Platelets Morphology
Hemostasis
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Primary hemostasis
Platelet plug formation
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Disorders of primary hemostasisSecondary hemostasis
Disorders of secondary hemostasis
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Tests to assess hemostasis
Anticoagulants
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PlateletsCharacteristics
Small 23 ?m discshaped, anuclear, reddishpurple
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cells.Platelet life span 710 days
Platelets count: 1.54 lakh/ mm3 of blood
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(Platelets are released from bone marrow to enter
2/3 peripheral blood and 1/3 seized in spleen.)
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Platelets-Production& IL3
Platelets are formed within the cytoplasm of
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megakaryocytes (1 megakaryocyte produces
about 2000 platelets)within bone marrow
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and released into the circulation.Platelets structure
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Peripheral zone:Responsible for platelet adhesion and aggregation
Glycocalyx: Fluffy surface coat contains
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glycoprotein receptors: GPIa & IIa binds to col agen,
GPIb binds von Wil ebrand's factor ; GPIIb/IIIa binds fibrinogen
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Membrane ZoneLayer cal ed PF3 (platelet factor) surface for interaction
of plasma coagulation factors, Initiation of formation of
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thromboxane A2
2 systems :Surface-connected open canalicular system (OCS)
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Dense tubular system(DTS).Cytoskeleton
Responsible for platelet retraction and platelet shape
Microtubules/Microfilaments
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Binding proteins: Actin & MyosinOrganelle zone
Responsible for storage and platelet release functions
Granules:Dense bodies, alpha granules, lysosomal granules and microperoxisomes. Mitochondria and Glycogen.
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HemostasisHemostasis is the natural process that stops blood loss when an injury occurs. It involves three steps that
occur in a rapid sequence:
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Primary Hemostasis: (1) vascular spasm, or vasoconstriction, a brief and intense contraction of blood
vessels; (2) formation of a platelet plug; and
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Secondary Hemostasis: blood clotting or coagulation, which reinforces the platelet plug with fibrin meshthat acts as a glue to hold the clot
fibrinolytic proteins system - Excessive blood clotting is prevented.
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Primary Hemostasis - Vasoconstriction
Vasoconstriction
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The vasoconstriction that occurs during hemostasis
is a brief reflexive contraction that causes a
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decrease in blood flow to the area and restrictblood loss.
The vasoconstriction response is triggered by
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factors such as secretion of serotonin from
activated platelets, a direct injury to vascular
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smooth muscle and nervous system reflexesinitiated by local pain receptors.
Platelets Function- Pri. Hemostasis - Platelets plug formation
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Platelets plug formation
1) Adhesion ? exposed collagen (GpIa & GpIIa and vWF-GpIb)
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2) Activation ?Initiation of formation of thromboxane A2 and secretion of granule contents speciallyADP & Ca++
3) Aggregation - Expression of GpIb-IIIa receptors on platelets to glue together
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Formation of thromboxane A2 and Antiplatelet activity of Aspirin
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(ASPIRIN)Thromboxane synthetase
Platelets Function- Pri. Hemostasis - Platelets plug formation
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Abnormalities in primary hemostasis-Purpura
Purpura is purple-colored spots and patches that
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occur on the skin, and in mucus membranes,
including the lining of the mouth. Purpura occurs
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when small blood vessels leak blood under the skin.Purpura measure between 4 and 10 mm
(millimeters) in diameter. When purpura spots are
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less than 4 mm in diameter, they are called
petechiae. Purpura spots larger than 1 cm
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(centimeter) are called ecchymoses.Abnormalities in primary hemostasis
Defects in the blood vessel wall- lead to hemorrhage from mucosal surfaces (epistaxis, gingival bleeding, melaena,
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haematuria), and into skin and mucosae (petechial or ecchymotic haemorrhages - Purpura).
Decreased platelets number (Thrombocytopenia) or function (Thrombosthenia)
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Abnormal vWF- Bernard Soulier Syndrome
Primary haemostasis inhibitors - natural inhibitors of platelet function - such as prostacyclin, bradykinin released by
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endothelial cells.Induced inhibition of platelet function - more commonly, platelet function is inhibited intentional y by the
administration of agents such as aspirin for the prevention of thrombosis.
