments is increased differentially.

Agene
Nitrogen Trichloride (NCl3).

Agglomerate
Suspended solids clustered together to form larger clumps or masses that are easier to remove by filtration or settling.

Agglutination
The sticking together of insoluble antigens such as bacteria, viruses or erythrocytes by a particular antibody. Agglutination assays are used to type human blood before a transfusion.

AHF (Antihemophilic Factor)
In the clotting of blood it is also known as Factor VIII.

Airborne Particulate Cleanliness Classes
Statistically allowable number of particles equal to, or larger than 0.5µm in size per cubic foot of air. According to ISO 14644-1, a classification number, N, shall designate airborne particulate cleanliness.

Air Change Rate
The number of times the total air volume of a defined space is replaced in a given unit of time. This is computed by dividing the total volume of the subject space (in cubic feet) into the total volume of air exhausted from (or supplied to) the space per unit of time.

Air Cleaners
Filtration systems that may be freestanding or installed in a ceiling or wall to remove contaminants such as bacteria, viruses, and dust from the air. Air cleaners may incorporate HEPA filters.

Airflow Visualization
Using chemical smoke or fog to visualize flow patterns in a cleanroom or clean space.

Air-Lift Bioreactor
A reactor in which the source of agitation is air sparged upwards through a draft tube - most widely used for cell culture applications and monoclonal antibody production.

Airlock
A room or space designed to act as a means of segregating areas of different air classification or quality. It may contain a method to remove particulate contamination from clean room garments as personnel pass through, and usually includes HEPA filtered air supply and interlocking doors. Airlocks pressure will "float" between those of the spaces being protected. With all doors closed, the airlock pressure will be somewhere between that of the highest adjoining room and that of the lowest adjoining room as air flows through it from room to room. "Ventilated airlocks" are in neutral ducted air balance (supply CFM = return CFM).

Air Velocity Meters/Monitors
Meters to measure and indicate the force and speed of airflow. Meters may use a variety of probes for measuring near HEPA filters and at right angles. Monitors check and record air velocity.

Alarms
Audible or visual signals used to warn of unacceptable conditions at monitored sites. They may be buzzers, horns, speakers, bells, or warning lights. They can be Advisory, Alert, or Action alarms. The first two are for operation and maintenance information, to alert of abnormal situations that do not compromise product SISPQ. The Action alarm is for GMP records, indicating that product SISPQ may have been compromised, but Alert alarms are also usually recorded.

Albumin
Commonly, the white of egg is a simple protein widely distributed throughout the tissues and fluid of plants and animals. Soluble in pure water it is also precipitable from a solution by mineral acids, and coagulable by heat in acid or neutral solution.

Albuminoid
Resembling albumin, a simple protein present in horny and cartilaginous tissues, insoluble in neutral solvents. Keratin, elastin, and collagen are albuminoids.

Alert Point
Used in determining when a parameter is drifting toward extremes of the operating range.

Aliquot
Of, pertaining to, or designating an exact divisor or factor of a quantity, specially of an integer. To divide out a sample to multiple containers for multiple analytical tests.

Alkalinity
An expression of the total amount of basic anions (hydroxyl groups) present in a solution. In water analysis, it also represents the presence of carbonate, bicarbonate, and occasionally borate, silicate, and phosphate salts that react to produce hydroxyl groups. Bicarbonate and carbonate ions are expected to be in most waters. Hydroxide may occur in water that has been softened by the lime soda process or has been in contact with fresh concrete. Alkalinity furnishes a guide in choosing appropriate treatment of either raw water or plant effluents.

Allantoic Fluid
The clear white portion of an egg. In influenza vaccine manufacturing, the virus is propagated in the embryonic chick and sloughed into the allantoic fluid that is harvested to produce the vaccine.

Allele
Alternative form of a genetic locus; a single allele for each locus is inherited separately from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes)

Allergenic Extract
An extract in a solvent of a substance that causes an allergic reaction. They are relative crude drugs by contemporary standards and are manufactured by specialty companies and in some cases, by a practicing allergist. Also, allergenic extracts are generally difficult to filter since they most frequently are extracts of natural substances such as foods, house dust, animal hair, etc.

