Haemostais, Haemorrhage And Shock Flashcards
What does excessive blood loss result in
- medical emergency
- impaired delivery of nutrients to cells
- state is called shock
Immediate physiological response to blood loss
Stop the bleeding
Short term physiological responses to blood loss
Restore blood pressure
Medium term physiological responses to blood loss
Restore fluid volume
Long term physiological response to blood loss
Replace blood constituents
What components are involved in immediate blood loss control
- vascular response
- platelet response
- plasma response (coagulation)
Describe the vascular response to immediate blood loss
- smooth muscle : spasm due to trauma, myogenic response, humoral factors (vasoconstrictors)
- endothelium : platelet adhesion and aggregation, anti clotting and fibrinolysis
What induces the platelet response to blood loss
Damage to blood vessel > turbulent blood flow > platelets come into contact with the vessel wall (collagen)
Describe the platelet response immediately after blood loss
- platelets adhere - clump together
- release chemicals that cause further aggregation (positive feedback)
- formation of platelet plug
- effective in sealing small blood vessels
Describe the process of a platelet plug forming
Damaged blood vessel causes platelets to aggregate and release chemicals which results in the platelet plug
What causes vasoconstriction in the platelet plug
Thromboxane A2
Describe coagulation in the immediate response to blood loss
- various plasma proteins and tissue components combine to convert fibrinogen > fibrin to form the blood clot
- numerous clotting factors are involved
Where are the clotting factors made
Many made in the liver
What vitamin is required for synthesis of clotting factors
Vitamin K
The clotting factors are involved in…
An enzyme cascade
What disease can affect the production of clotting factors
Liver disease
What deficiency can affect the production of clotting factors
Vitamin K deficiency
Examples of blood clotting factors
I - Fibrinogen
II - prothrombin
III - tissue factor (thromboplastin)
IV - calcium ions
V - proaccelerin
VI - calcium ions ???? Doesnt exist
VII - proconvertin
VIII - antihaemophilic globulin
IX - Christmas factor
X - Stuart-prower factor
XI - plasma thromboplastin antecedent
XII - Hageman factor
XIII - Laki-Lorand factor
Describe the intrinsic coagulation pathway
- vascular damage
- contact activation involving factors : XII, XI, IX, VIII
What converts factor X to factor Xa
Phospholipid and calcium ions
Describe the extrinsic pathway
- tissue damage
- tissue factors (tissue thromboplastin) factor VII
Where is the extrinsic pathway more important
Seems to be more important in initiating clotting after an injury
Where is the intrinsic system more important
Serves to maintain the process once it has started
(Extrinsic pathway first)
Plasminogen is converted to…
Plasmin by a plasminogen activator
Fibrin is converted into
Soluble fibrin fragments by plasmin
Describe the short term response to blood pressure
- loss of blood volume
- fall in blood pressure
- compensatory mechanisms triggered by the arterial baroreceptors
- these mechanisms aim to restore the blood pressure
What mediates baroreceptor reflexes
Mediated by
- sympathetic nerves
- hormones : adrenaline, angiotensin II, vasopressin (ADH)
Decrease in blood pressure results in ….
Decrease in baroreceptor firing > CVS centres brainstem > increase in sympathetic NS activity > increase heart rate >increases cardiac output > increases mean arterial blood pressure
What is the most important function of a haemorrhage
Increasing mean arterial pressure
Describe medium term responses to blood loss
Restore blood loss by
- shifting interstitial fluid back into blood vessels
- decreasing fluid loss in kidney
- increasing fluid intake
What does a decrease of fluid loss in the kidney cause
Decrease in glomerular filtration
Increase in reabsorption of Na+ and H20 by stimulating the release of
- renin-angiotensin aldosterone
- antidiuretic hormone
Both vasoconstrictors
What hormone drives erythropoesis
Erthyropoietin (EPO) which is a glycoprotein cytokine
What causes erythropoietin
Decrease in red blood cell numbers > decrease in oxygen levels > kidney > erythropoietin > red bone marrow > increase in red blood cell production
What is shock
Shock is characterised by inadequate blood flow to tissues
Often associated with decreased cardiac output, decreased blood or ECF volume
Describe hypovolaemic shock
Decrease in extracellular fluid volume, due to haemorrhage, sweating, diarrhoea, burns, ect
Describe low resistance (or distributive) shock
Decrease in peripheral resistance, due to widespread vasodilation eg anaphylactic shock
Describe cardiogenic shock
Heart fails as a pump
Describe the long term responses to blood loss
- restore plasma proteins (released from liver 3-4 days)
Describe the stimuli associated with first
Increases plasma osmolarity > decreases ECF volume
Angiotensin II also promotes thirst
Dry mouth
Describe how medium term responses restore blood volume
- shifting interstitial fluid back into blood vessels
- decreasing fluid loss in kidney
- increasing fluid intake
Renin converts…
Angiotensinogen to angiotensin I
What converts Angiotensin I to angiotensin II
Angiotensin converting enzyme (ACE)
Increase in aldosterone release causes
Increases Na+ and H20 reabsorption in DCT and cortical collecting ducts
Decrease in plasma volume…
Decrease in plasma volume> decrease baroreceptor distension > increases ADH release (post pituitary) > increases H2) permeability of collecting ducts
Increase in plasma osmolarity…
Increases osmoreceptor activation > increases ADH release (post pituitary) > increasing H20 permeability of collecting ducts
