P

Paradoxical Embolus

Paradoxical emboli are systemic embolisms of venous origin that can occur in patients with an atrial or ventricular septal defect, through which an embolus may pass into the arterial system.

Peptide

Any of various natural or synthetic compounds containing two or more amino acids linked by the carboxyl group of one amino acid to the amino group of another.

Peroxidase

Any of a group of enzymes that occur especially in plant cells and catalyze the oxidation of a substance by a peroxide.

Phagocyte

Any type of cell that engulfs and destroys invading organisms.

Phagocytosis

The engulfing and ingestion of bacteria or other foreign bodies by phagocytes.

Phenotype

1. The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences.
2. The expression of a specific trait, such as stature or blood type, based on genetic and environmental influences.

Phosphatase

Any of numerous enzymes that catalyze the hydrolysis of esters of phosphoric acid and are important in the absorption and metabolism of carbohydrates, nucleotides, and phospholipids and in the calcification of bone.

Phosphate

A salt or ester of phosphoric acid.

Phosphoric Acid

A clear colorless liquid, H3PO4, used in pharmaceuticals.

Phospholipid

Amphipathic biological molecule containing a polar, hydrophilic phosphate head group, and a hydrophobic hydrocarbon tail, which allows phospholipids to self assemble in water into a bi-layer.

Plaque

A deposit of fatty material on the inner lining of an arterial wall, characteristic of atherosclerosis.

Plasma

The viscous living matter of a cell surrounding the nucleus, the protoplasm.

Plasmin

Fibrinolysin. A proteolytic enzyme that is formed from plasminogen in blood plasma and dissolves the fibrin in blood clots.

Plasminogen

The inactive precursor to plasmin that is cleaved by plasminogen activators tor form the active serine protease plasmin.

Plasminogen Activator

A group of serine proteases that cleave plasminogen to form plasmin including tPA, streptokinase, and urokinase.

Plasminogen Activator Inhibitor (PAI)

A class of serpin glycoprotein serpins that modulate the fibrinolytic system including PAI-1, PAI-2, PAI-3, and protease nexin.

Platelet

A microscopic, noncellular disk found in large numbers in vertebrate blood, produced in bone marrow from megakaryocyte, that is involved in the activation of prothrombin. Platelets are necessary for normal blood clotting. Most importantly, they aggregate (clump) together to plug small holes in damaged vessels. They also activate factor VIII and release phospholipids necessary for the coagulation cascade. MEDLINEplusBloodlineGray's Anatomy

Platelet Activation

One of the first steps in the coagulation process. Platelet activation in vitro can occur as a result of agitation of blood in the tube, difficult phlebotomy, shear stress arising from the phlebotomy process, and from increased contact with the inner surface of the tube, if the latter is comprised of an activating material. Once activated, platelets release protein, lipid, and other mediators which lead to aggregation and can result in shortened clotting times.

Platelet Aggregation

The term that refers to the platelet's ability to clump or attach to each other.

Platelet Aggregation Test

A test of the ability of platelets to clump together (aggregate) and cause blood clotting that helps to diagnose diseases of platelet dysfunction and distinguish between inherited bleeding problems (such as hemophilia or von Willebrand disease) and acquired bleeding problems (those that occur because of such things as another disorder or medication). MEDLINEplus

Platelet Antibodies

Antibodies to platelet antigens that are IgG or IgM isotype and are called platelet associated immunoglobulin or PAIg. The presence of increased PAIg on the platelet surface is an indication of immune thrombocytopenia.

Platelet Antigen

Antibodies to platelet antigens that are located on the platelet glycoproteins GPIa/IIa, GPIb/IX, and GP IIb/IIIa. Platelet antigen PLA1 is the most common antigen seen in alloimmune thrombocytopenia and in autoimmune thrombocytopenic purpura.