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Causes of Thrombocytopenia
Bone Marrow Dysfunction ?Many conditions and factors can damage stem cells
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Cancer- leukemia or lymphoma. Cancer treatments, such as radiation and chemotherapy.
Toxic Chemicals- pesticides, arsenic, and benzene
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Medicines-diuretics and chloramphenicol (aspirin or ibuprofen, also can affect platelets functioning)Alcohol-especial y if they're eating foods that are low in iron, vitamin B12, or folate.
Viruses-Chickenpox, mumps, rubel a, Epstein-Barr virus, HIV and dengue fever virus etc often develop thrombocytopenia.
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Genetic Conditions-Wiskott-Aldrich syndromes.
The Body Destroys Platelets at a higher rate
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ITP (Idiopathic thrombocytopenic purpura)Autoimmune Diseases-immune thrombocytopenia . An autoimmune response is thought to cause most cases of ITP eg
SLE and RA
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Margination in congestive splenomegaly
Medicines-quinine; antibiotics that contain sulfa; dilantin, vancomycin, and rifampin.
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Infection-a widespread bacterial infection septicemia, mononucleosis or cytomegalovirusSurgery-Prosthetic heart valves, blood vessel grafts, or machines and tubing used - blood transfusions or bypass surgery.
Pregnancy-About 5 percent of pregnant women develop mild thrombocytopenia when they're close to delivery.
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Process of secondary hemostasis-Blood Coagulation-Clotting Factors
Process of secondary hemostasis-Blood Coagulation
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Disorders of Blood Coagulation- Coagulopathy
Coagulopathy is a condition in that the blood's ability to coagulate is
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impaired. This condition can cause a tendency toward prolonged orexcessive bleeding (bleeding diathesis), which may occur
spontaneously or following an injury
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Disorders of Blood Coagulation- Hypocoagulopathy -CAUSESMajor causes of coagulation disorders resulting in bleeding include:
?Hemophilia-Factor VIII deficiency (X chromosome linked disorder)
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?Von Willebrand disease
?Other clotting factor deficiencies (Christmas disease)
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?Disseminated intravascular coagulation?Liver Disease
? Vit K deficiency
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Disorders of Blood Coagulation- Hyper-coagulopathy - CAUSES
?Conditions increasing the risk of a blood clot:
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?Inherited (genetic) abnormalities that cause an increased tendency to clot?A surgical procedure
?Sitting or lying down for long periods (more than 4 hours)- for example, after surgery
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or on long plane or car rides. This lack of movement reduces blood flow in the legs by
50%.
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?Major injury?Increasing age
?Cancer
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?Heart failure
?Pregnancy
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?Use of hormone therapy such as birth control pills or hormone replacement therapy?Having a history of DVT
?Tobacco
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Fibrinolytic System
Process of Thrombosis & Bleeding (fibrinolysis) should be balanced
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Clotting factor deficiencies may cause the
development of a significant bleeding tendency.
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Formation of clots inside blood vessels is calledthrombosis due to hyper coagulability of blood
Thromboses are a major medical problem.
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They frequently occlude the arterial supply to the
organs in which they form, and bits of thrombus
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(emboli) sometimes break off and travel in thebloodstream to distant sites, damaging other organs.
An example is obstruction of the pulmonary artery or
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its branches by thrombi from the leg veins
(pulmonary embolism).
Tests of Hemostasis-Laboratory Investigations
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Capil ary Fragility Test ? The test is defined by the WHO as one of the necessary requisites for diagnosis of Dengue fever. ? A
blood pressure cuff is applied and inflated to a point between the systolic and diastolic blood pressures for five minutes. ?
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The test is positive if there are 10 or more petechiae per square inch. ? In DHF the test usual y gives a definite positive resultwith 20 petechiae or more. Indicative of hemorrhagic tendency of a person
Platelet Count ? Platelet Count can be determined by improved Neubauer's counting chamber with RBC pipette & 1%
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ammonium oxalate. ? They can be seen as tiny diameter, well seprated, highly refractile rounded bodies with silveryappearance. ? N : 1.5 ? 4 lacs / cumm. ? Leishman stain : in clumps, blue cytoplasm, reddish purple granules, no nucleus. ?
