Vasculature: arterial blood flow, peripheral resistance Flashcards
Describe streamlined flow of blood and how it occurs.
- when blood flows at a steady rate through a long smooth blood vessel it has streamlined flow
- each layer of blood remains the same distance from the vessel wall and the centre most portion of blood remains in the centre
What is turbulent flow of blood?
-when the rate of blood flow becomes too great flow becomes disordered and turbulent
What 3 potential things can cause the flow of blood to become turbulent?
-blood passing over an obstruction, when it makes a sharp turn, passes over a rough surface in the vessel floor
why does turbulent blood flow flow with greater resistance in the vessel?
blood flows crosswise in the vessel creating whorls of blood called eddies. these eddies add tremendously to the overall friction of the vessel
What is reynolds number?
a measure of the tendency of turbulence to occur
which factors determine whether flow is streamlined or turbulent?
- tendency for turbulent flow increases in direct proportion to the velocity of blood flow, the diameter of the blood vessel and the density of the blood
- reynolds number varies inversely with blood viscosity
What are Korotkoff sounds?
artificially generated turbulence
What is laplace’s law?
T=PR
-distending presssure (p) produces an opposing tension (T) proportional to the radius of the vessel (R)
what are the 3 practical consequences of LaPlace’s law?
- control of blood flow
- capillaries
- aneurysm
Use LaPalces law to describe the practical consequences of an aneurysm.
- weakening of vessel wall causing ballooning because wall is damaged
- more tension therefore needs to be generated because the radius has increased
- hence overall effect is ballooning increases
how is blood flow regulated through the microcirculation?
- Active and reactive hyperemia
- flow autoregulation
- vasomotion
- response to injury
What is vasomotor?
spontaneous oscillating contraction of blood vessels
how is flow regulated in response to injury?
endothelium-1 is released from endothelial cells causing potent vasoconstriction
How is flow auto regulated by arterioles?
changes in arterial pressure such as an increase causes arterioles to constrict to reduce flow therefore protecting downstream vessels which would not be able to cope with the increased pressure
What is reactive hyperemia?
occurs when the blood supply to a vessel is blocked for a long time. Once unblocked blood flow through the tissue increases greatly above the normal to supply the tissue with oxygen and nutrients and remove waste products
What is active hyperemia? what do cells release as a result?
when tissue becomes highly active during exercise for example. blood flow rate increases through the tissue.
-increase in local metabolism causes cells to devour nutrients and release vasodilators to allow increase in blood flow
Describe how blood flows through capillaries.
intermittent flow. flow turns on and off every few minutes and seconds
What are the 3 regulatory mechanisms of blood flow?
- neural
- hormonal
- local
which nerves cause vasoconstriction?
sympathetic nerves
What are 3 hormonal vasoconstrictors?
- adrenaline
- angiotensin 2
- vasopressin
what re the 2 local vasoconstrictors?
- myogenic response
- endothelium-1
what are examples of local vasodilators?
- decrease in O2
- potassium
- hydrogen ions
- NO
- CO2
How is flow through the capillaries controlled to allow exchange of substances?
velocity of blood flow is slowest hence allowing time for diffusion and exchange of nutrients and waste
How is capillary structure designed for efficient substance exchange?
unicellular layer of endothelial cells surrounded by thin basement membrane
how do lipid soluble molecules cross capillaries? examples of lipid soluble molecules.
- O2 and CO2
- diffuse directly through the cell membrane of the endothelium
how do water and non lipid soluble molecules cross capillaries?
diffuse through intracellular pores in the capillary membrane
