Blood Vessels and Blood Flow Flashcards
What divisions of blood vessels has the largest cross-sectional area?
Capillaries
How does the amount of blood stored in the veins change during exercise?
Exercise causes VENOCONSTRICTION leading to a decrease in the amount of stored blood, so there is more venous return.
State the equation relating blood flow, pressure difference and resistance.
Blood Flow = pressure difference/resistance
Where does the biggest drop in blood pressure take place?
In the arterioles
What three variables determine resistance to blood flow?
Fluid viscosity
Vessel radius
Length of tube
Describe how blood normally flows in vessels.
Normal blood flow is laminar - blood flows fastest in the middle and slowest around the outside.
What is shear rate?
The velocity gradient at any time
What is shear stress?
Velocity gradient x viscosity
What are the effects of a) high, and b) low shear stress?
High = promotes endothelial survival
Low (turbulent) = promotes endothelial proliferation, which affects vasoconstriction, platelet aggregation, coagulation
What are the equations for pulse pressure and mean arterial blood pressure?
Pulse Pressure = SBP - DBP
Mean Arterial Blood Pressure = DBP + 1/3 PP
How do aortic and ventricular pressure differ and what is the reason for this difference?
Once the aortic valves close, ventricular pressure falls but aortic pressure only falls slowly during diastole because the elasticity of the aorta buffers the pressure.
What is the name given to the dampening effect of the aorta?
Windkessel Effect
What are the consequences of a decrease in arterial compliance?
Pulse pressure will increase
State the Law of Laplace.
When the pressure within a vessel is kept constant, tension is directly proportional to the radius.
T = PR
What does circumferential stress equal?
Circumferential stress = tension/wall thickness
Circumferential stress = PR/h
What is compliance?
Change in volume of the vessel per unit change in pressure.
Describe how aneurysms are linked to the Law of Laplace.
The vessel radius increases meaning that greater wall tension is needed to withstand the internal pressure. If the structure of the wall is damaged and it can’t have the required tension, then the vessel will continue to dilate.
How do the compliance of arteries and veins differ?
Veins are a lot more compliant
What is the difference between the blood pressure in the ankle compared to the hand?
Blood pressure in the ankle is much greater than in the hand
Why don’t we faint every time we stand up due to blood pooling in our leg veins?
Standing causes activation of the sympathetic nervous system, which stiffens and constricts the veins resulting in greater venous return to the heart.
Constricted arteries means there is an increase in TPR to maintain blood pressure.
There is also a slight increase in heart rate and force of contraction.
What are the two pumps that facilitate the movement of venous blood back to the heart?
Skeletal muscle pump
Respiratory pump
