1.15 - Blood Flow Flashcards
What are cardiofugal vessels?
Vessels that carry blood away from the heart. i.e. Arteries
What are cardiopetal vessels?
Vessels that carry blood to the heart. i.e. veins
Define: Flow
Flow = volume (V) / unit time
Flow is results of pressure difference along vessel (ΔP)
Without a pressure difference, flow is zero
How are Flow and resistance related to Pressure Difference?
Ohm’s Law (Darcy’s Law): ΔP=RxF
Rewritten specifically for circulation –> MAP=TPRxCO
What determines resistance?
R proportional to (L.n)/r^4 L = length r = radius n = blood viscosity Change in radius has greatest effect on resistance --> Arterioles determine peripheral resistance.
What are the two types of flow in blood vessels?
Laminar
Turbulent
Where in the blood vessel is velocity fastest?
In the centre.
Describe the effect a change in TPR has on distal pressure
Vasoconstriction
Resistance increases –> Pressure decreases in capillaries/venous bed. Less Pressure “gets through”
Vasodilation
Resistance decreases –> Pressure increase in capillary/venous bed. More Pressure “gets through”
Changes in TPR have consequences on capillary/venous bed
Describe Pressure and Wall tension
Pressure (ΔP) is the same in all directions
Longitudinal (driving force for flow)
Transmural (“stiffness”/tension of vessel): circular “force” needed to counter it, i.e. to hold vessel together
What are the histological specialisation required to overcome the wall tension caused by pressure in the vessel?
Vessel wall tensions are matched by thickness of smooth muscle and connective/elastic fibres
Tension of big arterial vessels is biggest, even more so of vessels, which are pathologically extended (aneurysms)
Describe the Flow/Volumes in Vascular Beds
Most blood in systemic vessels
Very little is in systemic arteries
Most blood is in systemic veins
80% of blood is in low pressure part of circulation
v in veins < arteries
Very little blood is in heart
Cross-sectional area in capillaries is very large –> velocity is very small
