2 Physio: Hemostasis

Front 1

gen

Back 1

- fast
- localized
- carefully controlled

Front 2

steps

Back 2

1. vascular spasm
2. platelet plug formation: primary hemostasis
3. blood clot formation: coagulation: secondary hemostasis
4. healing
5. clot removal: fibrinolysis

Front 3

platelet characteristics

Back 3

platelets:
- 2-4 microm
- flat, round or oval discs
- enucleate in mammals
- reptiles, birds:4-8 microm, nucleate
- concentration 150-300K/ microL
- HL: 10 days

Front 4

platelet origin

Back 4

platelets derived from bone marrow megakaryocytes:
1. pluripotent stem cell
2. myeloid stem cell
3. CFU/Meg
4. megakaryoblast
5. megakaryocyte
6. fragmentation into hundreds of platelets
- controlled by hepatic thrombosthenin

Front 5

platelet content

Back 5

platelets:
1. contractile proteins: actin, myosin, thrombosthenin
2. ADP, ATP
3. prostaglandins, serotonin, clotting factors, endothelial growth factors
4. Ca

Front 6

platelet fx

Back 6

platelets:
1. release of chemicals which promote vasospasm: step 1
2. formation of platelet plugs: step 2
3. release of factors that promote coagulation (step 3) and healing processes (step 4)

Front 7

step 1: vasospasm: purpose

Back 7

step 1: vasospasm: purpose
- occurs immediately upon vessel injury to:
1. reduce BF and blood loss
2. facilitate subsequent steps of hemostasis

Front 8

step 1: vasospasm: process

Back 8

step 1: vasospasm:
1. immediate: release of endothelin from damaged cells, initiating vasospasm
2. later: release of thromboxane A2 (prostaglandin derivative) and serotonin from platelets to maintain vasospasm
- myogenic contraction of damaged smooth m cells lasting min- hours
- often what saves animal's life

Front 9

step 2: platelet plug formation/ primary hemostasis: initial steps

Back 9

step 2: platelet plug formation/ primary hemostasis: initial steps
1. damaged endothelial cells and membrane releases/ shows vWF
2. endothelial and plasma vWF bind to damaged cell membranes and collagen fibers
3. vWF undergoes confirmational change, expressing receptor sites for platelets
4. binding of platelets begins

Front 10

step 2: platelet plug formation/ primary hemostasis: platelet-vWF

Back 10

step 2: platelet plug formation/ primary hemostasis:
binding of vWF activates platelets to:
1. send out pseudopodia to interact with other platelets
2. release serotonin and thromboxane A2: promote vasospasm
3. release ADP and thromboxane A2: attracts more platelets
4. release ADP and fibronectin: glue-like substance to promote adhesion, platelet stability at site
5. release several platelet factors (3, 5, 8) involved in clotting
6. expose their own receptor sites for fibrinogen and prothrombin: essential for later clotting

Front 11

step 2: platelet plug formation/ primary hemostasis: gen

Back 11

step 2: platelet plug formation/ primary hemostasis:
- loose plug formed within 1-2 minutes to seal off injury site
- crucial for thousands of minute ruptures that occur everyday
- without: petechiae

Front 12

larger injuries

Back 12

larger injuries:
clotting cascade is activated concurrently to stabilize the platelet plug with fibrin strands

Front 13

step 3: clot formation/ secondary hemostasis: gen

Back 13

step 3: clot formation/ secondary hemostasis:
= coagulation
- cascades of chemical reactions leading to the formation of strong fibrin threads within the platelet plug
- fibrin gives strength
- complete in 3-6 minutes
- occurs in 3 stages

Front 14

step 3: clot formation/ secondary hemostasis: clotting factors

Back 14

step 3: clot formation/ secondary hemostasis:
>50 clotting factors (mostly enzymes) are involved:
1. hepatic plasma
2. platelet: produce and degranulate factors
3. tissue
4. Ca: bridge (-) factors
- lack of any can lead to bleeding disorders

