Circulation Flashcards
Elastic arteries
largest arteries, smooth muscle in medial layer largely replaced by elastic tissue
High compliance
recoil of elastic fibres forces blood to move
Muscular arteries
Arranged circumferentially
Majority of tunica media is smooth muscle
Greater vasoconstriction and vasodilation to adjust flow rate
Vascular tone - partial contraction maintains vessel pressure and flow
Arterioles
finer - smaller than artery
within tissues
Smooth muscle important for regulating diameter and controlling blood pressure
Venules
less muscular than arterioles
still some smooth muscle
within tissues
Veins
Less muscular and elastic but dispensable enough to adapt to variations in volume and pressure
Large veins
More muscular
Valves prevent backflow
Slow blood flow and low pressure
Capillaries
Endothelial cells and basement membrane
Exchange of substances between blood and interstitial fluid
continuous capillary, fenestrated capillary, sinusoidal capillary
Starlings forces
Fluid movement = hydraulic conductance ((capillary hydrostatic pressure - interstitial hydrostatic pressure) - (capillary oncotic pressure - interstitial oncotic pressure))
Oncotic pressure
form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that causes a pull on fluid back into the capillary
Principal proteins in plasma
Albumin
Fibrinogen
Globulin
Other coagulation factors
Neutrophil
phagocytose bacterial
Eosinophils
combat parasites and viruses
Basophils
release IL4, histamine, heparin, peroxidase
Lymphocytes
mature into T cells and B cells
Monocytes
macrophages and dendritic cells
Feedback mechanism for platelet production
Abundant platelets bind to TPO –> megakaryocytes not generated –> platelets not made –> receptors do not bind to TPO –> TPO stimulates megakaryocyte production –> platelets made
mechanism of haemostasis
Constriction of blood vessel
Formation of temporary platelet plug
activation of coagulation cascade
Formation of fibrin plug/clot - semi solid mass of platelets and fibrin mesh
what do blood clots consist of
Euthrocytes, leukocytes, serum, mesh of fibrin, platelets
intrinsic pathway of clotting
surface contact activation on membrane of activated platelets
activation of factor XII
kininogen and prekallikrein are proteins that facilitate this activation
Extrinsic pathway of clotting
(membrane bound tissue factor activation) activated when blood contacts material from damaged cell membranes
Tissue factor receptor on cell – binds to factor 7 at sight of injury (activated factor 7)
Forms Ca2+, factor 7 and tissue factor complex which activates factor 10
Sequence of depolarisation in the heart
SA node depolarises
cardiac cells conduct cell to cell through atrial muscle
Signal hits AV node
Antrioventricular ring prevents impulse spread to ventricles
Impulse sent to bundle of His and Purkinje fibres
Steps in the cardiac cycle
Atrial diastole - Blood flows into atria, AV valve closed
Atrial systole - atria contracts, blood leaves atria and enters lower chambers
Ventricular diastole - AV and SL valves closed, as pressure in ventricle decreases relative to atria, AV valves open and blood flows into ventricle
Ventricular systole - ventricles contract, pressure higher than atria, AV valves close, SL valves open, blood es ejected from heart
what does the P wave represent?
Atrial depolarisation
What does the QRS wave represent
Ventricular depolarisation
What does the T wave represent
Ventricular repolarisation
Main components of blood
Plasma, Ethrocytes, Leukocytes, Platelets
How do erythrocytes maintain their shape
cytoskeleton bound to plasma membrane by glycophorin and CL- HCO3 exchanger
What factors effect blood viscosity
haemocrit, fibrinogen plasma concentration, vessel radius, linear velocity, temperature
How is blood clotting prevented?
Anticoagulant molecules (TFPI, antithrombin, proteins S and C, thrombomodulin) move from endothelium to interact with elements in the coagulation pathways
Deep vein thrombosis (DVT) risk factors
venous stasis, vascular injury, hypercoagulability
Pressure in the arteries
Under high pressure as they receive blood directly from the heart
Pressure in the arterioles
walls have tonically active smooth muscle to maintain pressure
site of highest resistance to flow
How do blood vessels constrict?
innervated by sympathetic adrenergic nerve fibres, when activated cause constriction of vascular smooth muscle, reducing diameter of arteriole and increasing resistance to flow
Equation for velocity of blood flow
V (velocity) =Q (flow) /A (cross sectional area)
Equation for flow
Q (flow) = ΔP (pressure difference)/R (resistance)
Equation for resistance to blood flow
R (resistance) = 8n (viscosity of blood) l (length of blood vessel) /πr^4
Diastolic pressure
lowest arterial pressure during ventricular relaxation
Systolic pressure
highest arterial pressure after blood is ejected from ventricles
Pulse pressure
systolic pressure - diastolic pressure
Mean arteriole pressure
diastolic pressure + 1/3 pulse pressure
