Cardiac output Flashcards
What is is cardiac output?
Rate at which a ventricle pumps blood (L/min)
What is heart rate?
Number of contractions per minute
What is the calculation for cardiac output?
Heart rate x stroke volume
What is extrinsic control?
Regulation of the heart by neural input, circulating hormones or any other factor from outside the heart
What is intrinsic control?
Regulating factors originating in the heart
What does the CNS do?
Controls muscles and other organs by way of signals sent through the efferent branch of the peripheral nervous system
What are the two divisions of the autonomic nervous system?
Sympathetic and parasympathetic
Where are the parasympathetic nerves?
Craniosacral, ganglia in/near viscera
Where are the sympathetic nerves?
Thoracolumbar, paraspinal ganglia
What cranial nerve is commonly associated with the autonomic input to the heart?
Vagus
What is the parasympathetic neurotransmitter?
Acetylcholine
What is the sympathetic neurotransmitter?
Noradrenaline
What is the chain of events that occurs when there is increased sympathetic activity in the heart?
Acts on pacemaker cells of the SA node, more action potentials, increased heart rate so more cardiac output.
- Acts on AV node and conduction system, faster speed of conduction, ventricular contraction sooner after atrial contraction and less duration of systole
What is the chain of events that occurs when there is increased parasympathetic activity in the heart?
Acts on pacemaker cells of the SA node, less action potentials, decreased heart rate so less cardiac output
AV node and conduction system, slower speed of conduction, ventricular contraction longer than atrial contraction, longer duration of systole
What does adrenaline do?
Faster and more action potentials at SA node so increased heart rate.
What does thyroid hormones (glucagon and insulin) do?
Increased force of myocardial contraction, glucagon promotes increased heart rate
What are the three main things that affect stroke volume?
1) Ventricular contractility
2) End diastolic volume
3) Afterload
What is ventricular contractility?
Force of the ventricular contraction, sympathetic neurons project to the ventricular myocardium, influence on myocardial contractility.
Increased sympathetic activity, ventricular contractility and increased cardiac output
How does ventricular contractility work?
Increase of Ca concentration and permeability which increased contractility, adrenaline also increases myocardial contractility
What is Starling’s law of the heart?
When the rate at which blood flows into the heart from the veins (venous return) changes, the heart automatically adjusts its output to match the inflow
What does an increase in end diastolic volume result in?
Increased force of ventricular contraction, increased stroke volume and cardiac output
What does an increased stretch of cardiac muscle result in brought on by an increase in EDV?
Increased affinity of troponin in muscle fibres for calcium, more cross bridges activated with contraction.
Cardiac muscles optimum length is more than the resting length so increased EDV brings muscle fibres closer to optimum length for contraction, contract with greater force
What are the axis of Starlings curve?
Stroke volume (Y) End diastolic volume (x)
What does an increase in sympathetic activity show on Starlings curve?
Shifts curve upwards, due to an increase in ventricular contractility SV increases
How does Starlings law regulate heart size?
Adjusting SV so that CO matches venous return
What is preload?
End diastolic pressure - determined by pressure of blood inside heart before contraction-tension on the myocardium
What is preload determined by?
Filling time
Heart rate
Atrial pressure (dependent on venous return and force of atrial contraction)
What does an increase in arterial pressure result in?
Decreased stroke volume
What is after load?
Arterial pressure placing a load on the myocardium after contraction starts
What is after load determined by?
Pressure in the aorta
True or false - an increase in sympathetic innervation on pacemaker cells decreases heart rate?
False
True or false - the speed of conduction of an action potential is increased by noradrenaline released from the sympathetic nervous system?
True
True or false - an increase in venous return causes an increase in stroke volume and cardiac output?
True
True or false - after load is the pressure placed on the myocardium by the arteries after contraction starts?
True
