Localization of the haemostatic plug:Localization of the haemostatic plug:

The uncontrolled growth of the thrombi is The uncontrolled growth of the thrombi is limited by three mechanisms:limited by three mechanisms:

1.1. The blood flow removes activated The blood flow removes activated coagulation enzymes and platelet coagulation enzymes and platelet activating substances away from the site of activating substances away from the site of the injury. They are rapidly inactivate after the injury. They are rapidly inactivate after their passage through the liver.their passage through the liver.

2. Serine protases activated during 2. Serine protases activated during coagulation not only activate the coagulation not only activate the coagulation factors, but also degrade coagulation factors, but also degrade them. The degradation can be due to them. The degradation can be due to direct proteolytic effect, e.g. degradation direct proteolytic effect, e.g. degradation of Xa by thrombin, or result from of Xa by thrombin, or result from activation of an inhibitory system as in activation of an inhibitory system as in the case of protein C system the case of protein C system

3. The third mechanism of control involves 3. The third mechanism of control involves naturally occurring inhibitors in plasma. naturally occurring inhibitors in plasma. The major are: alpha-2-macroglolulin, The major are: alpha-2-macroglolulin, alpha-2-antitrypsin, antithrombin III, alpha-2-antitrypsin, antithrombin III, heparin cofactor and alpha-2-heparin cofactor and alpha-2-antiplasmin. antiplasmin.

Coagulation inhibitory factorsCoagulation inhibitory factors

These inhibit the coagulation cascade and These inhibit the coagulation cascade and ensure the action of thrombin is limited to the ensure the action of thrombin is limited to the site of injury.site of injury.

Antithrombin inactivates serinc protases, Antithrombin inactivates serinc protases, principally factor Xa and thrombin. Heparin principally factor Xa and thrombin. Heparin activates antithrombin.activates antithrombin.

œ2-Macroglohulins, œ2 antiplasmin, œI œ2-Macroglohulins, œ2 antiplasmin, œI antitrypsin and heparin cofactor II also inhibit antitrypsin and heparin cofactor II also inhibit circulating serine proteases.circulating serine proteases.

Protein C is activated via a thrombin--Protein C is activated via a thrombin--thrombo modulin complex and, like thrombo modulin complex and, like protein S inhibits coagulation by protein S inhibits coagulation by inactivating factors Va and VIIIa: it also inactivating factors Va and VIIIa: it also enhances fibrinolysis by inactivating the enhances fibrinolysis by inactivating the tissue plasmogen activator (TPA) tissue plasmogen activator (TPA) inhibitor.inhibitor.

Tissue factor pathway inhibitor (TFPI) Tissue factor pathway inhibitor (TFPI) inhibits the main In vivo coagulation inhibits the main In vivo coagulation pathway by inhibiting factor Vlla and Xa.pathway by inhibiting factor Vlla and Xa.

The fibrinolytic pathwayThe fibrinolytic pathway::– Deposition of fibrin and its removal from Deposition of fibrin and its removal from

circulation are regulated by the fibrinolytic system. circulation are regulated by the fibrinolytic system. – Fibrinolysis is the process whereby fibrin is Fibrinolysis is the process whereby fibrin is

degraded by plasmin. degraded by plasmin. – A circulating pro-enzyme, plasminogen, may be A circulating pro-enzyme, plasminogen, may be

activated to plasmin. activated to plasmin. – Plasmin digests fibrin (or fibrinogen) into fibrin Plasmin digests fibrin (or fibrinogen) into fibrin

degrada tion products (FDPs) and also degrades degrada tion products (FDPs) and also degrades factors V and VII. factors V and VII.

– Free plasmin is inactivated by plasma alpha-2-Free plasmin is inactivated by plasma alpha-2-antiplasmin and alpha-2-macroglohulin.antiplasmin and alpha-2-macroglohulin.

