coagulation

(kōăg'yo͞olā`shən), the collecting into a mass of minute particles of a solid dispersed throughout a liquid (a sol), usually followed by the precipitation or separation of the solid mass from the liquid. The casein in milk is coagulated (curdled) by the addition of acetic acid or citric acid. The albumin in egg white is coagulated by heating. The clotting of blood is another example of coagulation. Coagulation usually involves a chemical reaction. Lyophobic particles (see colloidcolloid
[Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. The mixture is also called a colloidal system, colloidal solution, or colloidal dispersion.
..... Click the link for more information. ) lose their electric charge by reacting with oppositely charged particles. Lyophilic particles undergo a reaction that causes them to lose their solubility. In either case coagulation occurs. The formation of a gel by evaporation or cooling of a sol is usually called gelation rather than coagulation.

Coagulation

the cohesion of particles in a colloidal system upon collision during thermal (Brownian) movement, mixing, or directed motion in a force field. Coagulation produces aggregates —larger (secondary) particles consisting of masses of small (primary) particles. The primary particles in such masses are held together by the force of intermolecular interaction directly or through an interlayer of the surrounding (dispersion) medium. Coagulation results in progressive enlargement of the particles (increase in the size and mass of the aggregates) and a decrease in their number in the dispersion medium (liquid or gas).

A distinction is made between rapid and slow coagulation. In rapid coagulation, almost every collision of the particles is effective—that is, causes them to combine. In slow coagulation, only some of the colliding particles combine. In a liquid medium— for example, in the coagulation of sols—enlargement of the particles to a certain point (approximately 10^-4 cm in diameter) does not result in their precipitation or emersion. This is latent coagulation, in which the system retains its resistance to sedimentation. Further growth of the particles results in the formation of lumps or flakes (floccules) that are precipitated (coagulum or coagel) or accumulate in the form of a film on the surface; this is visible coagulation. In some cases a loose three-dimensional network (a coagulation structure) forms throughout the dispersion medium, and the system does not divide into layers. If colloidal particles (droplets of liquid or gas bubbles) are present, coagulation may end in their adhesion or coalescence.

Coagulatior is a spontaneous process, which according to the laws of thermodynamics is a consequence of the system’s tendency toward a state with lower free energy. However, such a conversion is difficult and sometimes virtually impossible to achieve if the system has aggregate stability—that is, the ability to resist enlargement (aggregation) of the particles. The electric charge and/or adsorptive-solvate layer on the surface of the particles, which prevents them from coming together, may provide protection against coagulation in such cases. Aggregate stability can be disrupted, for example, by an increase in temperature (thermocoagulation), mixing or shaking, the introduction of coagulants, or other external influences on the system. The lowest concentration of a substance, electrolyte, or nonelectrolyte that brings about coagulation in a system with a liquid dispersion medium is called the coagulation threshold. Polydisperse systems, in which the particles have different sizes, may exhibit orthokinetic coagulation, which is the adhesion of small particles to larger particles upon their precipitation or emersion. The adhesion of similar particles is called homocoagulation, adhesion of dissimilar particles, heterocoagulation or adagulation. Heterocoagulation often occurs when disperse systems of different compositions are mixed. Coagulation may take place in the absence of any external action on the colloid system (autocoagulation), as a result of physical or chemical changes that occur during aging. Coagulation is sometimes reversible. Under favorable conditions, particularly after the introduction of surface-active agents that reduce interphase surface energy and promote dispersion, the aggregates may break down into the primary particles (peptization), and the coagel may become a sol.

Coagulation plays an important role in many technological, biological, atmospheric, and geological processes. When biopolymers (proteins or nucleic acids) are heated or subjected to some other influence—for example, a change in pH—they coagulate. Coagulation phenomena are important in many biological disperse systems (for example, blood and lymph) because of some aspects of their aggregate stability. The purification of natural water and sewage from highly disperse mechanical impurities, control of air pollution by aerosols, separation of rubber from latex, and the production of butter and other foods are typical examples of practical uses of coagulation. Coagulation is undesirable during the preparation and storage of suspensions, emulsions, powders, and other disperse systems used in industry or at home.

REFERENCES

Nauka o kolloidakh, vol. 1. Edited by H. Kruyt. Moscow, 1955. (Translated from English.)
Voiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964.

