Lecture 11- Controlling regional blood flow

Question 1

Which of the following statements about the human
cardiovascular system is INCORRECT?
A. Blood flow throughout the cardiovascular system is
unidirectional.
B. Arteries in the systemic circuit carry oxygen rich blood, while arteries in the pulmonary circuit carry oxygen
poor blood.
C. Blood flow is lower in the shorter pulmonary circuit
than in the longer systemic circuit.
D. The heart has four chambers.
E. Blood flows away from the heart in arteries and
towards the heart in veins.

Answer 1

C. Blood flow is lower in the shorter pulmonary circuit
than in the longer systemic circuit.

Blood flow must be equal in both circuits as they work in series

Question 2

What are the two reasons we need to maintain mean arterial blood pressure?

Answer 2

• difference between arteries and veins drives the movement of the blood
• Without can’t control the flow through the system

Question 3

Why is high pressure in important in arteries?

Answer 3

• Means there is fine control of blood flow out, need this as arteries carry blood to essential organs which need varying amounts.
• Not so important for veins

Question 4

Is the systemic circuit a single loop?

Answer 4

• No, there is continued branching of the arteries so that cardiac output is distributed to many different organs
• Therefore, we say there is parallel design of regional (organ) circulations within the systemic circuit

Question 5

What does the fact that regional organ flows of the systemic circuit are in parallel mean? How does this differ from the systemic and pulmonary circuits being in series?

Answer 5

• The flow is spilt between the parallel branches and so does not have to be equal between the organs
• For the systemic+ pulmonary circuits however, the blood flow does need to be equal as they work in series the same amount needs to leave the heart for lungs as arrives and subsequently leaves for the rest of the body.

Question 6

What do the individual blood flow into the different organs add up to?

Answer 6

The total, same as what left the heart

Question 7

What happens to blood flow in exercise?

Answer 7

• Metabolic demands are heightened during exercise in certain organs and decreased in others
• Increase in blood flows to Muscle, Heart, Skin
• Decrease in blood flows to GI tract, Kidneys

Question 8

Cardiac output increases during exercise, does the amount of blood flow to different organs increase proportionally as well?

Answer 8

No, the spilt is not even

Question 9

What area of the body receives a constant amount of blood no matter if exercising or not?

Answer 9

The brain, working hard all the time so has a constant need

Question 10

Why is the skin a particular area which receives increased amount of blood during exercise?

Answer 10

Need to get rid of heat that comes from exercising (burning more) so doesn’t effect core temp so direct more blood to skin in order to cool.

Question 11

Where does the most blood go during exercise?

Answer 11

Muscles, have the highest metabolic demand

Question 12

Which of the following events is NOT associated with
isovolumetric contraction of the ventricles?

A. Ventricular pressure increases rapidly
B. A “T wave” can be observed using ECG
C. A “lubb” sound can be heard with a stethoscope
D. The ventricle is depolarized
E. Ventricular volume stays relatively constant

Answer 12

B. A “T wave” can be observed using ECG

Question 13

How is MAP controlled during exercise?

Answer 13

• Important to maintain constant mean arterial blood pressure
• MAP = CO x TPR
• Cardiac output increases therefore must be a decrease in total peripheral resistance (TPR) to compensate

Question 14

What does total peripheral resistance actually mean? Do all the circuits have to be doing the same thing?

Answer 14

Total peripheral resistance is all of the resistances of different organ circuits (within systemic) added together. Some will be going up and some down but in exercise the total will go down

Question 15

Why does the fact that total peripheral resistance goes down in exercise make sense?

Answer 15

• If resistance goes down it will be easier for blood to drain into the capillaries and into tissues/ organs
• This makes sense as the whole reason cardiac output has gone up is to supply organs/tissues with more nutrients to meet metabolic demand
• Don’t want the extra blood to just be stuck in the arteries due to high resistance

Question 16

In regards to resistance what is happening to the muscles in exercise? How does this relate to flow?

Answer 16

Increased flow = decreased resistance

Question 17

In regards to resistance what is happening to the kidneys in exercise? How does this relate to flow?

Answer 17

Decreased flow = increased resistance

Question 18

What are arterioles?

Answer 18

Small vessels, exists between larger arteries and capillary beds

Question 19

Why are arterioles called resistance vessels?

Answer 19

They determine the resistance of flow of blood from arteries to capillaries by deciding how open or closed they will be.

Question 20

How does the internal radius of a vessel affect the

resistance of that vessel?

Answer 20

• The larger the lumen the lower the resistance as it is easier for blood to flow through
• In reverse, the smaller the lumen the higher the resistance as it will be harder for blood to flow through
• In other, words there is an inverse relationship

Question 21

What is the equation that defines the relationship between the radius of a vessel and resistance?

Answer 21

R= 1/r to the power of 4

Question 22

What does the fact that r is to the power of four in the resistance equation mean?

Answer 22

Even a tiny change in the size of a vessel will mean big changes in terms of the resistance

Question 23

What are vasoconstriction and vasodilation?

Answer 23

Vasoconstriction= radius of arteriole decrease
Vasodilation= radius of arteriole increase

This controls the blood flow to different regions of the body

Question 24

How do arterioles constrict and dilate?

Answer 24

-By controlling muscle tone of the blood vessel:
Constrict= smooth muscles in walls contract
Dilation= smooth muscles in walls relax

Question 25

What is the rule of 16?

Answer 25

-Due to r being to the power of 4 in the resistance equation
-If lumen doubles resistance is decreased by x16
therefore, multiply flow by 16
-If lumen halves resistance is increased by x16 therefore, divide flow by 16