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1. sour.
2. a substance that yields hydrogen ions in solution and from which hydrogen may be displaced by a metal to form a salt. For the various acids, see under the specific name, such as acetic acid. All acids react with bases to form salts and water (neutralization). Other properties of acids include a sour taste and the ability to cause certain dyes to undergo a color change. A common example of this is the ability of acids to change litmus paper from blue to red.

Inorganic acids are distinguished as binary or hydracids, and ternary or oxyacids; the former contain no oxygen; in the latter, the hydrogen is united to an electronegative element by oxygen. The hydracids are distinguished by the prefix hydro-. The names of acids end in -ic, except in the case in which there are two degrees of oxygenation. The acid containing the greater amount of oxygen has the termination -ic, the one having the lesser amount has the termination -ous. Acids with the termination -ic form the salts ending in -ate; those ending in -ous form the salts ending in -ite. The salts of hydracids end in -ide. These rules are demonstrated by the acids and salts: hydrochloric acid (HCl), sodium chloride (NaCl), sulfuric acid (H2SO4), sodium sulfate (Na2SO4), sulfurous acid (H2SO3), sodium sulfite (Na2SO3). Acids are called monobasic, dibasic, tribasic, and tetrabasic, respectively, when they contain one, two, three, or four replaceable hydrogen atoms.

The most common organic acids are carboxylic acids, containing the carboxyl group (-COOH); examples are acetic acid, citric acid, amino acids, and fatty acids. Their salts and esters end in -ate, e.g., ethyl acetate. Other organic acids are phenols and sulfonic acids.

Acids play a vital role in the chemical processes that are a normal part of the functions of the cells and tissues of the body. A stable balance between acids and bases in the body is essential to life. See also acid-base balance.
acid elution test air-dried blood smears are fixed in 80 per cent methanol and immersed in a pH 3.3 buffer; all hemoglobins are eluted except fetal hemoglobin (HbF), which is seen in red blood cells after staining.
inorganic acid an acid containing no carbon atoms.
acid perfusion test Bernstein test.
acid phosphatase a lysosomal enzyme that hydrolyzes phosphate esters liberating inorganic phosphate and has an optimal pH of about 5.0. Serum activity of the prostatic isoenzyme is greatly increased in metastatic cancer of the prostate and is used to monitor the course of the disease.


1. A compound yielding a hydrogen ion in a polar solvent (for example, in water); acids form salts by replacing all or part of the ionizable hydrogen with an electropositive element or radical.
2. Colloquially, any chemical compound that has a sour taste (given by the hydrogen ion).
3. Sour; sharp to the taste.
4. Relating to acid; giving an acid reaction. For individual acids not shown here, see specific names.
[L. acidus, sour]


/ac·id/ (as´id)
1. sour.
2. a chemical compound that dissociates in solution, releasing hydrogen ions and lowering the solution pH (a proton donor). An acidic solution has a pH below 7.0. Cf. base (3). For particular acids, see the specific names.

acid citrate dextrose  (ACD) anticoagulant citrate dextrose solution.
amino acid  see under amino.
carboxylic acid  any organic compound containing the carboxy group (—COOH), including amino and fatty acids.
fatty acid  see under F.
haloid acid  an acid which contains no oxygen in the molecule, but is composed of hydrogen and a halogen element.
hydroxy acid  an organic acid that contains an additional hydroxyl group.
inorganic acid  any acid containing no carbon atoms.
nucleic acid  see under N.
organic acid  an acid containing one or more carbon atoms; often specifically a carboxylic acid.


a. Any of a class of substances whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals to form salts.
b. A substance that yields hydrogen ions when dissolved in water.
c. A substance that can act as a proton donor.
d. A substance that can accept a pair of electrons to form a covalent bond.
1. Chemistry
a. Of, relating to, or containing an acid.
b. Having a high concentration of acid.
c. Having the characteristics of an acid.
a. Having a pH of less than 7.
b. Having a relatively high concentration of hydrogen ions.

ac′id·ly adv.
ac′id·ness n.


Etymology: L, acidus, sour
1 a compound that yields hydrogen ions when dissociated in aqueous solution (Arrhenius definition), acts as a hydrogen ion donor (Brønsted definition), or acts as an electron pair acceptor (Lewis definition). Acids turn blue litmus red, have a sour taste, and react with bases to form salts. Acids have chemical properties essentially opposite to those of bases. See also alkali base.
Usage notes: slang.
3 sour or bitter to the taste. acidify, v., acidic, adj.
Chemistry adjective Relating or referring to an acid, acidic
(1) A chemical that can accept a pair of electrons or donate a proton
(2) Any usually water-soluble compound that donates a hydrogen ion—H+—or proton in a chemical reaction, or can accept a pair of electrons and combine with metals to form salts
Drug slang LSD


Chemistry A chemical that can accept a pair of electrons or donate a proton adjective
1. Relating to an acid, acidic.
2. Sour in taste noun Any usually water-soluble compound that donates a hydrogen ion–H+ or proton in a chemical reaction, or can accept a pair of electrons and combine with metals to form salts. See Acetylsalicylic acid, Alpha-lipoic acid, Amino acid, Arachidonic acid, Azelaic acid, Benzoic acid, Betulinic acid, Bile acid, Binary acid, Cis fatty acid, Conjugated linoleic acid, Deoxyribonucleic acid, Decosaenoic acid, Delta-aminolevulinic acid, Dextromethorphan acetic acid, Diethylenetriaminepentaacetic acid, Dimethylxanthenone acetic acid, Domoic acid, DMSA acid, Eicosapentaenoic acid, Ellagic acid, Essential amino acid, Essential fatty acid, Excitatory amino acid, Fatty acid, acid, Free-form amino acid, Fibric acid, Folic acid, Formic acid, Gamma-linolenic acid, Glacial acetic acid, Homogentisic acid, Homovanillic acid, Hyaluronic acid, Hydrofluoric acid, 5-Hydroxyindole acetic acid, Hydrochloric acid, Ibotenic acid, Kainic acid, Lactic acid, Linoleic acid, Linolenic acid, Lipid-associated sialic acid, Methylmalonic acid, Mevalonic acid, n-3 fatty acid, Nalidixic acid, Nicotinic acid, Nitrilotriacetic acid, Nordihydroguaiaretic acid, Nucleic acid, Okadaic acid, Organic acid, Orotic acid, Oxolinic acid, Pangamic acid, Pantothenic acid, Paraaminobenzoic acid, Phosphoenolpyruvic acid, Phytanic acid, Picric acid, Polyunsaturated fatty acid, Retinoic acid, Ribonucleic acid, Saturated fatty acid, Uncoded amino acid, Uric acid. Cf Base Drug slang Popular for LSD, see there.


