Mairead - ANS and the Heart Flashcards
What affects does sympathetic activity have on the heart?
Increases heart rate
Increases force of contraction of the ventricles
What mediates increase of hr and force of contraction via sympathetic activity?
(3)
This is mediated by direct innervation of the heart and by the release of the hormones adrenaline and noradrenaline from the adrenal medulla
The sympathetic activation has a positive ionotrophic effect, acting on beta1 receptors of cardiac muscle
The hormones also stimulate ventricular muscle metabolism and perfusion of the myocardium
What receptors are found in cardiac muscle?
Beta1 receptors
What affect does adrenaline and noradrenaline have on the heart
(2)
They stimulate ventricular muscle metabolism and perfusion of the myocardium
They have a positive ionotrophic effect
What is the net effect of sympathetic activity on the heart?
(4)
Increased force
Increased in SV
Decrease in ESV
Increase in heart rate
What affect does the parasympathetic system have on the heart
Parasympathetic slows the heart rate and has a small decreasing effect on contractility
What mediates the effect of the parasympathetic system on the heart
Mediated through the vagus nerve
Negative ionotrophic effect
What does adrenaline and noradrenaline do to the heart?
Positive ionotrophic effect
What does glucagon do to the heart?
(2)
It’s released by the pancreas to increase glucose levels in blood
It has a positive ionotrophic effect
What affect do thyroid hormones have on the heart?
Thyroid hormones have a positive ionotrophic effect
Comment on the adjustment of heart rate
Heart rate is continually adjusted as circulatory system demands changes
What makes adjustments in heart rate?
ANS
Circulating hormones
ANS and circulating hormones have a chronotrophic effect, what is meant by this?
They have the ability to alter the heart rate
Where does the sympathetic and parasympathetic division innervate the heart?
The SA and AV nodes
Describe the ANS activation in the heart at rest?
There is resting autonomic tone
Both divisions are active at rest
At rest which division is slightly more dominant?
Parasympathetic
How does the ANS adjust cardiovascular function
By adjusting both the sympathetic and parasympathetic divisions
How exactly does ANS alter the HR?
(2)
Parasympathetic and sympathetic alter the HR by changing the permeability of the conducting system cells
This is done by altering SA node firing and altering the conduction time
What affect does altering SA node firing have?
It changes the permeability of the conducting system cells
What affect does increasing parasympathetic firing of SA node have on HR
Results in slower HR
How does increasing parasympathetic firing result in slowing heart rate?
By increasing the K+ permeability and hyperpolarizing the membrane
This Ach/Muscarinic action is a negative chronotrophic effect
What does increasing the sympathetic firing of the SA node do?
(4)
Releases noradrenaline at the B1 receptors
This increases the Na+ and Ca++ entry
This increases the rate of depolarisation and shortens repolarisation
This is a positive chronotrophic effect
What does a release of noradrenaline at B1 receptors do?
Increases the Na+ and Ca++ entry
What does increased Na+ and Ca++ entry do
This increases the rate of depolarisation and shortens repolarisation
What is another name for the Bainbridge reflex?
Atrial reflex
What activates the Bainbridge reflex
As the venous return increases, the walls of the right atrium are stretched
What does the Bainbridge reflex do?
(3)
It activates the ANS
Results in increased sympathetic activation i.e. increases SA node firing
The increase in HR matches the increase in venous return
What hormones affect the heart rate and what do they do?
(2)
Adrenaline, noradrenaline and thyroid hormones
They increase the heart rate and contractility of the heart
When is adrenaline or noradrenaline released
(2)
Sympathetic activation in a flight or flight response
Stimulates release of adrenaline and noradrenaline from the adrenal gland
How does adrenaline and noradrenaline increase the heart rate?
They increase the rate of depolarisation of the SA node and decrease the duration of repolarisation
What is the equation for cardiac reserve?
Max CO - resting CO
What may cause an increase in demand on the heart?
May increase due to muscle damage, valve damage or hypertension
What affects does increased demand on the heart have on the heart?
Cardiac output may be inadequate
Pulmonary pressures increase
What happens when CO may be inadequare
This may lead to poor perfusion, and therefore fatigue and poor exercise tolerance
What happens when pulmonary pressures increase?
This may lead to oedema in the lung tissue and poor O2 exchange, which results in breathlessness
What is it called if K+ is high?
Hyperkalemia
What is it called if K+ is low?
Hypokalemia
What happens if K+ is really high?
it’s life threatening
Write a note on high K+
Depolarisation normal
K+ movement inhibited as K+ channel opens
Therefore, repolarisation is inhibited
Muscle becomes weak
Write a note on low K+
Hyperpolarisation of muscle cells
Muscle more difficult to excite
Hyperpolarisation of nodal cells: hr down, blood pressure down
What is high calcium called?
Hypercalcemia
What is high Ca++?
(4)
EC Ca++ increased, SR Ca++ increased
Cells extremely excitable
More powerful and prolonged contractions
May be fatal
Write about low Ca++
Contractions weak
May stop
Write about low temperature
Slows SA depolarisation
Lowers HR
Reduced strength of contraction
Write about high temperature
Increased hr and force
What effects does caffeine have on the heart?
Caffeine, increased rate of depolarisation of the SA node
What effects does nicotine have on the heart?
Sympathetic neurons