L. A. SHITS

coagulation

[kō‚ag·yə′lā·shən] (chemistry) A separation or precipitation from a dispersed state of suspensoid particles resulting from their growth; may result from prolonged heating, addition of an electrolyte, or from a condensation reaction between solute and solvent; an example is the setting of a gel. (meteorology) agglomeration

coagulation

[ko-ag″u-la´shun] clotting.1. in surgery, the disruption of tissue by physical means to form an amorphous residuum, as in electrocoagulation" >electrocoagulation or hotocoagulation" >hotocoagulation.2. in colloid chemistry, solidification of a sol into a gelatinous mass.blood coagulation clotting.diffuse intravascular coagulation (disseminated intravascular coagulation (DIC)) see disseminated intravascular coagulation.coagulation factors factors essential to normal blood clotting, whose absence, diminution, or excess may lead to abnormality of the clotting. Twelve factors, commonly designated by Roman numerals, have been described (I–V and VII–XIII; VI is no longer considered to have a clotting function). (See table 6.)
Factor I is a high-molecular-weight plasma protein that is converted to fibrin through the action of thrombin; deficiency conditions are called afibrinogenemia and hypofibrinogenemia. Called also fibrinogen. Factor II is a glycoprotein present in the plasma that is converted into thrombin in the pathway of coagulation" >common pathway of coagulation; deficiency is called hypoprothrombinemia. Called also prothrombin. Factor III is involved in the pathway of coagulation" >extrinsic pathway of coagulation, activating factor X; called also tissue thromboplastin or factor.
Factor IV is calcium" >calcium, required in many stages of blood clotting. Factor V is a heat- and storage-labile material, present in plasma and not in serum and is involved in the intrinsic and pathways of coagulation" >extrinsic pathways of coagulation, causing the cleavage of prothrombin to the active thrombin. Deficiency causes parahemophilia. Called also accelerator globulin or factor and proaccelerin. Factor VI is no longer considered in the scheme of hemostasis, and hence is assigned neither a name nor a function.
Factor VII is a heat- and storage-stable material, present in serum and in plasma and participating in the pathway of coagulation" >extrinsic pathway of coagulation, acting with factor III to activate factor X. Deficiency, either hereditary or acquired (vitamin k deficiency), leads to hemorrhagic tendency. Called also proconvertin and serum prothrombin conversion accelerator (SPCA). Factor VIII is a relatively storage-labile material that participates in the pathway of coagulation" >intrinsic pathway of coagulation, acting as a cofactor in the activation of factor X. Deficiency, an X-linked recessive trait, results in hemophilia a (classical hemophilia). Called also antihemophilic factor (AHF) and antihemophilic globulin (AHG). Factor IX is a relatively storage-stable substance involved in the pathway of coagulation" >intrinsic pathway of coagulation, acting to activate factor X. Deficiency of this factor results in a hemorrhagic syndrome called hemophilia b (or Christmas disease), which is similar to classical hemophilia A. It is treated with purified preparations of the factor, derived from human plasma or recombinant, or with complex" >factor IX complex. Called also plasma thromboplastin component (PTC) and antihemophilic factor B.
Factor X is a heat-labile material with some storage stability, which is involved in both intrinsic and pathways of coagulation" >extrinsic pathways of coagulation, uniting them to begin the pathway" >common pathway. Once activated, it complexes with calcium, phospholipid, and activated factor V to form prothrombinase, which cleaves and activates prothrombin to thrombin. Called also Stuart or Stuart-Prower factor. Factor XI is a stable factor involved in the pathway of coagulation" >intrinsic pathway of coagulation, activating factor IX. Deficiency results in hemophilia c. Called also plasma thromboplastin antecedent (PTA) and antihemophilic factor C. Factor XII is a stable factor activated by contact with glass or other foreign substances, which initiates coagulation through the pathway" >intrinsic pathway by activating factor XI; called also Hageman factor. Factor XIII is a factor that polymerizes fibrin monomers, enabling fibrin to form a firm blood clot. Deficiency causes a clinical hemorrhagic diathesis. Called also fibrin-stabilizing factor.

co·ag·u·la·tion

(kō'ag-yū-lā'shŭn), 1. Clotting; the process of changing from a liquid to a solid, said especially of blood (that is, blood coagulation). In vertebrates, blood coagulation is a result of cascade regulation from fibrin. 2. A clot or coagulum. 3. Transformation of a sol into a gel or semisolid mass, for example, the coagulation of the white of an egg by means of boiling. In any colloidal suspension, the disperse phase is greatly reduced via coagulation, thereby leading to a complete or partial separation of the coagulant; usually an irreversible phenomenon unless the basic nature of the substance is chemically altered.

coagulation

Hematology Clot formation Surgery The physical disruption of tissue to form an amorphous residuum, as in electrocoagulation and photocoagulation. See Coagulopathy, Interstitial laser coagulation.

co·ag·u·la·tion

(kō-ag'yū-lā'shŭn) 1. Clotting; the process by which a liquid, especially blood, changes from a liquid to a solid. 2. A clot or coagulum. 3. Transformation of a solution into a gel or semisolid mass.

coagulation

the separation or precipitation of suspended particles from a dispersed state.

Coagulation

The entire process of blood clotting.Mentioned in: Fibrin Split Products, Partial Thromboplastin Time

co·ag·u·la·tion

(kō-ag'yū-lā'shŭn) 1. Clotting; the process of changing from a liquid to a solid, said especially of blood (i.e., blood coagulation). 2. A clot or coagulum.

coagulation

co·ag·u·late

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coagulation

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Coagulation

REFERENCES

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Synonyms for coagulation

noun the process of forming semisolid lumps in a liquid

Synonyms

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