coagulation

(redirected from Coagulation cascade)
Also found in: Dictionary, Thesaurus, Medical.
Related to Coagulation cascade: Coagulation factors

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)
References in periodicals archive ?
The coagulation cascade sustains a prothrombotic state when not actively being modulated by the anticoagulant pathways as a result of activation of TF pathways.
Second, triggers leading to thrombus formation may involve stimulation of monocytes in the blood that lead to activation of factor X, an important enzyme in the coagulation cascade. Thus, the physiological process related to inflammation may also be a factor in eventual development of clot formation (Frank et al., 2001).
Furthermore, estrogen levels have been connected to thrombin generation, a central molecule in the coagulation cascade in postmenopausal women [94].
Thrombin is the final mediator in the coagulation cascade that facilitates the conversion of fibrinogen to fibrin (Figure 1).
According to some other studies bleeding manifestations are seen in 76% and 87% of patients with DIC.3 Bleeding manifestations may occur as a single clinical phenomenon or may be part of a complex derangement of the coagulation cascade due to DIC in gram negative sepsis.13
The coagulation cascade is possibly activated because the inflammatory cascade stimulates tissue factor (TF) expression, attenuates fibrinolysis by stimulating the release of plasminogen activator inhibitors (PAI), and finally causes fibrin deposition in the airspaces and lung microvasculature (Levi and Ten Cate 1999; Abraham 2000; Ware et al.
The coagulation cascade (also called Limulus Enzyme Cascade) can be triggered by endotoxins, or alternatively by [beta]-glucans, which are short-chain polysaccharides found in the cell walls of yeasts and molds.
In addition to coagulation cascade activation, inflammatory response plays a role in thrombus formation via production of microparticles (MPs) that carry cell-specific molecules--proteins such as galectins (6).
Plasma hemostasis is a series of reactions known as the coagulation cascade, that is, a series of enzymatic reactions that ends in the formation of a fibrin protein fiber mesh (Vavilova et al., 2011; Butchart et al., 2002).
Fibrin sealants imitate the coagulation cascade, generating a strong fibrin clot.
The coagulation cascade is part of a series of events that leads to haemostasis after a vascular injury.
Blood clots form in the coagulation cascade and then fibrin--the mesh-like fibers that bind a blood clot together--is deposited in the clot.