16 Responses to Cardiovascular Stress

Question 1

Q: How does standing up affect blood pressure compared to lying down?

Answer 1

A: When you’re lying down, the effect of gravity is the same across the body

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

Q: Where do you usually take blood pressure from and why? What would be the effect otherwise?

Answer 2

A: take blood pressure from the arm, because it is level with the heart so gravity isn’t an issue

If you add the effects of gravity on top of the blood pressure generated by the heart, you add around 80 mmHg

Question 3

Q: How does gravity affect the blood in the arteries? why?

Answer 3

A: Arteries are very muscular and so gravity has little impact on blood in the arteries - the thick musculature maintains the blood pressure in the arteries

Question 4

Q: What can gravity do the blood in veins? why?

Answer 4

A: Veins are less muscular and so it is easier to cause venous distention

Question 5

Q: How does gravity affect venous return? Result for the CVS?

Answer 5

A: -The blood in the veins lower down is trying to return to the heart but you have gravity forcing the blood back down
-The veins then stretch and the blood begins to pool in the veins in the lower leg

• There is only a finite amount of blood in the cardiovascular system so having more blood in the venous reservoir means that there is less blood in the arterial system and hence lower blood pressure
• In other words, more volume in veins - less volume in arteries - lower blood pressure

Question 6

Q: Name 3 things that can cause CV stress.

Answer 6

A: exercise, haemorrhage, upright posture

Question 7

Q: What tends to happen due to blood pressure in capillaries/blood vessels? How is this affected when we stand? (3)

Answer 7

A: fluid is forced out due to hydrostatic pressure

gravity is added to the mix=> hydrostatic pressure AND gravity adding to the pressure

As a result, MORE fluid leaves the capillary and enters the tissue = more fluid loss to the interstitial compartment

= reduction in effective circulating blood volume

Question 8

Q: What can a reduction in effective circulating blood volume lead to? according to? Explain. (3)

Answer 8

A: when considering Starling’s law, this could induce a hypotensive state

There is more blood in veins and less blood re-entering the veins because you lose more fluid to tissues

(lost fluid will return to the circulation later on via the lymphatics but that takes a long time)

Starling’s Law suggests that end-diastolic volume (ventricular filling) determines the stroke volume and as less of the blood in the veins is returning to the heart (as gravity is pushing the blood down) so ventricular filling decreases so the volume of blood ejected during systolic contraction decreases as well = low bp = hypotension

Question 9

Q: What can cause Transient Hypotension?

Answer 9

A: stand up too quickly

Question 10

Q: What is a haemorrhage? How does our body deal with it?

Answer 10

A: REDUCTION in actual circulating blood volume

• lots of same compensatory mechanisms as with transient hypotension
• endocrine response
• autotransfusion

Question 11

Q: Main sensory mechanism for transient hypotension? where? (3) Response? Result? (3)

Answer 11

A: need to restore bp quickly

main sensory mechanism = baroreceptors that respond to pressure
-carotid sinus
-aortic arch
(arterial baroreceptors)

firing rate decreases in response to low bp

decrease in baroreceptor firing stimulates:

• Increase in heart rate
• Increase in heart contractility
• Organ specific vasoconstriction

Question 12

Q: When are baroreceptors most sensitive?

Answer 12

A: either side of mean arterial pressure

Question 13

Q: How does increasing heart rate and heart contractility affect bp? vasoconstriction?

Answer 13

A: more 1= increased CO
more 2= increased TPR

BP=COxTPR

more 3= improved venous return = increased SV= increases CO

Question 14

Q: How does a haemorrhage affect hydrostatic pressure? How does this affect fluid loss?

What other kind of pressure is present?

Explain autotransfusion as a compensatory mechanism against haemorrhage. (2)

Answer 14

A: with haemorrhage you get a drop in overall hydrostatic pressure but there is still higher hydrostatic pressure at the arteriolar end of the capillary than the venous end = still lose some fluid (much less) at the arteriolar end but you’ll retain a lot more at the venous end

but colloid osmotic pressure REMAINS THE SAME so you get

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

This is the body’s attempt to preserve blood pressure - you’re basically diluting the blood with fluid and increasing the blood volume

Question 15

Q: What are the 3 main hormones which are useful when haemorrhage occurs? What do they each do?

Answer 15

A: Angiotensin II = powerful vasoconstrictor (particularly in the kidney) and is good at reducing blood flow to the kidney thus reducing urine production

Aldosterone = stimulated sodium reabsorption

Vasopressin (ADH) = stimulates water retention

Aldosterone and Vasopressin work together in the collecting duct -> Promotes retention of fluid to preserve blood volume and pressure

Question 16

Q: What’s your body’s response when you lose:

10% of blood?
up to 30%?
over 30%?

Answer 16

A: You can lose 10% of your blood volume and your mechanisms can manage it

You can lose up to 30% of your blood and your mechanisms should be able to manage it though there will be a decrease in blood pressure

If you lose OVER 30% of your blood, your mechanisms can’t compensate for this loss and you will experience SHOCK

Question 17

Q: What do you want with exercise? How does your body achieve this? What is the side effect of this? (2)

Answer 17

A: increase blood flow to certain tissues (heart, lungs and skeletal muscle)

To increase blood flow you need vasodilation so when you exercise you get massive vasodilation in certain tissues in the body

If you massively increase blood flow to certain tissues you massively decrease total peripheral resistance

Question 18

Q: What happens when you exercise and utilise skeletal muscle? (3) What does this cause? Process is called?

Answer 18

A: metabolism in the tissues starts to INCREASE and there is an increase in oxygen and glucose usage

The increase in oxygen and glucose usage causes LOCAL VASODILATION = aim of increasing the supply of oxygen and nutrients

ACTIVE HYPEREMIA

Question 19

Q: Outline the control mechanisms that deal with exercise. 2 inputs and result.

Answer 19

A: the afferent input to the medullary cardiovascular centre comes from:

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

From the cardiovascular centre the sympathetic and parasympathetic neurons are activated or inhibited

Question 20

Q: How is TPR affected with exercise? response?

Answer 20

A: -There is still an OVERALL FALL IN TPR but the decrease is lessened as sympathetic nervous system tries to constrict any vessels it can

-profound vasoconstriction in the abdominal region (e.g. to the kidneys and GIT) = this increases TPR

Question 21

Q: How does exercise affect venous return?

Answer 21

A: skeletal muscle is very active so it squeezes the veins and forces blood up the body and has a profound on stroke volume by increasing venous return

Question 22

Q: How does CO change during exercise? causes? (2)

Answer 22

A: Cardiac output is increased increased sympathetic activity and decreased parasympathetic activity = causes an increase in stroke volume and heart rate

Question 23

Q: How is skin affected during exercise? cause?

Answer 23

A: -preprogrammed pattern decreases the sympathetic response to the skin as vasodilation from skin allows radiation of heat from the skin

Question 24

Q: What causes fluid loss during exercise? (2) What does this cause? Overall?

Answer 24

A: increased capillary pressure across muscle walls meaning more blood flows through skeletal muscle and more fluid lost to tissues

Sweating is another way of losing fluid

Therefore there is a decrease in plasma volume which opposes the venous return to a certain extent

despite ^ there is an overall positive effect on cardiac output

Question 25

Q: What is the overall effect of exercise on blood pressure? (use equation)

Answer 25

A: 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