Hemostasis & blood coagulation

Dr. Wasif Haq

Hemostasis• Hemostasis: prevention of blood

loss.• Is hemostasis same as

homeostasis?

Why doesn’t blood clot in body?

• Smooth endothelium surface.• Glycocalyx • Thrombomodulin binding with Thrombin

and activation of Protein C inactivating factor 5 and factor 8.

Hemostasis steps• Vascular spasm• Platelet plug formation• Blood clot formation & fibrous tissue

enclosure of blood clot.

HemostasisHemostasis

Primary Hemostasis:•Vascular

contraction, platelet adhesion &

formation of a soft aggregate plug.•Short lived.

Secondary Hemostasis:•Activation of clotting factors.•Stabilizes the clot.

Step 1.Vascular spasm

• Vessel wall contraction• Contraction related to severity of trauma.• Result of • A) Nervous reflex (pain and other

impulses from endothelium and adjacent tissue),

• B) Local myogenic spasm(major contributor)

• C) Humoral factors(from platelets Thromboxane A2 & Prostaglandins)

Step 1.Vascular spasm

Platelets• Also called as Thrombocytes.• Fragments of Megakaryocytes.• No nuclei.• Normal count 150,000-300,000 per micro

liter.

Platelet structure• Surface coating ‘Glycoprotein’

prevents platelet binding but stimulation in trauma and injury.

• Platelet wall also releases Phospolipids which has rolein extrinsic and intrinsic pathway of clotting.

Contents of Platelets• Contractile proteins e.g. Actin,Myosin &

Thrombosthenin.• Endoplasmic reticulum & Golgi apparayus

remanants- enzyme syntheisis and Ca++ storage.

• Mitochondria-ATP & ADP formation.• Enzymes-Prostaglandin synthesis.• Fibrin stabilizing factor-Strengthening the

clot• Growth factor- Vessel wall cells growth for

repairing damaged vessel wall.

Step 2.Platelet Plug• Platelet swelling upon contact with

injured vessel.• Release of sticky granuels helping to

adhere to injured collagen and protein ‘von Willebrand factor.’

• Activativation of adjacent proteins by A.D.P. & Thromboxane A2

• Platelet plug stabilized by fibrin threads.

Step 2.Platelet Plug

Step 2.Platelet Plug

Love your mistakes, they are improving you.

Step 3.Blood clot• Traumatized vessel wall,adherent proteins

and platelets release substances to activate clotting proteins.

• 3-6minutes plugging of small injuries followed by clot retraction in next 20-60mins.

• Clot can be covered completely by fibrous tissue or dissolved by plasmin protein.

Step 3.Blood clot

Mechanism of blood coagulation

Reactions in blood

Formation of activated substances(Prothrombin activator)

Prothrombin Thrombin

Fibrinogen Fibrin

Calcium and Platelets

Thrombin & Fibrinogen• Thrombin acts on Fibrinogen forming

Fibrin monomers which polymerize to form Fibrin.

• Fibrin stabilizing factor released from platelets which is activated by Thrombin,helps to stabilize clot.

• Thrombin once activated starts a vicious cycle,activating Fibrinogen and other clotting factors.

Thrombin & Fibrinogen

Coagulation pathways

Intrinsic Pathway:By blood itself.Proceeds slowly.

Extrinsic Pathway:Trauma to vessel wall & surrounding tissueRapid activation.

Ca++ essential as helps in thrombin activation and formation of fibrin fibers from fibrinogen

monomers.

Diseases and disorders

• Thrombus: Abnormal clot in blood vessel, static.

• Embolus: Freely flowing clot, mobile.• Hemophilia: Bleeding disease caused by

factor 8 deficiency. Treatment: injection of factor 8.

• Thrombocytopenia: very low quantity of plateets. Two types Thrombocytoenia purpura & Idiopathic thrombocytopenia.

Anticoagulants• For body:• Heparin-action lasts for 1.5-4 hours• Coumarin(Warfarin) action lasts for 1-3

days after therapy cessation.• For lab use:• citrates and oxalates.

Lab tests• Bleeding time:1-6 minutes. Depends

upon depth of wound and degree of hyperemia.

• Clotting time: 2-6minutes by Capillary tube method.

• Prothrombin time: indication of total quantity of Prothrombin in blood. 12 seconds.

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