Lecture 8 - Heart System Flashcards
(16 cards)
Which side of the heart receives oxygenated blood?
Left side
Which side receives de-oygenated blood?
The right side
How does the heart beat?
The heart is autorhythmic. Pacemaker cells in the sinoatrial node initiates the heartbeat which then spreads to the atrioventricular node. From the AV node the current passes along the bundles of his to the purkinje fibre network which carries the wave of excitation throughout the myocardium causing the ventricles to contract simultaneously, from base to apex.
Describe the pacemaker potential
An action potential that is constantly creeping therefore regulating the timing of the action potential preventing tetanus.
Is the action potential in the heart mediated by Na entry or Ca entry?
ca
Describe an action potential in the heart
At -60mV the Membrane is permeable to K and slow na entry. As it hist the threshold potential of -40mV the membrane becomes permeable to calcium as the fast calcium channels open. Shortly after reaching 0mV the calcium channels close and the k channels open causing a repolarisation.
How does the parasympathetic nervous system control heart rate?
The vagus nerve supplies parasympathetic innervation to the SA node decreasing the heart rate, this system falls silent under strenuous exercise. It does this by ACh being released from the nerve which acts on M2 receptors in the heart
How does the sympathetic nervous system affect heart rate?
The cardiac accelerator nerve provides sympathetic innervation to the heart, it causes increased heart rate. It does this by releasing noradrenaline from the nerve which acts together with adrenaline from the adrenal medulla on the B1 receptor in the myocardium.
What are the chronotropic effects of adrenergic activity?
The frequency of action potentials is increased
What is the chronotropic effect of parasympathetic innervation of the heart?
The frequency of action potentials reduces
What is the effect on contractility of the heart by the sympathetic system?
It is increased
What is the effect on contractility of the heart by the parssympathetic system..
It is reduced
What are the inotropic effects on the heart of noradrenaline?
Increase the force for the same size stimulus
How does the autonomic nervous system regulate blood vessel diameter?
Most vessels have resting sympathetic tone. To constrict the vessels the sympathetic innervation is increased and to cause vasodilation the sympathetic innervation is removed
What is the common adrenoceptor on the blood vessels?
Alpha 1
What adrenoceptor do some vascular beds express to increase blood flow to selected areas during exercise?
Beta 1
