8. Blood flow, blood pressure, and the vasculature

Imagine a sudden, large increase in sympathetic signaling to the heart. While sympathetic activity remains high:

a

diastole will be longer than it was prior to the increase.

b

ESV will be higher than it was prior to the increase.

c

the left AV valve will no longer close.

d

left ventricular pressure will peak at a higher value than it did prior to the increase.

D

what is the vasculature?

comprised of different vessel types of different sizes and functions

of a vasculature, list from biggest to smallest

• large artery

• arteriole

• capillary

what lines the lumen of a blood vessel of a large artery?

• endothelium → single-cell-thick epithelial tissue layer

describe the arteriole

• only has smooth muscle lining that helps it expand or contract

describe the capillary

just a thin small tube of epithelial cells, and the only one WITHOUT a layer of smooth muscle

where does the deoxygenated blood from body go to?

into a venule and then a large vein

• tend to have bigger lumens

cardiac output is the - but -

what is the equation?

cardiac output is the rate of blood flow through the total vasculature, but blood does not flow through every vessel equally

flow rate = deltaP/R

• delta P is the pressure difference between two points in a vessel

• R is the vascular resistance that depends strongly on one of the variables of R, which is is r^4, which is the radius of the vessel

  • basically, the smaller vessel have higher resistance and thus lower flow rates (think of the force you need to apply when sucking out of Molly Tea’s straw vs a KFT straw)

how can radius appreciably change over acute physiological time scales?

contraction/relaxation of smooth muscles lining the walls of blood vessels cause vasomotor responses

in addition to size of the vessels, what else do we need to account for?

• the total number of vessels at each stage

  • if we added more vessels of size B, it would fill at the same rate as size A

draw the diagram that map out total number of each and the velocity of blood traveling in each

is the blood returning to the atria occurring at the same rate as the blood exiting the ventricles?

yes because the circulatory system is a closed system over a short acute time

• even though each capillary is a lot slower, because there are a lot of them, it evens out

by the time blood enters the venous circulation …

most of the pressure generated by the ventricles have dissipated

which circulation have less pressure and why?

• pulmonary circulation is shorter and have less pressure because it has less resistance of flow

  • can achieve the same flow rate as the systemic circulation but with lower pressure

why is there a higher pressure for systemtic circulation?

• because it is needed to deliver blood to different parts of your body

what is the mean arterial pressure?

• it drives the flow of blood through the vasculature

• generally is referring to the pressure in the systemic arteries

• arterial walls stretch out during systole and then rebound back during diastole to help keep blood flowing during diastole and prevent pressure from dropping too fast during those periods

why is the pressure always lower in more downstream parts of the system?

• pressure always goes high to low

• this is so blood can continue to flow through in the veins

how do you calculate mean arterial pressure? how do you increase it?

MAP = CO x TPR

• CO = cardiac output

• TPR = total peripheral resistance (combined resistance of all the systemic arterial blood vessels)

can increase MAP by hypothetically keeping CO constant and if all the arteries in our bodies get constricted, in order to continue flowing at the same rate, the mean arterial pressure would have to increase to push the blood faster

What about the venous circulation?

-

what are the conditions of the vein part of the vasculature and why is that helpful?

• veins have very low resistance (due to their large diameters) which helps blood to keep flowing even with low deltaP (pressure)

• veins have smooth muscle and can have their diameters adjusted dynamically

• major veins are valved to only allow one-way flow back to the right atrium

what other conditions help with pushing more blood out of the body?

• many veins flow through large skeletal muscles, so when the muscles contract, they squeeze the veins and force blood forward (skeletal muscle pump)

• when breathing in, the increased abdominal pressure also squeezes veins and increases pressure within them (respiratory pump)

what happens if you sit for too long? for example, sitting on a plane for 10 hours?

when you are sitting, your skeletal muscles are not going through cycles of contraction and relaxation. not much blood would be able to go back up to the heart from your legs and can lead to swelling on your legs

since the vascaulture is a closed system over acute time scales, what must happen? how are they connected?

over a few beats, venous return must essentially equal cardiac output

• if there is increased activity of sympathetic nerves to veins/increased muscle pump, then there is more blood volume/inspiration movement

• both would increase venous return, and an venous return leads to an increase in atrial pressure, more end-diastolic ventricular volume, and then ultimately increase stroke volume (through the Frank-Starling mechanism)

TH: The average rate of blood flow through any single systemic ___ is ___ the average rate of blood flow through any single systemic ___.

Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer.

a

artery; slower than; capillary

b

vein; slower than; capillary

c

capillary; faster than; vein

d

capillary; slower than; vein

d) the average rate of blood flow through any single systemic capillary is slower than the average rate of blood through any single systemic vein

Comparing arteries and veins, pressure tends to be higher within ___, and resistance to flow tends to be higher within ___.

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a

arteries; arteries

b

arteries; veins

c

veins; arteries

d

veins; veins

pressure tends to be higher within arteries, and resistance to flow tends to be higher within arteries