Session 6.1 - Control of the Cardiovascular system Flashcards
What does the pumping action of the heart tend to do to vesicular volume?
Remove blood from viens, pumps blood to arteries
What does a decrease in cardiac output tend to do to vesicular pressure
Increase venous pressure, decrease arterial pressure
If total peripheral resistance falls, what will happens to vesicular pressure at a constant cardiac output?
Arterial pressure will fall, venous pressure will rise
If total TPR rises, what happens to vesicular pressure if cardiac output constant?
Arterial pressure will rise, venous pressure will fall
What is TPR inversely proportional to?
The body’s need for blood
What is the effect of metabolic changes on CVS, such as eating a meal?
TPR will change and generate signals in the form of changes in arterial and venous pressure
What is demand led pumping?
If the body needs more blood, the heart needs to pump more to meet the demand. This is expressed as changes in arterial and venous pressure
What is cardiac output?
Stroke volume x heart rate
Define stroke volume
The difference between end diastolic volume and end systolic volume. Amount of blood ejected at each heart beat
What is end diastolic volume determined by?
The filling of the heart, as during diastole the ventricles fill as venous pressure drives blood into them
What is end systolic volume?
The volume of blood in the left ventricle at the end of systole
What is end disastolic volume?
The volume of blood in the left ventricle at the end of diastole (filling)
To what pressure do the ventricles fill in diastole?
Until intraventricular pressure matches venous pressure `
What is the relationship between venous pressure and heart filling?
High the venous pressure, the more the hear fills in diastole
What is the relationship between venous pressure and ventricular volume known as?
Ventricular compliance curve
Why will TPR resistance change if metabolism changes?
Due to vasodilator metabolites produced proportionally
What are the three factors which determine how much the ventricles fill during diastole?
1) Venous pressure
2) Heart rate
3) Total peripheral resistance
What is starlings law?
The more the heart fills, the harder it contracts (up to a limit).
There harder it contracts, the bigger the stroke volume
Define pre load
The end diastolic stretch of the myocardion, determined by venous pressure
Define after load
Fore necessary to expel blood into the arteries - determines what happens during systole
What does a rise in venous pressure lead to?
A rise in stroke volume, due to increased ventricular filling
What does the yellow slope on this graph indicate
INSERT GRAPH
Contractility of the ventricle
What does the red circled point indicate?
The critical value - No further expansion possible as muscle can stretch no further, due to squashing/damage, Ventricles are at full capacity
Define contractility
The ability of the cardiac muscle fiber to shorten, causing muscle contraction in response to an electrical impulse
What does the green line indicate?
Sympathetic activity, causing an increase in contractility
What is the term for the effect noradrenaline and adrenaline have on the heart, and what does it do?
Positive inotropic effect
Incrrease stroke volume at a given pre-loa and after-load
What is force of contraction determined by?
End diastolic volume
Contractility
What are the two things which determine how much ventricle empties depend on?
How hard the ventricles contract
How hard it is to eject blood
How can difficulty of blood ejection be modified?
Depends mainly on TPR - The harder it is to ject blood, the higher the pressure rises in the arteries
What factor does after-load determine?
The effect of a given force of contraction during systole
What happens to systolic volume and stroke volume if arterial pressure falls?
End systolic volume falls and stroke volume rises
What happens to stroke volume if venus pressure rises?
Stroke volume will rise
What are baroreceptors?
Stretch receptors located in carotid sinus and aorta which sense arterial pressure and determine autonomic outflow to the heart
Where do baroreceptors send signals?
To the medulla oblongata
What happens if a baroreceptor detects a fall in arterial pressure
Increase heart rate
Increase contractility
How would a baroreceptor increase heart rate?
By reducing parasympathetic activity
By increasing sympathetic activity
How would a baroreceptor increase contractility?
By increasing sympathetic activity
What is the bainbridge reflex?
Sensed in right atrium - A rise in venous pressure causes a rise in heart rate, via reduced parasympathetic activity
Describe in general terms the role of the medulla of the brain in CVS reflexes
A collection of neurones which modify cardiac behabiour and circulation via the ANS
How does the medulla oblangata change heart rate and contractility?
Heart rate - Alters the firing of the SAN to change heart rate
Contractilty - Uses sympathetic nervous system
What does a rise in venous pressure cause?
Increase stroke volume
Increase heart rate
Increased cardiac output
If arterial pressure falls, what happens to blood flow resistance in certain tissues?
The resistance to blood flow through certain vascular beds such as the skin and gut will rise
What happens to venous capacitance if arterial pressure falls?
Venous capacitance will be reduced by veno-constriction
What are the consequences of an increase in heart rate?
Cardiac output rises
Subsequent decrease in venous pressure
Reduced diastolic filling due to reduced venous pressure
Reduced stroke volume
What happens to TPR if you are eating a meal?
Increased activity of gut leads to local vasodilation
Reduce TPR
What does reduced gut TPR during a meal lead to?
Rise in venous pressure - increased CO
Fall in arterial pressure - Rise in hr, so CO
Venous pressure reduced by extra pumping of heart, and arterial pressure raised
What happens in circulatory system in exercise?
Massively increased demand for blood
Muscle pumping forces extra blood back to the heart
Why can’t exercise produce response in same way as gastric?
Becase speed and scale of changes in venous pressure tend to overload the CVS
Huge increase in venous pressure, massive decrease in arterial
Why is the huge increase in venous pressure during exercise dangerous?
Tends to overfill the heart and pushes the ventricles onto the overloaded section of the starling curve. Risk of pulmonary oedema because the outputs of the right and left ventricle cannot be matched.
What does the starling curve provide?
Matching stroke volume to right and left side of heart
How does pulmonary oedema come about as a result of overfilled heart during exercise?
Left heart cannot respond to right due to increased venous return, so blood accumulates in the lungs. Water forced out, causing decreased lung function via oedema.
How is overfilling of the ventricles prevented in exercise?
Increase in heart rate, which occurs as exercise begins. When venous pressure starts to rise, heart rate already high.
What effect does standing up have on the CVS?
Blood pools in the superficial veins of the legs because of gravity, causing fall in central venous pressure
What are the consequences of standing up and the subsequent decrease in central venous pressure
Central venous pressure falls, so cardiac output falls.
Subsequent decrease in arterial pressure
Fall detected by baroreceptors, triggering rise in heart rate.
What are the three results of of a fall in arterial pressure detected by baroceptors on standing?
Rise in heart rate
Vaso constriction of skin and gut to increase TPR
Veno constriction to drive blood to heart
What condition do older people develop which accentuates effects on blood pressure when standing up?
Postural hypotension
What is the direct effect of haemorrhage?
Decreased venous pressure, causing fall in cardiac output
What does the fall in cardiac output after haemorrhage due to decreased venous pressure cause?
Arterial blood pressure to fall, which is detected by baroreceptors.
Heart rate increases, as does TPR.
What does the rise in heart rate and TPR as a result of haemorrhage cause to happen?
Further lower venous pressure - Rise of heart rate pumps blood out, TPR helps arterial pressure but lowers venous.
Thus, veno constriction must take place.
Describe the effects of a long term increase in blood volume
- Kidney controls blood volume
- If blood volume increases for days > venous pressure increases
- Increased cardiac output
- Increased arterial pressure (hypertrophy of smooth muscle)
- Increased TPR
- Increased arterial pressure (new set value)
- Hypertension (treatment: diuretic/vasodilator)