1. A compound yielding a hydrogen ion in a polar solvent (e.g., in water); acids form salts by replacing all or part of the ionizable hydrogen with an electropositive element or radical.
2. In popular language, any chemical compound that has a sharp or sour taste (given by the hydrogen ion).
3. Relating to acid; giving an acidic reaction.
4. Colloq. for lysergic acid diethylamide.
[L. acidus, sour]


(as'id) [L. acidus, sour]
1. Any substance that liberates hydrogen ions (protons) in solution; a hydrogen ion donor. An acid reacts with a metal to form a salt, neutralizes bases, and turns litmus paper red.
2. A substance that can accept a pair of electrons; a Lewis acid. See: alkali; base; indicator; Lewis acid; pH
3. A sour substance.
4. Slang term for lysergic acid diethylamide (LSD).

acetic acid

C2H4O2, the acid that gives the sour taste to vinegar. It is also used as a reagent. Glacial (highly purified) acetic acid contains at least 99.5% acetic acid by weight.
CAS # 64-19-7

acetoacetic acid

C4H6O3, a ketone body formed when fats are incompletely oxidized. It was formerly called acetylacetic acid. Synonym: diacetic acid; diacetic acid
CAS # 541-50-4

acetylacetic acid

See: acetoacetic acid

acetylsalicylic acid

Abbreviation: ASA
Aspirin (1).

acrylic acid

C3H4O2, a colorless corrosive acid used in making acrylic polymers and resins.
CAS # 79-10-7

adenylic acid

Adenosine monophosphate.

alpha-hydroxy acid

Abbreviation: AHA
Any of a class of water-soluble acids derived from fruit or milk, having a hydroxyl moiety in the first position in the molecule. AHAs are used in chemical peels and other skin care products to remove the outer layer of the epidermis. This chemical exfoliation is promoted for its cosmetic effects on wrinkled or sun-damaged skin.

alpha-linolenic acid

C18H30O2, an omega-3 fatty acid derived from plants, esp. seeds (canola oil, flaxseed, walnuts and pumpkins) and from some fish (salmon and mackerel).
CAS # 463-40-1

alpha-lipoic acid

C8H14O2S2, a natural coenzyme and antioxidant, used for short-term treatment of peripheral neuropathies.
CAS # 1200-22-2

amino acid

See: amino acid

aminoacetic acid


aminobenzoic acid

Para-aminobenzoic acid.

aminocaproic acid

C6H13NO2, a hemostatic drug. It is a specific antidote for an overdose of a fibrinolytic agent.
CAS # 60-32-2

aminoglutaric acid

Glutamic acid.

aminosalicylic acid

Para-aminosalicylic acid.

aminosuccinic acid

Aspartic acid.

arachidonic acid

C20H32O2, an omega-6 fatty acid formed by the action of enzymes on phospholipids in cell membranes. The acid is found in many foods. It is metabolized primarily by the cyclo-oxygenase or 5-lipoxygenase pathways to produce prostaglandins and leukotrienes, which are important mediators of inflammation. Corticosteroids inhibit formation of arachidonic acid from phospholipids when cell membranes are damaged. Nonsteroidal anti-inflammatory agents such as salicylates, indomethacin, and ibuprofen inhibit the synthesis of prostaglandins and leukotrienes.
CAS # 506-32-1

argininosuccinic acid

C10H18N4O6, a compound intermediate in the synthesis of arginine, formed from citrulline and aspartic acid.
CAS # 2387-71-5

aristolochic acid

C17H11NO7, an acid derived from Aristolochia, a genus of flowering plants, and used as an herbal remedy. It is promoted as an aphrodisiac, a weight loss agent, and an anticonvulsant.
CAS # 313-67-7


The acid is a known carcinogen, and its use has been associated with and may cause end-stage renal disease and cancers of the urinary tract that may occur many years after usage has stopped.

ascorbic acid

Vitamin C.

aspartic acid

C4H7NO4, a nonessential amino acid that is a product of pancreatic digestion. Synonym: aminosuccinic acid
CAS # 617-45-8

barbituric acid

C4H4N2O3, a crystalline acid from which phenobarbital and other barbiturates are derived.
CAS # 67-52-7

benzoic acid

C7H6O2, a white crystalline acid having a slight odor. It is used in keratolytic ointments and in food preservation. Saccharin is a derivative of this acid.
CAS # 65-85-0

bile acid

Any of the complex acids that occur as salts in bile, e.g., cholic, glycocholic, and taurocholic acids. They give bile its foamy character, are important in the digestion of fats in the intestine, and are reabsorbed from the intestine to be used again by the liver. See: enterohepatic circulation

binary acid

An acid containing hydrogen and one other element.

boric acid

H3BO3, a white crystalline acid that in water forms a very weak acid solution poisonous to plants and animals. It is soluble in water, alcohol, and glycerin. See: boric acid poisoning
CAS # 10043-35-3


Boric acid is toxic and should be used only rarely. It is particularly dangerous because it can be accidentally swallowed by children or used in food because of its resemblance to sugar.

butyric acid

C4H8O2, a viscous fatty acid with a rancid odor, derived from butter but rare in most fats. It is used in disinfectants, emulsifying agents, and pharmaceuticals.
CAS # 107-92-6

carbolic acid

Phenol (1).

carbonic acid

H2CO3, an acid formed when carbon dioxide is dissolved in water.
CAS # 463-79-6

carboxylic acid

Any acid containing the carboxyl group –COOH. The simplest examples are formic and acetic acids.

cell-free fetal nucleic acid

Free fetal nucleic acid.

cholic acid

C24H40O5, a bile acid formed in the liver by hydrolysis of other bile acids. It is formed from the breakdown of cholesterol and helps digest consumed fats.
CAS # 81-25-4

cinnamic acid

C9H8O2, an insoluble white powder derived from cinnamon. It is used as a flavoring agent in cooking and in the preparation of perfumes and medicines.
CAS # 140-10-3

citric acid

C6H8O7, an acid found naturally in citrus fruits or prepared synthetically. It acts as a sequestrant, helping to preserve food quality.
CAS # 77-92-9

conjugated linoleic acid

Abbreviation: CLA
Any of the isomers of linoleic acid effective against cancer, obesity, diabetes, and atheromata in laboratory rodents. CLAs have not been shown to have similar beneficial effects in humans.

cysteic acid

C3H7NO5S, an acid produced by the oxidation of cysteine. Further oxidation produces taurine.
CAS # 498-40-8

deoxycholic acid

C24H40O4, a crystalline acid found in bile.
CAS # 83-44-3

deoxyribonucleic acid

, desoxyribonucleic acid See: DNA

diacetic acid

Acetoacetic acid.

2,4-dichlorophenoxyacetic acid


p-dichlorosulfamoyl benzoicacid


4,8-dihydroxyquinaldic acid

Xanthurenic acid.

docosahexaenoic acid

, docosahexanoic Abbreviation: DHA
C22H32O2, an omega-3 fatty acid found in the oils of cold-water fish and in algae. DHA plays a role in the development of nerve cell membranes and is required for the normal growth and development of the infant brain. Lack of DHA has been linked to growing numbers of people suffering from depression.
CAS # 6217-54-5

domoic acid

C15H20NO6, a toxin that resembles glutamate, the main excitatory amino acid of the brain. When ingested, it may cause continuous seizures.
CAS # 14277-97-5

eicosapentaenoic acid

Abbreviation: EPA
C20H30O2, an omega-3 fatty acid found in fish oils, containing 20 carbons and five double bonds.
CAS # 10417-94-4

endogenous uric acid

Uric acid derived from purines undergoing metabolism from the nucleic acid of body tissues.

essential fatty acid

Abbreviation: EFA
A fatty acid (alpha-linoleic and linoleic) that is essential for health and must be present in the diet because it cannot be synthesized in the body. See: digestion

ethylenediaminetetraacetic acid

Abbreviation: EDTA
C10H16N2O8, a chelating agent that, in its calcium or sodium salts, is used to remove metallic ions such as lead and cadmium from the body and as a food preservative. See: chelation
CAS # 60-00-4

exogenous uric acid

Uric acid derived from purines from food made up of free purines and nucleic acids.
See: urate; uraturia

fatty acid

Any of numerous monobasic acids with the general formula CnH2n+1-COOH (an alkyl radical attached to a carboxyl group).

