Overview of Hemostatic Systems Flashcards
hemostatic system
ancestral system designed to keep an individual from bleeding
what other systems within the body does the hemostatic system include? (7)
vascular system coagulation system fibrinolytic system platelets kinin system serine protease inhibitors complement system
3 main stages of the hemostatic system
- vasoconstriction of blood vessels
- formation of a platelet plug
- blood clotting which reinforces the platelet plug with a fibrin mesh
what does a balance between procoagulant and anticoagulant forces maintain?
blood in a fluid state and flowing through the vasculature to deliver oxygen to tissues systemically and remove carbon dioxide and toxic waste products
where does the term hemostasis come from
greek words
heme=blood + states
halt= halt from blood
why do you pinch a cut?
to prevent blood flow
decreased blood pressure can lead to which 2 mechanisms?
endocrine mechanism
neural mechanism
endocrine mechanism
ASH, angiotensin 2, aldosterone, EPO released
increase in blood volume
homeostasis restored
neural mechanism
baroreceptors, chemoreceptors stimulated
cardiovascular centers stimulated
general sympathetic activation, release norepinephrine, epinephrine
increase cardiac output
peripheral vasoconstriction, increase blood pressure, decrease venous reserve
homeostasis restored
vasoconstriction
contraction of smooth muscle cells to vessel walls to restrict the loss/flow of blood at site of injury
what is the mechanism of vasoconstriction?
sympathetic nerves trigger reflexive contraction of vascular smooth muscle
what are the other regulatory substances which also affect vascular tone? (3)
serotonin
endothelia-1
histamine
serotonin is made and released by
platelets at neuromuscular junctions
what are the direct actions of serotonin?
vasoconstrictor where present at high concentrations at sites of injury
what are the indirect actions of serotonin?
can act as a vasodilator when stimulates nitric oxide release by endothelial cells
serotonin is also synthesized by serotonergic neurons of the CNS, where it regulates (3)
mood
appetite
sleep
endothelin-1 is made and released by
damaged endothelial cells
endothelin-1 is normally kept in balance by other mechanisms, but when over expressed can contribute to (3)
hypertension
heart disease
other vascular diseases of the heart, lung, kidney, and brain
histamine bind to
one of four different histamine GPCR on GI, uterus, lung, and vascular smooth muscle cells
histamine is produced and released from (2) during
basophils (circulation) and mast cells (connective tissue) during local immune responses
prostacyclin (PGI2) is a
vasodilator
thromboxane A2 is a
vasoconstrictor
PGI2
prostaglandin or eicosanoid
what does PGI2 inhibit?
platelet activation and is also an effective vasodilator (acts to counteract actions of TXA2)
prostacyclin (PGI2) mechanism
Mechanistically, PGI2 binds to the PGI2 receptor which is a Gs protein coupled receptor which signals via adenylyl cyclase to produce cAMP. cAMP activates protein kinase A which promotes the phosphorylation and inhibition of myosin light chain kinase which leads to vascular smooth muscle relaxation and vasodilation.
PGI2 half life
42 seconds and is broken down to a weaker chemical form
where is TXA2 made and released?
by activated platelets and endothelial cells
TXA2 is a
prostaglandin
TXA2 stimulates
activation of new platelets as well as increases platelet aggregation by increasing expression of glycoprotein complex GP2b/3a (fibrinogen receptor) on platelet membranes
TXA2 half life
30 seconds, limits action to near site of production
state of vascular tone
balance between constrictor and dilator influences
what are extrinsic factors? (2)
sympathetic nerves
circulating factors
what increases and what decreases vascular tone?
increase: constrictors
decrease: dilators
vasoconstrictor and vasodilator influences acting on arteries and veins determine their state of
vascular tone
what are intrinsic factors influencing vascular tone? (4)
myogenic
endothelial
local substances
metabolic byproducts or hypoxia
myogenic mechanisms arising from vascular smooth muscle
increase tone, constrict vessels
endothelial factors (2)
nitric oxide (vasodilator) endothelin (increase tone, vasoconstriction)
local factors (3)
arachidonic acid metabolites histamine bradykinin (vasodilator or vasoconstriction)
metabolic byproducts or hypoxia
generally decrease tone (vasodilation)
what are examples of extrinsic factors influencing vascular tone? (2)
angiotensin 2
circulating factors like atrial natriuretic peptide
angiotensin 2
increase vascular tone