Regulation of Stroke Volume Flashcards
(34 cards)
What is the function of pacemaker cells?
Responsible for the autorhythmicity of the heart
How does the sympathetic systemic increase heart rate?
Release of noradrenaline and adrenaline (form adrenal medulla) which act on B1 receptors win the SA node
What is the effect of activated B1 receptors in the SA node?
Increases ion flow through If (Na+ channel) and Ca channels which increases depolarisation so cells reach threshold faster -> increases slope of pacemaker potential which increases HR = tachycardia
Which nerve supplies the heart with parasympathetic supply?
Vagus nerve
What neurotransmitter does the vagus nerve release and what receptors does it act on?
Releases acetylcholine which acts on muscarinic receptors on SA node
What is the effect of activated muscarinic receptors on the SA node?
Increase K+ permeability, hyper polarising cell, and Ca2+ permeability decrease, which slows down the rate of depolarisation of pacemaker potential. Takes longer to reach threshold, decreasing slope and HR
What is stroke volume?
The volume of blood pumped per ventricle per contraction and is related to the force of contraction
What is the force of contraction dependent one?
Length of muscle fibres at the beginning of contraction
The contractility of the heart
Define Starling’s Law
The energy of contraction is proportional to the initial length of the cardiac muscle fibre
What is the relationship between the tension and the length of the sarcomere?
Tension increases steadily with increase of length, and then the increase slows until the peak tension is reached
After this the tension decreases
Why does increased preload increase force of contraction?
Stretch of ventricular wall increases with increased EDV which causes the contraction to be more forceful in order to eject more blood
What is preload?
The stretch prior to contraction and represents the land placed on the cardiac muscle before they contract
In vivo, what affects preload?
End diastolic volume (EDV)
How does increased venous return affect stroke volume?
Increases in EDV which causes an increased preload and so an increased SV
How does decreased venous return affect stroke volume?
Decreased the EDV, which decreases the preload, and thus SV
What does preload allow, in terms of cardiac output from left and right sides of the heart?
It ensures self-regulation - the resting EDV is not at the maximum for the max stroke volume, nor is at its minimum. This means stroke volume can vary to match the SV on the other side of the heart
What is afterload?
The load against which the muscle tries to contract
What determines the after load in vivo?
The arterial pressure against which the blood is expelled (this in dependent on TPR)
What are two factor which affect the aortic pressure?
How much blood is being pushed into aorta
How easy it is for the blood to get out of the aorta (the total peripheral resistance)
How does an increase in TPR affect SV?
Increase TPR, increase aortic pressure and so the ventricles have to work harder and use energy to build up sufficient pressure to open the aortic valve
This leaves it will less energy to contract to eject the blood, and therefore decreases SV
What pathological conditions increase afterload?
High BP in arteries
Loss of compliance in aorta
What occurs in after load becomes chronic?
Hypertrophy of myocardium
What are 4 factors with regulate SV?
Preload
Afterload
Neural
Pathological
What is an inotropic agent?
Any chemical that effects contractility (the inotropic effect)
