Haematolgy 3

Question 1

What is haemostasis

Answer 1

➢The mechanism for dealing with bleeding and clotting
➢Haemostasis comes from the Greek - heme meaning blood and stasis to halt

Question 2

Why and what happens during normal haemostasis

Answer 2

1. Maintain the fluidity of circulating blood
2. Limit and arrest bleeding following injury by formation of a blood clot whilst at the same time maintaining blood flow through the damaged vessel
3. Removal of a blood clot upon completion of wound healing

Question 3

Sequence of haemostasis

Answer 3

1) the endothelium/blood vessel Wall is destroyed
2)platelets cause coagulation
3)coagulation factors

Question 4

Platelets in haemostasis

Answer 4

-anuclear
-circulate for 7-10 days
-each days 100 billion is produced from megakaryocytes to maintain Normal count

Question 5

Role of platelets

Answer 5

➢Their primary physiological role is in blood clotting
➢Detect damaged vessel endothelium ➢Accumulate at the site of the vessel injury ➢initiate blood clotting to block the circulatory leak

➢They are involved in ALL stages of haemostasis ➢Primary haemostatic plug (platelet to platelet interactions)
➢Secondary haemostatic plug (platelet – coagulation protein interactions)
➢Involved in tissue injury, inflammation and wound healing by attracting and binding leukocytes

Question 6

Megakaryocytes

Answer 6

-Largest (50-100μm) and rarest cells in BM
-Polyploidal (More than one nucleus)
-Unique to mammals
-Can produce ~3000 platelets (compared to 2 daughter cells in other lineages)
-Platelet formation is far more complicated than the production of white cells

Question 7

Platelet production

Answer 7

Phase I
-Megakaryocyte maturation(need to be big to have enough protein)
→ Endomitosis (DNA replication without cell division)
→Cytoplasm enlargement (cytoskeletal proteins and platelet granules)
Phase II
-Platelet generation
→ Mature megakaryocytes extend long branching processes (proplatelets)
→ Organelles and granules are transported to proplatelets
→ Driven by the cytoskeleton
They migrate to blood vessels in bone Marrow
Stimulated by thrombopoietin tpo

Question 8

Processes that occur in a healthy blood vessel to prevent coagulation

Answer 8

-nitric oxide ptrostacyclin prevents platelets from being active as well as stops them from sticking

-continuous barrier of endothelium which prevents platelets sticking to collagen

-natural anticoagulants such as anti thrombotic which stops unwanted coaugulation

-platelets are not active

Question 9

What happens when a blood vessel becomes damaged (platelet activation)

Answer 9

-Platelets become active
-Endothelium is damaged to platelets stick to collagen and to Von willebrand factor(vwf) at site of blood vessel damage(it forms a bridge between collagen and platelets sticking, stick to vwf first then collagen)
-Platelets become activated, change shape, release granules and aggregate
-prothrombotic factors

Question 10

What is haemostasis and what does is require

Answer 10

-Fast series of reactions for stoppage of bleeding
-Requires clotting factors, and substances released by platelets andinjured tissues

Question 11

3 steps of haemostasis

Answer 11

1. Constriction of blood vessels (vasoconstriction)
2. Platelet plug formation
3. Coagulation (blood clotting)

Question 12

HAEMOSTASIS: VASOCONSTRICTION

Answer 12

➢Direct injury to vascular smooth muscle
➢Chemicals released by endothelial cells and platelets
➢Pain reflexes

Question 13

SECONDARY HAEMOSTASIS: COAGULATION

Answer 13

12 factors
Castcasereaction
Fibrinogen,prothrombin
Tissue factor

Question 14

Blood coagulation cascade

Answer 14

Vessel injury-tissue factor-blood coagulation cascade -thrombin-fibrin(net,sits over blood cloth,stabilising clotting-stable haemostatic plug

Question 15

Coagulation pathways

Answer 15

Consists of two distinct pathways:
-the extrinsic (tissue factor pathway)
-the intrinsic pathway
X marks the spot and is the common factor

Question 16

Clot stabilisation

Answer 16

➢Soluble fibrinogen converted to insoluble fibrin
➢Stabilises platelet clot

Question 17

FIBRINOLYSIS(removal of cloths when we don’t need them)

Answer 17

-Two mechanisms limit clot size
>Swift removal and dilution of clotting factors >inhibition of activated clotting factors
-Fibrinolysis breakdown of clots
>Removes clots after healing
>Begins within two days; continues for several

Question 18

DISORDERS OF HAEMOSTASIS

Answer 18

1. Thromboembolic disorders: undesirable clot formation
2. Bleeding disorders: abnormalities that prevent normal clot formation

Question 19

Thrombus

Answer 19

-clot that develops and persists in unbroken blood vessel
–May block circulation leading to tissue death
–Deep venous thrombosis (DVT) and pulmonary embolism

Question 20

Embolus

Answer 20

thrombus freely floating in bloodstream
Formed somewhere else ans a small piece fractured

Question 21

Embolism

Answer 21

The fracture get stuck somewhere else

Question 22

Risk factors of thromboembolic conditions

Answer 22

atherosclerosis, inflammation, slowly flowing blood or blood stasis from immobility

Question 23

Antithromboric drugs

Answer 23

-Aspirin= Cyclooxygenase inhibitor, that blocks thromboxane A2 synthesis and inhibits platelet aggregation(arteries )
-heparin = Anticoagulant used clinically for pre- and postoperative cardiac care(venous)
-Warfarin= for those prone to atrial fibrillation, interferes with action of vitamin k (its an antagonist)(rat poison),used in old patients
-Apixaban, Rivaroxaban= Factor X Inhibitors (DOACs (direct oral anticoagulants)/NOACs (novel oral anticoagulants)

Question 24

Bleeding disorders

Answer 24

➢Thrombocytopenia - deficient number of circulating platelets ➢Haemophilia includes several similar hereditary bleeding
disorders
➢Haemophilia A: most common type (77% of all cases); factor VIII deficiency ➢Haemophilia B: factor IX deficiency
➢Haemophilia C: mild type; factor XI deficiency
➢Von Willebrand’s Disease most common inherited bleeding disorder