Fatty acids are insoluble in water. This insolubility would prevent their being absorbed from the intestines, but the action of bile salts on the fatty acids enable thems to be absorbed. Fatty acids include acetic, butyric, capric, caproic, caprylic, formic, lauric, myristic, palmitic, and stearic acids. Unsaturated fatty acids have one or more double or triple bonds in the carbon chain. They include those of the oleic series (oleic, tiglic, hypogeic, and palmitoleic) and the linoleic or linolic series (linoleic, linolenic, clupanodonic, arachidonic, hydrocarpic, and chaulmoogric). See: fat

folic acid

C19H19N7O6, a water-soluble B complex vitamin needed for DNA synthesis and amino acid metabolism. It is present in green leafy vegetables, beans, and yeast. It is used to treat megaloblastic and macrocytic anemias and to prevent neural tube defects (NTDs) and cardiovascular disease in adults. The U.S. Public Health Service recommends that all women of childbearing age who may become or are pregnant should consume 0.8 mg of folic acid daily to reduce their risk of having a child affected with spina bifida or other NTDs. See: neural tube defect Synonym: folate; vitamin B9
CAS # 59-30-3


Folic acid should not be used to treat pernicious anemia (a vitamin B12 deficiency) because it does not protect patients against the development of changes in the central nervous system that accompany this type of anemia.

folinic acid

C20H23N7O7, the active form of folic acid. It is used to counteract the effects of folic acid antagonists and to treat folic acid deficiency anemia.
CAS # 1492-18-8

formic acid

HCOOH, the first and strongest member of the monobasic fatty acid series. It occurs naturally in certain animal secretions, e.g., the sting of insects such as bees and ants, and in muscle, but it is also prepared synthetically.
CAS # 64-18-6

formiminoglutamic acid

C6N2O4H10, an intermediate product in the metabolism of histidine.
CAS # 816-90-0

free fatty acid

Abbreviation: FFA
The form in which a fatty acid leaves the cell to be transported for use in another part of the body. FFAs are not esterified and may be unbound (not bound to protein). In the plasma, the nonesterified fatty acids released immediately combine with albumin to form bound free fatty acids.

free fetal nucleic acid

Abbreviation: ffNA
Fetal RNA or DNA in blood or body fluids. It is used to determine the sex of the fetus (as in pregnancies in which X-linked inherited diseases are a concern) or to identify other genetically transmitted illnesses, e.g., trisomies. Synonym: cell-free fetal nucleic acid

fumaric acid

C4H4O4, one of the organic acids in the Krebs cycle. It is used as a substitute for tartaric acid in beverages and baking powders.
CAS # 110-17-8

fuming nitric acid

Concentrated nitric acid (more than 86% nitric acid) that emits toxic fumes that cause choking if inhaled.
See: fumes

gadolinium-diethylenetriamine pentaacetic acid

Abbreviation: Gd-DTPA
A radiographic contrast agent, used in magnetic resonance imaging to enhance the appearance of blood vessels.


Contrast agents containing gadolinium should not be given to patients with diminished renal function.
CAS # 86050-77-3

gallic acid

C6H2(OH)3COOH, a colorless crystalline acid. It occurs naturally as an excrescence on the twigs of trees, esp. oaks, as a reaction to the deposition of gall wasp eggs. It is used as a skin astringent and in the manufacture of writing inks and dyes.
CAS # 149-91-7

gamma-aminobutyric acid

Abbreviation: GABA
C4H9NO2, the principal inhibitory neurotransmitter of the brain.
CAS # 56-12-2

gamma-linolenic acid

Abbreviation: GLA
C18H30O2, an essential fatty acid promoted by alternative medicine practitioners as a treatment for skin and inflammatory disorders, cystic breast disease, and hyperlipidemia.
CAS # 506-26-3

glucuronic acid

CHO(CHOH)4COOH, an oxidation product of glucose that is present in the urine. Toxic products (salicylic acid, menthol, phenol) that have entered the body through the intestinal tract are detoxified in the liver by conjugation with glucuronic acid.
CAS # 6556-12-3

glutamic acid

HOOC·(CH2)2·CH(NH2)·COOH, an amino acid formed in protein hydrolysis and an excitatory neurotransmitter in the central nervous system. Synonym: aminoglutaric acid
CAS # 617-65-2

glyceric acid

CH2OH·CHOH·COOH, an intermediate product of the oxidation of fats.
CAS # 473-81-4

glycocholic acid

C26H43NO6, a bile acid that hydrolizes to glycine and cholic acid.
CAS # 475-31-0

glycolic acid

C2H4O3, an alpha-hydroxy acid derivative used to remove the outer layer of skin to rejuvenate its appearance.
CAS # 79-14-1

glyoxylic acid

C2H2O3, an acid produced by the action of glycine oxidase on glycine or sarcosine.
CAS # 298-12-4

hippuric acid

C6H5CONHCH2COOH, an acid formed and excreted by the kidneys. It is formed from the combination of benzoic acid and glycine. The synthesis takes place in the liver and, to a limited extent, in the kidneys.
CAS # 495-69-2

guanidoacetic acid

An acid formed in the liver, kidney, and other tissues. It is metabolized to form creatine.

hexafluorosilicic acid


homogentisic acid

C8H8O4, an intermediate product of tyrosine catabolism. It is found in the urine in alkaptonuria. Synonym: alkapton
CAS # 451-13-8

hyaluronic acid

Abbreviation: HA
(C14H21NO11)n, an acid mucopolysaccharide found in the extracellular matrix of connective tissue that acts as a binding and protective agent. It is found in synovial fluid and in the vitreous and aqueous humors of the eye. Patients with osteoarthritis have elevated serum levels of HA. Synonym: hyaluronan
CAS # 9004-61-9

hydriodic acid

HI, an acid used in solution in various forms of chemical analyses. Synonym: hydrogen iodide
CAS # 10034-85-2

hydrochloric acid

HCl, an inorganic acid normally present in gastric juice. It destroys fermenting bacteria that might cause intestinal tract disturbances.

