hemostasis

Question 1

what are the 3 stages of bleeding control?

Answer 1

1. vasoconstriction
   
   1. over in 30 min
2. primary hemostasis
   
   1. platet aggregation and adhesion
   2. formation of temporary plug
3. secondary hemostasis
   
   1. fibrin clot fomration

Question 2

what stimulates vascular repair?

Answer 2

PDGF- platlet-derived growth factor

1. this is from the activated platlets?

Question 3

differentiate between the following terms

1. clot
2. thrombus
3. emboli

Answer 3

1. clot
   
   1. coagulation of blood at an extravascular site by vascular injury
2. thrombus
   
   1. clot in the vessel lumen
3. emboli
   
   1. bits of thrombus that break off and travel in the blood stream to distant sites

Question 4

pick up on vasoconstriction

Question 5

1. how long does vasoconstriction last?
2. mechanism

Answer 5

1. lasts 30 min
   
   1. temporarily closes small vessels to stop bleeding
2. platlets release
   
   1. thromboxane and serotonin(5HT
3. dying endothelial cells release
   
   1. endothelin, via thrombin
   2. NO
   3. PGI2
4. increase in tissue perfusion due to bloodleakage

Question 6

where are platlets stored?

whats their lifespan?

Answer 6

stored in spleen

10 days

Question 7

describe the regulation of platelet production

Answer 7

feedback on megakaryocytes via TPO thrombopoeitin, inducing maturation of the megakaryocytes

1. platlets have a TPO membrane receptor that remove it from the blood.
2. so, an increase in TPO concentration leads to and increase in platlets. a decrese leads to less platlet generation

Question 8

what are the four steps to formation of platlet plug?

1. what do the platlets bind to?
2. what do endtothelial and megakaryoctyes secrete to assist with step 1?
   
   1. describe this cascade
3. what is released by platlets? what kind of feed is this?

Answer 8

1. platlet adhesion to collagen
   
   1. platlett membranes contain integrin receptors, when exposed to collagen they bind
   2. vWF asists bond
2. platlets activate
   
   1. shape change, through canlicular system
      
      1. from binding to the collagen the influx of Ca, via PLc pathway
   2. release of : ADP, ATP, 5HT, clotting factor 5
   3. thrombaoxane and 5HT induce vasoconstiction and aggregattion
3. platlets recruitment of other platlets
   
   1. ADP, thromboxane and 5HT start a feedforward cycle
4. platlets adhering to each other
   
   1. vWF and fibrinogen receptors. fibrinogen -> fibrin

Question 9

what keeps platlets away from healthy tissue?(3)

Answer 9

platlets not activated have a charge difference from the edothelial tissue, and the smoothness and endothelial derived protcyclin keep the platlets off

1. charge
2. smoothness
3. enodthelial dervied prostacyclin

Question 10

what is the key step in blood clotting? and what enzyme is responsible for this?

Answer 10

conversion of soluble plasma protein fibrinogen -> insoluble fibrin

thrombin is a key enzyme in clot formation, negtaive/positive feedback.

Question 11

blood coagulation is initiated through what two pathways

Answer 11

both converge on the conversion of fibrinogen to fibrin

1. extrinsic-common
   
   1. damage of extravascuular tissuue andendothelium
   2. slow
   3. 2-6 min
   4. many mechanisms to combat
2. intrisic-not common
   
   1. damage of the enothelium and eposure of collagen, via toxins, pressur and chemical agents
   2. explosive in nature
      
      1. under 15 sec
   3. initiated by tissue thromboplastin
   4. no inhibitory mech to stop

Question 12

describe the common pathway.

describe the feedback mech.

Answer 12

1. X,V , phospholipids and Ca convert prothrombin -> thrombin
2. thrombin converts
   
   1. fibrinogen ->fibrin
   2. factor 8 to active factor 8
3. results in fibrin polymer

feedback mech

• positive feedback
  
  • thrombin catylyzes: fibrin and F8
  • activates platlets directly

Question 13

how do paracrine factors influence hemostasis?

Answer 13

• positivly
  
  • thrombin causes endothelial cells to release ADP, vWF
• negatively
  
  • NO(vasodilator and antiplatlet)
  • PGI2
  • tissue plasminogen activator

Question 14

describe the components and pathway involved in clot inhibition

Answer 14

1. thombomodulin on endothelial cell surface, binds thrombin.
   
   1. removing thrombin from the plasma
2. thrombomodulin-thrombin complex activates protein C and protein S
3. activated C-S inactivate factor 5 and 8

• ttissue factor pathway inhibitor (TFPI) on cell surface inhibits protease action of factor7a
• antithrombin 3 in plasma binds to thrombin, enhanced by heparin, inactivating it
  *

Question 15

what components are involved with fibrinolysis?

Answer 15

1. plasminogen-> plasmin via tPA protease and urokinase
2. this is the main enzyme that degrades fibrin
   
   1. digest fibers, fibrinogen, factor 5,7,8, and prothrombin

Question 16

what inactivates thrombin?

Answer 16

1. thrombomodulin
2. antithrombin3 (enhanced by heparin)
3. fibrin

Question 17

what inactivates factor 5 and 8?

Answer 17

protein C

Question 18

what inactivates factor 7a?

Answer 18

tissue factor pathway inhibitor (TFPI)

Question 19

what digests fibrin and is a mediator in fibrinolysis?

Answer 19

plamin