Lecture 22: Arterial Pressure Control

What are the 3 time scales of arterial blood pressure regulation?

- rapid controllers (seconds)

- intermediate controllers (minutes to hours)

- long-term controllers (days to weeks)

What is the equation relating MAP, CO, and TPR?

MAP = CO × TPR

Which variables are regulated by cardiovascular reflex pathways to control MAP?

HR, SV, and TPR

Which cranial nerves carry cardiovascular afferent information to the NTS?

CN IX (glossopharyngeal) and CN X (vagus)

What is the function of the NTS in cardiovascular regulation?

receives and integrates cardiovascular afferent sensory information

Which cardiovascular centers control autonomic efferent activity?

vasomotor center and cardiac center

What does the vasomotor center regulate?

sympathetic adrenergic nerve activity controlling TPR

What does the cardiac center regulate?

- vagal activity controlling HR

- sympathetic adrenergic activity controlling HR and force of contraction

high-pressure sensory receptors that respond to mechanical stretch of arterial vessel walls

arterial baroreceptors

What is the primary function of the arterial baroreflex?

short-term regulation of arterial blood pressure

What stimulates arterial baroreceptors?

mechanical stretch caused by internal vessel pressure

What would happen to arterial BP without the arterial baroreflex?

wide variations in arterial blood pressure

Where are arterial baroreceptors located?

carotid sinus at the carotid artery bifurcation and aortic arch

What 2 pressure variables stimulate arterial baroreceptors?

- mean arterial pressure

- arterial pulse pressure

What is the relationship between pulse pressure and stroke volume?

increased pulse pressure always corresponds to increased stroke volume

What does the arterial pressure and baroreceptor firing graph demonstrate?

- firing increases with elevated MAP or increased pulse pressure

- decreases with reduced MAP

Which 2 autonomic pathways carry the efferent response of the baroreflex?

sympathetic and parasympathetic pathways

Which cardiac structure is labeled as a parasympathetic target in the baroreflex diagram?

SA node

What happens to baroreceptor firing when arterial BP increases?

increases

How does increased baroreceptor firing affect sympathetic and parasympathetic outflow?

decreases sympathetic outflow and increases parasympathetic outflow

What is the sequence of the baroreceptor reflex during increased BP?

↑MAP → ↑baroreceptor firing → ↓SNS and ↑PNS → ↓HR, peripheral vasodilation, venodilation → ↓MAP

What happens to baroreceptor firing when arterial BP decreases?

decreases

How does decreased baroreceptor firing affect sympathetic and parasympathetic outflow?

increases sympathetic outflow and decreases parasympathetic outflow

What is the sequence of the baroreceptor reflex during decreased BP?

↓MAP → ↓baroreceptor firing → ↑SNS and ↓PNS → ↑HR, peripheral vasoconstriction, venoconstriction → ↑MAP

What is the primary function of the peripheral chemoreflex?

adjusts ventilation and cardiovascular function in response to arterial blood gas changes

Which blood gas disturbance particularly stimulates peripheral chemoreceptors?

decreased O2 (hypoxia)

Where are the peripheral chemoreceptors located in this lecture?

carotid body at the carotid artery bifurcation

What happens to ventilation during spontaneous breathing in a hypoxic environment, such as high altitude?

increases

What receptors are stimulated by increased ventilation during hypoxia?

lung stretch receptors

How does spontaneous breathing during hypoxia affect the cardioinhibitory center?

inhibits the cardioinhibitory center which increases HR

How does spontaneous breathing during hypoxia affect sympathetic activity to peripheral resistance vessels?

increases sympathetic activity which increases TPR

What is the overall MAP response to hypoxia while spontaneously breathing?

increases MAP

What happens to ventilatory activity during breath-holding underwater?

no ventilatory activity

How does the peripheral chemoreflex affect parasympathetic activity during breath-holding hypoxia?

increases parasympathetic activity to the heart which decreases HR

How does sympathetic activity to peripheral resistance vessels change during breath-holding hypoxia?

increases sympathetic activity which increases TPR

What is the primary purpose of the chemoreflex during breath-holding hypoxia?

oxygen conservation

What is a major determinant of arterial blood pressure besides CO and TPR?

blood volume

How does increasing blood volume affect BP?

increases BP

What do atrial low-pressure receptors detect?

fullness of the venous circulation

(intermediate controllers)

What mechanisms are adjusted by atrial stretch reflexes to regulate plasma volume?

kidney function and thirst

Where are cardiopulmonary receptors located?

- atria

- junctions of veins with atria

- ventricles

- pulmonary artery

What is another name for low-pressure receptors involved in the atrial stretch reflex?

cardiopulmonary receptors

What do cardiopulmonary receptors sense?

atrial filling - reflects the amount of blood in the atrium

What stimulates cardiopulmonary receptors?

increased central venous volume

(or pressure)

Which cranial nerve carries afferent signals from cardiopulmonary receptors?

CN X (vagus)

Where are cardiopulmonary receptor afferent signals integrated?

NTS in the brainstem

Which efferent pathways mediate the cardiopulmonary receptor reflex?

vagus and sympathetic nerves

what is the result of the atrial stretch reflex in response to increase in central volume/pressure?

- increased loss of water and salt via the kidneys

- decrease in blood volume

What is the sequence of the atrial stretch reflex during increased central volume?

↑central venous volume/pressure → ↑atrial stretch → inhibition of renal SNS and vasopressin, ↑ANP → ↑renal salt and water loss → ↓blood volume and MAP

what is the result of the atrial stretch reflex in response to a decrease in central volume/pressure?