CAS# 7647-01-0

hydrocyanic acid

HCN, a colorless, extremely poisonous, highly volatile acid that occurs naturally in plants but is also produced synthetically. It acts by preventing cellular respiration. Hydrocyanic acid is used in electroplating, fumigation, and in producing dyes, pigments, synthetic fibers, and plastic. Exposure of humans to 200 to 500 parts of hydrocyanic acid per 1,000,000 parts of air for 30 min is fatal. Synonym: hydrogen cyanide
CAS # 74-90-8

hydrofluoric acid

HF, a corrosive solution of hydrogen fluoride in water. It can be used in dentistry to etch composites and porcelain surfaces and is used industrially to etch glass. See: hydrogen fluoride


Exposure to the skin and aerodigestive tract causes severe burns with local necrosis and systemic manifestations resulting from disordered calcium and potassium metabolism. Treatments with calcium gluconate can be beneficial.
CAS # 7664-39-3

hydrosulfuric acid

Hydrogen sulfide.

hydroxy acid

Any of the acids containing one or more hydroxyl (–OH) groups in addition to the carboxyl (–COOH) group, e.g., lactic acid, CH3COHCOOH).

hydroxy-iminodiacetic acid

Abbreviation: HIDA
A chemical that, when bound to radioactive technetium, is used to demonstrate the formation and flow of bile.
See: HIDA scan

hydroxybutyric acid

C4H8O3, any of the acids present in the urine, esp. in diabetic ketoacidosis, when the conversion of fatty acids to ketones increases.

hydroxycitric acid

C6H8O8, an herbal extract promoted for the treatment of weight loss. Placebo-controlled studies have not found any benefit to the treatment.
CAS # 6205-14-7

hypochlorous acid

HClO, an acid used as a disinfectant, deodorant, and bleaching agent. It is usually used in the form of one of its salts.
CAS # 7790-92-3

imino acid

An acid formed as a result of oxidation of amino acids in the body.

inorganic acid

An acid containing no carbon atoms.
Synonym: mineral acid

iocetamic acid

C12H13I3N2O3, a radiopaque agent formerly used in cholecystography.
CAS # 16034-77-8

iopanoic acid

C11H12I3NO2 , a radiopaque contrast medium used in radiographic studies of the gallbladder.
CAS # 96-83-3

keto acid

Any organic acid containing the ketone CO (carbonyl radical).

lactic acid

C3H6O3, an organic acid formed in muscles during anaerobic cell respiration in strenuous exercise. It is also formed during anaerobic muscle activity when glucose cannot be changed to pyruvic acid in glycolysis. It contributes to muscle aches and fatigue. Synonym: lactacid
CAS # 50-21-5

levulinic acid

CH3COCH2CH2COOH, an acid formed when certain simple sugars are acted on by dilute hydrochloric acid.
CAS # 123-76-2

lignoceric acid

C24H48O2, a saturated, naturally occurring fatty acid present in certain foods, including peanuts. It is also found in wood tar, various cerebrosides, and in small amounts in most natural fats. The acid is also a by-product of lignin production.
CAS # 557-59-5

linoleic acid

C18H32O2, an omega-6 fatty acid found in vegetables, nuts, grains, seeds, fruits and their oils. Oils rich in linoleic acid include (in descending order) safflower, sunflower, corn, soybean and cottonseed.
CAS # 60-33-3

linolenic acid

C18H30O2, an omega-6 fatty acid, thought to be cardioprotective. It reduces the production of cytokines and down-regulates serum cell adhesion molecules thought to be intermediates in atherosclerosis.
CAS # 506-26-3

lithic acid

An obsolete term for uric acid.

lysergic acid

C16H16N2O2, a crystalline acid derived from ergot. Its derivative, lysergic acid diethylamide (LSD), is a potent hallucinogen. See: LSD
CAS # 82-58-6

lysophosphatidic acid

Abbreviation: LPA
C21H41O7P, an acid purified from the ascitic fluid of patients with ovarian cancer. LPA stimulates the growth of ovarian cancer and may be a useful screening test for the disease.
CAS # 22002-87-5

malic acid

C4H6O5, an acid found in sour fruits such as apples and apricots and active in the aerobic metabolism of carbohydrates.
CAS # 6915-15-7

malonic acid

C3H4O4, a dibasic acid formed by the oxidation of malic acid and active in the Krebs cycle in carbohydrate metabolism. Malonic acid is found in beets. Its inhibition of succinic dehydrogenase is the classic example of competitive inhibition.
CAS # 141-82-2

mandelic acid

C8H8O3, a colorless hydroxy acid. Its salt is used to treat urinary tract infections. Synonym: phenylglycolic acid
CAS # 90-64-2

mineral acid

Inorganic acid.

methacrylic acid

C4H6O2, a colorless acid used to make methyl methacrylate.

monounsaturated fatty acid

A fatty acid containing one double bond between carbon atoms. It is found in olive oil and is the predominant fat in the Mediterranean diet. It is thought to reduce low-density lipoprotein levels without affecting high-density lipoprotein levels.
See: Mediterranean diet

muriatic acid

A nontechnical term for hydrochloric acid.
CAS # 7647-01-0

n-3 fatty acid

Omega-3 fatty acid.

n-6 fatty acid

Omega-6 fatty acid.

nicotinic acid


nitric acid

HNO3, a colorless, poisonous, fuming corrosive acid, widely used in industry and in chemical laboratories.
CAS # 7697-37-2

nitrous acid

HNO2, a weak acid chemical reagent used in biological laboratories.
CAS # 7782-77-6

nonvolatile acid

An acid, such as lactic acid or sulfuric acid, that accumulates in the body as a result of digestion, disease, or metabolism. It cannot be excreted from the body by ventilation but must be excreted by organs other than the lungs, e.g., by acidification of the urine.
Enlarge picture

nucleic acid

Any of the high-molecular-weight molecules that carry the genetic information crucial to the replication of cells and the manufacturing of cellular proteins. They have a complex structure formed of sugars (pentoses), phosphoric acid, and nitrogen bases (purines and pyrimidines). Most important are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). See: illustration

octadecanoic acid

Stearic acid.

okadaic acid

C44H68O13, a toxic acid found in shellfish. The toxin is produced by oceanic phytoplankton consumed by filter-feeding marine animals such as clams, crabs, and mussels and is the cause of diarrheal shellfish poisoning. Ingestion of these shellfish by humans results in profuse watery diarrhea.
CAS # 78111-17-8

oleic acid

C18H34O2, a monounsaturated fatty acid found in most organic fats and oils.
CAS # 112-80-1

omega-3 fatty acid

, ?-3 fatty acid
Any of the long-chain polyunsaturated fatty acids found in the oils of some saltwater fish, and in canola, flaxseed, walnuts, and some vegetables. These acids include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Alpha-linolenic acid (found in flaxseed and chia) can be metabolically converted to omega-3 fatty acids in the body. People whose diets are rich in omega-3 fatty acids have a reduced incidence of cardiovascular disease. Synonym: n-3 fatty acid

omega-6 fatty acid

, ?-6 fatty acid
Any of the long-chain polyunsaturated fatty acids, such as linoleic acid and arachidonic acid, thought to influence cardiovascular and growth function when balanced with omega-3 fatty acids in eicosanoid production. Linoleic acids are derived from vegetable oils; arachidonic acids, from animal fats. Synonym: n-6 fatty acid

omega-9 fatty acid

, ?-9 fatty acid
Any of the nonessential unsaturated fatty acids that have a double carbon bond in the ninth position from the end of their fatty acid tail. They include oleic acid (present in olive oil), stearic acid, and erucic acid.

organic acid

An acid containing the carboxyl radical, –COOH. Organic acids include acetic acid, formic acid, lactic acid, and all fatty acids.

orotic acid

C5H4N2O4 , a crystalline acid occurring in milk. It is a precursor in the formation of pyrimidine nucleotides.
CAS # 65-86-1

osmic acid

Osmium tetroxide.

