Blood - Blood Clotting Flashcards
Class I Haemorrage
up to 15% blood volume
medical intervention not required
blood donor sessions typically remove 8-10% blood volume
Class II Haemorrhage
15-30% blood volume
Rapid heart rate, systolic and diastolic blood pressure variance decreases, body compensates with peripheral vasoconstriction, skin pale and cool
treat by increasing volume - saline solution - and blood transfusion
Class III Haemorrhage
30-40% Blood volume
Blood pressure drops, heart rate increases, brain function decreased
treat by increasing volume - saline solution - and blood transfusion
Class VI Haemorrhage
> 40% blood volume
Body can no longer compensate - aggressive resuscitation required
3 steps of haemostasis
Vascular spasm
Formation of platelet plug
Formation of blood clot
Vascular spasm
On damage
Intrinsic mechanisms trigger a constriction
Increases resistance to blood flow
Damage activates sympathetic nervous system
Triggers further vasoconstriction
Reduced blood flow minimises blood loss - but not sufficient
Platelets
Colourless cell fragments that break off from Megakaryocytes
Smaller than erythrocytes
Contain: mitochondria, smooth endoplasmic reticulum, cytoplasmic granules
Have no nucleus
100000 to 500000 per ul
Platelet plug
Platelets are sticky under certain conditions
Von Willibrand Factor:
vWf secreted by megakaryocytes, platelets and endothelial cells
upon damage, vWf binds to exposed collagen
Platelets bind to vWf and this triggers stickiness
Platelets begin to secreted serotonin, epinephrine, ADP
Factors involved in platelet function
Collagen
vWf
Serotonin
ADP
Platelet-activating factor
Thromboxane A2
Platelet-derived growth factor
Blood clots
Plasma proteins Fibrinogen is essential for clot formation
Fibrin clot formation is secondary to platelet plug formation
Requires activated platelets
Requires secretory products from activated platelets
All triggered by the coagulation cascade
Factors involved in coagulation
Collagen
vWf
Tissue factor
Prothrombin and thrombin
Fibrinogen and Fiblin
Fibrin-stabilising factor
Ca2+
Vitamin K
What prevents coagulation from continuing until the entire circulation has clotted?
Inhibition of platelet adhesion
Inhibition of the coagulation cascade and fibrin production
Anticoagulant drugs
Prescribed for people at risk of forming small blood clots that may block small vessels in brain, heart or lungs
Coumarin anticoagulants x include warfarin
Block the action of Vitamin K - a co-factor in tsh synthesis of factors II, VII, IX and X
Discovered by investigating why cattle developed server bleeding problems after eating spoiled sweet clover
Ca2+ removal
Anticoagulants can remove free Ca2+ from plasma
Acetylsalicylic acid (aspirin)
Prevents platelet plug formation by inhibiting COX enzymes that promote activation of thromboxane A2
