CVS 16: Responses to cardiovascular stress

Question 1

What is the pressure gradient in the body?

Answer 1

• Blood above the heart is at a lower pressure

- Blood below the heart is at higher pressure

Question 2

What is the problem with standing and why is lying down okay?

Answer 2

• standing: gravity pushes a column of blood from your head to your toes + pressure created by heart
• lying: Effect of gravity is the same across the body

Question 3

Where is blood pressure normally taken from and why?

Answer 3

Taken from the arm

-> it is level with the heart so gravity isn’t an issue

Question 4

What are the effects of standing on arteries?

Answer 4

• gravity has little impact

- very muscular so muscle maintains the bp in the arteries

Question 5

Explain the effects of standing on veins?

Answer 5

• less muscular –> VENOUS DISTENSION
• blood in veins in lower limbs trying to return to heart
• gravity pushes it back down
• veins stretch-> blood pools in lower leg veins-> less blood in arteries-> lower bp

Question 6

What happens to the hydrostatic pressure in the legs whilst standing?

Answer 6

• Increase in hydrostatic pressure

- because you have hydrostatic pressure generated by the heart and then the effect of gravity

Question 7

So what happens to fluid movement in the legs whilst standing?

Answer 7

• More fluid loss to the interstitial compartment from the capillary which reduces the circulating blood volume

Question 8

Why might standing induce a hypotensive effect?

Answer 8

• more blood in veins
• less blood re-entering the veins, more fluid lost to tissues but fluid returned slowly through lymphatics
• end-diastolic volume (ventricular filling) determines stroke volume
• less blood in veins returning to heart
• less ventricular filling (lower diastole) so volume of blood ejected during systole decreases as well
  = TRANSIENT HYPOTENSION

Question 9

What detects changes in blood pressure? Where are they located?

Answer 9

Baroreceptors

• carotid sinus
• aortic arch

Question 10

What BP are baroreceptors most sensitive at? and why

Answer 10

100mmHg

This is similar to the mean arterial blood pressure

Question 11

In terms of nervous stimulation, what happens when you have a fall in blood pressure?

Answer 11

• decreased firing of the baroreceptor
• less parasympathetic stimulation and less inhibition of the sympathetic
• more noradrenaline
• increased contractility and HR –> increases CO
• increased vasoconstriction of splanchnic/ renal which increases TPR

Question 12

What happens if compensatory mechanisms fail?

Answer 12

• brain switches off

- faint and go to heart level

Question 13

Which factors increase your risk of fainting whilst standing?

Answer 13

• if you are taller- increased gravity and less venous return
• dehydration/ sweating

Question 14

What is the consequence of a haemorrhage

Answer 14

A reduction in the actual circulating blood volume

Question 15

What are the compensatory mechanisms for a haemorrhage?

Answer 15

• same compensatory mechanisms for transient hypotension so:
  
  • increase in hr-> increase in CO
  • increase in heart contractility -> increase in CO
  • organ specific vasoconstriction -> increase in TPR
• AUTOTRANSFUSION

Question 16

Define auto transfusion?

Answer 16

The significant reabsorption of fluid back into the capillaries from the tissue to try and preserve the blood pressure

Question 17

Explain the process of auto transfusion

Answer 17

• hydrostatic pressure at capillaries is much lower when you lose blood
• so you lose some fluid but retain a lot more at the venous end
• this is because osmotic pressure stays the same and pulls the fluid back in
• so you lose blood but replace it with fluid and dilute the blood to maintain its volume and you can replace the RBCs later

Question 18

Which three hormones are useful when haemorrhage occurs?

Answer 18

• Angiotensin II
• aldosterone
• vasopressin ADH

Question 19

What is the function of Angiotensin II?

Answer 19

A powerful vasoconstrictor

• reduces blood flow to the kidneys
• decreases urinary output
• retain this fluid

Question 20

What is the function of aldosterone?

Answer 20

Sodium retention

Question 21

What is the function of vasopressin?

Answer 21

Water retention

Question 22

What volume of fluid can you lose for the effects to be felt?

Answer 22

• lose 10%, body can manage it
• lose up to 30% body can manage it but you will get a decrease in BP
• lose over 30% body can’t compensate and you will experience shock because of poor oxygenation of tissues

Question 23

Which tissues need the most blood flow during exercise?

Answer 23

• heart
• lungs
• skeletal muscle

Question 24

How do you increase blood flow to these tissues during exercise? What is the consequence of this?

Answer 24

• vasodilation in certain tissues in the body

- increased blood flow = decrease TPR = decreased BP because BP = CO x TPR

Question 25

What is active hyperaemia?

Answer 25

- exercise --> increase in tissue metabolism - > increase in O2 and glucose usage - > local vasodilation - > increase in supply of O2 and glucose

Question 26

What does the afferent input from the medullary cardiovascular centre come from?

Answer 26

1. pre-programmed pattern= autonomic activation in anticipation of exercise 2. Muscle chemoreceptors= detect changing environment - - send signal to the medullary cardiovascular centre--

Question 27

What does the Medullary Cardiovascular system do in response to the afferent input to exercise?

Answer 27

- sympathetic and parasympathetic neurones are activated or inhibited

Question 28

The sympathetic nervous system do to counteract the fall in TPR during exercise? What is the exception to this?

Answer 28

Vasoconstriction to the other vessels - vasoconstriction of abdominal region - decrease in vasoconstriction to the skin so that you can have heat loss by radiation

Question 29

How is BP maintained during exercise?

Answer 29

- TPR falls because of vasodilation to skeletal muscle which would normally decrease BP but this effect is reduced by vasoconstriction to abdominal vessels which increases BP but fall in BP is still > rise in BP - BUT CO is increased because of increased sympathetic activity to the heart so BP increases - CO also increases because of skeletal muscle contraction increasing venous return

Question 30

What are the negative effects caused by exercise?

Answer 30

- increased capillary pressure across the muscle walls= more blood flows through skeletal muscle and more fluid lost to the tissues - lose fluid and salt through sweat - DECREASE IN PLASMA VOLUME which opposes venous return - BUT still positive overall effect on CO

Question 31

What is the overall effect of exercise in terms of the BP = CO x TPR equation?

Answer 31

``` BP = CO x TPR 1. CO - RISE IN HR (+ve) - RISE IN CONTRACTILITY (+ve) - rise in venous return (-ve_ 2. TPR - RISE IN VASODILATION (-ve) - rise in vasoconstriction (+ve) increase in CO > decrease in TPR so overall increase in BP ```