ThrombinThrombin

Fibrinogen fibrin monomers + peptides A Fibrinogen fibrin monomers + peptides A & B& B

Fibrin monomers AggregatesFibrin monomers Aggregates

Fibrin Aggregates Fibrin s Fibrin Aggregates Fibrin s ( polymerization) ( polymerization)

Fibrin Fibrin i (cross Fibrin Fibrin i (cross l l linked)XIII linked)XIII

Fibrin s = Soluble in 5ml ureaFibrin s = Soluble in 5ml urea Fibrin i = Insoluble in 5ml ureaFibrin i = Insoluble in 5ml urea

Thrombin (IIa)

Prothrombin (II)

Xa

VIIa

TF

IXa

Revised Coagulation Pathway(Tissue Factor Pathway)

IX

NB: production of IXaInteraction of intrinsic and extrinsic pathways

Thrombin (IIa)

Prothrombin (II)

Xa

VIIa

TF

IXa

Tissue Factor Pathway Inhibitor

IX

TFITFPI

NB: Inhibition of Xa and VIIa

VIIa forms as usual via binding of VII to TFVIIa forms as usual via binding of VII to TF VIIa activates some XVIIa activates some XXaXa Xa converts a small amt of prothrombin to thrombin; Xa converts a small amt of prothrombin to thrombin;

this thrombin is used to produce small amts of VIIIa this thrombin is used to produce small amts of VIIIa and Vaand Va

As the concentration of TF-VIIa-Xa-thrombin As the concentration of TF-VIIa-Xa-thrombin increases, Tissue Factor Pathway Inhibitor inactivates increases, Tissue Factor Pathway Inhibitor inactivates this complex stopping further production of thrombin.this complex stopping further production of thrombin.

New: VIIa also activates IXNew: VIIa also activates IXIXa (Key to new IXa (Key to new scheme) scheme)

IXa, with VIIIa (produced as above), produces Xa; this IXa, with VIIIa (produced as above), produces Xa; this Xa with Va (produced as above) produces new Xa with Va (produced as above) produces new thrombin; this thrombin produces more VIIIa and Va thrombin; this thrombin produces more VIIIa and Va and now we get lots of thrombin and fibrin!and now we get lots of thrombin and fibrin!

Physiologic Inhibitors of coagulationPhysiologic Inhibitors of coagulation

Antithrombin III (serpin)Antithrombin III (serpin) Activated Protein C + protein SActivated Protein C + protein S

– Inactivates Va and VIIIa (via proteolysis)Inactivates Va and VIIIa (via proteolysis)– NB: Factor V LeidenNB: Factor V Leiden

Thrombomodulin Thrombomodulin – Binds to thrombinBinds to thrombin– Decreases ability to produce fibrinDecreases ability to produce fibrin– Increases ability to activate Protein CIncreases ability to activate Protein C

Non-physiologic inhibitors of Non-physiologic inhibitors of coagulationcoagulation

Vitamin K antagonists (in vivo)Vitamin K antagonists (in vivo) Ca chelators (in vitro only)Ca chelators (in vitro only)

– EDTAEDTA– CitrateCitrate– OxalateOxalate

* Heparin (in vivo and in vitro)* Heparin (in vivo and in vitro)

Role of factor XIIaRole of factor XIIa

Bleeding Disorders (1)Bleeding Disorders (1)..

Causes of bleeding disorders:Causes of bleeding disorders:

VESSEL DEFECTSVESSEL DEFECTS PLATELET DISORDERSPLATELET DISORDERS FACTOR DEFICIENCIESFACTOR DEFICIENCIES OTHER DISORDERSOTHER DISORDERS

VESSEL DEFECTSVESSEL DEFECTS::

Can be caused by Can be caused by AcquiredAcquired or or hereditaryhereditary causes:causes:

A- Hereditary:A- Hereditary: Hereditary haemorrhagic telangiectasia:Hereditary haemorrhagic telangiectasia:

Typically in nasopharynx and gastroin Typically in nasopharynx and gastroin testinal tract, which bleed spontaneously or testinal tract, which bleed spontaneously or following minor trauma.following minor trauma.

