Upload
dennis-valdez
View
222
Download
0
Embed Size (px)
Citation preview
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 1/7
PLATELETS
Maturation sequence of megakaryoblast takes about 5 days. Platelets are produced directly from the mekaryocytecytoplasm. As the megakaryocyte matures, clusters of granules aggregate to form platelets.
1. Megakaryoblast 20-50 um diameter
Blue cytoplasm
N/C ratio is about 10:1 Multiple nucleoli
Fine chromatin
2. Promegakaryocyte 20-60 um diameter
Less basophilic cytoplasm Chromatin becomes coarse
Irregularly shaped nucleus, may show showslight lobulation
N/C ratio is 4:1 to 7:1
3. Granular megakaryocyte
4. Mature megakaryocyte
40-120 um diameter Cytoplasm contains coarse clumps of granules
aggregating into little bundles, which bud offfrom the periphery to become platelets
Multiple nuclei are present No nucleoli is visible
N/C ratio is less than 1:1
5. Platelet/thrombocyte
1-4 um diameter Light blue to purple, very granular
o Chromomere – granular and located
centrallyo Hyalomere – surrounds the chromomere,
nongranular and clear to light blue
MORPHOLOGIC DIFFERENTIATION OF MEGAKARYOCYTIC CELL SERIES
Maturation Stage Cytoplasmic
Granules
Cytoplasmic
Tags
Nuclear Features Thromocytes
Visible
Megakaryoblast Absent Present Single nucleus, finechromatin, nucleoli
No
Promegakaryocyte Few Present Double nucleus No
Megakaryocyte Numerous Usually absent Two or more nuclei No
Metamegakaryocyte Aggregated Absent Four or more nuclei Yes
PLATELET STRUCTURE
Composed of 60% protein, 30% lipid, 8% carbohydrate, various minerals, water and nucleotides
Divided anatomically into four areas: peripheral zone, sol-gel zone, organelle and membranous system
1. Peripheral zoneGlycocalyxPlasma membrane
Submembranous area
2. Sol-gel zoneMicrofilaments: actin and myosinMicrotubules
3. Organelle zoneAlpha, dense granulesMitochondria, lysosomal granules
4. Membranous systemDense tubular systemOpen canalicular system
(surface connecting system)
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 2/7
SUMMARY OF MOST IMPORTANT SUBSTANCES SECRETED BY PLATELETS AND THEIR ROLE IN
HEMOSTASIS
ROLE IN
HEMOSTASIS SUBSTANCE SOURCE COMMENTS ON PRINCIPAL
FUNCTION Promote coagulation HMWK Alpha granules Contact activation of intrinsic coagulation
pathway Fibrinogen Alpha granules Converted to fibrin for clot formation
Factor V Alpha granules Cofactor in fibrin clot formation Factor VIII:vWF Alpha granules Assists platelet adhesion to subendothelium
to provide coagulation surface
Promote aggregation ADP Dense bodies Promote platelet aggregation Calcium Dense bodies Same Platelet factor 4 Alpha granules Same Thrombospondin Alpha granules Same
Promotevasoconstriction
Serotonin Dense bodies Promotes vasoconstriction at injury site Thromboaxane A2 precursors
Membrane phospholipids
Same
Promote vascular
repair Platelet-derived growth
factor Alpha granules Promotes smooth muscle growth for vessel
repair Beta thromboglobulin Alpha granules Chemotactic for fibroblasts to help in vessel
repair Other systems
affected Plasminogen Alpha granules Precursor to plasmin, which induces clot lysis
2 – antiplasmin Alpha granules Plasmin inhibitor; inhibits clot lysis
C1 esterase inhibitor Alpha granules Complement system inhibitor
HEMOST SIS
Process that retains the blood within the vascular system during periods of injury, localizes the reactions involvedto the site of injury, and repairs and re-establishes blood flow through the injured vessel
A system in dynamic balance that when tipped by deficiencies (congenital or acquired) of the procoagulant portionor excesses of the fibrinolytic portion, results in uncontrolled bleeding (hemorrhage); when tipped by deficiencies(congenital or acquired) of the fibrinolytic portion or uncontrolled activation of the procoagulant portion, the resultis excessive clot formation or persistence of clot (thrombosis)
SUMMARY OF MOST IMPORTANT SUBSTANCES SECRETED BY PLATELETS AND THEIR ROLE IN HEMOSTASIS
ROLE IN
HEMOSTASIS SUBSTANCE SOURCE COMMENTS ON PRINCIPAL
FUNCTION Promote coagulation HMWK Alpha granules Contact activation of intrinsic coagulation
pathway Fibrinogen Alpha granules Converted to fibrin for clot formation Factor V Alpha granules Cofactor in fibrin clot formation
Factor VIII:vWF Alpha granules Assists platelet adhesion to subendothelium to provide coagulation surface
Promoteaggregation
ADP Dense bodies Promote platelet aggregation Calcium Dense bodies Same Platelet factor 4 Alpha granules Same Thrombospondin Alpha granules Same
Promotevasoconstriction
