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blood
physiology 2007
5
Physiology
Undergraduate 2
12/13/2007
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Cards

Term
Phases of homeostasis
 Definition
  1. Vascular Spasms
  2. Platelet Plug Formation
  3. Coagulation (Has three phases)
Term

Vascular Spasms

 

Phase 1 of Hemostasis 

 Definition
-Immiediate response to blood vessel injury is constriction of blood vessel. 
 
-Triggered by direct injury to vascular smooth muscle (chemicals released by endothelial cells and platelets, and reflexes intitiated by local pain receptors. 
 
-A strongly constricted artery can reduce blood loss for 20-30 minutes, allowing platelet plug formation and clotting to occur.  
Term

Platelet Plug Formation

 

Phase 2 of Hemostasis 

 Definition
-Platelets form plug which temporarily seals break. 
 
-When endotheliem is damaged and underlying collagen fibers are exposed, platelets:
    - swell and form spiked processes
    -become sticky and adhere to exposed collagen.
    -once attached, platelets degranulate and release chemicals:
1.Serotonin- enhances vascular spasms
2. ADP- Attracks more platelets
3. Thromboxane A2- Stimulates both of above.
 
-Positive feedback cycle which attracks and activates a greater and greater # of platelets.
 
-Within 1 min. a plug is formed which further reduces blood loss.  
Term

Coagulation

 

Phase three of Hemostasis  

 Definition
-Blood is transformed from a liquid to a gel.
 
-It is considered a complicated process which involves  over 30 different factors.
 
-Factors which enhance clotting: coagulation or procoagulants
 
-Factors which inhibit coagulation: anticoagulants.
 
-Clotting may be initiated by intrinsic or extrinsic pathways (Both pathways require ionic calcium and involve activation of a series of procoagulants, each functioning as an enzymeto activate the next proagulant in the sequence) 
 
-Inside the body both pathways are usually triggered by the same tissue damaging events. 
 
-Outside the body (testtube) clotting is only initiated by the intrinsic pathway.  
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