Marlan's syndromeMarlan's syndrome : rare connective tissue : rare connective tissue disordersdisorders

B. Acquired:B. Acquired:1- Infections:1- Infections: Bacterial.Bacterial. Viral.Viral. Rickettsial.Rickettsial.2- Allergic:2- Allergic: Drugs Drugs Food.Food.3- Atrophic:3- Atrophic: Dysproteinaemia Dysproteinaemia Cushing's syndrome and steroid therapy.Cushing's syndrome and steroid therapy.4- Miscellaneous:4- Miscellaneous: Simple easy bruisingSimple easy bruising Autoerythrocyte sensitization Autoerythrocyte sensitization Vitamin C deficiency.Vitamin C deficiency.

1.1. THROMBOCYTOPENIATHROMBOCYTOPENIA

2.2. THROMBOCYTOPATHYTHROMBOCYTOPATHY THROMBOCYTOPENIATHROMBOCYTOPENIA: INADEQUATE : INADEQUATE

NUMBER OF PLATELETSNUMBER OF PLATELETS THROMBOCYTOPATHYTHROMBOCYTOPATHY: ADEQUATE : ADEQUATE

NUMBER BUT ABNORMAL FUNCTIONNUMBER BUT ABNORMAL FUNCTION

22 . .PLATELET DISORDERSPLATELET DISORDERS::

ThrombocytopeniaThrombocytopenia Thrombocytopenia (or -paenia, or Thrombocytopenia (or -paenia, or

thrombopenia in short) is the presence of thrombopenia in short) is the presence of relatively few relatively few plateletsplatelets in in bloodblood..

Generally speaking a normal platelet count Generally speaking a normal platelet count ranges from 150,000 and 450,000 per ranges from 150,000 and 450,000 per mm3. mm3.

Note: The number of platelets in a blood Note: The number of platelets in a blood sample also decreases rather quickly with sample also decreases rather quickly with time, and a low platelet count may be time, and a low platelet count may be caused by a delay between sampling and caused by a delay between sampling and analysis.analysis.

Signs and symptoms:Signs and symptoms: Often, low platelet levels do not lead to clinical Often, low platelet levels do not lead to clinical

problems; rather, they are picked up on a routine problems; rather, they are picked up on a routine full blood count (or CBC, complete blood count ). full blood count (or CBC, complete blood count ).

Occasionally, there may be bruising, particularly Occasionally, there may be bruising, particularly purpura in the forearms, nosebleeds and/or purpura in the forearms, nosebleeds and/or bleeding gums.bleeding gums.

Note: Note: It is vital that a full medical history is elicited, to It is vital that a full medical history is elicited, to

ensure the low platelet count is not due to a ensure the low platelet count is not due to a secondary process. secondary process.

It is also important to ensure that the other blood It is also important to ensure that the other blood cell types (red blood cells, and white blood cell types (red blood cells, and white blood cells), are not also suppressed.cells), are not also suppressed.

Causes of thrombocytopenia:Causes of thrombocytopenia:

Decreased platelet counts can be due to a number Decreased platelet counts can be due to a number of disease processes:of disease processes:

1. Decreased production:1. Decreased production:

A. Selective megakaryocyte depression: A. Selective megakaryocyte depression: Decreased production of thrombopoietin by the Decreased production of thrombopoietin by the

liver in liver failure. liver in liver failure. Sepsis, systemic viral or bacterial infection Sepsis, systemic viral or bacterial infection Dengue fever can cause thrombocytopenia by Dengue fever can cause thrombocytopenia by

direct infection of bone marrow megakaryocytes direct infection of bone marrow megakaryocytes as well as immunological shortened platelet as well as immunological shortened platelet survival survival

B. Part of general bone marrow B. Part of general bone marrow failurefailure::

– Megaloplastic anaemia (Vitamin B12 or folic Megaloplastic anaemia (Vitamin B12 or folic acid deficiency). acid deficiency).

