Pathological thrombosis Flashcards
Thrombosis occurs in 3 predisposing situations
Virchow’s triad consists of:
- Changes in the intimal surface of a vessel
- Changes in the pattern of blood flow
- Changes in the blood constituents
Pathological thrombosis occurs
in the absence of a cut or trauma.
arteriole =
normal small artery
Endothelial cell lines
lumen
Endothelial cells make
basal lamina (basement membrane) to ‘sit on’
Around basal lamina are
smooth muscle cells
Around smooth muscle cells are
interstitial collagen fibres
Physiological thrombosis often occurs
after a cut or injury
in physiological thrombosis what stops bleeding?
Contraction of the vessel and the thrombus stop the bleeding.
clot fills the defect
thrombus is good if
it allows blood flow along vessel to continue.
platelet thrombus
in physiological thrombosis, when wound heals
with a scar and blood vessel is repaired.
repaired vessel has normal blood flow.
The 3 predisposing situations that may result in thrombus formation are known as
Virchow’s triad
Coronary artery thrombosis
Coronary arteries are the main arteries in heart
They supply the heart muscle
Cigarette smoking (and other things such as high lipid in the blood) can also predispose to atheroma in the coronary arteries
why is smoking bad for pathological thrombosis
Smoking cigarettes increases the ‘stickiness’ of platelets (they find it easier to aggregate).
This alteration in the properties of blood is a change in blood constituents which is part of Virchow’s triad
Atheroma is a
disease of coronary arteries which results in a build up of lipid under the intimal surface.
- The lipid can result in abnormal blood flow – can get both slow and turbulent flow
- Slowed blood flow predisposes to fibrin and platelet clumping
This alteration in the pattern of blood flow is part of Virchow’s triad
Lipid (and collagen) can also
rupture through the intimal surface
- Platelets and fibrin are now exposed to an abnormal substance (lipid and collagen) and turbulent flow and are deposited as a thrombus
- The thrombus blocks the lumen of the coronary artery
- Clot can now form in the stagnant blood behind the thrombus
This change in the intimal surface is again part of Virchow’s triad
layers of clot when lipid and collagen rupture the through the intimal surface
1st layer = thrombus (platelets and fibrin)
2nd layer = red blood cells trapped in fibrin meshwork so clot forms
3rd layer = This complex structure now protrudes even further into lumen causing more turbulence/slowing so get we get another layer of thrombus
Mulitple layers of thrombus and clot =
lines of Zahn (pale layers of thrombus alternating with red layers of clot)
Changes in the intimal surface of a vessel example
atheroma lipid coming onto surface
Changes in the pattern of blood flow example
a bulge of atheroma changing the flow of blood
Changes in the blood constituents example
smoking making it more likely that platelets aggregate
Consequences of a thrombus blocking an artery are bad:
Complete obstruction
leads to no flow beyond blockage
Consequences of a thrombus blocking an artery are bad:
partial obstruction
leads to decreased flow beyond blockage.
- The tissue supplied by this artery receives less blood flow
ischaemia =
tissue supplied by artery that receives less blood flow
hypoxia =
if severe enough ischaemia leads to decreased oxygenation of tissues.
tissue is said to be ischaemic and ischaemic heart tissue is often painful
when hypoxia occurs
it can lead to localised area of tissue dying
infract/infraction =
localised area of dead tissue.
necrosis as a result of ischaemia
necrosis =
process of tissue dying.
ischaemia =
ischaemic death
Coronary artery thrombosis can lead to
infraction in brain tissue or heart
Mesenteric artery thrombosis can lead to
infraction in gut
Embolism =
A mass of material moving in the vascular system and able to become lodged in a vessel and block its lumen
most emboli are derived from
thrombi or clots.
They break off and go elsewhere in the circulation
thromboembolism =
When thrombi/clots embolise
Commonest example of thromboembolism
Pulmonary embolism (lungs)
How does pulmonary embolism occur?
- Sluggish flow in leg veins leads to thrombosis and clot formation
- Part of thrombus (and clot) breaks off and travels up vein
- Embolus passes into inferior vena cava, then right heart, then pulmonary trunk, and lodges in pulmonary artery branch
- Embolus blocks pulmonary artery and get pulmonary infarct
Other forms of embolism:
Marrow embolism
Fracture a leg —> marrow enters ruptured vein —> marrow embolises to lung vessels
Other forms of embolism:
Air embolism
Knife wound to neck.
Air enters vein —> air embolises to heart
