Control of Circulation

Question 1

What is the basal arterial tone?

Answer 1

It is a theoretical reference point, and is the amount of vascular contraction found under resting conditions without neural or hormonal (extrinsic) influences.

Question 2

What is the resting sympathetic tone?

Answer 2

It is the amount of vascular constriction found under resting conditions as a result of tonic sympathetic nerve activity. The resistance is higher than the basal arterial tone due to the presence of tonically- released norepinephrine.

Question 3

How do active mechanisms affect the vascular resistance?

Answer 3

They induce a change in the resistance AWAY from the basal tone.

Question 4

How do passive mechanisms affect the vascular resistance?

Answer 4

They induce a change in the resistance TOWARDS the basal tone.

Question 5

What is passive vasoconstriction?

Answer 5

Increase in pressure towards the basal tone

Question 6

What is passive vasodilation?

Answer 6

Decrease in pressure towards the basal tone

Question 7

What is active vasoconstriction?

Answer 7

Increase in pressure away from the basal tone

Question 8

What is active vasodilation?

Answer 8

Decrease in pressure away from the basal tone

Question 9

How do α-receptors mediate vascular tone?

Answer 9

They are located on vascular smooth muscle and cause vasoconstriction.

Question 10

How do β-1 receptors mediate vascular tone?

Answer 10

They are the primary adrenergic receptor on cardiac muscle and they stimulate heart rate and contractility.

Question 11

How do β-2 receptors mediate vascular tone?

Answer 11

They are in vascular smooth muscle and stimulate vasodilation.

Question 12

Describe the arterial baroreceptor reflex.

Answer 12

It is a negative feedback loop in order to control arterial pressure and works by making short term adjustments.

Question 13

Where are baroreceptors found?

Answer 13

They are located in the walls of the carotid sinus and the aortic arch.

Question 14

How do the baroreceptors respond to a decrease in arterial pressure (hemorrhage/standing up in the morning)?

Answer 14

Stimulates the sympathetics and inhibits the parasympathetics.

• Increased vasoconstriction
• Increased HR
• Increased contractility

Opposite occurs for increased arterial pressure.

Question 15

How does the baroreceptor firing frequency change with increased arterial pressure and decreased arterial pressure?

Answer 15

It increases with increased arterial pressure and decreases with decreased arterial pressure.

Question 16

What kinds of pressures are baroreceptors more responsive to?

Answer 16

Pulsatile rather than static

Question 17

What are peripheral chemoreceptors?

Answer 17

They are small vascular bodies located in the aortic arch that are activated mainly by low arterial PO2 and also low pH

Question 18

What is the function of chemoreceptors?

Answer 18

Involved in regulation of respiration and mainly only affect eh cardiovascular system during severe hypoxia. It affects the respiratory system much more.

Question 19

Where is chemoreceptor nerve activity from the carotid carried?

Answer 19

CN IX

Question 20

Where is chemoreceptor nerve activity from the aorta carried?

Answer 20

CN X

Question 21

What do the chemoreceptors stimulate?

Answer 21

Sympathetic - Vasoconstriction

Parasympathetic - Bradycardia

Question 22

In real life though, what does hypoxia actually cause?

Answer 22

Tachycardia because increase in ventilation by the respiratory system will serve to increase the heart rate.

Question 23

How does the amount of CO2 affect the response of chemoreceptors?

Answer 23

It increases their sensitivity to O2

Question 24

When the PO2 decreases or PCO2 increases or pH decreases, what will be activated?

Answer 24

Peripheral chemoreceptors

Question 25

What effect do the peripheral chemoreceptors have on the cardiovascular center of the brainstem?

Answer 25

It will stimulate both the sympathetics and parasympathetics

Question 26

How is the parasympathetic activation of the chemoreceptors inhibited?

Answer 26

Increase in rate and depth of respiration will stimulate the mechanoreceptors in the lungs that will inhibit the parasympathetic activity and increase HR.

Question 27

What is the main mechanism for long term regulation of blood pressure?

Answer 27

Renin-Angiotensin-Aldosterone

Question 28

Describe the Renin-Angiotensin-Aldosterone control.

Answer 28

When arterial pressure is low ->
Sympathetic stimulation ->
Renin release from kidney ->
Renin coverts angiotensinogen to angiotensin I ->
ACE is released from endothelial cells and it changes angiotensin I into angiotensin II ->
Angiotension II causes vasoconstriction and stimulates thirst and release of ADH ->
Aldosterone release from adrenal cortex which increases Na resorption

Question 29

What do ACE inhibitors do?

Answer 29

They lower blood pressure by inhibiting the activity of angiotensin converting enzyme (ACE)