Cardiovascular physiology 2 Flashcards
What is the heart rate set by ?
The pacemaker cells
What can be used to speed up or slow down the heart rate ?
The sympathetic and parasympathetic nervous system
How does the sympathetic NS affect HR ?
The sympathetic nervous system works in two ways, the sympathetic nerves releases noradrenaline and the adrenal medulla releases adrenaline. Noradrenaline and adrenaline act on the B1 receptors in the SA node and increase the rate of the pacemaker potentials
How does the parasympathetic NS affect HR ?
The parasympathetic nervous system decreases the heart rate when the vagus nerve releases AcH which acts on muscarinic receptors on the SA node.
What is stroke volume ?
the volume of blood pumped out by the heart in one beat
What is starlings law?
Starlings law states that the energy of a contraction (tension) is proportional to the initial length of the cardiac muscle fibre
How does starlings law apply to the control of our heart?
The greater the tension the greater the stoke volume. The lengths of the cardiac muscles fibres is determined by the volume of blood in the ventricles. The relationship can be seen in the graph. To a certain point the longer the fibres the greater the tension however after a certain point this is no longer the case.
How can stoke volume be regulated by the sympathetic NS?
The stoke volume can be regulated by adrenaline and noraadrenaline released by the sympathetic NS and adrenal medulla. The noradrenaline and adrenaline acts on B1 receptors and cause a stronger and shorter contraction. It also increases contractility (an inotropic effect).
How can stoke volume be regulated by the parasympathetic NS?
The parasympathetic pathway has very little effect because the vagus does not innervate the ventricular muscle.
What is the afterload ?
the load against which the muscle contracts
The larger the … the larger the afterload
the resistance in the vascular system
When happens to the stroke volume when the afterload increases
The larger the resistance in the vascular system the larger the load against which the muscle contracts and the higher the required ventricular pressure for the aortic valve to open (remember that happens when the aortic pressure is less than the ventricular pressure). The resistance in the system can be controlled by the arterioles. If there is a large afterload then there will be less ‘energy’ to eject blood and so there is an decrease in stroke volume.
What is the preload ?
how full the ventricles are before the contraction starts
What is the preload affected by ?
the state of the contracted venules/veins
What is another name for the volume of blood in the heart?
end diastolic volume.
What is contractility ?
How strong a contraction is
What affects the contractility ?
The sympathetic system
EQUATION: Cardiac output =
Heart rate x stroke volume
How do you get from an increased vagal tone and increased in sympathetic tone to a reduced in afterload ?
An decrease in vagal tone (activity) and an increase in sympathetic tone (activity) causes an increase in HR and contractility (inotropic effect). Here is an decrease in length of systole. Sympathetic system works on the veins causes an increases venous return, and this maintains preload. The sympathetic system works on the arteries and causes a reduction in resistance and therefore a reduction in afterload.
By what mechanisms is venous return controlled ?
Pressure Gravity Skeletal muscle pump Respiratory pump Venomotor tone
How does pressure affect the venous return ?
Pressure falls as you move through the vascular tree. There is a small drop in pressure between the arteries, a large drop into the arterioles and it then continues to fall until it is back in the heart. The pressure different through the system is what drives the movement on blood.
How does gravity affect venous return ?
Always pulling downwards
How does the skeletal muscle pump affect venous return ?
The skeletal muscle pump increases the movement of venous blood back to the heart. It occurs where there is a rhythmic contraction of skeletal muscles in the legs i.e. when you are exercising. A lack of skeletal muscle pump use can cause a DVT.
How does the respiratory pump affect venous return ?
The respiratory pump also increases venous return. An increase in respiratory rate and depth increases venous return and EDV. This is because inspiration causes a decrease in alveolar pressure adding to the pressure gradient and pulling blood up towards the lungs.
