Distribution of cardiac output

Question 1

at rest 5l/min what percentage of blood flow goes to parts of the body at rest

Answer 1

bone marrow - 5%
brain - 18%
heart - 5%
liver - 25%
kidneys - 20%
muscles - 20%
skin - 7%

Question 2

during exercise 40l/min what percentage of blood flow goes to parts of the body

Answer 2

muscles - 87%
target Organs - 13%

Question 3

how does redistribution of cardiac output occur

Answer 3

The receptors send a message to our vcc which stimulates the vascular shunt mechanism

Question 4

what do we detect so the vascular shunt mechanism can occur

Answer 4

we detect: the start and increased intensity of exercise detected by receptors that monitor changes in the body

Question 5

how does the brain then act after detection in the vascular shunt mechanism

Answer 5

the receptors relay the messages to the vcc. the vcc sends a message via the sympathetic nervous system to increase or decrease sympathetic stimulation to the arterioles and pre-capillary sphincters

Question 6

how does the shunt then occur

Answer 6

the VCC decrease stimulation of arterioles and pre-capillary sphincters at the muscles. vasodilation happens and blood rushes through. The opposite happens (vasoconstriction) at the organs.

Question 7

what is the venous return

Answer 7

the return of blood to the heart during the cardiac cycle
- we need to keep VR high in order too keep SV high
-> essential for the delivery of oxygen during exercise
- the more blood returning, the more the heart is stretched to deal with the blood
-> increased stimulation of the SA node, which in turn increases HR + SV

Question 8

what does starlings law state is the problem with venous return

Answer 8

2 problems that might delay or slow down VR:
- the blood pressure in the veins is very low
- most of the blood has been distributed lower than the heart and therefore has to fight against gravity to make its way back to the heart

Question 9

what are the solutions for starlings law

Answer 9

1. pocket valves
2. skeletal muscle pump
3. smooth muscle
4. respiratory pump
5. gravity

Question 10

explain pocket valves

Answer 10

they are in veins to stop back flow of blood. this means once the blood reaches a certain point it cannot return.
- can be a risk with blood pooling if not continuous

Question 11

explain skeletal muscle pump

Answer 11

• when the muscles in the lower leg contract, they squeeze the surrounding veins and force the blood back to the heart
• links with pocket valves to keep the blood moving

Question 12

explain the role of smooth muscle

Answer 12

• veins are lined with smooth muscle that can venoconstrict and force the blood back towards the heart
• cannot constrict as much as an artery

Question 13

explain the role of the respiratory pump

Answer 13

• as the diaphragm flattens and we inhale the pressure of the thoracic cavity is increased and forces blood back to the heart
• this happens more the higher our breathing rate is

Question 14

explain the role of gravity on venous return

Answer 14

blood from the heart returns via gravity