Control of Circulation Flashcards
What is the basal arterial tone?
It is a theoretical reference point, and is the amount of vascular contraction found under resting conditions without neural or hormonal (extrinsic) influences.
What is the resting sympathetic tone?
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.
How do active mechanisms affect the vascular resistance?
They induce a change in the resistance AWAY from the basal tone.
How do passive mechanisms affect the vascular resistance?
They induce a change in the resistance TOWARDS the basal tone.
What is passive vasoconstriction?
Increase in pressure towards the basal tone
What is passive vasodilation?
Decrease in pressure towards the basal tone
What is active vasoconstriction?
Increase in pressure away from the basal tone
What is active vasodilation?
Decrease in pressure away from the basal tone
How do α-receptors mediate vascular tone?
They are located on vascular smooth muscle and cause vasoconstriction.
How do β-1 receptors mediate vascular tone?
They are the primary adrenergic receptor on cardiac muscle and they stimulate heart rate and contractility.
How do β-2 receptors mediate vascular tone?
They are in vascular smooth muscle and stimulate vasodilation.
Describe the arterial baroreceptor reflex.
It is a negative feedback loop in order to control arterial pressure and works by making short term adjustments.
Where are baroreceptors found?
They are located in the walls of the carotid sinus and the aortic arch.
How do the baroreceptors respond to a decrease in arterial pressure (hemorrhage/standing up in the morning)?
Stimulates the sympathetics and inhibits the parasympathetics.
- Increased vasoconstriction
- Increased HR
- Increased contractility
Opposite occurs for increased arterial pressure.
How does the baroreceptor firing frequency change with increased arterial pressure and decreased arterial pressure?
It increases with increased arterial pressure and decreases with decreased arterial pressure.
What kinds of pressures are baroreceptors more responsive to?
Pulsatile rather than static
What are peripheral chemoreceptors?
They are small vascular bodies located in the aortic arch that are activated mainly by low arterial PO2 and also low pH
What is the function of chemoreceptors?
Involved in regulation of respiration and mainly only affect eh cardiovascular system during severe hypoxia. It affects the respiratory system much more.
Where is chemoreceptor nerve activity from the carotid carried?
CN IX
Where is chemoreceptor nerve activity from the aorta carried?
CN X
What do the chemoreceptors stimulate?
Sympathetic - Vasoconstriction
Parasympathetic - Bradycardia
In real life though, what does hypoxia actually cause?
Tachycardia because increase in ventilation by the respiratory system will serve to increase the heart rate.
How does the amount of CO2 affect the response of chemoreceptors?
It increases their sensitivity to O2
When the PO2 decreases or PCO2 increases or pH decreases, what will be activated?
Peripheral chemoreceptors
What effect do the peripheral chemoreceptors have on the cardiovascular center of the brainstem?
It will stimulate both the sympathetics and parasympathetics
How is the parasympathetic activation of the chemoreceptors inhibited?
Increase in rate and depth of respiration will stimulate the mechanoreceptors in the lungs that will inhibit the parasympathetic activity and increase HR.
What is the main mechanism for long term regulation of blood pressure?
Renin-Angiotensin-Aldosterone
Describe the Renin-Angiotensin-Aldosterone control.
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
What do ACE inhibitors do?
They lower blood pressure by inhibiting the activity of angiotensin converting enzyme (ACE)
