haemostasis, haemorrhage and shock Flashcards
what is haemorrhage?
an acute loss of blood from a damaged blood vessel
what is shock?
the state in which the decreased blood volume results in a fall in blood pressure and impaired delivery of nutrients to cells
what should the immediate action to blood loss be?
stop the bleeding
what should the short term action to blood loss be?
restore the blood pressure
what should the medium term action to blood loss be?
restore fluid volume
what should the long term action to blood loss be?
replace blood consitiuents
what is haemostasis?
stopping blood loss
what are the components involved in haemostasis?
- vascular response
- platelet response
- plasma response
what is coagulation?
plasma response
describe the vascular response in haemostasis?
Smooth muscle
- Spasm due to trauma
- Myogenic response
- Humoral factors (vasoconstrictors)
Endothelium
- Platelet adhesion and aggregation
- Anticlotting and fibrinolysis
describe the platelet response in haemostasis?
- Damage to blood vessel causes turbulent blood flow so platelets come into contact with vessel wall (collagen)
- Platelets adhere; clump together (aggregate)
- Release chemicals that cause further aggregation (Positive feedback)
- Formation of platelet plug
- Effective in sealing small blood vessels
describe the formation of a platelet plug
- damaged blood vessel
- platelets aggregate and release chemicals
- thromboxane A2 and ADP
- vasoconstriction
- platelet plug
describe coagulation in haemostasis?
- Various plasma proteins and tissue components combine to convert fibrinogen to fibrin to form the blood clot
- Numerous ‘clotting factors’ are involved (many made in the liver)
- The synthesis of several clotting factors requires the presence of vitamin K
- The clotting factors are activated in an enzyme cascade
- One activated factor activates the next one in the sequence
where are many of the clotting factors involved in coagulation made?
the liver
what is required for the synthesis of many clotting factors?
vitamin K
what can have an affect on coagulation?
calcium deficiency
which blood clotting factor doesnt exist?
VI (same as IV)
what are the two pathways of coagulation?
intrinsic and extrinsic
how is the intrinsic coagulation pathway activated?
vascular damage
how is the extrinsic coagulation pathway activated?
tissue damage
what are required for both the intrinsic and extrinsic coagulation pathways?
phospholipid and calcium ions
which blood coagulation pathway is more important at initiating clotting after injury?
extrinsic
which blood coagulation pathway is more important to maintain the process?
intrinsic
what is thrombosis?
blood clots form inside intact blood vessels causing blockages
which coagulation pathway is involved in thrombosis?
intrinsic
what is fibrinolysis?
dissolving the blood clot once it has served its purpose
which enzyme is involved in fibrinolysis?
plasmin
what triggers the compensatory mechanisms when there is a fall in blood pressure?
arterial baroreceptors
what are the hormones released in baroreceptor relflexes?
adrenaline
angiotensin II
vasopressin (ADH)
which nerves control baroreceptor reflexes?
sympathetic
sequence of events following a decrease in blood volume
- decrease in BP
- decrease in baroreceptor firing
- CVS centres
- increase in sympathetic NS activity
- increase in HR, vent. const, veso const. and arteriole const
- increase in ventricular and vaso constriction increases stroke volume
- increase in HR increases cardiac output
- increase in artieriole const, increases peripheral resistance
- overall increase in mean arterial blood pressure
what are the medium term responses to blood loss?
- Shifting interstitial fluid back into blood vessels
- Decreasing fluid loss in kidney
- Increasing fluid intake
what does a decrease in arterial blood pressure cause through baroreceptor reflexes?
- vasoconstriction of arterioles
- increases total peripheral resistance
- decreases capillary blood pressure
- decreases hydrostatic pressure pushing fluid out the capillary
- more fluid is drawn back into the capillaries by oncotic pressure
what does a decrease in fluid loss in the kidney cause?
- decreased glomerular filtration
- increased reabsorption of sodium ions and water by stimulating the release of renin-angiotensin-aldesterone and the antidiuretic hormone (both vasoconstrictors)
renin-angiotenisn-aldosterone system
antidiuretic system
antidiuretic system
what are stimuli of thirst?
- increase in plasma osmolarity and decrease in ECF volume
- angiotensin II
- dry mouth
feed-forward regulation
what are the long term responses after blood loss?
Restore plasma proteins
- Released from liver (3-4 days)
Replace blood cells, esp. RBCs
Erythropoiesis
- Regulated by erythropoeitin (EPO)
- EPO released from kidney
- Stimulates RBC production in bone marrow
- Return to normal in 2-3 months
what are the different types of shock?
- hypovolaemic shock
- low resistance/distributive shock
- cardiogenic shock
describe hypovolaemic shock
- decrease in ECF volume due to haemorrhage
- sweating, diarrhoa, burns etc
describe low resistance/distributive shock
- decrease in peripheral resistance due to vasodilation
- eg anaphylactic shock
