L15: Modulating Flow & Baroreflex Flashcards
What is the most important requirement for proper operation of the cardiovascular system? (not the heart/ vessels)
Systemic arterial pressure, the pressure gradient which ensures adequate perfusion of tissues. Elaborate control mechanisms control this.
What are 2x mechanisms by which we can alter mean arterial pressure?
change CO and arteriolar resistance through vasoconstriction or dilation
Describe the pressure changes in the vascular tree
- the pressure changes continuously from the aorta continuously back to the right atrium (despite systole/ diastole fluctuations)
- pulse dampened at arterioles
- 40mmHg arteriolar ends
- 20mmHg at venous ends
- Pressure almost 0 back to right atrium
Can the pressure in the venules change the pressure back up in the arteries?
Nope! pressure almost 0 back to right atrium.
Flow/__ is directly proportional to _____ _____, inversely proportional to _____.
Flow/ CO is directly proportional to pressure gradient, inversely proportional to resistance
MAP is directly proportional to __ and to ___.
MAP is directly proportional to CO and arteriolar resistance because (MAP= CO x TPR)
An increase in HR and SV will increase …
contractility and venous return
An increase in arteriolar resistance will affect …
mean arterial pressure
What does the baroreflex regulate?
MAP with -ve feedback
What is the stimulus for baroreceptors
stretch (arterial)
pressure/ stretch (cardiopulmonary)
Where are the high pressure baroreceptors located
Aortic arch
Cartoid sinus
Where are cardiopulmonary baroreceptors located
@ junctions great veins + atria, ventricles, pulmonary veins
What are the high pressure baroreceptors
Arterial stretch receptors
What are the low pressure baroreceptors
sense central blood volume (pressure)
where are arterial stretch receptors found
Aortic arch/ carotid stinus
What is the type of response of the high pressure receptors
Rapid response to change in pressure, buffering sudden changes.
If pressure remains elevated for longer periods of time, firing rate of receptors decreases leading to new “set point”
What is the type of response of the low pressure receptors, including details of the nervous innervation
Respond to absolute pressure (rather than changes) I.e. respond to changes in BV in heart and great veins (Venous return) Nerve fibres run in vagus nerve to medulla DEC stretch (reduction in central BV) --> INC sympathetic drive to heart & BV & DEC parasympathetic drive to heart
Which nerves conduct afferent messages from the baroreceptors to change mean arterial pressure
Glossopharyngeal nerve (CN9) & vagus nerve (CN 10)
Describe the central integration of baroreceptor messages
medullary cardiovascular centre @ medulla and 2x regions in vasomotor centre are the pressor region (sympathetic) and depressor region (parasympathetic)
Is the pressor region sympathetic or parasympathetic
Sympathetic
Is the depressor region sympathetic or parasympathetic
Parasympathetic
What is the general action of the pressor region
normal tonic stimulation to blood vessels
What is the general action of the depressor region
inhibitory action on sympathetic nerves and excitatory action on parasympathetic. Specifically @ SA node to DEC rate.
What are the specific actions of the pressor region on the heart and vessels ?
- SA node –> INC rate
- Myocardium –> INC force
- Arterioles –> INC TPR
- Veins –> INC venous return
cardiopulmonary baroreceptors fire at normal pressure, when do they stop firing, what is there action?
stop firing when pressure drops
stops the inhibitory actions of the depressor centre on the pressure centre
–> allows the pressure centre to use symp action to increase HR, contractility, arterial and venous tone
therefore increase SV and CO
MAP = CO x SV
why is flow important?
flow is critical to maintaining perfusion to tissues
what is the flow equation
flow = pressure gradient / resistance
from the flow equation, a change in pressure is CRITICAL for flow, flow is therefore said to be mean arterial pressure, what two things can influence MAP
CO and TPR
flow = pressure gradient / resistance
therefore
pressure gradient = flow x resistance
flow = CO (how much BLOOD FLOWS/time)
resistance = TPR (proportional to 1/radius - arterioles = biggest resistance to flow)
pressure has to continuously fall from LV to RA for forward flow, if the pressure increased flow would decrease.
why is it important that the distributing arteries are complient?
decrease pulsative flow from the heart (creating a larger pressure difference), create a more steady flow to the tissue
