Lecture 23: Circulation Through 'Special Regions' During Exercise

Question 1

What tissues other than muscle have increased blood flow to them with exercise intensity?

Answer 1

The coronary system (heart) and cutaneous system

Question 2

Which regions have a major decrease in blood flow to them?

Answer 2

The Splanchnic region and the kidneys

Question 3

How does blood flow to the heart change with exercise? (requires values)

Answer 3

0.25 L.min –> 1.25 L.min

30% oxygen extraction –> 90% oxygen extraction

Question 4

What property aids the heart’s high oxygen extraction?

Answer 4

Very high capillary density

Question 5

What is the main vasodilator for the heart and where does it exert its influence?

Answer 5

Adenosine and it stimulates alpha-2 receptors

Question 6

What is the difference in chronotropic and inotropic influence on the heart?

Answer 6

Chrontropic: increasing HR via nerve stimulation
Inotropic: increasing heart contractility

Question 7

Why does 80% of vessel flow occur during diastole?

Answer 7

Because the vessel compresses during systole

Question 8

How can coronary artery disease/ischeamia be identified with an exercise stress test?

Answer 8

At rest, an obstruction in the coronary artery may still be able to get sufficient oxygen to the heart, therefore it is difficult to identify whether one is present.
Exercising allows for identification, as if there is a blockage conditions will become hypoxic and ischaemia will occur as there is less time for diastole (vasodilation).
This causes a prolonged ST depression on the ECG.

Question 9

Summarise coronary circulation blood flow during exercise.

Answer 9

1. High oxygen extraction
2. Increased blood flow aided by a large network of capillaries
3. Vasodilation mediated by adenosine
4. High potential for ischaemia
5. Flow occurs mainly during diastole

Question 10

How does cutaneous system blood flow change between rest and maximally intense exercise?

Answer 10

It increases from 100-300ml.min to 7-8L.min

Question 11

What kind of control is skin blood flow under?

Answer 11

Neural

Question 12

How is blood flow regulated to non-hairy skin and hairy skin?

Answer 12

Adregenic vasoconstrictor: regulates blood flow for non-hairy skin at low temperatures
Cholinergenic vasodilator: regulates blood flow for hairy skin at high temperatures

Question 13

How does cutaneous blood flow change with increased heat stress?

Answer 13

At cold temperatures there is increased activation of adregenic vasoconstrictors by noradrenaline for non-hairy skin.
As temperatures increase adregenic vasoconstrictor activity decreases.
When a temperature threshold is reached, cholinergenic vasodilation increases due to increased activation by achetycholine.
The blood flow at this point then plateaus.

Question 14

During dynamic exercise, what happens to the vasodilatory threshold with increased temperature, compared to rest?

Answer 14

It occurs at a higher temperature

Question 15

Why must vasodilation occur at a higher temperature during exercise?

Answer 15

Increased demand by skeletal muscle therefore vasodilation must occur at a higher temperature so as to reduce the amount of competition for blood flow as much as possible.

Question 16

How can skin thermoregulation limit blood flow to the coronary system during continuous exercise?

Answer 16

In high heat blood moves from the core to the surface.
This means there is little pooling of blood for the muscle pump to return.
This stimulates the requirement for vasoconstriction to maintain blood flow via increased blood pressure.
In effect, venous return is reduced and therefore so is stroke volume.

Question 17

Other than temperature, what else can influence vasoconstriction?

Answer 17

Menstrual Cycle
Circadian Rhythm
Acclimitisation to Temperature
Hydration

Question 18

How does blood flow to the sphlancnic region differ between rest and exercise? (requires values)

Answer 18

Rest: 1500 ml.min (25% of CO)
Exercise: 350 ml.min (5% of CO)

Question 19

How do oxygen consumption and oxygen extraction change in the splanchnic region between rest and exercise?

Answer 19

Oxygen consumption stays the same

Oxygen extraction increases: 15-20% –> 75%

Question 20

Why does vasoconstriction to the splanchnic region occur during exercise?

Answer 20

To provide more blood for the heart, therefore increasing cardiac output

Question 21

What occurs to splanchnic region blood flow under heat stress?

Answer 21

Becomes even more vasoconstricted in order to provide more cardiac output for the skin

Question 22

What happens to renal blood flow and oxygen extraction?

Answer 22

BF decreases: 1200ml.min –> 360 ml.min

O2 extraction: 6% –> 18%

Question 23

What is proteinura and what stimulates it?

Answer 23

The increased presence of protein in the urine due to high heat stress

Question 24

How is skin blood flow regulated throughout exercise?

Answer 24

Onset: vasoconstriction to skin to maximise huge increase in skeletal muscle blood flow
Temperature threshold: reached therefore vasodilation of blood flow to skin in order to lose heat
Prolonged exercise: vasoconstriction to skin once again, in order to maintain central blood volume