Controlling Regional Blood Flow

Question 1

Describe pressure and control of flow

Answer 1

Need high pressure to be able to control flow

Q = change in P / R

Question 2

Describe the parallel design of systemic circulation

Answer 2

• Cardiac output is distributed to all organs
• Continual branching of arterial network
• Divides blood flow among the region (organ) circulations

Question 3

Describe the distribution of cardiac output at rest

Answer 3

• Both circuits have the same flow, so they have the same cardiac output
• As the arteries branch the blood is distributed differently between them, but this doesn’t change the flow

Question 4

Describe the distribution of cardiac output during excersise

Answer 4

When exercising blood is distributed differently to when at rest. Just because we are increasing CO doesn’t mean that all areas get an equal increase.

Increase in blood flows to:
- Muscle (working harder and burning fuel so needs more delivered to it)
- Heart (because its pumping harder and faster so needs to be replenished its nutrients)
- Skin (for sweat to get rid of excess heat)

Decrease in blood flows to:
- GI tract
- Kidneys
(Due to reduced need for digestion and urine production while exercising)

Constant blood flow to:
- The brain (so it can continually function at maximum capacity at all times)

Question 5

How is Mean Arterial Pressure (MAP) controlled during excersise?

Answer 5

Systemic circulation:
- Increased cardiac output
- Constant mean arterial pressure
- Decreased total peripheral resistance

MAP = CO X TPR

Question 6

Describe the resistance involved in controlling regional blood flows during excersise

Answer 6

Q = change in P / R
There is an overall decrease in resistance, but not everything went up.

Increase: kidneys, intestines, spleen etc.
Decrease: muscle, heart and skin

Increased flow = decreased resistance
Decreased flow = increased resistance

Question 7

Describe how blood flow is increased or decreased to certain areas

Answer 7

Smooth muscle can contract or relax to dilate or constrict the blood vessels - which makes it harder or easier for blood to flow through those capillaries.
- There is a direct correlation between the size of the lumen and the flow of blood through it

Question 8

What is the rule of 16 and how does it relate to blood flow?

Answer 8

Rule of 16: if you change the lumen space by a factor of two (doubling or halving), then we are changing the factor of resistance by 16 (multiplying or dividing resistance by 16)
- The radius of the lumen has a HUGE effect on blood flow

It is the rule of 16 and the vasoconstriction and vasodilation of blood vessels that allows us to have blood flow to different places.

Arterioles contract and relax via smooth muscle called pre capillary sphincters.