Session 6 - Responses of the whole system

Question 1

At a constant CO, falls in TPR do what to venous and arterial pressure?

Answer 1

• Decrease arterial pressure

- Increase venous pressure

Question 2

At a constant TPR, increasing CO has what effect on venous and arterial pressure?

Answer 2

• Increases arterial pressure

- Decreases venous pressure

Question 3

Increasing venous pressure increases…

Answer 3

-CO

Question 4

Decreasing arterial pressure increases…

Answer 4

…CO

Question 5

How do falls in arterial pressure effect the bloodflow to the gut and skin, and the veins? What is the benefit of this?

Answer 5

• Increases the flow resistance to divert blood from non-important tissues
• Venoconstriction
• Short-term defence to a decrease in AP as will counteract it

Question 6

What happens if HR increases with no other change?

Answer 6

-Increased HR = increased CO -> increased AP and decreased VP -> SV falls (diastole shorter and VP decreased) -> CO decreased

Question 7

How is it ensured that the left and right stroke volumes match?

Answer 7

-Starlings law, if the right pumps more the left fills more

Question 8

What is the consequence of right heart stroke volume being greater than the left?

Answer 8

-Pulmonary oedema as blood becomes congested in the lungs increasing hydrostatic pressure -> forces fluid out into interstitial space =oedema

Question 9

In what situation would the right heart SV be higher then the left?

Answer 9

-Anything which comprimises LV filling or ejection eg LHF

Question 10

How is an extremely high VP and thus overfilling of the RH avoided during exercise?

Answer 10

-Increase in HR before VP starts to rise as this shortens the length of diastole and avoids overfilling

Question 11

What transient problem is faced during standing up?

Answer 11

-Both venous pressure and arterial pressure decrease

Question 12

What causes both venous pressure and arterial pressure to decrease transiently when standing up?

Answer 12

-Blood pools in the superficial veins of the legs -> reduction in central venous pressure -> reduced filling of RV -> decrease CO-> TPR remains the same so decrease in AP

Question 13

What is the normal control mechanism of decreased AP?

Answer 13

-Increase CO through baroreceptors

Question 14

Why would increasing CO to counteract the decreasing AP when standing not work?

Answer 14

-Venous pressure is already low -> would exacerbate the problem

Question 15

How is the decrease in VP and AP on standing controlled?

Answer 15

-Bloodflow to the gut and skin shut down for a transient time to increase TPR which counteracts the decrease in CO and increases AP

Question 16

Why does bloodflow to the gut and skin only need to be shut down temporarily on standing and not throughout the duration?

Answer 16

-When standing muscle pumping aids venous return to the heart so no need for decreased bloodflow to gut and skin

Question 17

What is postural hypotension?

Answer 17

-A transient fall in blood pressure associated with moving to a vertical position

Question 18

What can cause postural hypotension?

Answer 18

• Reflex of shutting down bloodflow to gut and skin dont work
• If VP is already low
• Fluid imbalance
• Problems with ANS adjusting TPR

Question 19

What occurs to the volumes, pressures, CO and TPR during haemorrhage?

Answer 19

Less blood in veins -> decreased VP -> decreases end diastolic volume -> decreased SV -> decreased CO whilst TPR is the same -> decreased AP-> detected by baroreceptors -> increases HR -> more blood removed from veins -> VP drops more-> heart fills less -> signals to increase CO but heart filing inadequately so low force of contraction -> increase in TPR and blood diverted from skin and gut -> helps AP a little but lowers VP -> cycles

Question 20

How can the CVS remain uncomprimised when loosing upto 1-1.5L of blood?

Answer 20

• Venoconstriction -> smooth muscle in veins normally relaxed -> contracts and helps venous ret5urn, increasing venous pressure
• Autotransfusion

Question 21

What is autotransfusion?

Answer 21

-Tissue fluid moves from the interstitial space into the vessels due to low pressure in vessels

Question 22

What is the first line of treatment in haemorrhage?

Answer 22

-Infusion of fluids (doesnt have to be RBCs at this stage just water salts and protein -> need to increase volume!!)

Question 23

What controls blood volume in the long term?

Answer 23

-The kidneys through controlling Na/water reabsorption

Question 24

What is the result of long term increase in blood volume on pressures, CO and TPR?

Answer 24

-Increased venous pressure -> increases CO (TPR unchanged as bodys need for blood unchanged)-> Increases arterial pressure -> Increased bloodflow to tissues -> vasodilator metabolites washed away-> TPR increases -> AP rises further (self-sustaining system)

Question 25

What is average arterial pressure related to?

Answer 25

-Blood volume

Question 26

What is the consequence of prolonged increased TPR in hypertension?

Answer 26

-Hypertrophy of smooth muscle in vessels leading to further vasoconstriction

Question 27

TPR is inversely proportional to…

Answer 27

…the body’s need for blood