Week 6 - Circulatory responses to exercise and special circulations

Question 1

Describe the anatomy of the peripheral circulatory system and their role.

Answer 1

Artery - blood delivery
Small arteries + Arterioles - flow regulation (vascular shunting)
Capillaries - fluid/nutrient exchange
Venules - collection
Veins - return to heart

Question 2

What does macrocirculation involve? What does microcirculation involve?

Answer 2

Macrocirculation involves conduit arteries (aorta) and feed arteries (branches of aorta e.g. carotid artery).

Microcirculation involves resistance arteries and resistance arterioles (where vasoconstriction occurs), terminal arterioles and capillaries (gaseous exchange).

Question 3

Hyperaemia

Answer 3

blood flow increases in relation to the metabolic activity of a tissue/organ

Question 4

List metabolic factors that regulate resistance vessels (arteries and arterioles).

Answer 4

These factors cause hyperaemia (increased blood flow/vasodilation)

• Tissue hypoxia (lack of oxygen)
• CO2 increase
• pH decrease
• Lactate production
• Breakdown products of ATP (adenosine, Pi)
• Potassium
• Osmolality

Question 5

What does endothelial derived relaxing factors (EDRFs) refer to?

Answer 5

As blood moves through the vasculature, smooth muscles are lined with endothelial cells and they release nitric oxide. They go into the vascular smooth muscle and release CGMP which allows for vasodilation to occur.

Question 6

Describe 3 factors that regulate blood flow in relation to vessel type and location.

Answer 6

• Sympathetic vasoconstriction
• Metabolic vasodilation
• Endothelial derived relaxing factors (e.g. NO)

Question 7

Describe how blood flow is redistributed during exercise?

Answer 7

Increases in blood flow to working skeletal muscle:
- At rest, 15-20% CO to muscle.
- During maximal exercise, 80-85% of CO.

Decreased blood flow to less active organs:
- Liver, kidney, GI tract.
- Redistribution depends on metabolic rate.
- Exercise intensity.

Question 8

At rest what % of Cardiac Output goes to skeletal muscle? How does this change during maximal exercise?

Answer 8

At rest: 15-20% of cardiac output (0.75L/min)

Maximal exercise: 80-85% of cardiac output (20L/min)

Question 9

At rest what % of Cardiac Output goes to the brain? How does this change during maximal exercise?

Answer 9

15% and it decreases to 3-4% (note doesn’t actually decrease due to greater Q)

Question 10

In the transition from rest to exercise, what happens to the % of cardiac output and volume of blood going to the heart?

Answer 10

% of cardiac output is unchanged, but the volume of blood increase

Question 11

Describe the two factors that regulate local blood flow during exercise.

Answer 11

Skeletal muscle vasodilation (decreased vascular resistance):
- Blood flow increase to meet metabolic demands of tissue
- Magnitude of vasodilation in proportion to the size of recruited muscle mass.
- Due to changes in locally produced factors (incr NO, prostaglandins, ATP and adenosine).

Vasoconstriction to visceral organs and inactive tissues (increased vascular resistance)
- SNS responsible for vasoconstriction.
- Blood flow reduced to 20-30% of resting values.

Question 12

Other than skeletal muscle, what are the other major users of cardiac output during exercise?

Answer 12

Skin and coronary circulation

Question 13

Describe the circulation of blood to special (specific) regions during exercise.

Answer 13

• Sympathetic vasoconstriction in inactive organs - resting muscle, skin, splanchnic, renal.
• Metabolic vasodilation in active organs - active muscle, coronary.
• Thermoregulatory vasodilation in skin.

Question 14

How does splanchnic circulation (liver, GI tract, pancreas, spleen) change during exercise?

Answer 14

• Flow decreases from 20-25% at rest to 3-5% of CO during exercise (1500ml/min to 350ml/min)
• Oxygen consumption remains the same (5-60ml/min)
• Oxygen extraction increases (15-20% to 75%)

Question 15

Summarise blood flow through splanchnic circulation.

Answer 15

Blood leaves the aorta and goes to coeliac arteries, superior and inferior mesenteric arteries to the stomach, spleen, intestine and pancreas.
30% of blood containing waste products go to the liver via the hepatic artery.
70% of blood goes from the stomach, intestine etc. and to the liver via the portal vein.
Blood then returns to the inferior vena cava via hepatic veins.

(Slide 14)

Question 16

Why does splanchnic circulation decrease during exercise?

Answer 16

Due to sympathetic vasoconstriction and circulating catecholamines

Question 17

Why does oxygen extraction increase to the splanchnic region?

Answer 17

it increases to compensate for the reduced blood flow

Question 18

Why does oxygen consumption in splanchnic region remain the same during exercise despite a 20% reduction in flow?

Answer 18

the body becomes more efficient in being able to extract oxygen

Question 19

Why is sympathetic vasoconstriction greater in the splanchnic region greater during exercise in heat?

Answer 19

more cardiac output is directed towards the skin for thermoregulation

Question 20

What can vasoconstriction in the splanchnic circulation increase?

Answer 20

increase venous return

Question 21

During rest, how much blood is circulated to the skin? How does this change during maximal exercise?

Answer 21

100-300mL-min and during maximal exercise this changes to 7-8L-min

Question 22

Describe the sympathetic neural control of cutaneous (skin) circulation.

Answer 22

There is a sympathetic neural control of skin blood vessels.

1) Adrenergic vasoconstrictor (non-hairy skin e.g. palms, sole of foot, lips)
2) Cholinergic vasodilator (hairy skin) to allow for sweat response

Adrenergic (noradrenaline)
Cholinergic (acetylcholine)

Question 23

How does cutaneous circulation respond to:
a) Cold stress
b) Heat stress

Answer 23

a) Cold stress leads to increase sympathetic constrictor activity to keep the blood in the core to maintain core body temperature.

b) Heat stress leads to decreased sympathetic constrictor activity and when it passes the temperature threshold we get an increased sympathetic dilator activity (initiate sweat response and cool body temp)

Question 24

During exercise, why do we see drops in cutaneous (skin) circulation?

Answer 24

the competition between skeletal muscle and skin can explain drops in blood flow

Question 25

Compared to heating at rest, does active vasodilation occur at a higher or lower threshold during dynamic exercise?

Answer 25

Higher threshold

Question 26

List the different factors that influence skin (cutaneous) circulation.

Answer 26

1. Thermoregulatory factors (internal temperature, skin temperature) causing vasodilation.
2. Non-thermoregulatory factors such as baroreceptors that detect decreases in BP and this results in vasoconstriction (incr. bp)
3. Central modifiers such as circadian rythm, hydration, training, menstrual cycle and acclimatization.
4. Sympathetic controllers: vasodilation and vasoconstriction

Question 27

What happens to renal blood flow and oxygen extraction from rest to exercise?

Answer 27

• Flow decreases from 20% of CO to 4% of CO during exercise (1200mL-min to 360mL-min) as blood is redirected to muscles
• Oxygen extraction increases from 6% to 18% (becomes more efficient as less blood supply)

Question 28

What is the autoregulation of blood flow to contracting muscles during exercise due to?

Answer 28

locally produced factors such as nitric oxide, prostaglandins, and adenosine

Question 29

What does sympatholysis refer to?

Answer 29

local inhibition of sympathetic-induced vasoconstriction