Clot Types

Compared at equal concentrations, a fibrin clot is considerably more rigid than a gel of even a relatively undegraded gelatin from 

Rigidities of fibrin clots plotted against pH, at thrombin concentration 4 unit/cc., and ionic strength 0.30. Fibrinogen concentrations in g./ liter 1, 23.4 2, 11.7 3, 5.8 4, 2.0. From Ferry and Morrison (1947a). 

Logarithm of rigpdity at pH 6.8 plotted against logarithm of fibrinogen concentration. Thrombin co n centra-tions in unit/cc. , 0.2 , 1.0 O, 4.0. From Ferry and Morrison (1947a). 

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Recently, a superior therapy has been approved for use by the federal government tissue-type plasminogen activator (tPA). This naturally occurring enzyme dissolves blood clots as part of the normal healing process. By administering relatively large quantities of it, clot breakdown time can be shortened from about a week to under an hour. 

Three types of thrombi or clots are distinguished. All three contain fibrin in various proportions. 

A17. Aznar, J., Estelles, A., Breto, M., Espana, F., and Aids, T., Euglobulin clot lysis induced by tissue-type plasminogen activator is reduced in subjects with increased levels of lipopro-tein(a). Thromb. Res. 66, 569-582 (1992). 

Chimeric Antibodies The first generation is the chimeric antibodies (chimeric comes from the word Chimera, a Greek mythology beast made of three animals a lion, a snake, and a goat). This type of antibody consists of both murine and human parts. The murine Fv fragments are retained and linked to the Fc fragment of human IgG. An example of the chimeric antibody is ReoPro, which prevents blood clots by binding to a receptor on platelets. 

Bone marrow is the spongy tissue inside the cavities of our bones. Bone marrow stem cells grow and divide into the various types of blood cells white blood cells (leukocytes) that fight infection, red blood cells (erythrocytes) that transport oxygen, and platelets that are the agents for clotting. 

In addition to erythrocytes, blood contains white blood cells, called leukocytes, of several types, and platelets, also called thrombocytes, which control blood clotting. Hematopoiesis (from the Greek, haimo, for blood, and poiein for to make ) is the process by which the elements of the blood are formed. The marrow of bone contains so-called stem cells which are immature predecessors of these three types of blood cells. Chemicals that are toxic to bone marrow can lead to anemia (decreased levels of erythrocytes), leukopenia (decreased numbers of leukocytes), or thrombocytopenia. Pancytopenia, a severe form of poisoning, refers to the reduction in circulatory levels of all three elements of the blood. One or more of these conditions can result from sufficiently intense exposure to chemicals such as benzene, arsenic, the explosive trinitrotoluene (TNT), gold, certain drugs, and ionizing radiation. Health consequences can range... 

Since predators of snakes (and humans) have to deal with snake venoms as defenses, they are included here, even though they serve in predation. Snake venoms are primarily enzymes (proteins), especially of the phospholipase A2 type, which breaks down cell membrane phospholipids hydrolytically. Other snake venoms such as cobrotoxin contain peptides with 60-70 amino acid residues. Pharmacologically, they have neurotoxic, cytotoxic, anticoagulant, and other effects. The neurotoxins, in turn, can have pre- or postsynaptic effects. Snake venoms with both neurotoxic and hemolytic effects on the heart are known as cardiotoxins. Cytotoxins attach to the cells of blood vessels and cause hemorrhage. Snake venom factors may stimulate or inhibit blood clotting. Finally, platelet-active factors can contribute to hemorrhage. 

The classical example is blood clotting, where successive steps involving enzyme-catalyzed proteolysis converts an inactive (or weakly active) proenzyme into its highly active form. Although unknown at the time of Wald s classical report, kinase-type and nucleotidyltransferase-type reactions (See Enzyme Cascade Kinetics) are frequently the source of biological signal transduction and amplification. 

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