L15: Modulating Flow & Baroreflex

Question 1

What is the most important requirement for proper operation of the cardiovascular system? (not the heart/ vessels)

Answer 1

Systemic arterial pressure, the pressure gradient which ensures adequate perfusion of tissues. Elaborate control mechanisms control this.

Question 2

What are 2x mechanisms by which we can alter mean arterial pressure?

Answer 2

change CO and arteriolar resistance through vasoconstriction or dilation

Question 3

Describe the pressure changes in the vascular tree

Answer 3

• 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

Question 4

Can the pressure in the venules change the pressure back up in the arteries?

Answer 4

Nope! pressure almost 0 back to right atrium.

Question 5

Flow/__ is directly proportional to _____ _____, inversely proportional to _____.

Answer 5

Flow/ CO is directly proportional to pressure gradient, inversely proportional to resistance

Question 6

MAP is directly proportional to __ and to ___.

Answer 6

MAP is directly proportional to CO and arteriolar resistance because (MAP= CO x TPR)

Question 7

An increase in HR and SV will increase …

Answer 7

contractility and venous return

Question 8

An increase in arteriolar resistance will affect …

Answer 8

mean arterial pressure

Question 9

What does the baroreflex regulate?

Answer 9

MAP with -ve feedback

Question 10

What is the stimulus for baroreceptors

Answer 10

stretch (arterial)

pressure/ stretch (cardiopulmonary)

Question 11

Where are the high pressure baroreceptors located

Answer 11

Aortic arch

Cartoid sinus

Question 12

Where are cardiopulmonary baroreceptors located

Answer 12

@ junctions great veins + atria, ventricles, pulmonary veins

Question 13

What are the high pressure baroreceptors

Answer 13

Arterial stretch receptors

Question 14

What are the low pressure baroreceptors

Answer 14

sense central blood volume (pressure)

Question 15

where are arterial stretch receptors found

Answer 15

Aortic arch/ carotid stinus

Question 16

What is the type of response of the high pressure receptors

Answer 16

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”

Question 17

What is the type of response of the low pressure receptors, including details of the nervous innervation

Answer 17

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

Question 18

Which nerves conduct afferent messages from the baroreceptors to change mean arterial pressure

Answer 18

Glossopharyngeal nerve (CN9) & vagus nerve (CN 10)

Question 19

Describe the central integration of baroreceptor messages

Answer 19

medullary cardiovascular centre @ medulla and 2x regions in vasomotor centre are the pressor region (sympathetic) and depressor region (parasympathetic)

Question 20

Is the pressor region sympathetic or parasympathetic

Answer 20

Sympathetic

Question 21

Is the depressor region sympathetic or parasympathetic

Answer 21

Parasympathetic

Question 22

What is the general action of the pressor region

Answer 22

normal tonic stimulation to blood vessels

Question 23

What is the general action of the depressor region

Answer 23

inhibitory action on sympathetic nerves and excitatory action on parasympathetic. Specifically @ SA node to DEC rate.

Question 24

What are the specific actions of the pressor region on the heart and vessels ?

Answer 24

• SA node –> INC rate
• Myocardium –> INC force
• Arterioles –> INC TPR
• Veins –> INC venous return

Question 25

cardiopulmonary baroreceptors fire at normal pressure, when do they stop firing, what is there action?

Answer 25

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

Question 26

why is flow important?

Answer 26

flow is critical to maintaining perfusion to tissues

Question 27

what is the flow equation

Answer 27

flow = pressure gradient / resistance

Question 28

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

Answer 28

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.

Question 29

why is it important that the distributing arteries are complient?

Answer 29

decrease pulsative flow from the heart (creating a larger pressure difference), create a more steady flow to the tissue