Alum
Aluminum sulfate, commonly added during municipal water treatment to cause insoluble colloids to coalesce into larger particles that can be removed by settling.

Alzheimer's Disease
A disease that causes memory loss, personality changes, dementia and, ultimately, death. Not all cases are inherited, but genes have been found for familial forms of Alzheimer's disease.

Ambient
The normal environment conditions such as temperature, relative humidity, or room pressure of a particular area under consideration.

Ames Test
A simple bacterial test for carcinogens.

Amine
A substance that may be derived from ammonia by the replacement of one or more of the hydrogen atoms by hydrocarbon radicals.

Amino Acids
Any of a group of twenty hydrocarbon molecules (containing the radical group NH2) linked together in various combinations to form proteins in living things. Synthesized by living cells or obtained as essential components of the diet of human and animals, these twenty amino acids are divided into four (4) groups on the basis of their side-chain properties:
1. Neutral, hydrophobic side chains,
2. Neutral, hydrophilic side chains,
3. Acid, hydrophilic side chains,
4. Basic, hydrophilic side chains.

In addition to the twenty common amino acids there are less common derivatives (e.g. hydroxyproline, found in collagen) formed by the modification of a common amino acid.
Ampholyte
Amphoteric electrolyte. Electrolyte that can either give up or take on a hydrogen ion and can thus behave as either an acid or a base.

Amphoteric
Having two opposite characteristics.

Ampicillin
An antibiotic widely used in clinical treatment and rDNA research. It is a derivative of penicillin, which kills bacteria by interfering with the synthesis of the cell wall.

Amplification
An increase in the number of copies of a specific DNA fragment; can be In Vivo or In Vitro.

Amplification
The production of additional copies of a chromosomal sequence, found as either intrachromosomal or extrachromosomal DNA.

Ampoule or Ampule
A small glass vial sealed after filling and one of the earliest devices developed for safe storage of sterile injectable unit.

Amyotrophic Lateral Sclerosis
An inherited, fatal degenerative nerve disorder, also known as Lou Gehrig's disease.

Anabolism
The intracellular process involved in the synthesis of more complex compounds than those involved in catabolism (for example, glucose to glycogen) and requires energy.

Anaerobe
A microorganism that thrives best, or only, when deprived of oxygen.
1. Facultative anaerobe: one able to grow in the presence or absence of free oxygen.
2. Obligate or obligatory anaerobe: one that will grow only in the absence of free oxygen.

Anaerobic
Relating to an anaerobe.

Anaerobic Bacteria
Bacteria capable of growing in the absence of Oxygen.

Analog
Pertaining to data that consists of continuously variable physical qualities.

Analytical Data Interchange (ANDI)
A generic file format. It was common practice before CFR 21 Part 11 to save information from analytical instruments in this file format. The disadvantage now is that the approach does not allow replaying of data on a different system to yield the same result.

Analytical Method
Small scale process used to characterize and/or separate a mixture, a compound, or an unknown material into its constituent parts or elements.

Ancillary Material
Material used in preparing drugs that does not become a component of the drug (e.g. steam, air, N2, DI water).

ANDI

Anemometer
A device that measures air speed.

Angstrom (?)
A unit of length equal to one hundred-millionth of a centimeter (one ten-thousandth of a micron) used especially to specify radiation wavelengths.

Anion
A negatively charged particle or ion.

Anion Exchange Resin
An ion exchange material that removes anions from solution by exchanging them with hydroxyl ions.

Anneal
The process by which the complementary base pairs in DNA strands combine.

Annealing
A treatment process for steel in which the metal is heated and held at a suitable temperature and then cooled at a suitable rate for the purpose of reducing hardness, improving machinability, facilitating cold working, producing a desired microstructure, or obtaining desired mechanical, physical, or other properties.

Antibiotic
An organic substance of microbial origin (usually mold or actinomycete bacteria) that is either toxic or growth inhibiting for other organisms. Also with the advent of synthetic methods of production, a substance produced by a microorganism or a similar substance (produced wholly or partly by chemical synthesis) which, in low concentrations, inhibits the growth of other microorganisms. Penicillin, tetracycline, and erythromycin are examples of antibiotics.

