Week 6 - Circulatory responses to exercise and special circulations Flashcards

1
Q

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

A

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

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2
Q

What does macrocirculation involve? What does microcirculation involve?

A

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).

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3
Q

Hyperaemia

A

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

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4
Q

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

A

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
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5
Q

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

A

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.

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6
Q

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

A
  • Sympathetic vasoconstriction
  • Metabolic vasodilation
  • Endothelial derived relaxing factors (e.g. NO)
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7
Q

Describe how blood flow is redistributed during exercise?

A

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.

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8
Q

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

A

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

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

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

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

A

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.

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12
Q

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

A

Skin and coronary circulation

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13
Q

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

A
  • Sympathetic vasoconstriction in inactive organs - resting muscle, skin, splanchnic, renal.
  • Metabolic vasodilation in active organs - active muscle, coronary.
  • Thermoregulatory vasodilation in skin.
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14
Q

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

A
  • 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%)
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15
Q

Summarise blood flow through splanchnic circulation.

A

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)

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16
Q

Why does splanchnic circulation decrease during exercise?

A

Due to sympathetic vasoconstriction and circulating catecholamines

17
Q

Why does oxygen extraction increase to the splanchnic region?

A

it increases to compensate for the reduced blood flow

18
Q

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

A

the body becomes more efficient in being able to extract oxygen

19
Q

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

A

more cardiac output is directed towards the skin for thermoregulation

20
Q

What can vasoconstriction in the splanchnic circulation increase?

A

increase venous return

21
Q

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

A

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

22
Q

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

A

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)

23
Q

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

A

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)

24
Q

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

A

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

25
Q

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

A

Higher threshold

26
Q

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

A
  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
27
Q

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

A
  • 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)
28
Q

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

A

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

29
Q

What does sympatholysis refer to?

A

local inhibition of sympathetic-induced vasoconstriction