16. Responses to CVS stress

Question 1

Why do you take blood pressure from the arm?

Answer 1

Because it is level with the heart so gravity is the same. Blood pressure below the heart is going to be higher while BP above is lower.

Question 2

Does gravity have an effect on arteries?

Answer 2

No, they are very muscular meaning they can maintain the BP

Question 3

Does gravity have an effect on the veins?

Answer 3

Yes, less muscular therefore they are more prone to venous distention

Question 4

When someone changes posture from lying to standing what happens to the BP?

Answer 4

When someone stands the blood temporarily pools in the veins in the legs. This reduces the volume in the arteries and lowers blood pressure

Question 5

Why does blood pool in the legs?

Answer 5

There is an increase in hydrostatic pressure and gravity which results in more fluid loss to the interstital compartment

Question 6

What does an increase in fluid loss to surrounding tissue from the capillaries result in?

Answer 6

A reduction in effective circulating blood volume = transient hypotension

Question 7

Where does the lost fluid from the capillaries go?

Answer 7

It returns via the lymphatics

Question 8

What happens to the ventricular filling during transient hypotension?

Answer 8

It decreases so the volume of blood ejected during systolic contraction decreases as well

Question 9

Define haemorrhage

Answer 9

A reduction in actual circulating blood volume

Question 10

What does a decrease in baroreceptor firing stimulate?

Answer 10

Increase in heart rate
Increase in heart contractility
Organ specific vasoconstriction

Question 11

Which end has the higher hydrostatic pressure, arteriolar or venous end?

Answer 11

Arteriolar

Question 12

Which end has the higher colloid osmotic pressure, arteriolar or venous end?

Answer 12

The colloid osmotic pressure remains the same

Question 13

During haemorrhage what happens to the hydrostatic pressure at the venous end?

Answer 13

It is much lower so you retain a lot more fluid at the venous end

Question 14

Define autotransfusion

Answer 14

During haemorrhage you get significant reabsorption of fluid back into the capillaries from the tissue to try and preserve the blood pressure

Question 15

What are the 3 main useful hormones when haemorrhage occurs?

Answer 15

Angiotensin II
Aldosterone
Vasopressin (ADH)

Question 16

What is the function of angiotensin II during haemorrhage?

Answer 16

Powerful vasoconstrictor that reduces blood flow to the kidney = reducing urine produced hence retaining more fluid

Question 17

What is the function of aldosterone?

Answer 17

Stimulates sodium reabsorption

Question 18

What is the function of vasopressin?

Answer 18

Stimulates water retention

Question 19

What do all 3 of the useful hormones aim to do?

Answer 19

Decrease urinary output to maintain BP.

o Reduce blood flow to the kidneys thus reducing urine production
o Promotes retention of fluid to preserve blood volume and pressure

Question 20

What percentage of blood can be lost before the body undergoes shock?

Answer 20

30%

Question 21

Describe the process of active hyperemia

Answer 21

Excercse -> Increase in metabolism -> increase in oxygen and glucose usage -> local vasodilation -> increase in blood flow

This would happen in skeletal muscle

Question 22

What is the autonomic response in anticipation of exercise?

Answer 22

Pre-programmed pattern

Question 23

Where does the afferent input to the medullary cardiovascular centre come from?

Answer 23

Preprogrammed pattern

Muscle chemoreceptors

Question 24

Which nervous system tries to counteract the fall in TPR due to the dilation of vessels during excercise

Answer 24

The sympathetic nervous system

Question 25

How does the sympathetic nervous system counteract the fall in TPR?

Answer 25

It causes the vasoconstriction in the abdominal region - increasing TPR

Question 26

How does the preprogrammed pattern interact with the sympathetic nervous response in counteracting a fall in TPR?

Answer 26

The sympathetic system has a negative response on the skin so the preprogrammed patter decreases the sympathetic response. It allows for vasodilation for heat radiation

Question 27

Overall how does the TPR change during exercise?

Answer 27

There is an overall fall in TPR but the decrease is lessened

Question 28

How is cardiac output affected?

Answer 28

It is increased by the increased sympathetic activity and decreased parasympathetic activity

Question 29

How do the skeletal muscles ensure the cardiac output is increased?

Answer 29

It squeezes the veins increasing venous return increasing stroke volume

Question 30

What slight negative effects are there with exercise?

Answer 30

There is decrease in plasma volume that opposes the venous return

Question 31

What causes the decrease in plasma volume during exercise?

Answer 31

Sweating and more fluid lost to tissues due to higher capillary pressure in muscle

Question 32

What are the overall effects of exercise?

Answer 32

1) Cardiac output increases due to increased sympathetic effects and venous return 2) Overall decrease in TPR However the cardiac output is greater than the fall in TPR so there in an increase in BP