HAEMOSTASISRefers to the complicated chemical interplay thatmaintains blood viscosity, or thickness.Blood disorders occur when haemostasis falls outof balance.If blood becomes too thin, it loses the ability toform the blood clots that stop bleeding.When blood becomes too thick, the risk of bloodclots developing within the blood vessels risescreating a potentially life-threatening condition.
PLATELETSPlatelets are produced in bone marrow by a process knownas thrombopoiesis. They are formed in the cytoplasm of the megakaryocyte (avery large cell).The cytoplasm of the megakaryocyte fragments at the edgeof the cell.This is called platelet budding.Megakaryocytes mature in about 10 days, from a large stemcell, the megakaryoblast.
PLATELET NUMBERS• Among all the formed elements, platelets are thesmallest.They are estimated to be 150,000 –450,000 per cubicmm.• Their half life is around 10 days.
• Vitamin K needed to form four ofthe clotting factors• Within 30 minutes platelets begin toretract the clot by pulling edges ofcut vessel together
FIBRINOLYSISIs the process where a fibrin clot, the product ofcoagulation, is broken down.Its main enzyme, plasmin, cuts the fibrin mesh atvarious places, leading to the production of circulatingfragments that are cleared by other proteinases or bythe kidney and liver.
CLOT DISSOLVING• As repair of a cut or damaged vessel proceeds,a series of enzyme catalyzed reactions calledfibrinolysis slowly dissolves the clot• An enzyme called tissue plasminogenactivator catalyzes the conversion of inactiveplasminogen enzyme to active plasmin• Active enzyme catalyzes the dissolving of clot
INTRAVASCULAR CLOT• Intravascular clot – clot within closed vessel• Damaged vessel lining or slowing of blood flowPlatelets aggregate and release clotting factors• Resulting clot called a thrombus• Moving piece of the clot is an embolus• Clot moves downstream and blocks smallervessel embolism• May cut off blood supply to organ
ANTICOAGULANTS• Chemicals that decrease or prevent blood clottingare called anticoagulants• Heparin is administered medically and it occursnaturally in our bodies. It works by decreasingthrombin production• Coumadin (warfarin) is effective as a long-termanticoagulant. It is an antagonist of vitamin K.• EDTA and CPD are used in blood banks to keepthe donated blood from clotting. They both workby tying-up and removing calcium.
Coagulation and DiseaseHemophiliaCardiovascular DiseasesKey problem – clots block undamaged bloodvesselsAnticoagulants prevent coagulationKeep platelets from adheringPrevent fibrin coagulation"Clot Busters": Prevent further clottingSpeed fibrinolysisLimit tissue damage (heart, brain…)
HEMOPHILIA–Inherited clotting disorder due to a deficiency in a clottingfactor.–Hemophilia is perhaps the best known of the bleedingdisorders.–Hemophilia is a genetic disorder caused by mutations of geneson the X chromosome.–Because the mutated gene is recessive, the majority ofhemophiliacs are male.
Von Willebrands Disease Von Willebrands disease is the most common ofthe inherited bleeding disorders, includinghemophilia. Von Willebrands disease affects up to onepercent of the population, and may be found in both sexes (as opposed tohemophilia, which primarily affects males). Von Willebrands factor is a protein that allowsplatelets to form temporary plugs at sites of bloodvessel injury: Defects in von Willebrands factor, impair theability of platelet cells to cling to an injury andform a plug.
THROMBOCYTOPENIAThrombocytopenia occurs when platelet cells fall toabnormally low levels, impairing coagulation.Leukemia, lymphoma, and some other cancers areknown to cause thrombocytopenia. Cases of thrombocytopenia have also occurred due toheparin, a blood thinning medication.
LIVER DISORDERSLiver cirrhosis interferes with the livers ability toproduce vital proteins, including coagulation factors.Low levels of coagulation factors in turn may lead tobleeding disorders.
THE END“Our greatest gloryis not in neverfailing but in risingup every time wefail.”Ralph WaldoEmerson