L3-Control of Cardiac output(Stroke volume & Heart rate) Flashcards
(22 cards)
Describe the variables that determine Cardiac output?
-Heart rate = 👆sed heart rate increases CO. but high heart rates can reduce efficiency.
-Stroke volume = amount of blood ejected by the heart with each beat.
-Venous return
-hormones, O2 demand, autonomic nervous system activity, excercise.
Describe how heart rate is controlled by the autonomic nervous system
heart rat is not relying on any nervous inputs. Its not relying on anything that’s circulated around the body in order to generate that electrical activity.
What are the roles of veins in determining Cardiac output ?
-veins control the amount of deoxygenated blood that’s returning to heart which directly affects CO.
-veins are highly compliant, so they can stretch and store blood.
-venous return, when exercising muscles contractions squeeze veins, propelling blood back to heart.
Describe the intrinsic and extrinsic mechanisms that can alter SV, and thus CO ?
-I-heart can increase stroke volume in response to increased venous return.
-at excessive high heart rates, ventricular filling time decreases, leading to lower SV. So a short diastole, ventricle don’t have enough time fully fil.
-E-adrenaline and noradrenaline can increase contractility and heart rate.
-RAAS -Renin-Angiotensin-Aldosterone System regulates blood volume and venous return, indirectly influencing SV.
Equation with CO, SV, HR
CO = HR x SV
The output of the hear depends on the number of beats inn a minute and how much volume is chucked out in a minute(5L/min).
Another way to represent SV ?…
> SV = (EDV-ESV)
Difference between end diastolic volume and end systolic volume.
Difference between Amount ejected by the heart is the amount started with at the end of diastole minus the amount left at the end of systole.
What is heart rate?
how many times the ventricle beats in a minute.
Why is the heart myogenic?
Heart is not relying on nervous input in order to generate that contraction hence called myogenic. (generate activity on its own) bc there are pacemaker cells in the SA node and they have the ability to generate electrical activity without any nervous input.
Briefly describe the electrical activity of the heart ?
Cardiac muscle cells depolarise & contract rhythmically without nerves: myogenic rhythmicity or auto rhythmicity. Electrical impulses cause the muscles to contract.
Then the conduction then occurs in a highly coordinated way.
What are the 2 ways of autonomic control of the CVS?
- parasympathetic control
- sympathetic control
Describe the 1. parasympathetic(PS) way autonomic control of the CVS
- The cell bodies of the parasympathetic nerve which is the Vegas nerve are found up in the medulla. in the PS there are LONG preganglionic neurones and SHORT postganglionic neurones. Cell bodies of the preganglionic neurones are located in the brain stem. Vegas nerve is all of the axons of all preganglionic neurones that goes to the heart. in PS the synapse between the pre and post ganglion is either really close to the organ or part of the organ.
Describe the 2. sympathetic(SP) way autonomic control of the CVS
The cell bodies of the SHORT pre ganglionic neurones (SP nervous system) are found in the spinal cord. There’s a whole organisation of sympathetic neurones at different parts of the spinal cord that come out of and goes to different places. Then down either sides of the spinal cord we can find sympathetic ganglion chain. The LONG postganglionic neurones reach to blood vessels, heart and other places.
Is PS or SP nervous system is controlled by the brain?
PS is not controlled by the brain as it does not go through the spinal cord and comes out of one of the cranial nerves and forms the Vegas.
SP is controlled by the brain as it goes through the spinal cord.
Describe the branching of the sympathetic and parasympathetic neurones when it reaches the heart ?
Sympathetic nerve splits and branches of to SA node, AV node and the ventricles separately and we can change the activity of each of the branches.
Parasympathetic nerve(Vegas nerve) only branches to the SV node and the AV node and there is not a lot of vagal innervation of the ventricles. Its there but not much.
How does the increased sympathetic activity increases Heart rate?
-increases the permeability to Na+ and Ca+
-Each of the action potentials lead to a heart beat. When we stimulate the sympathetic fibres that go to the SA node, it will release noradrenaline. These hits the beta-1 receptors on the SA node. IT MAKES IT EASIER FOR THE CELLS TO GET TO THRESHOLD(QUICKER). s more AP per minute, more steeper so more heart beat.
How does the increased parasympathetic(vagal) activity decreases Heart rate?
-less permeable to Na and pull away from the threshold (harder to reach).
-When we stimulate the Vegas nerve which releases Acetylcholine. It takes longer to reach threshold>less action potentials> heart rate decreases.
Define intrinsic rate of the SA node?
When we take the heart out, it will still beat 100 beats per minute.
SA node intrinsic rate is 100 action potentials/min so why is resting heart rate 60-70 beats/min?
Because there is ongoing vagal activity.
Why is it still beating at rest? What is this called? What happens when the Vegas nerve is cut?
-It’s sending activity down even at rest because it is REDUCING the heart rate at rest.
-Its called Vagal tone > tone=tonic > tonic means ongoing activity.
-When the Vegas nerve is cut, the heart rate will go down as there is ongoing vagal activity.
What is the only way the HR can be changed?Examples?
By changing the electrical activity(Action potentials) at the SA node. / pulling away from the thresholds. - autonomic nervous system does all of this.
Ie:-exercise
stress
temperature - when its hot, heart rate
goes up > DIRECT EFFECT on the SA node
cells.
drugs
Define tidal volume
This is the amount of air you breathe in and out with each normal breath
Define stroke volume and cardiac output
Stroke Volume (SV) is the amount of blood pumped by the heart per beat.
Cardiac Output (CO) is the total amount of blood pumped by the heart per minute.
