Control of Cardiac Output Flashcards
What is the cardiac output?
The volume of blood ejected by each ventricle per minute
What are the parameters the cardiac output (CO) is dependent on?
- heart rate
- heart contractility, preloading
- afterload
What influences the stroke volume of the ventricles?
- heart contractility
- preloading (the ventricles with blood)
- afterload
What can preload be considered as?
The degree of myocardial extension prior to shortening by contraction
What are the units of CO (cardiac output)
litres per minute (l in^-1)
How can you calculate cardiac output?
heart rate x stroke volume
What is the heart rate (HR)?
number of contractions (beats) per minute
What is the stroke volume (SV)?
The volume of blood ejected by each ventricle per beat
What is different about an athletic heart compare to a normal one?
It is paced slower and has a greater stroke volume so pumps blood more efficiently
What is the heart rate intrinsically generated by?
The SA node
What is the intrinsic beating of the heart further regulated by?
autonomic innervation and hormones
What is the stroke volume the difference between?
The difference in blood at the end of the diastolic period and the end of the systolic period
How are blood volume reflexes formed?
- through links between different sensory elements associated with the cardiovascular system
- links between the periphery and central nervous system
What are blood volume reflexes generated by?
The detection of pressure of the walls of the blood vessels
Which receptors are pressure detectors?
Baroreceptors
Where are baroreceptors found and why is this useful?
- found in the blood vessels that lead up to the CNS and in the aortic arch
- they are therefore able to detect changes in blood pressure at strategic points and relay them to the CNS
What does the autonomic innervation of the heart consist of?
- parasympathetic fibres
- sympathetic fibres
What do parasympathetic fibres innervate?
The SA node but NOT the ventricles
What do sympathetic fibres innervate?
Both the SA node and the ventricles
What does the sympathetic nervous system innervate the cells of the adrenal medulla to do?
Produce adrenaline and noradrenaline
What does adrenaline have actions on?
- the cardiovascular system
- it has specific actions on blood vessels and the muscle of the cardiac tissue
What are the two main cardio centres of the CNS?
- cardio-acceleratory centres
- cardio-inhibitory centres
What does the CNS do in regards to the cardiac system?
receives information from sensory neurones about the cardiac system. This information is largely received in centres of the CNS and then brings about a change through the autonomic and sensory pathways
What is the key parasympathetic fibre?
the vagus nerve
What is the key neurotransmitter associated with the parasympathetic system?
acetylcholine
What is the key neurotransmitter associated with the sympathetic system?
noradrenaline
Where is noradrenaline primarily released?
The sympathetic nerve fibres
Where is adrenaline released?
From the adrenal medulla
Where is the adrenal medulla found?
The adrenal glands
What is an influence upon the heart rate termed?
A chronotropic effect?
Why does acetylcholine have a negative chronotropic effect?
- slows the heart rate
- does this because it activated K+ channels in the SA node and this draws the membrane potential more towards the hyperpolarized channel
- slows the rate of spontaneous depolarization and slightly extends the duration of repolarization
- so heart rate declines
What is a slow heart rate called under pathological conditions?
Bradycardia
Why do noradrenaline and adrenaline have positive chronotropic effects?
- increase the heart rate
- work upon the HCN channel which is hyperpolarisation activated
What is a fast heart rate called under pathological conditions?
tachycardia
How are action potentials generated in the Sinoatrial Node?
through expression of a set of different ion channels in the cell membranes of the SA node cells