Serotonin Dense bodies Promotes vasoconstriction at injury site Thromboaxane A2 precursors
Membrane phospholipids
Same
Promote vascularrepair
Platelet-derivedgrowth factor
Alpha granules Promotes smooth muscle growth for vesselrepair
Beta thromboglobulin Alpha granules Chemotactic for fibroblasts to help in vesselrepair
Other systemsaffected
Plasminogen Alpha granules Precursor to plasmin, which induces clot lysis
2 – antiplasmin Alpha granules Plasmin inhibitor; inhibits clot lysis
C1 esterase inhibitor Alpha granules Complement system inhibitor
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 3/7
BASIC TERMINOLOGY FOR CLINICAL FINDINGS IN BLEEDING DISORDERS:1. Petechiae – purplish red pinpoint hemorrhagic spots in the skin caused by loss of capillary ability to withstand
normal blood pressure and trauma2. Purpura – hemorrhage of blood into small areas of skin, mucous membranes, and other tissues3. Ecchymosis – form of purpura in which blood escapes into large areas of skin and mucous membranes, but not
into deep tissues4. Epistaxis – nosebleed
5. Hemarthosis – leakage of blood into joint cavities6. Hematemesis – vomiting of blood7. Hematoma – swelling or tumor in the tissues or a body cavity that contains clotted blood8. Hematuria – rbc in urine9. Hemoglbinuria – hb in urine10. Melena – stool containing dark red or black blood
11. Menorrhagia – excessive menstrual bleeding
COAGULATION FACTORS1. Coagulation factors are also known as enzyme precursors or zymogens. They are found in plasma along with
nonenzymatic cofactors and calcium,2. Zymogens are substrates having no biologic activity until converted by enzymes to active forms called serine
proteases.
a. The zymogens include II, VII, IX, X, XI, XII and prekallikreinb. The serine proteases are IIa, VIIa, IXa, Xa, XIa, XIIa and kallikrein
3. Cofactors assist in the assist in the activation of zymogens and include V, VIII, tissue factor, and HMWK
4. In its active form, factor XIII is a transglutamase.5. Fibrinogen is the only substrate in the cascade that does not become an activated enzyme.
Blood factors are produced mostly in the LIVER and circulate in an inactive precursor form.
COAGULATION FACTOR NOMENCLATURE WITH PREFERRED NAMES AND SYNONYMS
NUMERAL PREFERRED NAME SYNONYMS
I Fibrinogen
II Prothrombin Prethrombin
III Tissue factor Tissue thromboplastinIV Calcium
V Proaccelerin Labile factor Accelerator globulin (aCg)
VII Proconvertin Stable factorSerum prothrombin conversion accelerator (SPCA)
VIII:C Antihemophilic factor (AHF) Antihemophilic factor globulin (AHG) Antihemophilic factor APlatelet cofactor 1
IX Plasma thromboplastin component (PTC) Christmas factor Antihemophilic factor BPlatelet cofactor 2
X Stuart-Prower factor Stuart factorPrower factor Autoprothrombin III
XI Plasma thromboplastin antecedent Antihemophilic factor C
XII Hageman factor Glass factorContact factor
XIII Fibrin stabilizing factor Laki-Lorand factorFibrinasePlasma transglutaminaseFibrinoligase
- Prekallikrein Fletcher factor
- High-molecular-weight kininogen Fitzgerald factorContact activation cofactor
Williams factorFlaujeac factor
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 4/7
SCHEMATIC DIAGRAM OF
PHYSIOLOGIC HEMOSTASIS. Note thatthe ‘contact phase’ factors comprisingfactor XII, HK (high molecular weightkininogen) and PK (prekallikrein) are showngrayed; although factor XI can be activatedby this route under artificial in vitroconditions such as in the PTT test (see Fig.38-8 ), this pathway is not believed tocontribute to normal physiologichemostasis. Similarly, whereas Tissuefactor/VIIa can directly activate X to Xa inthe in vitro PT test under conditions whichsupra-physiological concentrations of
Tissue factor are employed, this reaction isshown as grayed because it does notcontribute significantly to clot formationunder normal in vivo physiologicalconditions. Normal clotting in vivoaccordingly is initiated when sufficientTissue factor/VIIa becomes available toactivate factor IX to IXa. Subsequently, IXain the presence of VIIIa activates X to Xa,which in turn activates prothrombin tothrombin in the presence of Va. Thrombinnot only then proceeds to clot fibrinogenand to activate platelets (see Fig. 38-2 ),
but additionally exerts critically important positive feedback by activating factors VIIIand V. Thrombin has further been showncapable of activating factor XI, thereby providing an additional pathway for theactivation of factor IX. PL (phosopholipid present on the surface membranes of platelets in vivo) and Ca
++ (calcium ions)
contribute to reactions as indicated.
