Responses of the Whole System -- 6.2

Question 1

What does more metabolic activity lead to?

Answer 1

Decreased TPR

Question 2

What does a fall in arterial pressure do?

Answer 2

• • increase flow resistance to certain tissues (skin, gut)

- - venoconstriction

Question 3

What occurs when you eat a meal?

Answer 3

Local vasodilation –> TPR falls
Increase in venous pressure (increase CO)
Decrease in arterial pressure (increase HR & CO)
Increasing CO –> decreases venour pressure and increases arterial pressure –> demand is met –> system is stable

Question 4

What is “muscle pumping”?

Answer 4

Muscle action forces extra blood back to the heart

Question 5

What happens when the heart rate increases but nothing else changes?

Answer 5

initially cardiac output will tend to rise, but TPR is the same
Increased CO –> decreased venous pressure –> decreased stroke volume –> CO back to normal
** heart rate is driven by the circulation**

Question 6

How is the huge demand increase during exercise met?

Answer 6

Large decrease in the TPR so there is a surge of blood back to the heart (increased venous pressure)

Question 7

What are the things that must be coped with during exercise?

Answer 7

venous pressure increases greatly
arterial pressure falls greatly
– can be too big to cope with

Question 8

Which of the changes in exercise is the bigger problem?

Answer 8

Increased venous pressure

• • tends to overfill the heart
• • ventricle is pushed onto flat portion of Starling curve

Question 9

How do you match the left and right ventricle?

Answer 9

Beat at the same rate so have to match the stroke volume (relies on Starling curve)

Question 10

What is there a risk of developing if the right and left ventricular stroke volumes do not match?

Answer 10

Pulmonary oedema

• • is RH pumps more, L fills more and pumps more
• • when on top of Starling curve, L cannot respond, so blood will accumulate in the lungs –> pulmonary oedema

Question 11

How is overfilling of the ventricles prevented in exercise?

Answer 11

By increasing the heart rate as you begin exercise

• • is driven by the brain
• • lower stroke rate is needed when the increase blood volume arrives in the heart

Question 12

What happens when you stand up?

Why are deep veins not affected?

Answer 12

Blood pols in superficial vein the the legs due to gravity
– causes central venous pressure to fall

Deeper veins are surrounded by water in tissues, as there is less pressure difference

Question 13

What happens to CO when you stand up?

Answer 13

CO falls

• -> arterial pressure falls
• -> arterial and venous pressure are both falling
• • cannot be corrected by normal mechanisms

Question 14

How are pressure changes combatted when you stand up?

Answer 14

Baroreceptors detect fall in AP –> raise HR

• • TPR increases to defend the arterial pressure 1. divert blood away from skin and gut to the brain to prevent fainting
    2. movement after standing pumps blood in veins to restore blood flow
    3. central venous pressure increases to get more blood into the heart

Question 15

What is the condition that occurs when the mechanisms to restore normal pressure do not work upon standing?

Answer 15

Postural hypotension

Question 16

What are the changes in circulation that occur during haemorrhage?

Answer 16

Reduced blood volume will decrease venous pressure

• • causes CO and arterial pressure to fall
• • heart rate increases after detection by baroreceptors which increases TPR

Question 17

Why is an increase heart rate detrimental in haemorrhage?

Answer 17

Increase HR removes more blood from veins which lowers the venous pressure, decreases heart filling and lowers stroke volume. Causes a weak and rapid pulse.

Pale as diverting blood to brain

Question 18

What are the control mechanisms for haemorrhage?

Answer 18

Increase venous pressure

1. veno-constriction (contract smooth muscles in walls) to increase stroke volume
2. “auto-transfustion” - replaces blood volume lost
   - - short term method
   - - increase blood fluid by drawing it from the extracellular space

Question 19

What organ controls the volume of the blood?

Describe the relationship between blood volume and venous pressure

Answer 19

kidneys

– increase blood volume, increase venous pressure

Question 20

What occurs when you increase the blood volume over a long period of time?

Answer 20

venous pressure increases
Co increases
Arterial pressure rises – more blood forced through tissues –> increases TPR –> increasing AP more which then remains high

Question 21

What controls mean blood pressure?

In which illness are these important?

Answer 21

Blood volume control mechanisms
e.g. kidneys

Hypertension

Question 22

What is the arterial pressure determined by?

Answer 22

Blood volume in the arteries

Question 23

What occurs in shock?

Answer 23

Blood pressure drops

Arterial pressure drops