Feb 17 , 2012 Human Physiology II
Systemic Pressure Gradient
Vascular network is like upside down tree.
-One big massive root is aorta that distributes all the blood that came from left ventricle
That aorta branches into smaller arteries.
-Then the arteries branch off further.
--The blood gets ejected into aorta (75ml normal) has to travel down to aorta, but gets
distributed to thousands of arterioles and millions of capillaries.
-The graph is showing what happens to pressure as you move from left ventricle to all the way
to circulatory system (arteries, arterioles, capillaries, to veins and back to heart again)
-Pressure in left ventricle oscillates whilely , we have diastolic pressure of approx. 0.
-Complete oscillation occurs through this entire process
--As soon as the blood gets into aorta, that changes , now we have systolic pressure that
continues to match what the left ventricle has initiated (120mmHg)
Now we will never see diastolic pressure dropping to 0 it stays high (80mmHg)
--Feature of circulatory system (diastolic pressure never drops down)
Pressure in arteries continues to oscillate (change)
-As the blood moves through the large , there is no change in pressure in aorta.-Will be same if
measured since there is no loss of pressure occurring
-If the blood goes to the smaller blood vessels we will see a steep drop in blood
pressure.The arterials are the site in the circulation where you see a largest decrease in
PRESSURE due to their characteristic ability to regulate where blood goes, (gatekeeper
role in activiely determing diameter, resistance direction of blood)
-Capillaries, blood pressure goes down further and all way back to right atrium where its
-Pressure is always going from higher to lower point. The pressure gradient that drives flow
from the left ventricle to the right atrium. This pressure gradient is why we don’t have blood flowing opposite dirtection. Blood goes with the pressure gradient.
--There is NEVER NO FLOW, but it does increase and decrease in the amount.
-The oscillation continues in the arterials but by the time it gets into capillaries and veniules
there is NO DETECTABLE ossciallations and pressure. You only have 1 pressure to measure.
If you measure pressure in capillary, you would not get any indiactino of cardiac cycle.You would
not be able to detect effect of siastole and diastole. You needto be in the larger vessels and
most easily in the arteries, to see shifting cardiac pressure.
ARTERIES= Conduit Vessels
Conduit = good at moveing blood from one location to another, do it rapidly and without much
In order for arteries to distribute blood they need to have large diameter ( to hold large vol of
- Low contractile( contraction is an active process , arteries have layers special type of
muscles surround them, vascular smooth musles,
When would it be a good time for AORTA to contract? NEVER , you always want these arteries
to be relaying the blood as easily possible.
-High distensible (PASSIVE FEAUTRE, Compliant if you apply pressure how much it would
-You need it so when blood pumps from ventricles into arteries, arteriest can
capture vol of blood and handle it well.
These things allow them to be low resistance vessel. (ie taking EXPRESS LANE)
ARTIERIES need to be strong to withstand the high pressure ( high systolic pressure) to prevent
Elasticity (distensible) SYSTOLE
-Left ventricle will be pumping blood into aorta,
-A typical stroke vol is 75mL of blood is being squeezed into aorta during systole (0.3 sec)
300ms (normal cardiac cycle at rest)
-What happens to blood when to come to aorta?
Some of the blood will keep shooting down to the rest of the vascular system. Therefore since
this is large vol some of it will be pushing on the walls of aorta, since the aorta is elastic and it
will stretch out.
- Some vol blood is allowed to stay in aorta during systole and help to push the walls of aorta to
push it more open for larger vol of blood
-This elastic feature is very imp in maintaining reasonable pressure in the arteries because
there is this relationship between amount of vol the blood has to occupy to the pressure it’s
going to create by occupying that space.
- If we could take the 75mL of blood and put it in aorta with the smaller diameter (the smallest
one will have the HIGHEST PRESSURE). As the 75mL comes in, aorta helps to minimize the
increasing pressure with having the blood pushed into it. If aorta was not able to stretch out like
that, that blood will be confined to smaller diameter and pressure will go higher.
THIS DISTENSIBLITY (ELASTICITY) HELPS MAINTAIN THE LOWER SYSTOLIC BLOOD
-This is PASSIVELY stretching out,
-Left ventricles stop contracting, no more blood coming from left ventricle, no blood entering. We
have chance for blood to exit,. This is an open network and blood will continuously flowing
downstream where there is lower pressure following its pressure gradient… There will be less of
distensing pressure on aorta, and aorta will tend to come back to its original size. (PASSIVE not
-Walls of aorta were stretched out and now it rebounds back to its original size
-This is occurring when the heart is not pumping blood ( no blood entering vascular system but
its continuing to flow out of aorta into the downstream network. This is where we convert
intermittent pump every so often into a continuous flow through the rest of the network
(which means all the hardworking cells in the body are going to see continuous delivery of
oxygen and nutrient rich blood, they don’t have to wait for next systole to provide them the blood.
-We are able to now maintain a continuous flow through the rest of vasculature.
-The aorta is doing this in large part due to the distensibility.
What is it structurally that allows the aorta to do this?
Because of very large amount of protein called Elastin
Elastin= organized in these concentric rings in the walls of aorta,
Cross-section of aorta
Lumen will have blood
Thick wall and black lines are wings of elastin
-The amount and organization of protein is the most important
Elastin has a structure which has many connective pieces put together which allows them to be
folded up like an accordion (instrument) under unstressed state, then if you put pressure