Antibody
A modified protein molecule present in the blood serum or plasma (and other body fluids), whose activity is associated chiefly with gamma globulin. Produced by the immune system in response to exposure to a foreign substance, it is the body's protective mechanism against infection and disease. An antibody is characterized by a structure complementary to the foreign substance, the antigen that provokes its formation, and is thus capable of binding specifically to the foreign substance to neutralize it.

Antigen
Any of various foreign substances such as bacteria, viruses, endotoxins, exotoxins, foreign proteins, pollen, and vaccines, whose entry into an organism induces an immune response (antibody production, lymphokine production, or both) directed specifically against that molecule. Response may be demonstrated as an increased reaction, such as hypersensitivity (usually protein or a complex of protein and polysaccharide, or occasionally a polysaccharide of high molecular weight), a circulating antibody that reacts with the antigen, or some degree of immunity to infectious disease if the antigen was a microorganism or its products.

Anti-interferon
An antibody to an interferon. Used for the purification of interferons.

Antiseptic
Acting against sepsis. An antiseptic agent is one that has been formulated for use on living tissue such as mucous membranes or skin to prevent or inhibit growth or action of organisms. Antiseptics should not be used to decontaminate inanimate objects.

Antiserum
The blood serum obtained from an animal after has been immunized with a particular antigen. It contains antibodies specific for that antigen as well as antibodies specific for any other antigens with which the animal has previously been immunized.

Antistatic
Reducing static electric charges by retaining enough moisture to provide electrical conduction.

Antistatic Cleaners
Liquid cleaners that enhance surface conductivity of cleanroom tabletops, workstations, and other surfaces.

Antitoxin
An antibody that is capable of neutralizing the specific toxin that stimulated its production in the body. Antitoxins are produced in animals for medical purposes by injection of a toxin or toxoid, with the resulting serum being used to counteract the toxin in other individuals.

API (Active Pharmaceutical Ingredient)
Also called Drug Substance. Any substance or mixture of substances intended to be used in the manufacture of a drug (medicinal) product and that when used in the production of a drug becomes an active ingredient of the drug product. Such substances are intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure and function of the body.

API Starting Material
A material used in the production of an API which is itself or is incorporated as a significant structural fragment into the structure of the API. A starting material may be an article of commerce, a material purchased from one or more suppliers under contract or commercial agreement, or it may be produced in-house. Starting materials are normally of defined chemical properties and structure.

Apoenzyme
The protein moiety of an enzyme - determines the specifity of the enzyme reaction.

Application Software
Any executable program developed or modified specially for customer applications.

Appropriated login or Impersonation
Someone using the authorization code, usually user ID and password of another person to secure access to network resources for which he or she does not have privileges or authorization. Can be intentional or not. CFR 21 Part 11 mandates technical controls that prevent this.

Aquifer
An underground layer of permeable rock, sand, or gravel that contains water for wells or springs.

Arithmetic Average Roughness (Ra)
The arithmetic average height of roughness component irregularities from the mean line measured within the sample length (L). This measurement conforms to ANSI/ASME B46.1 "Surface Texture - Surface Roughness, Waviness and Lay". Ra (formerly known as AA or Arithmetic Average in the U.S., and CLA Centerline Average in the U.K.) is usually expressed in microinches (µin), and performed by moving a stylus or profilometer in a straight line along the surface. A consistent and measurable surface finish can be specified for a desired roughness i.e., 9-11 microinch.

"As-Built" Cleanroom
ISO 14644-1 defines the "as built" occupancy state as "condition where the installation is complete with all services connected and functioning but with no production equipment, materials, or personnel present".

Ascomycetes
A family of fungi marked by long spore-containing cells. Form sexual spores called ascospores, which are contained within a sac (a capsule structure). Ergot, truffles, some molds of the genera Neurospora and Aspergillus, and yeasts belong to this category.

Asepsis
A condition in which living pathogenic (causing or capable of causing disease) organisms are absent.

Aseptic
Marked by or relating to asepsis.

Aseptic Processing
Processing conditions designed to achieve a sterile product.

