exam 2 (ch. 11, 12, 14) Flashcards
chapters 11, 12, 14
hemostasis
- hemo = blood
- stasis = remain
- the stopping of bleeding
- the process is rapid and localized
the primary layers in hemostasis include
- blood vessels
- platelets
- plasma proteins (coagulent proteins)
What are plasma proteins made by
liver
Vascular system
Intact endothelial cells inhibit platelet adherence and blood coagulation
Injury to endothelial cells promotes…
localized clot formation
Injury to endothelial cells: Phases
Phase 1: vasoconstriction
Phase 2: Platelets
Phase 3: Coagulation
First phase: Vasoconstriction
- Narrows the lumen of the vessel to minimize the loss of blood
- Brings the hemostatic components of the blood (platelets and plasma proteins) into closer proximity to the vessel wall
- Collagen = enhances contact activation of platelets
- Von Willebrand factor = made by endothelial cells
What does collagen initiate
vasoconstriction
Second phase: Platelets
- Circulate in resting state approximately 10 days
2. At rest = minimal interaction with other blood components or the vessel wall
When stimulated by endothelial damage, platelets function to…
- Plug the defect = round and sticky platelets, aggregate to site and build a hemostatic plug
- Release vasoconstrictors
- Cause more platelets to aggregate
- Secretion of active substances to initiate coagulation
Platelets are cells fragments of what?
megakarocyte
When platelets aggregate to site, the release what?
- ADP (recruit more platelets)
- Vasoconstrictive amines
- epinephrine (vasoconstrictor) - Thromboxane A2
- amplifies the initial aggregation of platelets into a large platelet mass
Von Willebrand Factor
Secreted by endothelial cells
- important for adhesion and aggregation of platelets
Third phases: Coagulation
To go from liquid to semisolid mass.
- need calcium and vitamin K
what are the two pathways of coagulation
- Extrinsic
- Intrinsic
- they both come together to form a common pathway; you need both for normal coagulation
Describe the coagulation cascade
Phase 1: intrinsic and extrinsic pathways come together and form common pathway
Phase 2: Prothrombin to thrombin
Phase 3: Fibrinogen to fibrin
Platelets and coagulation factors
Distinct but complimentary and mutually dependent
- platelets interact with coagulation factors by providing binding sites
- thrombin activates platelets
Coagulation Inhibitors
Counterbalance coagulation factors; restrict clot by keeping it at one location. Substances: - Antithrombin - Protein C - Plasminogen
Fibrinolysis
Plasminogen activated to plasmin
- by Tissue plasminogen Activator (TPA), released by endothelial cells
- plasmin dissolves fibrin
Fibrinolysis is activated at the same time as what?
Coagulation
Disturbances of Blood Coagulation: 4 types
- Abnormalities of small blood vessels
- Abnormality of platelet formation
- Deficiency of one or more plasma coagulation factors
- Liberation of thromboplastic material into circulation
Abnormalities of small blood vessels
Abnormal bleeding resulting from failure of small blood vessels to contract after tissue injury
- rare genetic disease
Reduced platelet numbers or function
- Thrombocytopenia (reduced platelet number in blood)
- Causes: genetic, acquired (radiation)
- Disease: leukemia
- Autoimmune
- Hypersplenism
- Leads to petechiae
Petechiae
small pinpoint hemorrhages