Front 15

step 3: clot formation/ secondary hemostasis: stage 1

Back 15

step 3: clot formation/ secondary hemostasis: stage 1:
1. extrinsic
2. intrinsic
- both systems:
1. localized
2. require plasma and platelets factors, Ca
3. active simultaneously in most injuries

Front 16

step 3: clot formation/ secondary hemostasis: stage 1: extrinsic system

Back 16

step 3: clot formation/ secondary hemostasis: stage 1: extrinsic system
- faster and more powerful
- tissue based
1. injured tissue expresses tissue factor
2. tissue factor (thromboplastin) activates an enzymatic cascade, factors 5, 7, 10 and Ca, leading to
3. prothrombin activator complex in 15-30 sec

Front 17

step 3: clot formation/ secondary hemostasis: stage 1: intrinsic system

Back 17

step 3: clot formation/ secondary hemostasis: stage 1: intrinsic system
- plasma based
1. change in surface charge (mem pot) of endothelial mem binds and activates plasma factor 12
2. factor 12 activates an enzymatic cascade, kallekrein, factors 5, 8-11, Ca, leading to
3. prothrombin activator complex in 1-6 min

Front 18

step 3: clot formation/ secondary hemostasis: stage 1: triggers of intrinsic system

Back 18

step 3: clot formation/ secondary hemostasis: stage 1: triggers of intrinsic system
- change in mem pot caused by:
1. inflammatory rxns: endotoxins
2. activated platelets
3. contact with glass surface
4. parasites
5. allergic reaction
6. artheroschlerosis
- can be triggered without bleeding

Front 19

step 3: clot formation/ secondary hemostasis: stage 2: common pathway

Back 19

step 3: clot formation/ secondary hemostasis: stage 2:
common pathway
- prothrombin activator complex converts proenzyme prothrombin to active enzyme, thrombin

Front 20

step 3: clot formation/ secondary hemostasis: stage 2: common pathway: prothrombin

Back 20

step 3: clot formation/ secondary hemostasis: stage 2: common pathway:
prothrombin
1. hepatic alpha globulin
2. synthesis is vit K dependent
3. attaches itself to activated platelets

Front 21

step 3: clot formation/ secondary hemostasis: stage 2: common pathway:
thrombin

Back 21

step 3: clot formation/ secondary hemostasis: stage 2: common pathway:
thrombin:
- most powerful proteolytic enzyme in hemostasis
1. positive feedback effect on extrinsic and intrinsic system, platelet aggregation
2. fibrin formation
3. thrombin hydrolyzes fibrinogen into fibrin monomers: polymerize into long fibrin fibers that cross-link into a strong meshwork in and around the platelet plug
= stable clot, bleeding stops within 3-6 min after injury

Front 22

fibrinogen

Back 22

fibrinogen:
- hepatic soluble protein
- already bound to activated platelets

Front 23

step 3: clot formation/ secondary hemostasis: stage 2: common pathway:
clot retraction

Back 23

step 3: clot formation/ secondary hemostasis: stage 2: common pathway:
clot retraction:
- within 30 minutes after clot formation
- platelets contract more, pulling fibrin threads together
- clot tightens and pulls edges of injured blood vessel together

Front 24

Step 4: Healing

Back 24

Step 4: Healing:
- fibrin meshwork serves as scaffolding for invading fibroblasts
- fibroblasts are stim by platelet (and endothelial) derived endothelial growth factor
- wound healing/ scar formation begins

Front 25

step 5: fibrinolysis process

Back 25

step 5: fibrinolysis:
1. injured tissue and endothelium very slowly release tissue-Plasminogen activator (tPA) 1-2 days after clot formation
2. tPA activates the hepatic plasma factor plasminogen to plasmin = proteolytic enzyme
( also allows WBCs and neoplastic cells to migrate)
3. plasmin hydrolyzes fibrin and clotting factors which are removed by macrophages

Front 26

step 5: fibrinolysis results

Back 26

step 5: fibrinolysis results:
- dissolves clot and opens the blood vessel
- should finish after about a week

