Week 6 - Circulatory responses to exercise and special circulations Flashcards
Describe the anatomy of the peripheral circulatory system and their role.
Artery - blood delivery
Small arteries + Arterioles - flow regulation (vascular shunting)
Capillaries - fluid/nutrient exchange
Venules - collection
Veins - return to heart
What does macrocirculation involve? What does microcirculation involve?
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).
Hyperaemia
blood flow increases in relation to the metabolic activity of a tissue/organ
List metabolic factors that regulate resistance vessels (arteries and arterioles).
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
What does endothelial derived relaxing factors (EDRFs) refer to?
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.
Describe 3 factors that regulate blood flow in relation to vessel type and location.
- Sympathetic vasoconstriction
- Metabolic vasodilation
- Endothelial derived relaxing factors (e.g. NO)
Describe how blood flow is redistributed during exercise?
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.
At rest what % of Cardiac Output goes to skeletal muscle? How does this change during maximal exercise?
At rest: 15-20% of cardiac output (0.75L/min)
Maximal exercise: 80-85% of cardiac output (20L/min)
At rest what % of Cardiac Output goes to the brain? How does this change during maximal exercise?
15% and it decreases to 3-4% (note doesn’t actually decrease due to greater Q)
In the transition from rest to exercise, what happens to the % of cardiac output and volume of blood going to the heart?
% of cardiac output is unchanged, but the volume of blood increase
Describe the two factors that regulate local blood flow during exercise.
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.
Other than skeletal muscle, what are the other major users of cardiac output during exercise?
Skin and coronary circulation
Describe the circulation of blood to special (specific) regions during exercise.
- Sympathetic vasoconstriction in inactive organs - resting muscle, skin, splanchnic, renal.
- Metabolic vasodilation in active organs - active muscle, coronary.
- Thermoregulatory vasodilation in skin.
How does splanchnic circulation (liver, GI tract, pancreas, spleen) change during exercise?
- 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%)
Summarise blood flow through splanchnic circulation.
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)