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 5/7
CHARACTERISTICS OF COAGULATION FACTORS
Factor Active Form PathwayParticipation
Vitamin KDependent
Present in BaSO4 Adsorbed Plasma
I Fibrin clot Common No Yes
II Serine protease Common Yes No
V Cofactor Common No Yes
VII Serine protease Extrinsic Yes No
VIII:C Cofactor Intrinsic No Yes
IXSerine protease
Intrinsic Yes No
X Serine protease Common Yes No
XI Serine protease Intrinsic No Yes
XII Serine protease Intrinsic No Yes
XIII Transglutaminase Common No Yes
Prekallikrein Serine protease Intrinsic No Yes
HMWK Serine protease Intrinsic No Yes
INHIBITORS OF COAGULATIONMajor site of inhibition: endothelium and platelet1. Protein C – degrades factor Va and VIIIa2. Protein S – degrades factor Va and VIIIa
3. Antithrombin III – major inhibitor of thrombin, also inhibits factors IXa, Xa, XIa, XIIa, kallikrein and plasmin4. Heparin cofactor II – inhibit thrombin
5. 2 macroglobulin – forms a complex with thrombin, kallikrein and plasmin, thus inhibiting their activities6. Extrinsic pathway inhibitor (EPI)
Lipoprotein assoc. coagulation inhibitor (LACI) – inhibits the VIIa-tissue factor complex7. C1 inhibitor – inactivator of factor XIIa and kallikrein, it also inhibits factor XIa and plasmin
8. 1 antitrypsin – inhibitor of thrombin, Xa and XIa
DISORDERS OF COAGULATION CAUSING CLOTTING FACTOR DEFICIENCIES
FACTOR INHERITED COAGULOPATHIES ACQUIRED COAGULOPATHY
INHERITANCE
PATTERN
COAGULOPATHY
I Autosomal recessive
Autosomal dominant
Afibrinogenemia
Dysfibrinogenemia
Severe liver disease
Diffuse intravascular coagulationFibrinolysis
II Autosomal recessive Prothrombin deficiency Liver diseaseVit K deficiency Anticoagulant therapy
V Autosomal recessive Factor V deficiency(OWREN’S dis, Labile factordef)
Severe liver diseaseDiffuse intravascular coagulationFibrinolysis
VII Autosomal recessive Factor VII deficiency Liver diseaseVit K deficiency Anticoagulant therapy
VIII X-linked recessive
Autosomal dominant
Hemophilia A
vWD
Diffuse intravascular coagulationFibrinolysis
IX X-linked recessive Hemophilia B Liver diseaseVit K deficiency Anticoagulant therapy
X Autosomal recessive Factor X deficiency Liver diseaseVit K deficiency Anticoagulant therapy
XI Autosomal recessive Hemophilia C(common in EasternEuropean Jewish descent/ Ashkenazi Jews)
*
XII Autosomal recessive Factor XII deficiency *
XIII Autosomal recessive Factor XIII deficiency Liver diseaseDiffuse intravascular coagulationFibrinolysis
Prekall Autosomal recessive Fletcher trait *
HMWK Autosomal recessive Fitzgerald trait *
* Unclear whether any acquired disorders cause factor XI or XII deficiencies or prekallikrein or HMK deficiency
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 6/7
CLASSIFICATION OF VON WILLEBRAND DISEASE
TYPE DESCRIPTION
1 Partial quantitative deficiency of von Willebrand factor (vWF)
2 Qualitative deficiency of vWF
2A Decreased platelet-dependent vWF function with selective deficiency of high-molecular-weight multimers
2B Increased affinity for platelet glycoprotein Ib
2M Decreased platelet-dependent vWF function with high-molecular-weight multimers present
2N Markedly decreased binding of factor VIII to vWF
3 Complete deficiency of vWF
Lee and White clotting time methodEquipment: water bath 37
oC; glass test tubes 13 x 100 mm; stopwatch and plastic syringe (10 mL) and 20-
gauge needle. (Brown page 215)From Brown
Prothrombin Time:
Test tubes, 13 x 100 mm 0.1 mL patient’s plasma 0.2 mL (200 µL) thromboplastin-calciumreagent
APTT:
13 x 100 mm tube 0. 2mL plasma 0.2 mL APTT reagent 0.2 mLCaCl2 From Steiniger
