Blood and Bleeding Flashcards
what are the structural features of a red blood cell and how do these assist its function? (2)
- biconcave disc - increase surface area and provide flexibility in capillaries with smaller diameter than that of the cell
- no nucleus - more space for Hb
what are the 3 requirements of a red blood cell?
- pass repeatedly through micro circulation where diameter may be smaller than that of RBC
- maintain Hb in a reduced (ferrous) state
- maintain osmotic equilibrium despite high protein concentration
what are the main cytoskeleton proteins in RBCs?
actin and spectrin
what is the structure of a RBC? (3)
- protein with quaternary structure - 4 polypeptide chains: 2 alpha and 2 beta
- each chain has its own haem group
- each haem ring has a ferrous (Fe 2+) atom at its centre
describe how the confirmation of Hb changes (3)
- Hb can bind to a max of 4 O2 atoms - shape changes as more O2 atoms bind
- no O2 - taut with fewer binding sites available
- 1 O2 binds - more relaxed shape, therefore increased O2 affinity
describe the Bohr shift using P50 (4)
- P50 is the ppO2 at which 50% of Hb is saturated
- during high energy usage (eg. exercise), increased CO2 conc. lowers blood pH
- blood lowers O2 affinity to increase unloading to supply respiring tissues
- O2 dissociation curve shifts to right (decreased O2 saturation at a given ppO2)
how is normal blood distributed when a sample is centrifuged?
- largest top layer of plasma (~55%)
- very think buffs coat containing leukocytes
- bottom haematocrit layer containing RBCs and platelets (~45%)
what is the difference between plasma and serum?
- plasma contains fibrinogen + components in preparation coagulation
- serum is what remains after components are used in coagulation
from what cell are platelets derived and how are they formed? what is this cell’s lineage?
- megakaryocyte - platelets bed off from cell surface
* myeloid lineage
what is the structure of a platelet? (3)
- small and disc-shaped
- no nucleus
- contain granules involved in clot formation
what is the sequence of primary haemostasis? (4)
1 - endothelium of a blood vessel is breached, so cells release endothelin to cause vasoconstriction
2 - von Willerbrand factor is exposed and collagen forms to promote platelet adherence and activation
3 - platelets attach, change shape and release granules
4 - allows platelets to aggregate and form a primary platelet plug
what is the principle behind the coagulation cascade?
circulating tissues are activated to form proteases to catalyse the next reaction
what are the differences between coagulation in vivo and in vitro? (3)
- in vitro - tissue factor has a different role
- 2 separate pathways that are not integrated
- thrombin does not have an amplifying effect
describe the coagulation pathway in vitro (6)
1 - -ve charged surface (eg. glass beads) added to solution
2 - activates intrinsic cascade culminating in activation of IX (Xmas)
3 - extrinsic pathway involves the activation of VII using tissue factor
4 - pathways converge as both VIIa and IXa are required to activate X (Stuart)
5 - (common pathway) Xa catalyses prothrombin to thrombin
6 - thrombin then catalyses the conversion of soluble fibrinogen into fibrin to form clot
what is the basic coagulation sequence of clotting in vivo? (6)
1 - tissue factor exposed after vascular damage
2 - activates VII, which activates IX (Xmas factor)
3 - IXa activates X (Stuart factor)
4 - Xa catalyses prothrombin to thrombin
5 - thrombin catalyses fibrinogen to fibrin to form clot
6 - thrombin also enhances cascade processes further up (+ve feedback loop amplifying the effect of tissue factor)
describe how a fibrin clot is formed (3)
1 - fibrinogen (soluble) is catalysed by thrombin -> peptidolysis
2 - fibrin is insoluble and begins to form a soft clot with lattice structure
3 - hard clot develops as fibrin cross-links form
why is fibrinolysis necessary?
after endothelium of blood vessel is restored, thrombus must be removed to restore normal blood flow
describe the process of fibrinolysis (3)
1 - endothelial cells release plasminogen activator
2 - converts plasminogen to plasmin
3 - plasmin digests both fibrin and fibrinogen to break down the clot
what is the broad definition of shock?
a clinical syndrome where tissue perfusion (fluid in organs) and hence oxygenation is inadequate to maintain normal metabolic function
what are the 5 main types of shock?
1 - hypovolaemic: haemorrhagic, burns, severe dehydration
2 - cardiogenic: pump failure
3 - septic: fluid redistribution due to leaking capillaries + vasodilation (usually in response to severe infection)
4 - spinal / neuro: loss of proper vascular tone
5 - anaphylactic: allergic reaction resulting in a combination of the above
why does shock lead to increased heart rate an breathing rate?
hypoperfusion -> not enough blood is being pumped around the body, therefore body compensates
why does blood pressure only drop in class III and IV shock?
HR and BR try to maintain BP as long as possible
what is the ABCDE of advanced trauma life support?
Airway w/ cervical spine control
Breathing with oxygenation
Circulation with haemorrhage control
Disability - assessment with Glasgow Coma Scale
Exposure (eg. cover with warm blankets etc.)
how much blood is lost in the classifications I - IV of hypovolaemic shock?
I: <750ml
II: 750-1500ml
III: 1500-2000ml
IV: >2000ml
what response does each colour warrant in the Manchester Triage System? give examples of each category
red: see immediately - airway compromise, unresponsive, shock
amber: within 10 mins - very low perforation, very low oxygen saturation, acute onset after injury
yellow: within 1 hour - low perforations, low oxygen saturation, chest pain while breathing
green: within 2 hours - wheeze, chest infection, recent problem
blue (non-urgent) - none of the above
how are the 2 coagulation pathways assessed?
extrinsic - prothrombin time (PT)
intrinsic - activated partial thromboplastin time (APTT) assay
what effect does heparin have on the APTT?
no coagulation because heparin is an anti-coagulant
what is the effect of removing Ca ions from solution in the APTT?
no coagulation as calcium is an essential component of coagulation
what effect does benzamidine have on the APTT?
time for clot to form increases because benzamidine acts as a protease inhibitor