Surgical bleeding usual y does not occur until the platelet count is less than 50,000/mm3. ? Spontaneous bleeding does not
occur until the platelet count is less than 10,000-20,000/mm3. Platelet Count ? THOMBOCYTOPENIA : ? Bone marrow
depression ? Aplastic anemia ? Hypersplenism ? Viral infections ? Drugs : Aspirin, Heparin, Chemotherapy ? ITP ? TTP ?
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DICBleeding Time ? It is the time taken from the puncture of the blood vessel to the stoppage of bleeding. N : 1-6 minutes
? The bleeding time test is a useful tool to test for platelet plug formation and capil ary integrity.
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? BT is more imp. than CT.
? CT concerns the blood only i.e. how firm the clot is formed, whereas BT involves the interaction of blood with injured
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tissues.? People with von Wil ebrand disease usual y experience increased bleeding time. ? Von Wil ebrand factor is a platelet
agglutination protein, but this is not considered an effective diagnostic test for this condition.
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Tests of Hemostasis-Laboratory Investigations
Clotting Time It is the time taken from the puncture of the blood vessel to the formation of a fibrin thread. ? A. Capil ary Glass
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Tube Method : Here the blood is collected in capil ary tube & total time is noted to form FIBRIN THREADS on breaking tubeevery 30 seconds. N : 3-8 minutes ? Mechanism Involved is INTRINSIC Pathway. ? CT depends on presence of all clotting
factors. ? It gets prolonged in : - 1. Deficiency of clotting factors ? Hemophilia. - 2. Vitamin K Deficiency ? Factor II, VII, IX
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& X. - 3. Anticoagulant overdose. ? BT & CT is measured before surgery & liver or bone marrow biopsy. ? PURPURA : BT
increased, CT normal. ? HEMOPHILIA : BT normal, CT increased.
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Prothombin Time ? The prothrombin time (PT) and its derived measures of prothrombin ratio (PR) and international normalisedratio (INR) are measures of the extrinsic pathway of coagulation. ? They are used to determine the clotting tendency of blood, in
the measure of warfarin dosage, liver damage and vitamin K status. ? PT measures factors I, II, V, VII and X. ? The reference
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range for prothrombin time is usually around 11-16 seconds; the normal range for the INR is 0.8?1.2.
APTT ? The partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT or APTT) is a performance
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indicator measuring the efficacy of both the intrinsic and the common coagulation pathways. ? Apart from detectingabnormalities in blood clotting, it is also used to monitor the treatment effects with heparin, a major anticoagulant. ? Normal
PTT times require the presence of the following coagulation factors: I, II, V, VI I, IX, X, XI & XII. ? Deficiencies in factors VI or
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XII wil not be detected with the PTT test.
ANTICOAGULANTS
Heparin is a naturally occurring anticoagulant
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that facilitates the action of anti-thrombin III. Low-molecular weight fragments with an average molecular weight
of 5000 have been produced from unfractionated heparin, and these low-molecular-weight heparins are seeing
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increased clinical use because they have a longer half-life and produce a more predictable anticoagulantresponse than unfractionated heparin.
In vivo, a plasma Ca2+ level low enough to interfere with blood clotting is incompatible with life, but clotting can
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be prevented in vitro if Ca2+ is removed from the blood by the addition of substances such as oxalates, which
form insoluble salts with Ca2+, or chelating agents, which bind Ca2+. Used in vitro only.
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Coumarin derivatives such as dicumarol and warfarin are also effective anticoagulants. They inhibit theaction of vitamin K, which is a necessary cofactor for the enzyme that catalyzes the conversion of glutamic acid
residues to -carboxyglutamic acid residues. Six of the proteins involved in clotting require conversion of a
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number of glutamic acid residues to -carboxyglutamic acid residues before being released into the circulation,
and hence all six are vitamin K-dependent. These proteins are factors II (prothrombin),VII, IX, and X, protein C,
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and protein S.Self Assessment
Megakaryocyte produces about ..........................platelets.
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Platelet life span ....................... Days.
...............................receptors causes gluing of platelets together.
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? Spontaneous bleeding does not occur until the platelet count is less than........................../mm3.
? Surgical bleeding does not occur until the platelet count is less than
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.................................../mm3.
? Secondary Hemostasis includes ....................................processes.
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? Liver Disease results in hyp0coagulability of blood because...........................Thank you