Week 17: (C) Pressure gradients, blood flow & peripheral resistance Flashcards
What are all blood vessels lined with?
a layer of endothelial cells
What are the 3 layers of a blood vessel?
endothelial cells (intimal layer) Smooth muscle cells (medial layer) Connective tissue (adventitial layer)
What is the emption of the capillaries?
just a thin layer of endothelial cells
What provides elastin and collagen?
tunica media
What pathway innervates the smooth muscle of arterioles?
sympathetic, allow regulation of blood flow
What changes the venous reservoir?
contraction and relaxation of smooth muscle veins. altered vol of blood back to the heart known as venous return
What are arterioles, venues and capillaries collectively known as?
microcirculation
What is the lumen diameter of the capillaries?
~3 micrometers
What pressures does F go to and from?
always from region of higher pressure to a region of lower
What do you call the pressure exerted by a fluid called?
hydrostatic pressure
What are the units of flow?
volume per unit time (l/min or ml/min)
What are units of the pressure difference (deltaP)?
mmHg
this drives the flow
What do we need to calculate flow rate?
the pressure difference between 2 points (delta P) & the resistance (R)
What does resistance measure?
how difficult it is for blood to flow between two points at any given pressure difference.
i.e a measure of the friction impeding flow
What does blood flow through a vessel depend upon?
pressure gradient and vascular resistance
What is the blood flow equation?
change in pressure/ resistance
What is a pressure gradient?
difference in pressure between beginning and end of vessel
What causes friction in resistance?
the friction between moving blood and stationary vessel wall
If resistance increases, what must be altered to maintain flow rate?
pressure must increase
What is parabolic distribution?
blood in contact with the epithelial wall, move slower due to increased friction (resistance). Blood flowing the centre has less resistance, flows quicker
What 3 factors does resistance to blood flow depend upon?
1) viscosity of blood (n eta)
2) vessel length (L)
3) vessel radius (r)
Why is L unimportant?
the length is constant
What is the major determinant of resistance to flow along a vessel?
radius (r)
slight change in radius = notable change in flow
What is the effects of a 2-fold change in radius on flow?
produce a 16-fold change in flow
Flow
How to calculate mean arterial pressure?
= diastolic pressure + 1/3 pulse pressure
What does arterial blood pressure fluctuate in relation to?
ventricular systole and diastole
How to calculate pulse pressure?
systolic arterial pressure - diastolic arterial pressure.
Why does arterial pressure not drop to zero during diastole?
as arterioles have a higher resistance to blood than
How much blood enters arteries and flows to arterioles?
more blood enters arteries than leaves to arterioles
what happens to arteries when heart is reeling and filling?
passively recoil, like a balloon
exerting pressure on the blood in the arteries during diastole, pushes blood into vessels downstream. ensuring continued blood flow to organs as heart is relaxing
Where so the arteries store excess pressure energy during systole?
in their stretched walls
What does the pressure drop to on arterioles?
~37 mmHg
What vessel has the slowest velocity? and why?
capillaries, to allow adequate time for the exchange of nutrients and waste products between the blood and cells of tissues
What vessel has the highest cross sectional area?
capillaries
What happens to the pressure in the arterioles?
They have high resistance so results in decreased pressure
What the the change in mean pressure in the arterioles from~93 to ~37mmHg result in?
pressure drop
pressure gradient helps drive blood from the heart to the tissue capillary beds.
What is the thick layer in arteriolar walls?
smooth muscle
What type of nerves innervate the smooth muscle of arteriolar walls?
sympathetic
What is the smooth muscle also sensitive to?
many local chemical changes and certain circulatory hormones
What happens when contraction of the smooth muscle or arteriole occurs?
contraction= decreased radius,
increased resistance= decreased blood local flow= vasoconstriction
What happens when relaxation of the arteriole occurs?
relaxation= increased radius,
decreased resistance= increased local blood flow= vasodilation
What is vascular tone?
when the arteriolar smooth muscle displays a state of partial constriction
What 2 factors are responsible for vascular tone?
1) myogenic activity
2) sympathetic activity
What is myogenic activity?
relates to the contraction initiated by smooth muscle itself, independent any external occurrence or nerve stimulation
What is sympathetic activity (smooth muscle)?
increase sympathetic activity, increase contraction, vasoconstriction…decrease blood flow through vessel
Why is vascular tone important?
makes it possible to decrease or increase contractile activity
What is Poiseulle’s law?
any change in contractility of arteriolar smooth muscle will substantially change resistance to flow in these vessels