– Leukemia.Leukemia.– Myelodysplastic syndromeMyelodysplastic syndrome

Marrow infiltration. Marrow infiltration.

A plastic anaemia.A plastic anaemia.

Multiple myeloma.Multiple myeloma.

22 - -Increased destructionIncreased destruction::– Idiopathic thrombocytopenic purpuraIdiopathic thrombocytopenic purpura (ITP) (ITP) – Disseminated intravascular coagulationDisseminated intravascular coagulation (DIC) (DIC) – Paroxysmal nocturnal hemoglobinuriaParoxysmal nocturnal hemoglobinuria (PNH) (PNH) – Secondary immune thrombocytopenia (Secondary immune thrombocytopenia (

systemic lupus erythematosussystemic lupus erythematosus (SLE), post (SLE), post infections and infections and antiphospholipid syndromeantiphospholipid syndrome).).

– Splenic sequestration of platelets due to Splenic sequestration of platelets due to hypersplenismhypersplenism

– Dengue feverDengue fever has been shown to cause has been shown to cause shortened platelet survival and immunological shortened platelet survival and immunological platelet destruction platelet destruction

– HIV HIV

Clinical features of immune Clinical features of immune thrombocytopeniathrombocytopenia::

Degree of thrombocytopenia:

Symptoms.Physical findings

Mild (>50 000/mm)NoneNone.

Moderate (30-50000/mm)Bruising with minor trauma

Scattered ecchymosses at trauma site.

Sever (10-30000/mm)Spontaneous bruising, menorrhagia(heavy menstrual bleeding)

Petechiae and purpura, more prominent on extremities.

Marked (<10000/mm)Spontaneous bruising, mucosal bleeding, risk for CNS bleeding.

Generalized purpura.

IMMUNE THROMBOCYTOPENIAIMMUNE THROMBOCYTOPENIA::

The platelets are coated with autoantibody The platelets are coated with autoantibody (immunoglobulin) and are removed by the (immunoglobulin) and are removed by the macrophages of the reticuloendothelial macrophages of the reticuloendothelial system. Their lifespan is therefore reduced system. Their lifespan is therefore reduced from 7-10 days to a few hours.from 7-10 days to a few hours.

A. Autoimmune thrombocytopeniaA. Autoimmune thrombocytopenia

A. AcuteA. Acute

1.1. Usually presents in childhood (2-7 years).Usually presents in childhood (2-7 years).

2.2. Often follows a viral infection.Often follows a viral infection.

3.3. Purpuric rash or epistaxis frequent.Purpuric rash or epistaxis frequent.

4.4. Typically resolves spontaneously. A Typically resolves spontaneously. A minority develop mucosal bleeding. Up to minority develop mucosal bleeding. Up to 20% develop chronic immune 20% develop chronic immune thrombocytopenia.thrombocytopenia.

B. B. ChronicChronic

1.1. Immune thrombocytopenia in adults is Immune thrombocytopenia in adults is less likely to resolve without therapy and less likely to resolve without therapy and usually chronic. usually chronic.

2.2. It is more common in females (ratio 1:4). It is more common in females (ratio 1:4).

3.3. Autoantibody is present on the platelet Autoantibody is present on the platelet surface and may also he present as free surface and may also he present as free antibody in serum.antibody in serum.

B. Alloimmune thrombocytopeniaB. Alloimmune thrombocytopenia

Mothers who have been sensitized (e.g. by Mothers who have been sensitized (e.g. by blood transfusion or previous pregnancy) to blood transfusion or previous pregnancy) to platelet antigens may develop antibodies which platelet antigens may develop antibodies which cross the placenta and coat fetal and neonatal cross the placenta and coat fetal and neonatal platelets, which are then removed in the rcticulo platelets, which are then removed in the rcticulo endothelial system. typically resolves endothelial system. typically resolves spontaneously over a few weeks. spontaneously over a few weeks.

Individuals with such platelet alloanti bodies can Individuals with such platelet alloanti bodies can also become thrombocytopenic after blood also become thrombocytopenic after blood transfusion (post-transfusion purpura). transfusion (post-transfusion purpura).

