Venous return and blood redistribution Flashcards
What is venous return
Volume of blood that returns to the right side of the heart via veins and venules
What does Starling’s law state
Decreased venous return = decrease in SV (therefore Q) and vice versa
How does venous return lead to increased HR and SV
Blood to right atrium stretches its chamber, so SA node firing rate increases along with HR
What happens to venous return at rest
VR is sufficient to maintain SV and Q to meet demand for O2
What happens to venous return during exercise
Blood pressure in veins is too low to maintain VR, so SV and Q decrease so body needs extra help to combat gravity
What are the 5 main mechanisms to aid venous return
Pocket valves
Muscle pump
Respiratory pump
Smooth muscle
Gravity
What is the role of pocket valves when aiding venous return
Prevent backflow and direct blood to heart
What is the role of a muscle pump when aiding venous return
Veins between muscles squeeze blood back to the heart when muscles contract
What is the role of a respiratory pump when aiding venous return
Deeper/faster breathing causes pressure changes in thorax and abdomen, squeezing large veins to pump blood back to the heart
What is the role of a smooth muscle when aiding venous return
Contraction/relaxation of SM in middle layer of vein walls helps push blood back to heart
What is the role of gravity when aiding venous return
Blood from upper body is aided by gravity
What is blood pooling
Lack of pressure in veins so blood sits in pocket valves
How does VR impact performance
Increased O2 and aerobic capacity decreases speed of fatigue and delays OBLA, and oxidises lactic acid
How do mechanisms of VR continue post exercise
Cool down
What is the vascular shunt mechanism
Redistribution of blood to active skeletal muscles and away from inactive organs (partially to skin)
What is the process of the vascular shunt mechanism
Arterioles lead to capillary beds, where gas exchange occurs. Blood flow here is controlled by precapillary sphincters which vasoconstrict/dilate
What is the 80/20 rule
80% blood to organs at rest, 80% to muscles during exercise
What control blood redistribution
Vasomotor control centre
Where is the VCC located
Medulla oblongata
Where does the VCC receive information
Chemoreceptors, baroreceptors, proprioceptors
What are chemoreceptors
Detect chemical changes (O2, CO2 and pH)
What are baroreceptors
Detect pressure changes (blood pressure)
What are proprioceptors
Detect changes in movement
Where does the VCC send its info to cause vasocontstriction
Sympathetic nervous system, increased sympathetic stimulation = increased vasoconstriction