oxalic acid

C2H2O4, the simplest dibasic organic acid. Its potassium or calcium salts occur naturally in rhubarb, wood sorrel, and other plants. It is the strongest organic acid and is poisonous. When properly diluted, it removes ink or rust stains from cloth. It is used also as a reagent.
CAS # 144-62-7

oxaloacetic acid

, oxalacetic acid
C4H4O5, a product of carbohydrate metabolism resulting from oxidation of malic acid during the Krebs cycle. It may be derived from other sources.
CAS # 328-42-7

palmitic acid

C16H32O2, a saturated fatty acid occurring as esters in most natural fats and oils.
CAS # 57-10-3

pantothenic acid

C9H17NO5, an acid of the vitamin B complex, occurring naturally in yeast, liver, heart, salmon, eggs, and various grains. It is part of coenzyme A, which is necessary for the Krebs cycle and for conversion of amino acids and lipids to carbohydrates. Synonym: vitamin B5
CAS # 137-08-6

para-aminobenzoic acid

Abbreviation: PABA
NH2C6H4COOH, an acid of the vitamin B complex, used as a dietary supplement, an antirickettsial drug, a reagent, and a sunscreen agent. Synonym: aminobenzoic acid
CAS # 150-13-0

para-aminohippuric acid

Abbreviation: PAH, PAHA
C9H10N2O3, a derivative of aminobenzoic acid. The salt, para-aminohippurate, is used to test the excretory capacity of the renal tubules.
CAS # 61-78-9

para-aminosalicylic acid

Abbreviation: PAS, PASA
C7H7NO3, a white or nearly white, practically odorless powder that darkens when exposed to air or light. It is a second-line drug used to treat multidrug-resistant tuberculosis. Synonym: aminosalicylic acid
CAS # 65-49-6

pectic acid

C17H24O16, an acid derived from pectin by hydrolyzing its methyl ester group.

pentanoic acid

Valeric acid.

peptide nucleic acid

Abbreviation: PNA
A synthetic nucleic acid analog in which natural nucleotide bases are linked to a peptide-like backbone instead of the sugar-phosphate backbone found in DNA and RNA. PNA has numerous uses in gene regulation, splicing, and therapy; in hybridization; and as a molecular diagnostic assay.

perchloric acid

HClO4, a colorless unstable liquid compound. It is the highest oxygen-containing acid of chlorine, strong and dangerously corrosive.
CAS # 7601-90-3

phenylglycolic acid

Mandelic acid.

phosphoric acid

An acid formed by oxidation of phosphorus. The phosphoric acids are orthophosphoric acid, H3PO4; pyrophosphoric acid, H4P2O7; metaphosphoric acid, HPO3; and hypophosphoric acid, H4P2O6. The salts of these acids are phosphates. Orthophosphoric acid, a tribasic acid, is used as a 30% to 50% solution to etch enamel of teeth in preparation for bonding of resin dental restorations.
CAS # 7664-38-2

phosphorous acid

H3PO3, a crystalline acid formed when phosphorus is oxidized in moist air.
CAS # 13598-36-2

phytic acid

C6H18P6O24, a pale, water-soluble acid that is found in cereal grains and, if ingested, may interfere with the absorption of calcium and magnesium.
CAS # 83-86-3

picric acid

C6H2(NO2)3OH, a yellow crystalline powder that precipitates proteins and explodes when heated or charged. It is used as a dye and a reagent. Its salts are used in the Jaffé reaction (used to measure serum creatinine). Synonym: trinitrophenol
CAS # 88-89-1

poly DL lactic acid


polyglycolic acid

(C2H2O2)n, a polymer of glycolic acid anhydride units. It is used to manufacture surgical sutures, clips, and mesh.
CAS # 26009-03-0

polylactic acid


propionic acid

C3H6O2, a carboxylic acid present in sweat.
CAS # 79-09-4

4-pyridoxic acid

C8H9NO4, a crystalline acid that is the principal end product of pyridoxine metabolism, excreted in human urine.

pyruvic acid

C3H4O3, an organic acid that plays an important role in the Krebs cycle. It is an intermediate product in the metabolism of carbohydrates, fats, and amino acids. Its quantity in the blood and tissues increases in thiamine deficiency because thiamine is essential for its oxidation.
CAS # 127-17-3

quinic acid

C7H12O6, a crystalline acid present in some plants, including cinchona bark, and berries.
CAS # 77-95-2

retinoic acid

C20H28O2, a metabolite of vitamin A used in the treatment of cystic acne.
CAS # 302-79-4

ribonucleic acid

See: RNA

ricinoleic acid

C18H34O3, an unsaturated hydroxy acid making up about 80% of fatty acids in the glycerides of castor oil. It has a strong laxative action.
CAS # 141-22-0

salicylic acid

C7H6O3, a white crystalline acid derived from phenol used to make aspirin, as a preservative and flavoring agent, and in the topical treatment of some skin conditions such as warts and wrinkles. See: chemical peeling
CAS # 69-72-7

salicyluric acid

C9H9NO4, an acid found in the urine after ingestion of salicylic acid or its derivatives.

saturated fatty acid

A fatty acid in which the carbon atoms are linked to other carbon atoms by single bonds.
See: fatty acid; unsaturated fatty acid

silicic acid

Any of a family of acids containing silica, such as H2SiO3 (metasilicic acid), H2SiO4 (orthosilicic acid), or H2SiO7 (pyrosilicic acid). When silicic acid is precipitated, silica gel is obtained.
CAS # 10193-36-9

stearic acid

C18H36O2, a monobasic fatty acid occurring naturally in plants and animals. It is used in the manufacture of soap and pharmaceutical products such as glycerin suppositories. Synonym: octadecanoic acid
CAS # 57-11-4

succinic acid

C4H6O4, an intermediate in carbohydrate metabolism.
CAS # 110-15-6

sulfonic acid

Any of the organic compounds having the general formula SO2OH, derived from sulfuric acid by replacement of a hydrogen atom.

sulfosalicylic acid

C7H6O6S3, a crystalline acid soluble in water or alcohol. It is used as a reagent for precipitating proteins, as in testing for albumin in urine.
CAS # 97-05-2

sulfuric acid

H2SO4, a colorless, corrosive, oily, viscous acid prepared from sulfur dioxide and used in many industrial processes and in clinical laboratories. Industrial accidents involving sulfuric acid through contact with skin or inhalation of aerosols are common.
CAS # 7664-93-9

sulfurous acid

H2SO3, an inorganic acid and a powerful chemical reducing agent used commercially, esp. for as a bleach.
CAS # 7782-99-2

tannic acid

C76H52O46, a mixture of digallic acid esters of d(+) glucose prepared from oak galls and sumac. It yields gallic acid and glucose on hydrolysis.
CAS # 1401-55-4

tartaric acid

C4H6O6, an acid obtained from by-products of wine fermentation. It is widely used in industry in the manufacture of carbonated drinks, flavored gelatins, dyes, and metals. It is also used as a reagent. It is thought to be an allergen.
CAS # 526-83-0

taurocholic acid

C26H45NO7S, a bile acid that hydrolyzes to cholic acid and taurine.
CAS # 81-24-3

teichoic acid

Any of the polymers found in the cell walls of some gram-positive bacteria, such as the staphylococci.

tranexamic acid

C8H15NO2, an antifibrinolytic drug that has approx. 10 times the potency of and more sustained activity than aminocaproic acid. It is used to decrease bleeding time during surgical procedures. Loss of blood is decreased when this drug is used.
CAS # 1197-18-8

trans-fatty acid

The solid fat produced by heating liquid vegetable oils in the presence of hydrogen and certain metal catalysts. Partial hydrogenation changes some of the unsaturated bonds to saturated ones. The more trans-fatty acids in the diet, the higher the serum cholesterol and low-density lipoprotein cholesterol.

trichloroacetic acid

Abbreviation: TCA
A drug used as a caustic to destroy certain types of warts, condylomata, keratoses, and hyperplastic tissue.

