L18 Circulation- Control of Circulation

Question 1

Define basal arterial tone.

Answer 1

Amount of vascular contraction found under resting conditions without neural or hormonal influences
-Theoretical reference point, never happens physiologically

Question 2

Define resting sympathetic tone.

Answer 2

Amount of vascular constriction found under resting conditions as a result of tonic sympathetic nerve activity

• Higher resistance than basal arterial tone b/c of tonically-released NE
• Due to small symp. nerve activation when awake

Question 3

Define passive and active vasoconstriction.

Answer 3

• Active vasoconstriction is change in vascular resistance away from the basal arterial tone by sympathetic adrenergics
• Passive is by sympathetic cholinergics

Question 4

Define passive and active vasodilation.

Answer 4

• Passive vasodilation is change in vascular resistance toward basal arterial tone by sympathetic adrenergics
• Active is by sympathetic cholinergics

Question 5

Explain how a1 and B2 adrenergic receptors mediate regulation of vascular tone.

Answer 5

• Stimulated by isoproterenol, NE, Epi
• a1 located on vascular smooth muscle cause VASOCONSTRICTION
• B2 located on cardiac muscle cause INCREASE HR and CONTRACTILITY
• B2 located on vascular smooth muscle cause VASODILATION

Question 6

Identify the anatomy of arterial baroreceptors.

Answer 6

Found in the walls of the carotid sinus and aortic arch

• Have less vascular smooth muscle
• Carotid sinus baroreceptors are more sensitive than aortic arch

Question 7

Explain arterial baroreceptor reflex.

Answer 7

Decrease in arterial P= sympathetic stimulation and PS inhibition= peripheral vasoconstriction, increase HR and ventricular contractility
-Response to ABRUPT changes in blood volume, CO or peripheral resistance

Question 8

Explain the anatomy of peripheral chemoreceptors.

Answer 8

Located in aortic arch and medial to carotid sinus, near baroreceptors

Question 9

Explain the function of peripheral chemoreceptors.

Answer 9

Primarily activated by low arterial PO2, also high arterial PCO2 and low arterial pH (high H+)

• In CV system, only play a role in severe hypoxia and cause bradycardia
• Respiratory response overcomes CV reflex and causes tachycardia

Question 10

Explain the renin-angiotensin-aldosterone mechanism of blood volume regulation.

Answer 10

Primary mechanism responsible for long-term regulation of BP

• Low arterial P= baroreceptors activated= symp. activation= reaches kidneys and glomerulus cells release Renin= converts angiotensinogen to AT I= reaches endothelium in lungs and kidneys where ACE converts to AT II
• AT II is most powerful vasoconstrictor= vasoconstriction of renal and systemic vessels, stimulates aldosterone release, increases Na reabsorption in kidneys, acts on hypothalamus to stimulate thirst and ADH= increased water retention

Question 11

How do PCO2 and PO2 affect chemoreceptor response?

Answer 11

Increases in PCO2 above normal and decreases in PO2 below normal lead to large responses in chemoresponses