14- Responses To CVS Stress

Question 1

Why does standing present a challenge to BP

Answer 1

When you stand up, gravity pushes a column of
blood from your head to your toes
• If the blood is above the heart, gravity is going to
force it down to the heart so the pressure in the
arteries above the heart will be lower
• Blood pressure below the heart is going to be
higher

Question 2

In haemorrhage what does a decrease in baraoreceptor stimulation cause

Answer 2

Increase in heart rate
Increase in heart contractility
Organ specific vasoconstriction

Question 3

What causes auto transfusion- fluid moving back into blood

Answer 3

There is higher hydrostatic pressure at the arteriolar end of the capillary than the venous end - so pressure decreases across the capillary but colloid osmotic pressure REMAINS THE SAME
• So you get fluid loss at the arteriolar end and fluid retention at the venous end

Question 4

Which 3 hormones are realised in haemorrhage

Answer 4

Angiotensin II Aldosterone Vasopressin (ADH)

Question 5

How do hormones help With Haemorrhage

Answer 5

Angiotensin II is a powerful vasoconstrictor (particularly in the kidney) and is good at reducing blood flow to the kidney, so reduces urine production
• Aldosterone stimulated sodium reabsorption
• Vasopressin stimulates water retention
Promotes retention of fluid to preserve blood volume and pressure

Question 6

How much blood has to be lost for the body to go into shock

Answer 6

30%

Question 7

Why does exercise present a challenge to maintaining BP

And how is this resolved

Answer 7

If you massively increase blood flow to certain tissues you massively decrease total peripheral resistance
BP= COx TPR

Reduce blood flow to GIT + kidneys
Increase blood flow to skin increases TPR
CO increases

Question 8

What is active hyperaemia

Answer 8

The increase in oxygen and glucose usage causes LOCAL VASODILATION

Question 9

What are the 2 inputs to the medullary cardiac centre in exercise

Answer 9

Pre-programmed Pattern - autonomic response in anticipation of exercise
Muscle Chemoreceptors - detect a changing environment

Question 10

What is the overall effect of exercise

Answer 10

Cardiac output increases massively because
of the increase sympathetic effects and
increased venous return
• Overall there is a fall in TPR
• If we put the two together, the increase in
cardiac output is greater than the fall in TPR so there is an INCREASE IN BLOOD PRESSURE

Question 11

How could standing cause hypotension

Answer 11

There is an increase in
hydrostatic pressure in the
blood vessels of the legs
• You have hydrostatic pressure
AND gravity adding to the
pressure
• As a result, MORE fluid leaves
the capillary and enters the tissue

Question 12

How is change in posture compensated for

Answer 12

Baroreceptor firing drops,increased sympathetic+ reduced parasympathetic, increased HR and vasoconstriction+ venoconstriction