Cardiac Output and Regulation of Cardiac Function Flashcards
At rest how much blood does each ventricle pump out?
5L of blood/min
Define cardiac output
The rate at which ventricle pumps blood is called the cardiac output
Define heart rate
Number of contraction per minute
How do you calculate cardiac output (CO)?
Heart rate x stroke volume
HR x SV=CO
Define extrinsic control
Regulation of the heart by neural input, circulating hormones or any other factor from OUTSIDE the heart
Define intrinsic control
Regulation by factors originating in the heart
What does the central nervous system (CNS) do?
Controls muscles and other organs by way of signals sent through the efferent branch of the peripheral nervous system
How many branches does the peripheral nervous system (PNS) have? Name them
2 branches
The branches: Autonomic and somatic
How many branches does the autonomic system have? Name them
2 branches
The branches:
Sympathetic and parasympathetic
What is the parasympathetic nervous system described as?
Resting state
“Rest and Digest”
What is the sympathetic nervous system described as?
Fight or flight
The autonomic nervous system consists of ________ neurones. Which 3 different types of cells do these neurones control?
Efferent neurones
The three types of cells of cells they control are:
- Smooth muscle
- Cardiac muscle
- Some gland cells
Give 5 features of the sympathetic nervous system
- Starts at the middle of the spinal cord
- Usually consists go a chain of 2 neurones from CNS to target cells
- It changes blood flow from intestines to skeletal muscles
- increases heart output
- Activates sweat glands
Give 5 features of the parasympathetic nervous system
- Starts in either the brain stem or bottom of the spinal cord
- Usually consists go a chain of 2 neurones from CNS to target cells
- Increases blood flow to intestines as you are ‘resting and digesting”
- Decreases heart rate
- Activates salivary glands
Which neurotransmitters is associated with the sympathetic nervous system?
Noradrenaline
Which neurotransmitters is associated with the parasympathetic nervous system?
Acetylcholine
What is the range for a normal heart rate?
30-180bpm
Explain the sympathetic control of heart rate
When sympathetic activity increases:
Pacemaker cells of the SAN produce more action potentials. So heart rate increases and cardiac output also increases
Speed of conduction also increases. So ventricular contraction occurs more rapidly after atrial contraction. This decreases the duration of systole
Explain the parasympathetic control of heart rate
When parasympathetic activity increases:
Pacemaker cells of the SAN produce less action potentials. So heart rate decreases and cardiac output also decreases
Speed of conduction decreases. So ventricular contraction occurs less rapidly after atrial contraction. This increases the duration of systole
Describe 2 ways hormones can affect heart rate
- Adrenaline in the blood stream can increase action potentials from the SAN increasing heart rate (speed of action potentials also increases)
- Thyroid hormones, like glucagon and insulin, increase the force of myocardial contractions increasing heart rate
What three factors affect stroke volume?
Ventricular contractility
End diastolic volume
Afterload
What is ventricular contractility
The force of the ventricular contraction
Explain how ventricular contractility affects stroke volume
Sympathetic neurons project to the ventricular myocardium influencing the myocardial contractility
Increase in sympathetic activity leads to an increase in ventricular contractility which ultimately increases cardiac output
How does ventricular contractility increase?
Increase in Ca^2+ concentration and permeability which increases contractility
Which hormone can also increase myocardial contractility?
Adrenaline
Is end diastolic volume controlled by intrinsic or extrinsic factors?
Intrinsic control
State Starling’s Law of the heart
When the rate at which blood flows into the heart from the veins (that is venous return) changes, the heart automatically adjusts its output to match the inflow
Explain how end diastolic volume affects stroke volume
End diastolic volume increases then force of ventricular contraction increases and as a result both stroke volume and cardiac output increases.
How does an increase in end diastolic volume affect muscle fibres of ventricular myocardium?
Muscle fibres of ventricular myocardium lengthen.
This stretch increases the force of contraction
How does an increase in end diastolic volume lengthen the muscle fibres of ventricular myocardium and result in a greater ventricular contractility?
- Affinity of troponin in muscle fibres for calcium increases. This increases number of cross bridges activated by contraction
- Cardiac muscle increases to the optimum length. So EDV brings muscle fibres closer to their optimum length for contractility which results in a contraction of greater force.
How does sympathetic activity affect Starling’s curve?
Increase in sympathetic activity shifts Starling’s curve upwards. This increases stroke volume at any EDV due to increased ventricular contractility
How does Starling’s law regulate heart size?
By adjusting stroke volume so that cardiac output matched venous return
What 2 factors affect end diastolic volume?
End diastolic pressure
Preload
What is end diastolic pressure determined by?
Determined by the pressure of blood inside the heart before contraction tension on the myocardium
What is preload determined by?
Is determines by the filling time and atrial pressure
What does increasing the arterial pressure do to the stroke volume?
When the heart ejects blood it has to work against arterial pressure
increasing the arterial pressure causes the stroke volume to decrease
What is after load?
Arterial pressure places a load on the myocardium after contraction starts. This is called after load
What is the afterload determined by in the left ventricle?
Pressure in the aorta
