Haemostasis, Haemorrhage and Shock Flashcards
what does excessive blood loss lead to
fall in blood pressure
impaired delivery of nutrients to cells
what is shock
this is when blood pressure and nutrient delivery decreases due to an excessive loss of blood
what are the physiological responses to blood loss
immediate
short term
medium term
long term
describe the immediate response to blood loss
stopping the bleeding
what is the short term response to blood loss
restore the blood pressure
what is the medium term physiological response to blood loss
restore fluid volume
what is the long term response to blood loss
replace blood constituents
what are the components of haemostasis
vascular response
platelet response
plasma response - coagulation
describe what happens to smooth muscle in haemostasis
spasms due to trauma, myogenic response and humoral factors (vasoconstrictors)
describe what happens to endothelium during haemostasis
platelet adhesion and aggregation
anticlotting and fibrinolysis
describe the process of platelet response
- damage to blood vessel
- turbulent blood flow
- platelets come into contact with vessel wall
- platelets adhere and clump together
- release chemicals that cause further aggregation
- formation of platelet plug
- effective in sealing small blood vessels
describe the role of thromboxane A2 in forming platelet plugs
vasoconstriction
describe the role of ADP in platelet plug formation
involved in aggregation and release chemicals in platelets
where are most clotting factors synthesised
liver
what is used for synthesising most clotting factors
vitamin K
why do platelets only aggregate in veins that are unhealthy
the increased turbulence caused by trauma allows for them to touch the walls, and then the collagen in the walls allow for adhesion
describe the whole platelet plug formation
- damaged blood vessels allow aggregation of platelets
- these platelets release ADP and thromboxane to act on the aggregation and increase it
- vasoconstriction facilitates the sealing of blood vessels, and this is done through the thromboxane
how are clotting factors in the blood activated
through an enzyme cascade
describe the common pathway for coagulation
- fibrinogen is converted to soluble fibrin
- by thrombin
- thrombin comes from prothrombin, conversion uses factor Xa, calcium, factor V and phospholipids
- soluble fibrin is converted to insoluble fibrin by a cascade that is created by thrombin converting factor
what is used to convert prothrombin to thrombin
factor Xa
factor V
phospholipids
calcium
how many different blood clotting factors are there
13 (technically 12 as 6 does not exist)
what is factor I
fibrinogen
what is factor II
prothrombin
what is factor III
tissue factor thromboplastin
what is factor IV
calcium ions
what is factor V
proaccelerin
what is factor VII
proconvertin
what is factor VIII
antihaemophilic globulin
what is factor IX
christmas factor
what is factor X
stuart prower factor
what is factor XI
plasma thromboplastin antecedent
what is factor XII
hageman factor
what is factor XIII
laki lorand factor
which blood clotting factors are associated with well known genetic conditions
factors 9 and 10
what are the two pathways that can activate factor 10
intrinsic and extrinsic
describe the intrinsic pathway to activating factor 10
vascular damage leads to contact activation involving factors XII, XI, IX, VIII, calcium ions and phospholipids
describe the extrinsic pathway to activating factor 10
tissue damage, tissue factor tisssue thromboplastin and factor VII, phospholipids and calcium ions are used as well
which pathway is more important for initiating a clot after injury
the extrinsic pathway
which pathway maintains the clot production after initiation
the intrinsic pathway
what is thrombosis
this is when a clot forms in a vessel that has not been injured, and is usually associated with the intrinsic coagulation pathway
what is fibrinolysis
this is when a blood clot is dissolved after it has served its purpose
which enzymes undertakes fibrinolysis
plasmin
describe how fibrinolysis occurs
plasminogen is converted to plasmin via the plasminogin activator
plasma acts on fibrin to produce soluble fibrin fragments
describe the short term impacts on blood pressure
loss of blood volume leads to a fall in blood pressure
there are compensentory mechanisms triggered by the arterial baroreceptors, and these mechanisms aim to resotre the blood pressure
