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VASCULAR SYSTEM (VENOUS RETURN MECHANISMS - venous return is the return of…
VASCULAR SYSTEM
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Blood vessels
ARTERIES AND ARTERIOLES transport blood from heart to muscles and organs, aorta carries blood at high pressure directly from left V
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Arterioles are blood vessels carrying oxygenated blood from arteries to capillary bed and have a large layer of smooth muscle allowing both vasodilation and constriction to regulate blood flow and control blood pressure
Ring of smooth muscle at junction of a capillary and arteriole - pre capillary sphincters which can dilate or constrict to control blood flow through capillary bed
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VEINS AND VENULES - transport deoxygenated blood from muscles and organs back to heart - venules leaving capillary bed reconnect to form veins
Veins and venules - small layer of smooth muscle allowing them to venodilate and constrict to maintain slow blood flow towards heart
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VENOUS RETURN MECHANISMS - venous return is the return of blood to heart through the venules and veins back to the right atrium, largely against gravity
Rest- BP and structure of veins will maintain venous return but during exercise, a far greater demand for oxygenated blood requires a far greater venous return to increase SV and therefore Q
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GRAVITY - blood from the upper body, above heart, is helped to return by gravity
MUSCLE PUMP- skeletal muscles contract compressing veins located between them, squeezing blood back to heart
RESPIRATORY PUMP - during inspiration and expiration, a pressure difference between thoraic and abdominal cavity is created, squeezing blood back to heart.
Once we reach recovery, Q is still high and there may not be sufficient pressure to return vast quantity of blood to heart - can cause dizziness
Blood may sit in pocket valves and pool - blood pooling and is described as feeling of 'heavy legs' after exercise. Active recovery combats this effect as low intensity exercise maintains muscle and respiratory pump to aid return of blood to heart
REDISTRIBUTION OF Q
Q at rest is approx 5l/min but can rise to more than 20l/min during exercise. Difference in Q from rest to exercise is not only in volume; where the blood is sent to also changes
At rest, our body primarily serves to digest, filter and excrete - vast majority of O2 and nutrient rich blood is required around organs (approx 75%)
Exercise: demand from muscles for O2 and nutrients step up and more intense the exercise the higher the demand (88% at max effort)