Aseptic Processing Area
Area in which sterile product is formulated, filled into containers, and sealed.

Aseptic Transfer (in Isolators)
The key issue in all contained aseptic environments. Aseptic transfer is essential for change parts, components, and even product to enter and exit an isolator system without sterility challenges. There are an increasing number of ways to make an aseptic transfer. The following is a brief list of some of the key techniques:
1. Alpha Beta Systems Double Door Systems: also called RTPs (Rapid Transfer Ports) and HCT (High Containment Transfer). When mated, the two ports act as one door, protecting the internal and external environments.
2. Alpha Beta Dry Heat Sterilized: similar to Alpha Beta port with the additional safeguard of a heat sterilized seal.
3. UV and Pulsed Light: light sterilization/sanitization. Sterilizing the system by making use of a wide spectrum of light within the transfer chamber.
4. One Shot Systems: basically, two halves coming together. Similar to an Alpha Beta port but simpler, cheaper, and capable of only a single connection.
5. Heat Welded Bag Systems: passed in or passed out using a continuous polyethylene liner which is heat sealed and cut to maintain the integrity of the internal and external environments.
6. Steam Sterilized: the liquid component or powder path is clean steam sterilized after connection and prior to transfer.
7. Autoclave/Depyrogenation/Dryheat: pass through for batch. Use of conventional autoclave to sterilize a canister provided with an Alpha Beta port and filters to allow the passage of steam and safe aspiration on cooling. Depyrogenation/Dryheat uses dry heat to sterilize and at sufficient temperature depyrogenate components, typically glassware, in a batch oven
8. Depyrogenation Tunnel: standard volume glassware entry. Depyrogenation/Dry heat uses dry heat to sterilize and at sufficient temperature to depyrogenate components, typically glassware, in a tunnel allowing continuous input.

ASME Bioprocessing Equipment (BPE- 1997)
An American National Standard that covers, either directly or by reference, requirements for materials, design, fabrication, examination, inspection, testing, certification (for pressure systems), and pressure relief (for pressure systems) of vessels and piping for bioprocessing systems, including sterility and cleanability (Part SD), dimensions and tolerances (Part DT), surface finish requirements (Part SF), material joining (Part MJ), and equipment seals (Part SG) for the bioprocessing systems in which the pressure vessels and associated piping are involved. This Bioprocessing Equipment (BPE) Standard does not address all aspects of these activities, and those aspects that are not specifically addressed should not be considered prohibited.
Requirements of this Standard apply to:
1. All parts that contact the product, raw materials, and/or product intermediates during manufacturing, process development, or scale-up.
2. All equipment or systems that are critical part of product manufacture, such as Water For Injection (WFI), clean steam, ultrafiltration, intermediate product storage, and centrifuges. ASME/ANSI B31 Code for Pressure Piping
A number of individually published Sections, each an American National Standard. Rules for each Section reflect the kinds of piping installations considered during its development, as follows:
1. B31.1 Power Piping: piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems.
2. B31.3 Process Piping: piping typically found in petroleum refineries, chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants, and related processing plants and terminals. Certain piping within a facility may be subject to other codes and standards, including but not limited to: (a) ANSI Z223.1 National Fuel Gas Code: piping for fuel gas from the point of delivery to the connection of each fuel utilization device. (b) NFPA Fire Protection Standards: fire protection systems using water, carbon dioxide, halon, foam, dry chemical, and wet chemicals. (c) NFPA 99 Health Care Facilities: medical and laboratory gas systems. (d) Building and plumbing codes, as applicable, for potable hot and cold water, and for sewer and drain systems.
3. B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids: piping transporting products that are predominately liquids between plants and terminals and within terminals, pumping, regulating, and metering stations.
4. B31.5 Refrigeration Piping: piping for refrigerants and secondary coolants.
5. B31.8 Gas Transportation and Distribution Piping Systems: piping transporting products that are predominately gas between sources and terminals, including compressor, regulating, and metering stations; gas gathering pipelines.
6. B31.9 Building Services Piping: piping typically found in industrial, institutional, commercial, and public buildings, and in multi-unit residences, which does not require the range of sizes, pressures, and temperatures covered in B31.1.
7. B31.11 Slurry Transportation Piping Systems: piping transporting aqueous slurries between plants and terminals and within terminals, pumping, and regulating stations.

