Blood Vessels and Blood Flow 4 Flashcards
(22 cards)
What regulates structure and resistance in small arteries/arterioles?
Smooth muscle
What acts as a reservoir for blood volume?
The veins
What akes the largest cross-sectional area in the CVS?
The capillaries
What is Darcys Law?
Pressure Difference = Flow x Resistance
P=QxR
Q = Cardiac output R = Peripheral vascular resistance P = Mean blood pressure
`Why does pressure fall across the CVS?
Viscous pressure losses and resistance
What are the 3 variables of resistance?
- Fluid viscosity
- Length of tube (fixed)
- radius of tube (variable)
Which equation shows importance of vessel radius for resistance?
Poisuille’s
How much would halving the radius decrease blood flow?
16 times
What are the two types of blood flow?
Laminar and turbulent
Where does blood flow the quickest?
In the middle of the vessel, slowest at the sides
What is the Shear Rate?
The difference in velocity between the highest in the middle of the lumen and the lowest that adheres to the lumen walls
What does shear stress do?
Disturbs endothelial function
What does low shear stress cause?
Endothelial proliferation and therefore vasoconstriction, coagulation, platelet aggregation and atheroma formation
What is the pulse pressure?
The difference between diastoic and systolic blood pressure
How do you calculate mean blood pressure?
Diastolic + a third of pulse pressure
What is the Windkessel effect?
Aortic elasticity keeping blood pressure a lot higher than in the pulmonary artery
What is pressure inside a vessel called?
Transmural pressure
How does an aneurysm form?
Weakened blood vessel walls over a prolonged period of time as a result of the law of laplace.
Why dont we faint when were standing?
Standing activates the sympathetic nervous system which stiffens and contracts the veins, especially in the legs. This increases total peripheral resistance and paired with slightly higher heart rate and cardiac contractile strength allows blood pressure to be maintained
What is a skeletal pump?
The contraction of the muscles squeezes blood back through the veins and to the heart
What is the respiratory pump?
During inspiration, our chest expands and intrathoracic pressure decreases allowing blood to come back into the right atrium and increase venous return
What do incompetent valves cause when standing?
Varicose veins and oedema of the feet