- decreased loss of water and salt via the kidneys

- increase in blood volume

What is the sequence of the atrial stretch reflex during decreased central volume?

↓central venous volume/pressure → ↓atrial stretch → ↑renal SNS and vasopressin, ↓ANP → ↓renal salt and water loss → ↑blood volume and MAP

movement of fluid between vascular and interstitial compartments

capillary fluid shift

(intermediate controller)

What determines the direction of capillary fluid movement?

Starling forces

What changes can alter capillary hydrostatic pressure (Pc)?

changes in MAP or arteriolar resistance

What happens when capillary hydrostatic pressure changes?

fluid shifts across capillary walls

How does increased MAP affect sympathetic vasoconstriction?

decreases sympathetic vasoconstriction

What is the sequence of capillary fluid shift during increased MAP?

- ↑MAP

- ↓sympathetic vasoconstriction

- arteriolar vasodilation

- ↑Pc

- ↑filtration into interstitium

- ↓intravascular volume

- ↓MAP

How does decreased MAP affect sympathetic vasoconstriction?

increases sympathetic vasoconstriction

What is the sequence of capillary fluid shift during decreased MAP?

- ↓MAP

- ↑sympathetic vasoconstriction

- arteriolar vasoconstriction

- ↓Pc

- ↓filtration and fluid movement into capillaries

- ↑intravascular volume

- ↑MAP

Which 3 major hormonal systems regulate intermediate arterial pressure control?

- RAAS

- vasopressin (ADH)

- atrial natriuretic peptide (ANP)

Where is renin released?

juxtaglomerular cells of the kidney

What 3 factors stimulate renin release?

- decreased BP

- decreased blood volume

- increased renal sympathetic stimulation

What is the function of renin in RAAS?

cleaves angiotensin I from angiotensinogen

Which enzyme converts angiotensin I into angiotensin II?

angiotensin-converting enzyme (ACE)

(located in the lungs and kidneys)

What are the 2 major effects of angiotensin II?

potent vasoconstriction and stimulation of aldosterone release

what are the effects of angiotensin II acting as a potent vasoconstrictor?

increases TPR and increased MAP

Where does angiotensin II stimulate aldosterone release?

adrenal cortex

What is the primary renal action of aldosterone?

increases Na+ and water absorption

How does aldosterone affect extracellular fluid volume?

increases extracellular fluid volume which increases MAP

What is the sequence of RAAS activation during decreased MAP?

↓MAP → ↑renin → ↑angiotensin I → ↑angiotensin II → vasoconstriction and ↑aldosterone → ↑Na+ and water retention → ↑blood volume and MAP

What is another name for vasopressin?

antidiuretic hormone (ADH) or arginine vasopressin (AVP)

How does vasopressin indirectly regulate BP?

changes blood volume through renal water reabsorption

What are the 2 major effects of vasopressin?

- vasoconstriction via V1 receptors

- increased renal water reabsorption via V2 receptors

Where is vasopressin released?

posterior pituitary

What 3 conditions stimulate vasopressin release?

- decreased MAP

- decreased blood volume

- high plasma osmolarity

How is decreased MAP detected to stimulate vasopressin release?

baroreceptor unloading

How is decreased blood volume detected to stimulate vasopressin release?

atrial receptor unloading

Where is high plasma osmolarity detected to stimulate vasopressin release?

hypothalamus

How does increased vasopressin affect renal water absorption?

increases water absorption which increases blood volume and MAP

What is the vasopressin response to decreased blood volume?

increased ADH release → decreased renal water excretion → increased blood volume and MAP

What is the vasopressin response to increased blood volume?

decreased ADH release → increased renal water excretion → decreased blood volume and MAP

How does ANP indirectly regulate BP?

changes blood volume through renal salt and water excretion

Which cells release ANP?

atrial myocytes in response to increased atrial stretch

What is the primary function of ANP?

defends against excessive blood volume

(decreases Na+ reabsorption and decreases water reabsorption)

What is the sequence of ANP action during increased blood volume?

↑blood volume → ↑atrial stretch → ↑ANP release → ↓renal Na+ and water reabsorption → ↑salt and water excretion → ↓blood volume and MAP

How do ADH and ANP differ in their effects on renal water handling?

- ADH increases water reabsorption

- ANP decreases water reabsorption

What is the major determinant of long-term arterial pressure maintenance?

maintaining constant blood volume

Which organ is the major long-term regulator of blood volume?

kidney

Which 2 substances do the kidneys regulate to maintain blood volume?

water and salt

How do the kidneys and cardiovascular system maintain long-term BP?

work together as an integrating system

(does not fatigue or adapt)

What happens to renal output of water and electrolytes when arterial pressure increases?

increases

How does increased renal water and electrolyte output affect extracellular fluid volume?

decreases extracellular fluid volume which decreases blood volumee

How does decreased blood volume affect circulatory filling pressure?

decreases circulatory filling pressure

How does decreased circulatory filling pressure affect venous return and CO?

decreases venous return and CO

How does decreased CO affect arterial pressure?

decreases arterial pressure

How do the kidneys respond when arterial pressure decreases?

conserve water and electrolytes by reducing renal output

How do diuretics lower arterial pressure?

increase renal fluid and salt loss from the kidneys

What 3 RAAS targets are used for antihypertensive therapy?

- ACE

- angiotensin II AT1 receptors

- renin

Which drug class blocks angiotensin II production?

ACE inhibitors

Which drug class blocks angiotensin II receptors?

AT1 inhibitors