16 Responses to Cardiovascular Stress Flashcards
Q: How does standing up affect blood pressure compared to lying down?
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
Q: Where do you usually take blood pressure from and why? What would be the effect otherwise?
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
Q: How does gravity affect the blood in the arteries? why?
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
Q: What can gravity do the blood in veins? why?
A: Veins are less muscular and so it is easier to cause venous distention
Q: How does gravity affect venous return? Result for the CVS?
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
Q: Name 3 things that can cause CV stress.
A: exercise, haemorrhage, upright posture
Q: What tends to happen due to blood pressure in capillaries/blood vessels? How is this affected when we stand? (3)
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
Q: What can a reduction in effective circulating blood volume lead to? according to? Explain. (3)
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
Q: What can cause Transient Hypotension?
A: stand up too quickly
Q: What is a haemorrhage? How does our body deal with it?
A: REDUCTION in actual circulating blood volume
- lots of same compensatory mechanisms as with transient hypotension
- endocrine response
- autotransfusion
Q: Main sensory mechanism for transient hypotension? where? (3) Response? Result? (3)
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
Q: When are baroreceptors most sensitive?
A: either side of mean arterial pressure
Q: How does increasing heart rate and heart contractility affect bp? vasoconstriction?
A: more 1= increased CO
more 2= increased TPR
BP=COxTPR
more 3= improved venous return = increased SV= increases CO
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)
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
Q: What are the 3 main hormones which are useful when haemorrhage occurs? What do they each do?
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
Q: What’s your body’s response when you lose:
10% of blood?
up to 30%?
over 30%?
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
Q: What do you want with exercise? How does your body achieve this? What is the side effect of this? (2)
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
Q: What happens when you exercise and utilise skeletal muscle? (3) What does this cause? Process is called?
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
Q: Outline the control mechanisms that deal with exercise. 2 inputs and result.
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
Q: How is TPR affected with exercise? response?
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
Q: How does exercise affect venous return?
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
Q: How does CO change during exercise? causes? (2)
A: Cardiac output is increased increased sympathetic activity and decreased parasympathetic activity = causes an increase in stroke volume and heart rate
Q: How is skin affected during exercise? cause?
A: -preprogrammed pattern decreases the sympathetic response to the skin as vasodilation from skin allows radiation of heat from the skin
Q: What causes fluid loss during exercise? (2) What does this cause? Overall?
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
Q: What is the overall effect of exercise on blood pressure? (use equation)
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