Prothrombin Time:
0.1 mL plasma 0.2 mL (200 µL) PT reagent
APTT:
12 x 75 mm tube 0.1 mL PPP 0.1 mL APTT reagent 0.1 mL CaCl2
DIFFERENTIAL DIAGNOSIS OF ABNORMAL COAGULATION SCREENING TESTS
Abnormal partial thromboplastin time (PTT) alone
Associated with bleeding: VIII, IX, XI defectsNot-associated with bleeding: XII, prekallikrein (PK), high-molecular-weight kininogen, lupus anticoagulants
Abnormal prothrombin time (PT) alone
Factor VII defects
Combined abnormal PTT and PT Medical conditions: anticoagulants, DIC, liver disease, vitamin K deficiency, massive transfusionRarely dysfibrinogenemias, factors X, V, and II defects
FAMILIES OF COAGULATION PROTEINS
THROMBIN-SENSITIVECOAGULATION PROTEINS
PROTHROMBIN FAMILY CONTACT FAMILY
I, V, VIII and XIIINot vitamin K dependentConsumed during coagulation
Absent in serum
Present in adsorbed plasma
II, VII, IX and XVitamin K dependentPresent in serum (except II)
Absent in adsorbed plasma
XII, XI, prekallikrein,HMWKNot vitamin K dependentPresent in serum
Present in adsorbed plasma
SUBSTITUTION STUDIES
DEF. PT APTT TT SUBSTITUTION STUDIES
Normal Plasma Adsorbed Plasma Aged Serum
I Abn Abn Abn C C NC
II Abn Abn N C NC NC
V Abn Abn N C C NC
VII Abn N N C NC C
VIII N Abn N C C NC
IX N Abn N C NC C
X Abn Abn N C NC C
XI or XII N Abn N C C CN – Normal NC – NOT CORRECTEDAbn – Abnormal C – CORRECTEDPT – Prothrombin TimeAPTT – Activated Partial Thromboplastin TimeTT – Thrombin Time
8/12/2019 Pl a t el e ts
http://slidepdf.com/reader/full/pl-a-t-el-e-ts 7/7
CIRCULATING ANTICOAGULANTS
Prolonged APTT and PT not corrected Inactivate an activated coagulation factor or block interaction between coagulation factors and platelets Ex L upus inhib i tor
Nonsp anticoagulant IgG, IgM and IgA which interfere with phospholipid portion of the complex: Xa-Va-calcium-plt phospholipid
Platelet neutralization procedure Dilute Russell Viper Venom time
INSTRUMENTATION FOR TESTS OF HEMOSTASIS
1. Visual detection of fibrin clot formation
Tilt tube method
2. Electromechanical detection of fibrin clot formation
Fibrin strand formation is detected using a wire
loop or hook; has been incorporated into a semi-
automated mechanical instrument
Instrument: FIBROMETER
3. Photo-optical detection of fibrin clot formation
Detection of fibrin clot formation depends on the
increase in light scattering associated with the
conversion of soluble fibrinogen molecules to theinsoluble polymerized fibrin clot
Semi-automated instruments: Electra 750 and
750A, Fibrintimer series, and FP 910 Coagulation
Analyzer
Automated instruments: Ortho Koagulab 16S and
40A, the Coag-A-Mate X2 and XC, and the MLAElectra 700 and 800
FIBRINOLYSIS Digestion of fibrin clot, keeps the vascular system free of deposited fibrin/fibrin clot
Occurs when plasminogen is converted to plasmin
PLASMINOGEN ACTIVATORS1. Intrinsic activators
Factor XIIaKallikreinHWK
2. Tissue typeUrokinase-like PA
3. Therapeutic activatorsTreatment for thromboemboli
StreptokinaseUrokinaseTissue-like PA
INHIBITORS OF FIBRINOLYSIS
1. 2 antiplasmin ________________2. 2 macroglobulin3. Thrombospondin4. PA inhibitor 1 and 2
Degradation of cross-linked fibrin by plasmin Degradation of fibrinogen and non-crosslinked fibrinby plasmin
PATHOLOGIC FIBRINOLYSISPRIMARY FIBRINOLYSIS Excessive amounts of plasminogen activators from damaged cells/malignant cells Converts plasminogen to plasmin in the absence of fibrin formation
SECONDARY FIBRINOLYSIS DIC: uncontrolled, inappropriate formation of fibrin within the blood vessels
Infection; Neoplasm; Snake bite; HTR