Platelet Associated Antibodies

A test to identify the presence of abnormal antiplatelet antibodies in plasma.MEDLINEplus

Platelet Count

Thrombocyte count. A test that measures the number of platelets in blood.A diminished number of platelets (below the lower limit of normal) is called thrombocytopenia and an elevated number (above the upper limit of normal) is called thrombocytosis. MEDLINEplus

Platelet Factor 4 (PF4)

A high-affinity heparin-binding protein that is stored in platelet alpha granules.

Platelet Rich Plasma

The preparation of whole blood by centrifugation to produce a supernatant fraction of high platelet content.

pNA

para-nitroaniline

Polybrene®

hexadimethrine bromide

Polyclonal

Descended from more than one group of cells, especially of genetically different origins.

Polymorphism

The occurrence of different forms, stages, or types in individual organisms or in organisms of the same species, independent of sexual variations. A genetic mutation with a frequency in the population of at least 1%

Polypeptide

A peptide, such as a small protein, containing many molecules of amino acids, typically between 10 and 100.

Prekallikrein

Fletcher factor

Primary Thrombocythemia

Primary thrombocythemia is a condition of overproduction of the platelet cells without a recognizable cause. MEDLINEplus

Protease (Proteolytic Enzymes)

Enzymes that degrade proteins into smaller peptides or amino acids to be used either as an energy source or as building blocks for resynthesis of proteins. See Proteolysis

Protein

Any of a class of naturally occurring, usually colloidal, complex combinations of amino acids (containing carbon, hydrogen, oxygen, nitrogen, usually sulfur, occasionally phosphorus) which are essential constituents of all living cells, being responsible for growth and maintenance of all tissue, and the essential nitrogenous constituent of the food of animals. They can be synthesized from inorganic nitrogenous material by plants, but apparently not by animals.

Protein C

A vitamin K-dependent protein produced in the liver that, when enzymatically converted to activated protein C, cleaves factors Va and VIIIa, and inactivates factors V and VIII. Deficient protein C can result in excessive clotting. These clots tend to form in veins, not arteries. MEDLINEplus

Protein C Deficiency

Protein C deficiency can be either inherited or acquired in association with other conditions. Liver disease, DIC, warfarin, and chemotherapy can result in decreased protein C levels. MEDLINEplus

Protein S

A vitamin K-dependent glycoprotein produced in the liver that serves as a cofactor to the activities of protein C. It inactivates factors V and VIII. MEDLINEplus

Protein S Deficiency

Deficient protein S can result in excessive clotting tendencies. These are usually vein clots, such as DVT, but occasionally this disorder can be associated with arterial clots. Deficiency may be inherited or acquired due to other conditions. This can be due to oral contraceptive use or pregnancy, and diseases such as DIC and HIV infection may also be associated with decreased levels of this protein. MEDLINEplus

Proteolysis

The hydrolytic breakdown of proteins into simpler, soluble substances such as peptides and amino acids, as occurs during digestion.

Prothrombin

Factor II. A carbohydrate-proteincompound in plasma that is converted by thromboplastin into thrombin during blood clotting.

Prothrombin Complex Concentrate (PCC)

PCC are plasma-derived and can be used to treat patients with deficiencies of factors II, VII and X as well as certain patients with inhibitors to factors VIII and IX.

Prothrombin Deficiency

See Factor II deficiency

Prothrombin Time (PT)

Prothrombin time; Pro-time. A test used for evaluation of the extrinsic and common coagulation pathway. The PT is the time in seconds required for a fibrin clot to form after tissue thromboplastin and an optimal amount of calcium chloride have been added to the sample (citrated plasma). Because it is sensitive to deficiencies of factor II, VII, and IX, the PT is the most common assay used to monitor warfarin therapy. MEDLINEplus

PTT

APTT; Partial thromboplastin time; Activated partial thromboplastin time. A test that measures the intrinsic clotting time in plasma. MEDLINEplus

Pulmonary Embolism

Sudden occlusion of the pulmonary artery or its branches by an embolus.