arterial and venous thrombosis Flashcards
Why don’t blood clots form all the time?
reasons from lecture: 1. laminar flow - cells travel un the centre of a vessel and don't come into contact with the walls 2. endothelial cells are not sticky when healthy reasons from last year endothelial cells, anticoagulant pathway and fibrinolytic pathway keep it fluid platelets and coagulation proteins circulate in an inactive form
what is the definition of thrombosis?
solid mass of blood constituents formed within intact vascular system during life
What are the components of Virchow’s triad?
- change in vessel wall
- change in blood flow
- change in blood constituents
What is the first stage of thrombosis?
platelet aggregation
What type of feedback does thrombosis involve?
positive feedback
What protein is formed as a product of the clotting cascade?
fibrin
Which cascade does platelet activation trigger?
coagulation cascade
Referring to Virchow’s triad, what does smoking cause?
change in vessel wall
change in blood flow (over the injured/absent cells)
What interventions in hospital can reduce risk of thrombosis?
early mobilisation after operation
low dose subcutaneous heparin
venous stockings
According to Virchow’s triad, what is venous thrombosis due to?
change in blood flow (stasis of blood)
How does aspirin work?
Inhibits platelet aggregation - antiplatelet drug, irreversibly inhibtis COX to reduce production of pro-aggregatory factor thromboxane from arachidonic acid.
What is an embolus?
mass of material in the vascular system able to become lodges within a vessel and block it
How does a DVT embolise?
The distal part of the thrombus breaks off and travels to the vena cava, then right side of the heart and then to the lungs - pulmonary arteries
What are the other types of embolism other than that from thrombosis?
air (pressurised systems of IV fluids/blood in infants and children)
cholesterol crystals (from an atheromatous plaque)
tumour
amniotic fluid (may happen in women with precipitate labour - i.e. very fast labour)
fat (severe trauma with multiple fractures)
Where do arterial thrombi embolise to?
if the thrombus is in the heart, the embolus can travel anywhere in the systemic circulation e.g. lower limb and renal arteries
Give examples of complications of arterial thrombi
stroke
heart attack
Give an example of complication of a venous thrombus
PE
How does thrombosis occur on top of an atheroma?
The plaque ruptures, exposing collagen, leading to platelet aggregation and activation of the clotting cascade
Why is oedema seen with venous thrombosis?
impaired venous drainage
What do alpha granules contain?
substances involved in platelet adhesion such as fibrinogen, fibrognectin, platelet derived growth factor
What do dense granules contain?
ADP
Name two factors that cause platelets to degranulate when they come into contact with the substance?
fibrin
collagen
Describe the steps of arterial thrombosis
- turbulent flow (e.g. caused by endothelial damage or a plaque)
- leads to loss of endothelial cells
- exposure of underlying collagen
- platelet activation
- fibrin deposition
- RBCs trapped
- alternating layers of platelets and RBCs in fibrin mesh
Describe the steps of venous thrombosis
- low blood pressure in veins
- valves produce turbulence
- thrombi form due to endothelial damage, exposure of collagen, activation of platelets, fibrin formation, trapping of RBCs
in lec - if BP drops, then cells settle to the bottom of a vessel, so no longer laminar flow
What can cause BP drop in venous circulation?
blood loss
anaesthesia
following MI
State 5 causes of thrombi in the heart
- atheromatous plaque
- valve vegetation
- atrial thrombus (AF)
- old myocardial infarct (adynamic part of myocardium)
- recent myocardial infarct (fibrosis)
Why does vegetation in the heart cause emboli?
infective endocarditis
the vegetations are very friable (crumbly)
and contain bacteria
How do the lungs act as a filter for emboli?
The vessels become very small –> capillaries only allowing one RBC at a time
What are the clinical signs of arterial thrombosis?
- loss of pulse distal to thrombus
- cold, pale area (blood is prevented form entering the area)
- very painful
tissue dies –> gangrene
What are the clinical signs of venous thrombi?
- tender, due to ischaemia
- swollen
- red - blood is still carried to the site, but cannot be drained by veins)
Name 4 effects of thrombi
lyres and resolution
organisation
recanalisation
embolism
What happens in lysis and resolution of thrombi?
complete resolution, as the thrombus is small
depends on fibrinolytic activity i.e. plasmin
What happened in organisation of thrombi?
thrombus is replaced by scar tissue
scar tissue contracts and occludes the lumen
scar tissue formed by invasion of macrophages that clear up the thrombus Fibroblasts replace the thrombus with collagen
What happens in recanalisation of thrombi?
ingrowth of new vessels, which join up to restore blood flow
the intimal cells proliferate and capillaries grow into the thrombus and fuse to form large vessels
the vessel becomes patent again
What are symptoms of PE?
chest pain
SOB (loss of lung area supplied by vessel)
Name two types of therapy fro PE
symptomatic
thromolytic
Name two types of therapy fro PE
symptomatic
thrombolytic
Which vessel can a thrombus in the gut occlude and what are the consequences?
superior mesenteric artery SMA
can cause death of whole sections of small bowel
this can lead to peritonitis and death due to perforation
Give reasons for a fat embolism
fracture of long bones
extensive softy tissue injury
severe burns
Give reasons for gas embolism
decompression sickness
vessel opened to the air in surgery