2,4,5-trichlorophenoxyacetic acid


unsaturated fatty acid

An organic acid in which some of the carbon atoms are linked to other carbon atoms by double bonds, thus containing less than the maximum possible number of hydrogen atoms, e.g., unsaturated oleic and linoleic acids as compared with the saturated stearic acid. Polyunsaturated fatty acids include linoleic acid and alpha-linoleic acid.
See: fatty acid; saturated fatty acid
Enlarge picture

uric acid

C5H4N4O3, a crystalline acid occurring as an end product of purine metabolism. It is formed from purine bases derived from nucleic acids (DNA and RNA). It is a common constituent of urinary stones and gouty tophi. See: illustration
CAS # 69-93-2


Uric acid must be excreted because it cannot be metabolized. Uric acid output should be between 0.8 and 1g/day if the patient is on an ordinary diet.

Increased elimination is observed after ingestion of proteins and nitrogenous foods, after exercise, after administration of cytotoxic agents, and in gout and leukemia. Decreased elimination is observed in kidney failure, lead poisoning, and in those who eat a protein-free diet.

valeric acid

C5H10O2, an oily fatty acid having a distinctly disagreeable odor, existing in four isomeric. Synonym: pentanoic acid
CAS # 109-52-4

valproic acid

Abbreviation: VPA
C8H16O2, an acid used to treat seizure disorders.
CAS # 99-66-1

vanillylmandelic acid

, vanilmandelic acid Abbreviation: VMA
C9H10O5, a principal metabolic product of catecholamines. VMA makes up approx. 90% of the metabolites of the catecholamines epinephrine and norepinephrine and is secreted in the urine. People with pheochromocytoma produce excess amounts of catecholamines; therefore there are increased amounts of VMA in their urine.
CAS # 55-10-7

volatile acid

An acid produced from carbon dioxide (CO2). It can be excreted by the body by ventilation (colloquially, “blowing off CO2”).

xanthurenic acid

C10H7NO4, an acid excreted in the urine of pyridoxine-deficient animals after they have been fed tryptophan. Synonym: 4,8-dihydroxyquinaldic acid
CAS # 59-00-7


1. Any compound capable of releasing hydrogen ions when dissolved in water.
2. A solution with a hydrogen ion concentration greater than that of pure water.
3. Having a pH of less than 7. pH is the common logarithm of the reciprocal of the hydrogen ion concentration.


any chemical substance that acts as a proton donor. Acids dissolve in water with the formation of hydrogen ions which may be replaced by metals to form salts.


Common street name for LSD.