Front 27

prevention of hemostasis

Back 27

prevention of hemostasis:
1. smoothness of endothelial cells: prevent platelet adhesion and activation
2. intact endothelial cells and WBCs secrete (vasodilators) prostacyclin and NO: inhibits platelet activation and adhesion
- stimulus has to be stronger than these forces to start clotting

Front 28

prevent of excessive clot formation

Back 28

prevent of excessive clot formation:
1. fibrin binds thrombin: limits fibrin formation and positive feedback
2. anti-thrombin III: alpha globulin which deactivates thrombin and other clotting factors
3. heparin from mast cells/ basophils combines with anti-thrombin III, greatly augmenting its effectiveness (heparin cannot work alone)

Front 29

in vitro anticoagulant agents

Back 29

in vitro anticoagulant agents:
1. heparin
Ca binding agents:
2. citrate
3. oxalate
4. EDTA
- do not use in vivo because leads to acute hypocalcemia= death

Front 30

in vivo anticoagulant agents

Back 30

in vivo anticoagulant agents:
1. heparin
2. vit K antagonists: K needed for prothrombin and other clotting factors
3. prostaglanding synthesis inhibitors: NSAIDs inhibit thromboxane and prostacyclin

Front 31

laboratory evaluation

Back 31

laboratory evaluation:
1. platelet counts
2. muscosal bleeding time
do not measure platelets:
3. OSPT
4. APTT

Front 32

platelet counts

Back 32

platelet counts:
- counting chambers, automatic counters or via blood smears
- all methods are rather inaccurate

Front 33

mucosal bleeding time

Back 33

mucosal bleeding time:
- time until bleeding stops after small incision into skin or mucosa
- expected time: 1-5 min
- measures functional ability of platelets and vWF to plug minute injuries

Front 34

OSPT

Back 34

OSPT ( one stage prothrombin time):
- measures clot formation in citrated plasma after addition of extrinsic tissue factor, platelet factors and Ca
- measures extrinsic and common pathway, NOT platelets
- focus: extrinsic plasma factors, prothrombin, fibrinogen
- expected time <10 sec

Front 35

APTT

Back 35

APTT ( activated partial thromboplastin time):
- measures clot formation in citrated plasma after addition of contact activator (- charged diatomaceous earth), platelet factors, and Ca
- measures intrinsic and common pathway, NOT platelets
- focus: intrinsic plasma factors, prothrombin, fibrinogen
- expected time: 60-120 sec

Front 36

thrombocytopenia

Back 36

thrombocytopenia:
decreased platelets from:
1. decreased production: bone marrow, drugs, FELV
2. increased destruction or consumption: immune-mediated
- doesn't change OSPT or APTT

Front 37

von Willebrand's disease

Back 37

von Willebrand's disease:
- most common bleeding disorder in animals due to genetic lack or insufficiency
- platelets fail to adhere to injury sites, resulting in spontaneous bleeding (petechial or ecchymotic)
- signs: mild- fatal
- described in 60 breeds of dogs: 70% of Dobermans

Front 38

Vit K deficiency/ rodenticide poisoning

Back 38

Vit K deficiency/ rodenticide poisoning:
- coumarin (warfarin): vit K antagonist which impairs synthesis of several clotting factors including prothrombin

Front 39

hemophilias

Back 39

genetic deficiencies in a clotting factor (usually factor 8)
- very rare

Front 40

thrombosis

Back 40

thrombosis:
- clotting in an unbroken blood vessel
- due to: stasis, atheroschlerosis, trauma, parasites, tumors
- thrombus dislodges: embolism--> blocks vessels--> ischemia

Front 41

saddle thrombus

Back 41

saddle thrombus (aortic thromboembolism):
- common in cats
- due to myocardial disease --> thrombus formation in LA--> into aorta
- will reoccur if myocardial dz not treated
- often lodges at ca trifurcation , blocking blood supply into the iliac arteries causing PL paralysis