Week 4 - Blood vessels: haemostasis Flashcards
What are the three functions of the blood?
transport, communication, defence
What is the basic blood vessel structure?
What is the blood supply of the tunica adventitia called?
vasa vasorum
What are the three types of artery?
elastic, muscular and arterioles
Give examples of elastic arteries
aorta, pulmonary artery
tunica media is broad and elastic with concentric sheets of elastin and collagen
What are the differences between elastic and muscular arteries?
muscular - less elastin, broad tunica adventitia, elastin in found in the internal and external elastic lamina
elastic - less smooth muscle, more elastin
What are the characteristics of the tunica intima layer of an elastic artery?
single layer of flattened epithelial cells, supporting layer of elastin rich collagen. Has ‘myointimal cells’ that accumulate lipid with ageing - first sign of atherosclerosis.
What is the most prominant layer of a vein?
tunica adventitia
has collagen fibres
Which is the artery and which is the vein in this histological slide?
vein has smaller muscle wall and the lumen is collapsed
What is the difference between a muscular vein and artery?
(muscular artery in picture)
in a muscular vein there is no inner or outer elastic layer
What is a severe reduction in the number of platelets called?
thrombocytopenia
What is the definition of primary haemostasis?
the formation of a primary platelet plug
What is the definition of a secondary haemostasis?
formation of a fibrin mesh by activation of coagulation factors
What three chemicals mediate the adhesion of other platelets (platelet aggregation)?
thromboxane A2, ADP and calcium ions
What is the mechanism of action of aspirin?
irreversibly inhibits COX which is needed for thromboxane production
aspirin is a type of NSAID but works differently because it irreversibly binds and other NSAIDs reversibly inhibit COX
What type of drug is clopidogrel?
ADP receptor antagonist
What shape change to platelets undergo when activated?
become more spherical with long thin cytoplasmic processes
What two substances normally prevent platelet aggregation?
nitric oxide and prostacyclin
What is the sequence of activated factors in the intrinsic pathway?
XII - XIIa (12)
XI - XIa (11)
IX - IXa (9) + VIII (8)
X - Xa (10) + V (5)
count down from 12 but swap 9 and 10 around
9 works with the number below it
10 works with its half
What is the first step in the conversion of fibrinogen to fibrin?
removal of fibrinopeptide A (FpA) from fibrinogen by thrombin
What happens when all of the fibrinopeptide A has been removed by thrombin?
a two-stranded protofibril is formed
What has to occur before protofibres can aggregate laterally?
cleavage of fibrinopeptide B from fibrinogen by thrombin
Name three anticoagulants
warfarin, heparin, ancrod
What is the most important physiological mechanism for haemostasis in venous vessels?
A) coagulation cascade
B) platelet thrombus
C) anti-thrombin
coagulation cascade
clotting factors are more important in low flow, low pressure vessels
platelets are more important in the arterial circulation where flow is high, blood must be stopped quickly, platelet plug is faster acting
What is the first reaction in activation of the extrinsic pathway of the clotting cascade?
tissue factor binds factor VII
(X - Factor)
Which factor that is released by endothelial cells causes platelet activation?
A) ADP
B) Histamine
C) Thrombin
D) Prostaglandin I2 (prostacyclin)
E) Fibrin
A) ADP
Platelets are activated by ADP, thromboxane A2, calcium and thrombin
ADP is released by damaged endothelial cells
What is the role of prostacyclin in blood vessels?
produced by endothelial cells
prevents the formation of a platelet plug by inhibiting platelet activation
effective vasodilator
What receptor mediates a strong bond between platelets in a thrombus?
glycoprotein IIb/IIIa
platelets have two main surface glycoprotein receptors: GpIb and GpIIb/IIIa
GpIb is always present and binds to subendothelial collagen via vWF following an injury. This causes acivation of platelets and GpIIb/IIIa is then expressed on platelet surface
What two granules are present in platelets?
dense and alpha granules
What two cells are the immediate precursors to red blood cells?
reticulocytes and myeloblasts