what mediates the baroreceptor reflexes
sympathetic nerves
which hormones are involved in restoring blood pressure after loss of blood volume
adrenaline
angiotensin II
vasopressin
which hormone is vasopressin
ADH
describe how a decrease in blood pressure from a decrease in blood volume is restored through baroreceptor reflexes
- decreased BP leads to decreased baroreceptor firing
- this goes to the CVS centres in the brainstem
- this increases sympathetic nervous system activity
- this increases heart rate, ventricular contraction, venous constriction, and arterial contration
- increased venous constriction and venous contraction increases stroke volume, which increases cardiac output
- increases arteriol constriction leads to increased peripheral resistance
- increased peripheral resistance and cardiac output increases the mean arterial blood pressure overall
what are the positive reflex compensations after haemorrhage
heart rate and total peripheral resistance
what are the negative reflex compensations after haemorrhage
stroke volume
cardiac output
mean arterial pressure
describe the medium term responses to restore blood volume
- interstitial fluid is shifted back into blood vessels
- there is decreased fluid loss in the kidneys
- increased fluid intake
describe how hydrostatic pressure is at the point where arterioles become capillaries through to the venule
35mmHg, to 15mmHg at the end
describe the oncotic pressure in capillaries
25mmHg
what does decreased arterial blood pressure cause through the baroreceptor reflexes
- arterioles will vasoconstrict to decrease the hydrostatic pressure that pushes fluid out of the capillary
- this means there is more fluid being drawn back into the capillaries by oncotic pressure
what does vasoconstriction of arterioles lead to
an increase in total peripheral resistance
a decrease in capillary blood pressure
describe how hydrostatic pressure is in the capillary during haemorrhage
at arteriole it is 25mmHg instead of 35, and at the venule it is 10mmHg instead of 15mmHg
does oncotic pressure change when there is haemorrhage
no it remains around 25mmHg
describe what happens in the kidney when there is decreased blood volume
there is less fluid loss in the kidney to increase the blood volume
- done by a decrease in glomerular filtration
- increase in reabsorption of sodium and water by stimulating the release of RAAS and antidiuretic hormone
does aldosterone release increase or decrease in response to a decreased blood volume
increases to increase reabsorption of sodium and water
describe the pathway of ADH release during decreased blood volume
decreased plasma volume causes a decrease in baroreceptor distension, releasing ADH from posterior pituitary
increased plasma osmorality increases the osmoreceptor activation, increasing ADH release from posterior pituitary
this increases the water permeability of collecting ducts in the kidney
describe thirst and how it happens
this is a desire to drink, and is controlled by the hypothalamus
what is the stimulus for feeling thirst
an increase in plasma osmorality and a decreased in extracellular fluid volume
angiotension II can promote thirst
dry mouth
what is feed forward regulation
this is when stretch receptors in the stomach suppress drinking
describe long term responses to a decreased blood volume
restored plasma proteins are released from the liver in 3-4 days
red blood cells are replaced
erythropoiesis occurs
describe erythropoiesis
- regulated by erythropoietin released from the kidney
- stimulates red blood cell production in bone marrow
- returns to normal in 2-3 months
describe the steps to erythropoiesis
- decreased red blood cell numbers
- decreased oxygen delivery
- kidney detects
- releases erythropoietin
- travels to red bone marrow
- increase in red blood cell production
what is shock characterised by
inadequate blood flow to tissues that is associated with decreased cardiac output and a decreased in blood/ECF volume
which shock can be fatal
irreversible
what are the three main types of shock
hypovolemic
low resistance shock
cardiogenic shock
describe hypovolemic shock
decreased ECF volume due to:
haemorrhage, sweating, diarrhoea, burns, cholera and ebola
describe low resistance shock
aka distributive shock
decreased peripheral resistance due to widespread vasodilation
that occurs in anaphyalxis
describe cardiogenic shock
this is when the heart fails to pump, and is a typical form of shock