Assay
A technique (test) for measuring a biological response or for determining characteristics such as composition, purity, activity, and weight.

Assimilation
The formation of cellular material utilizing small food molecules and energy.

Atmospheric Tank (Fire Code)
A storage tank designed to operate at pressures from atmospheric through 0.5 pounds per square inch (psig) (3.4 kPa).

Atomic Absorption Spectrophotometry
A highly sensitive instrumental technique for identifying and measuring metals in water.

At Rest
HVAC room condition when unmanned, and without machinery operating. Previously called "static condition".

"At-Rest" Cleanroom
ISO 14644-1 defines "at rest" occupancy state as "condition where the installation is complete with equipment installed and operating in a manner agreed upon by the customer and supplier, but with no personnel present".
European Community (EC) defines "at rest" state as "the condition where the installation is complete with production equipment installed and operating but with no operating personnel present". The Medicines Inspectorate, however, further clarifies, "It should normally be taken to mean that ventilation systems are operating and other equipment is present in an operational condition but not in use".

Audit Comment
A feature of the audit trail that aids both originator and reviewer in understanding why the originator performed a specific action. CFR 21 Part 11 does not require entering the reason for a record change, but some predicate rules (such as GLPs) do expect an explanation. It is important that the user interface for entering audit comments prevents users from changing the audit trail itself.

Audit Trail
A computer-generated and time-stamped record of who did what, when. CFR 21 Part 11 requires audit trails to be generated independently of operators. An audit trail must capture all activities related to creating, modifying, and destroying records on a system.

Auger Electron Spectroscopy (AES)
An alternative surface analysis that can detect all elements with an atomic number greater than that of helium with the additional ability to analyze sub micron-diameter features. It is not as quantitative as ESCA and cannot determine the chemical state of an element. The primary advantage of Auger is that when combined with etching, a chemical depth profile can be measured rapidly and can image the distribution on the surface of spatial limitation resolution of 100 to 1,000 angstroms (depending on the equipment capability).

Austenite
A face-centered cubic crystal with high solubility for carbon (about 2%); an allotropic form of iron resulting from steel being heated above the transformation temperature.

Autegoneous Weld
A weld made by fusion of the base material without the addition of filler.

Authentication
The process of identifying a person, system, or company sufficiently to allow access to a system or part of a system.

Authentication Mechanisms
Also known as authority checks, or authorized signers are mechanisms distinct from authorization that grants or denies access to a network resource, authentication programs are used by system administrators to establish and verify as conclusively as possible that a person logging in to the network is who he or she claims to be. FDA says that "authority checks" are to "ensure that only authorized individuals can use the system, electronically sign a record, access the operation or computer system, input or output device, alter a record, or perform operations".

Autoclave
An apparatus into which moist heat (steam) under pressure is introduced to sterilize or decontaminate materials placed within (e.g. filter assemblies, glassware, etc.). Steam pressure is maintained for pre-specified times and then allowed to exhaust. There are two types of autoclaves:
1. Gravity displacement autoclave: this type of autoclave operates at 121ºC. Steam enters at the top of the loaded inner chamber, displacing the air below through a discharge outlet.
2. Vacuum autoclave: this type of autoclave can operate with a reduced sterilization cycle time. The air is pumped out of the loaded chamber before it is filled with steam.

Auto Immune Disease
A disease in which the body produces an immunogenic response against self-antigens. In some cases, predominantly one organ is affected (e.g. hemolytic anemia and chronic thyroiditis); in others, the disease process is diffused through many tissues (e.g. SLE (Systemic Lupus Erythematosis)).

Automated System
Any facility system or piece of equipment that is controlled with limited or no manual intervention.

Automatic Welding
Welding with equipment that performs the welding operation without adjustment of the controls by a welding operator. The equipment may or may not perform the loading and unloading of the work.

Autoradiography
A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis.

Autosome
A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes.

Autotrophs
One of two categories in which microorganisms are classified on the basis of their carbon source. Autotrophs use carbon dioxide as a carbon source.