venous return

Question 1

what is venous return?

Answer 1

the return of blood to the right side of the heart via the vena cava

Question 2

what percent of blood is contained in the veins at rest?

Answer 2

70%

Question 3

what does storing blood in the veins during rest mean?

Answer 3

a large amount of blood can be returned to the heart when needed

Question 4

what happens to the amount of blood returning to the heart during exercise?

Answer 4

it increases (venous return increases)

Question 5

what is Starling’s Law?

Answer 5

more blood being pumped back to the heart = more blood will be pumped out
stroke volume will increase

Question 6

what are venous return mechanisms?

Answer 6

things within the body to aid venous return

Question 7

why does the body need venous return mechanisms?

Answer 7

the pressure of blood in large veins is very low which makes it difficult to return blood to the heart

Question 8

what are some mechanisms?

Answer 8

1) the skeletal muscle pump
2) the respiratory pump
3) pocket valves
4) very thin layers of smooth muscle in the walls of the veins
5) gravity
6) the suction pump action of the heart

Question 9

how does the skeletal muscle pump help?

Answer 9

muscles change shape when they contract and relax
the change in shape means that the muscles press on nearby veins and cause a pumping effect and squeezes the blood towards the heart

Question 10

how does the respiratory pump help?

Answer 10

during contraction and relaxation whilst breathing in and out the pressure changes in the thoracic and abdominal cavities
these changes in pressure compress and nearby veins assist blood return to the heart

Question 11

where is the thoracic cavity?

Answer 11

in the chest

Question 12

where is the abdominal cavity?

Answer 12

in the stomach

Question 13

how do pocket valves help?

Answer 13

it’s important blood in the veins only flows in one direction
the presence of valves ensures this happens
once the blood has passed the valves they close to prevent blood flowing back

Question 14

how does smooth muscle in veins help?

Answer 14

it helps squeeze blood back towards the heart

Question 15

how does gravity help?

Answer 15

it helps the blood return to the heart from the upper body

Question 16

why does venous return need to be maintained during exercise?

Answer 16

to ensure the skeletal muscles are receiving enough oxygen to meet demands of the activity

Question 17

what will keep the skeletal muscle pump and respiratory pump working?

Answer 17

performing an active cool down

Question 18

why do the mechanisms need to be kept working?

Answer 18

to prevent blood pooling (blood collecting in the veins)

Question 19

what happens when systolic pressure increases/decreases?

Answer 19

venous return will also increase/decrease

Question 20

what is venous return determined by?

Answer 20

a pressure gradient

Question 21

what is the pressure gradient?

Answer 21

the mean systemic pressure - the right arterial pressure
resistance = total peripheral vascular resistance

Question 22

pressure gradient equation:

Answer 22

venous pressure (Pv) - right arterial pressure (Pra) / venous vascular resistance (Rv)

Question 23

in regards to pressure gradient what can lead to an increase in VR?

Answer 23

an increase in venous pressure or a decrease in right arterial pressure or a decrease in venous resistance

Question 24

where is blood pressure usually low?

Answer 24

right atrium and peripheral veins

Question 25

what can large changes in pressure gradient can be caused by?

Answer 25

small changes in blood pressure
this can affect return of blood to the right atrium