Flashcards in Regulation of the Cardiovascular System Deck (21)
What neurotransmitter do all parasympathetic neurones release?
What neurotransmitters could sympathetic neurones release?
Noradrenaline, adrenaline or acetylcholine
What are the three ways of regulating blood flow?
Local controls (autoregulation), circulating hormones, autonomic nervous system
Describe the two theories of the local mechanisms of controlling blood flow.
Myogenic Theory - the vascular smooth muscle responds to stretch and constricts to maintain the blood flow
Metabolic Theory - if there is reduced flow, metabolites build up in the blood and signal to the smooth muscle to dilate. When the vessel dilates, the metabolites are washed away and the stimulus is removed.
State two molecules produced in the endothelium that cause vasodilation.
Nitric Oxide and Prostacyclin
State two molecules produced in the endothelium that cause vasoconstriction.
Thromboxane A2 and Endothelin-1
State five hormones that regulate blood flow.
Atrial Natriuretic Peptide
Kinins (e.g. bradykinin)
What effects does the sympathetic nervous system have on the cardiovascular system?
Increased sympathetic activity increases heart rate, increases force of contraction and decreases the vessel radius (increases resistance)
What effect does the parasympathetic nervous system have on the cardiovascular system?
It decreases heart rate
Causes vasoconstriction of the coronary arteries
The distribution of sympathetic nerve fibres is not even. Where do you find more sympathetic nerve fibres?
There are more sympathetic nerve fibres in the spleen, gut, kidneys and skin because there is more potential to divert blood away from these organs without causing damage. There are fewer sympathetic fibres in the skeletal muscle and brain.
What adrenoreceptors could circulating adrenaline bind to?
Beta-2 and alpha-1 (at high concentrations)
Binding to beta-2 has a vasodilator effect but then binding to alpha-1 has a vasoconstricting effect
Where is the vasomotor centre located?
VMC is located bilaterally in the reticular substance of the medulla
The lateral portions control heart rate and contractility
Medial portions transmit signals via the vagus nerve
What neurotransmitter is involved in controlling vessel radius?
Noradrenaline - from the sympathetic innervation
What are the three ways of controlling vessel radius?
What are the three ways in which stroke volume can be increased?
Starling's Law (increased venous return to the heart)
Increased plasma adrenaline and noradrenaline
Increased sympathetic innervation
Describe the mechanism of action of noradrenaline on the heart.
Noradrenaline binds to the beta-1 adrenergic receptor, which causes activation of adenylate cyclase and the upregulation of cAMP leading to the activation of PKA. PKA phosphorylates, hence activates, the L-type calcium channel, sarcoendoplasmic reticulum calcium ATPase, sarcoplasmic reticulum calcium release channel
How do respiratory movements affect the cardiac output?
Inspiring decreases the intrathoracic pressure meaning that the pressure on the blood vessels is decreased so the blood flows more easily into the heart and hence it increases the stretch on the heart (preload) so cardiac output increases (Starling's Law)
What nerves carry information from the two baroreceptors to the vasomotor centre?
Carotid Bodies - Glossopharyngeal nerves
Aorta - Vagus nerve
What is the consequence of increased baroreceptor activity?
Parasympathetic activity mirrors baroreceptor activity. Increases baroreceptor activity leads to increased parasympathetic activity and decreased sympathetic activity. The increase in parasympathetic activity leads to a reduction in heart rate.
What are the effects of a decrease in sympathetic activity?
Decrease in sympathetic activity decreases heart rate and decreases force of contraction of the heart. This also increases the blood vessel radius and decreases resistance.