Laboratory features of immune Laboratory features of immune thrombocytopeniathrombocytopenia::

Thrombocytopenia with increased Thrombocytopenia with increased numbers of large platelets (the normal size numbers of large platelets (the normal size is less than 3µm).is less than 3µm).

Increased numbers and size of Increased numbers and size of megakaryocytes (in the BM).megakaryocytes (in the BM).

Reduced intravascular platelet survival Reduced intravascular platelet survival Elevated levels of platelet associated IgGElevated levels of platelet associated IgG

Diagnosis of platelet defectsDiagnosis of platelet defects

Laboratory tests might include: Laboratory tests might include: Full blood countFull blood count Peripheral blood smear.Peripheral blood smear. Liver enzymes.Liver enzymes. Renal function, vitamin B12 levels, folic acid levels.Renal function, vitamin B12 levels, folic acid levels. Erythrocyte sedimentation rate.Erythrocyte sedimentation rate. If the cause for the low platelet count remains unclear, If the cause for the low platelet count remains unclear,

bone marrow biopsy is often undertaken, to differentiate bone marrow biopsy is often undertaken, to differentiate whether the low platelet count is due to whether the low platelet count is due to decreased decreased productionproduction or or peripheral destructionperipheral destruction..

Platelets dysfunction Platelets dysfunction (thrombocytopathy)(thrombocytopathy)::

These are characterized by: These are characterized by:

1.1. A prolonged bleeding time A prolonged bleeding time

2.2. Normal platelet count Normal platelet count

3.3. And disordered platelet aggrega tion. And disordered platelet aggrega tion.

The causes can be classified into The causes can be classified into acquiredacquired and and hereditary.hereditary.

The causes of The causes of acquired acquired platelet's dysfunction:platelet's dysfunction:– Ureamia.Ureamia.– Myeloproliferative disorders: Myeloproliferative disorders: polycythaemia polycythaemia

ruhra Vera, myelofihrosis.ruhra Vera, myelofihrosis.– Chronic hypoglycemia.Chronic hypoglycemia.– Liver diseases.Liver diseases.– Sever burns.Sever burns.– Drugs: Drugs: aspirin, other non-steroidal anti-aspirin, other non-steroidal anti-

inflammatory agents, some antibiotic therapy inflammatory agents, some antibiotic therapy (e.g. cephalosporins)(e.g. cephalosporins)

b- b- HereditaryHereditary disorders of platelet's disorders of platelet's dysfunction:dysfunction:

are rare and present with are rare and present with bruis ing/excessive bleeding after bruis ing/excessive bleeding after surgery or injury in childhood.surgery or injury in childhood.

1. Membrane abnormalities:1. Membrane abnormalities: Bernard-Soulier syndrome, associated with large Bernard-Soulier syndrome, associated with large

platelets platelets May-Hegglin anomaly, the combination of May-Hegglin anomaly, the combination of

thrombocytopenia, pale-blue leuckocyte inclusions, thrombocytopenia, pale-blue leuckocyte inclusions, and giant plateletsand giant platelets

Platelet factor-3 deficincy. Platelet factor-3 deficincy.

2. Intracellular abnormalities:2. Intracellular abnormalities: Alpha-granule deficiency.Alpha-granule deficiency. Defects of thromboxane synthesis.Defects of thromboxane synthesis. Defect response to thromboxane. Defect response to thromboxane.

3. Miscellaneous:3. Miscellaneous: Epstein's syndrome.Epstein's syndrome.

4. Dilutional loss:4. Dilutional loss: Massive transfusion of old blood to Massive transfusion of old blood to

bleeding patients. bleeding patients.

5. Medication-induced:5. Medication-induced: For example For example Heparin, Sulfonamide Heparin, Sulfonamide

antibiotics, Vancomycinantibiotics, Vancomycin and and Measles-Measles-mumps-rubella vaccine.mumps-rubella vaccine.