n a compound able to form hydrogen ions (H) when dissolved in aqueous solutions.
acid, alpha-linolenic,
n a polyunsaturated fatty acid found in the blood. Deficiencies and imbalances can affect blood pressure, blood cholesterol, premenstrual symptoms, and skin conditions.
acid, alpha-lipoic,
n a sulfurous antioxidant that is produced within the body as a constituent of multiple enzymatic systems and is also derived from food sources. Has been used to treat hypertension and as an adjunct to diabetes treatment and may benefit patients with cataracts or cardiovascular conditions. Also called
thioctic acid.
acid, arachidic (ar··ki·dik aˑ·sid),
n a saturated fatty acid that provides energy.
acid, arachidonic (ar··k·dˑ·nik aˑ·sid),
n an omega-6 polyunsaturated fatty acid prevalent in red meats and a key component of many metabolic processes.
acid, ascorbic,
n See vitamin C.
acid, azelaic (aˈ·z·lāˑ·ik aˑ·sid),
n a naturally occurring dicarboxylic acid commonly used as a topical treatment for acne.
acid, behenic (b·heˑ·nik aˑ·sid),
n a saturated fatty acid associated with degenerative neural diseases and some genetic disorders.
acid, capric (kaˑ·prik aˑ·sid),
n a saturated fatty acid that has been linked to multiple aryl-coenzyme and dehydrogenation disorders.
acid, caprylic (k·priˑ·lik aˑ·sid),
n a naturally occurring fatty acid used as an antifungal agent for treating candidiasis caused by the yeast
Candida albicans.
acid, carboxylic (kär·bkˑ·s·lik aˑ·sid),
n an organic compound that con-tains at least one carboxyl group; it is weaker than a mineral acid such as hydrochloric acid.
acid, conjugated linoleic,
n a mix-ture of fatty acids (specifically mixed isomers of linoleic acid) obtained through diet or supplementation. Claimed to be useful as a weight loss aid and as a treatment for adult-onset diabetes. No known precautions with this substance exist.
acid, dihomogammalinolenic (dīˈ·hōˈ·mō·gyaˈ·m·liˈ·n·lēˑ·nik aˑ·sid),
n a fatty acid necessary for proper cell and tissue functions.
acid, docosadienoic (dō·kōˈ·s·dīˈ·ē·nōˑ·ik aˑ·sid),
n omega-6 polyunsaturated fatty acid included in a typical fatty acid profile to study serum triglyceride analysis.
acid, docosahexaenoic (dōˈ·kōˈ·s·hek·s·ē·nōˑ·ik aˑ·sid),
n an unsaturated fatty acid important in early neurological development.
acid, docosapentaenoic (dōˈ·kōˈ·s·pen·t·ēˈ·nōˑ·ik aˑ·sid),
n an unsaturated fatty acid important in early neurological development.
acid, docosatetraenoic (dō·kōˈ·s·teˈ·tr·ē·nōˑ·ik aˑ·sid),
n omega-6 polyunsaturated fatty acid stored in adipose tissue and mobilized during fasting. High levels of this fatty acid in the blood are associated with obesity.
acid, eicosapentaenoic (īˈ·kōˈ·s·penˈ·t·ēˈ·nōˑ·ik aˑ·sid),
n fatty acid found in fish oils. Deficiency has been linked to arthritis, depression, heart disease, and high cholesterol.
acid, eicosatrenoic (īˈ·kō·saˈ·tr·nōˑ·ik aˑ·sid),
n an omega-3 series polyunsaturated fatty acid; represents less than 0.25% of serum phospholipid fatty acids in a normal individual.
Enlarge picture
Acid, eicosatrenoic.
acid, elaidic (ē·lāˑ·dik aˑ·sid),
n a trans-fatty acid found in hydrogenated oils. Elevated amounts have been linked to high cholesterol levels.
acid, erucic (i·rōōˑ·sik aˑ·sid),
n a fatty acid found in rapeseed (canola), mustard seed, and wallflower seed. This compound is linked to elevated levels of fatty acids and is being studied as a possible treatment for degenerative neurologic disorders. See also Lorenzo's oil.
acid, folic,
n See folate.
acid, gamma linolenic (gyaˑ·m li·n·lēˑ·nik aˑ·sid),
n an omega-6 polyunsaturated fatty acid found in black currant, borage, evening primrose oils, and hemp. It is a precursor of DGLA and arachidonic acid and is linked to reduced symptoms of rheumatoid arthritis and zinc deficiency but may also enhance tumor growth and formation if not supplemented by an omega-3 fatty acid.
acid, gamma-aminobutyric (gyaˈ· m-·mēˈ·nō·byōō·tirˑ·ik aˑ·sid),
n amino acid that serves as the governing neurotransmitter in the spinal cord and brain. Also present in the lungs, heart, kidneys, and some plants.
acid, heneicosanoic (heˈ·nā·ē·kōˈ· s·nōˑ·ik aˑ·sid),
n fatty acid formed from propionic acid under conditions of vitamin B12 deficiency.
acid, heptadecanoic (hepˈ·t·deˈ· k·nōˑ·ik aˑ·sid),
n colorless, crystalline fatty acid which accumulates because of a deficiency of vitamin B12. Also called
margaric acid.
acid, hexacosanoic (hekˈ·s·kōˈ·s·nōˑ·ik aˑ·sid),
n long-chain fatty acid whose elevated numbers in a fatty acid profile are associated with genetic disorders characteristic of sphingolipid accumulation. Also called
cerotic acid.
acid, hydroxycitric (hī·drōōkˑ·sē·si·trik aˑ·sid),
n an organic acid derived from the Malabar tamarind
(Garcinia cambogia) fruit and used in appetite suppression and weight loss. Also called
gorikapuli, hydroxycitrate, or
Malabar tamarind.
acid, lauric (lˑ·rik aˑ·sid),
n a medium-chain fatty acid, the levels of which have been shown to rise in fatty acid catabolic disorders known as multiple acyl–coenzyme A dehydrogenation disorders.
acid, lignoceric (lig·nō·seˑ·rik aˑ·sid),
n a long-chain fatty acid that has been linked to degenerative neural diseases and certain genetic disorders.
acid, linolenic (liˈ·nō·lēˑ·nik aˑ·sid),
n an essential omega-6 polyunsaturated fatty acid found in corn, safflower, and other oils. Deficiencies have been linked to a number of health problems, including behavioral difficulties, cardiovascular disease, hair loss, infections, kidney degeneration, liver degeneration, miscarriage, and sterility.
acid, lipoic (līˑ·pō·ik aˈ·sid),
n a vitamin-like antioxidant found in leafy greens, brewer's yeast, red meat, and organ meats, used intravenously to treat diabetic polyneuropathy and orally to treat autonomic neuropathy and for preventing diabetic cataracts. No known precautions exist, but caution is advised for patients who use insulin. Also called
alphalipoic acid or
thioctic acid.
acid, malic (maˑ·lik aˑ·sid),
n an organic acid involved in the Krebs cycle. Used for treating fibromyalgia. No known precautions exist. Also called
apple acid.
acid, myristic (m·riˑ·stik aˑ·sid),
n a medium-chain fatty acid that has been linked to fatty acid catabolic disorders known as multiple acylcoenzyme A dehydrogenation disorders.
acid, myristoleic (m·ri·stō·lēˑ·ik aˑ·sid),
n a mono-unsaturated fatty acid involved in maintaining membrane fluidity.
acid, nonadecanoic (n·n·de·k·nōˑ·ik aˑ·sid),
n an odd-numbered fatty acid that accumulates with deficiency of vitamin B12 and accumulates in the membrane lipids of neural tissue.
acid, oleic (ō·lāˑ·ik aˑ·sid),
n a mono-unsaturated fatty acid found in all fat-containing foods. Involved in maintaining membrane fluidity.
acid, palmitelaidic (päl·mi·t·lāˑ·dik aˑ·sid),
n a trans-fatty acid found in hydrogenated oils.
acid, palmitic (pal·miˑ·tik aˑ·sid),
n a saturated fatty acid converted into cholesterol by the liver. High levels have been linked to cardiovascular disease, atherosclerosis, and stroke.
acid, palmitoleic (pal·mi·t·lāˑ·ik aˑ·sid),
n a mono-unsaturated fatty acid involved in maintaining membrane fluidity.
acid, pentadecanoic (pen·t·de·k·nōˑ·ik aˑ·sid),
n an odd-numbered fatty acid that accumulates with deficiency of vitamin B12 and accumulates in the membrane lipids of neural tissue.
acid, phytic (fīˑ·tik aˑ·sid),
n dietary fiber found in cereals and legumes that has antioxidant and antitumor properties.
acid, p-aminobenzoic (a·mēˈ·nō·ben·zōˑ·ik aˑ·sid),
n commonly abbreviated as PAB or PABA, it is a substance essential for the absorption of folic acid in many organisms. It is used in topical sun-screen because it absorbs ultraviolet light.
acid, stearic (stē·arˑ·ik aˑ·sid),
n a saturated fatty acid that can be converted into cholesterol. High levels have been linked to atherosclerosis, and low levels may increase the growth or spread of tumors.
acid, tricosanoic (trī·kōˈ·s·nōˑ·ik aˑ·sid),
n fatty acid with odd number of carbon atoms which accumulates because of vitamin B12 deficiency.
acid, uric (yōōˑ·rik aˑ·sid),
n waste product of purine metabolism, high levels of which can be found in plasma. The kidneys produce the majority of uric acid in the body.
acid, usnic (usˑ·nik aˑ·sid),
n compound found in the lichen
Usnea barbata, which is used as an antibiotic.
acid, vaccenic (vak·senˑ·ik aˑ·sid),
n a crystalline unsaturated acid whose ratio to palmitoleic acid in a fatty acid profile may influence biotin needs.
acid profile, organic,
n an analysis of organic acids (other than amino acids) excreted in the urine, used to assess metabolic disorders and nutrient deficiencies.
acids, amino (·mēˑ·nōō aˑ·sidz), the 22 identified building blocks of proteins essential for growth and maintenance.
acids, branched-chain amino, a combination of three amino acids: leucine, isoleucine, and valine. It has been used for anorexia associa-ted with chronic illness, amyotrophic lateral sclerosis, tardive dyskinesia, and muscular dystrophy and to increase athletic performance. Precaution suggested for patients taking levodopa.
acids, essential fatty, fatty acids (structural components of larger, nutritional fat molecules) that cannot be synthesized by the body and that must be obtained through dietary sources. They are components of cell membranes, contribute to the development and function of the nervous system, are stored for energy, and are used in the synthesis of important biomolecules. The two main types of essential fatty acids are omega-3 and omega-6. See also acids, omega-3 fatty and acids, omega-6 fatty.
acids, long-chain fatty, fatty acids with a basic structure of 12 or more carbon atoms. Essential fatty acids are typically long-chain fatty acids. Certain disorders, including intestinal lymphangiectasia and short bowel syndrome, may interfere with the ability to absorb long-chain fatty acids. See also acids, essential fatty; acids, omega-3 fatty acids; and acids, omega-6 fatty.
acids, omega-3 fatty, essential fatty acids found in flaxseeds, pumpkin seeds, walnuts, salmon, trout, tuna, and other sources. Omega-3 fatty acids include alpha linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). See also Acid, alpha linolenic; acid, eicosapentaenoic; and acid, docosahexaenoic.
acids, omega-6 fatty, essential fatty acids found in many cooking oils, such as corn, soy, and sun-flower oils. Omega-6 fatty acids include linoleic acid, arachidonic acid, gamma linolenic acid, and dihomogamma linolenic acid.
acids, trans-fatty, a particular configuration of any of the unsaturated fats that have been hydrogenated. Hydrogenation can change a naturally occurring fatty acid from a
cis- to a
trans- configuration, which cannot be used by the body.
acids, unsaturated fatty,
n fatty acids in which the carbon atoms in the hydrocarbon chain are joined by double or triple bonds. Monounsaturated fatty acids have one double bond or triple bond, whereas polyunsaturated fatty acids have more than one double or triple bond. Diets rich in polyunsaturated fatty acids and low in saturated fatty acid levels are correlated with low levels of serum cholesterol. See also acids, omega-3 fatty; acids, omega-6 fatty; and polyunsaturated.


