Circulation 1 Flashcards
What is the precursor cell of platelets?
Megakaryocytes
What causes the maturation of megakaryocytes?
Erythropoietin
Where are clotting factors produced?
Mainly in the liver but also in endothelial cells.
Briefly describe the clotting factor cascade.
Damage caused interstitial collagen to be exposed and tissue factor to be released.
TF(factor III) reacts with clotting factor VIII
Interstitial collagen exposure/ plasma contact with subendothelial tissue causes a series of reactions.
The products (of these two pathways) then react and cause prothrombin (factor II) to convert to thrombin.
This causes fibrinogen(factor I) to convert to fibrin.
Are platelets involved in thrombus or clot formation?
Thrombus formation
What are the main differences between clot and thrombus formation?
Clots form in stagnant blood and contain RBC and fibrin
Thrombi form in flowing blood (at the side) and contain platelets and fibrin.
What is the difference between a clot and an embolus?
Embolus can be made out of many different materials, clots are always formed by fibrin and red blood cells.
Emboli move from where they originate, through the bloodstream and cause a clot somewhere else.
Clots for a blockage, where they are formed.
What are the components of Virchow’s triad?
Change in the intimal surface of a vessel
Change in the pattern of flow of blood
Change in the constituents of blood
What does any element of Virchow’s triad cause?
An thrombus to form
Define ischaemia
An insufficient supply of blood to a tissue
Define Hypoxia
severe lack of oxygen supply to the tissue
Define anoxia
Absence of oxygen supply to an organ/tissue
Define Necrosis
dead or dying tissue
Define infarct
Necrosis as a result of ischaemia
What are some reversible effects of ischaemia? (e.g. in the hand)
Numbness
Temperature drop
Change in colour
Tingling
Irreversible effects of ischaemia
Infarct, stroke, “heart attack” (myocardial infarct)
Define embolism
An obstruction in a blood vessel due to a blood clot or other foreign matter that gets stuck while travelling through the bloodstream.
What is the most common embolism?
Pulmonary thromboembolism
How does a pulmonary thromboembolism occur?
Usually a thrombus and clot will form in a leg vein due to slow blood flow, some of this breaks off and travels up the vein, in to the inferior vena cava, then in to the right heart, then the pulmonary trunk and lodges in a pulmonary artery
What does a pulmonary thromboembolism often cause?
A pulmonary infarct.
Define circulatory shock
Profound circulatory failure causing poor perfusion of vital organs
What are the classic clinical signs of shock?
Low blood pressure (e.g. 60/40)
fast (and weak) heart rate/pulse (>100 bpm)
What components does blood pressure rely on?
Enough blood in the system
Smooth muscle in vessels having a certain tone
Heart pumping blood effectively
What will happen if there is not enough blood in the system?
Vessels will collapse
What happens if the tone of the smooth muscle decreases?
The vessel will dilate and therefore the blood pressure will decrease
What part of the body can detect blood pressure and changes in it?
Carotid bodies at the bifurcation of the carotid arteries sense blood passing them and can detect the partial pressure of oxygen in the blood.
In oxygen partial pressure decreases then BP will decrease
What happens in blood pressure drops?
The carotid arteries sense this and send signals to the brain stem. The brain stem will then tell the heart to pump faster, it will also cause the vascular tone to increase in the limbs and abdomen. This forces blood back towards the chest and head, so that vital organs have enough blood.
The brain stem also stimulates adrenaline secretion form the adrenal gland, so the heart will pump even faster and harder.
Name the 3 types of shock
Septic (infection)
Hypovolaemic
Cardiogenic
What causes Hypovolaemic shock, what happens and what is the treatment?
the total volume of blood in the circulatory system falls significantly, (e.g. due to haemorrhage or dehydration)
Vessel start to collapse, then not enough blood is getting to vital organs. ( venous pressure would be low or 0)
Treatment-Transfuse blood through an IV cannula very quickly and try to stop/slow the bleeding.
What is cardiogenic shock and what is its treatment?
Heart is failing to pump effectively or consistently (e.g. due to a heart attack). Venous pressure would be normal.
Treatment- drugs to increase heart function
What is septic shock?
when large quantities of bacteria and their toxins begin to circulate in the bloodstream, due to and untreated or inadequately treated infection.
The foreign molecules in the blood cause vasodilation, so blood will pool in veins, so not enough blood will be getting back to the heart.
Venous pressure will be low, the right side of the heart will not be filling much.
Explain the 2 main examples of organ damage which occurs in shock
Brain injury- due to decreased perfusion to the brain (initially reversible), so then infarct occurs.
Renal injury( e.g. decrease renal function)- decreased perfusion of kidneys, which leads to necrosis of the kidney tubules.