1. A compound yielding a hydrogen ion in a polar solvent; acids form salts by replacing all or part of the ionizable hydrogen with an electropositive element or radical.
2. Colloquially, any chemical compound that has a sour taste.
3. Sour; sharp to the taste.
4. Relating to acid; giving an acid reaction.
5. A substance with a pH between 0 and 7.
[L. acidus, sour]

acid (as´id),

n a chemical substance that, in an aqueous solution, undergoes dissociation with the formation of hydrogen ions; pH levels range from 0 to 6.9. See also pH and acidic. Opposite: base.
acid, acetic,
n the acid of vinegar, sometimes used as a solvent for the removal of calculus from a removable dental prosthesis. See also solvent.
acid, ascorbic,
acid, carbolic,
n See phenol.
acid, cevitamic,
acid conditioning,
n the use of acid (such as phosphoric acid) to prepare the tooth surface for bonding of dental adhesives or enamel sealants.
acid etchant,
n an application of phosphoric acid used to prepare enamel surfaces to aid enamel sealant placement.
acid etching,
n the process of treating the tooth enamel, generally with phosphoric acid, by removal of approximately 40 mm of enamel rod to provide retention for enamel sealant, restorative material, or orthodontic bracket.
acid, folic,
acid, hydroxypropionic
n See acid, lactic.
acid, lactic (hydroxypropionic acid),
n a monobasic acid, C3H6O3, formed as an end product in the intermediary metabolism of carbohydrates. The accumulation of lactic acid in the tissues is in part responsible for the lowering of pH levels during inflammatory states; that is, the drop in pH level is believed to increase bone loss level.
acid, nicotinic,
n 1. a vitamin of the B complex group and its vitamer, niacinamide, specific for the treatment of pellagra. Niacinamide functions as a constituent of coenzyme I (DPN) and coenzyme II (TPN). Nicotinic acid is found in lean meats, liver, yeast, milk, and leafy green vegetables.
n 2. an acid (C5H4N [COOH]) that forms part of the B complex group of vitamins. It acts as a cofactor in intermediary carbohydrate metabolism. It is a constituent of certain coenzymes that function in oxidative-reductive metabolic systems. With niacinamide, it is a pellagra-preventive factor. Also called
niacin, P.-P. factor, pyridine 3-carboxylic acid, vitamin P.-P.
acid, orthophosphoric
n See acid, phosphoric.
acid, pantothenic
n a vitamin of the B complex group, the importance of which has not been established. It is a constituent of coenzyme A.
acid phosphatase,
n an enzyme found in the kidneys, serum, semen, and prostate gland. It is elevated in serum blood levels in individuals with prostate cancer and in individuals who have recently experienced trauma.
acid, phosphoric (HPO, orthophosphoric acid),
n the principal ingredient of silicate and zinc phosphate cement liquids.
acid, pteroylglutamic,
acid salt,
n a salt containing one or more replaceable hydrogen ions.
acid, strong,
n an acid that is completely ionized in aqueous solution.


1. sour.
2. a molecule or ion with a tendency to give up a proton to the solvent according to Bronsted and Lowry theory.
All acids react with bases to form salts and water (neutralization). Other properties of acids include a sour taste and the ability to cause certain dyes to undergo a color change. A common example of this is the ability of acids to change litmus paper from blue to red.
Acids play a vital role in the chemical processes that are a normal part of the functions of the cells and tissues of the body. A stable balance between acids and bases in the body is essential to life. See also acidic, acid-base balance, and individual acids.

amino acid
any one of a class of organic compounds containing the amino and the carboxyl group, occurring naturally in plant and animal tissues and forming the chief constituents of protein. See also amino acid.
bile a's
steroid acids derived from cholesterol. See also bile acids.
acid excretion
blood buffers prevent a sudden change in pH of body fluids when they receive excess acid or alkali from absorption or metabolic processes. This temporary measure is supplemented by a mechanism for the excretion of hydrogen ions via the kidney in the form of dihydrogen phosphate and ammonium ions.
fatty acid
any monobasic aliphatic acid containing only carbon, hydrogen and oxygen. See also fatty acids.
acid hydrolases
major group of enzymes present in lysosomes.
inorganic acid
an acid containing no carbon atoms.
keto a's
compounds containing the groups CO (carbonyl) and COOH (carboxyl).
acid methyl green stain
stains protozoal nuclei a bright green and is recommended for the detection of Balantidium coli in fecal smears.
nucleic a's
substances that constitute the prosthetic groups of the nucleoproteins and contain phosphoric acid, sugars, and purine and pyrimidine bases. See also nucleic acids.
acid phosphatase
see acid phosphatase.
acid retention
retention of metabolic acids, including sulfates and phosphates, as a result of acute and chronic renal disease.

Patient discussion about acid

Q. Why should I take folic acid? I heard that it is recommended for women to take folic acid every day. Should I take it even if I am not pregnant?

A. Folic acid is a B vitamin promoted mainly as part of a healthy diet to reduce the risk of neural tube birth defects (such as spina bifida and anencephaly), some types of cancer, and heart disease. It has also been studied for use in Alzheimer's disease and in chronic fatigue syndrome. While evidence of its ability to reduce neural tube defects in infants (when taken by the mother before and during pregnancy) is fairly strong, its effects against other conditions are still under study.

Q. Why to take Folic Acid during pregnancy? I am in the beginning of my pregnancy and the Doctor told me to take Folic Acid every day, why?

A. Folic acid can reduce your risk of having a baby with a serious birth defect of the brain and spinal cord, called the “neural tube.” A baby with spina bifida, the most common neural tube defect, is born with a spine that is not closed. The exposed nerves are damaged, leaving the child with varying degrees of paralysis, incontinence, and sometimes mental retardation. Recommended daily dose of Folic acid is 600 mcg.

to read my article about that, feel free to visit :

Q. Which foods contain folic acid? I was told by my Doctor to take folic acid. Which foods are rich with folic acid so I can add them to my diet?

A. Folic acid is a B vitamin found in many vegetables, beans, fruits, whole grains, and in fortified breakfast cereals.

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