Lecture 15: Regulation of Arterial Pressure Flashcards
When metabolic demand is high, more blood is released through capillary beds by doing what to the arterioles?
Reducing resistance = Vasodilation
What are the 2 general methods of control for arterial pressure?
1) Rapid, neuronally mediated
2) Slower, hormonally mediated
The neuronally mediated mechanism for controlling arterial pressure relies on what?
Pressure sensors, a control center and pressure control mechanism influencing the heart and vasculature (baroreceptor reflex)
What organ is most involved in the hormonally mediated mechanism for control of arterial pressure?
A large component of both the sensor and pressure influencing organs are the kidneys.
The baroreceptor reflex utilizes?
Classical reflex arc
What are the 2 types of receptors used by the baroreceptor reflex?
1) Mechanoreceptors - change in pressure
2) Chemoreceptors - change in PO2, PCO2, pH
How quick can these detectors act and how long can they last?
Can act within seconds and last indefinetely
How do the detectors sense change in pressure?
Through stretch receptors on vessel wall
Increased stretch causes; decreases stretch casuses?
Increased stretch = increased firing rate
Decreases stretch = decreased firing rate
The carotid sinus baroreceptors are innervated by?
Sinus nerve of Hering, a branch of the Glossopharyngeal nerve (CN IX)
The aortic sinus baroreceptors are innervated by?
Aortic nerve, a branch of the Vagus nerve (CN X)
The afferent neurons of the carotid and aortic sinus travel where?
Up the spinal cord, to the brain stem, and finally to the nucleus tractus solitarius (NTS)
What is the NT used by affernet neurons the NTS?
Glutamate
The rostral ventrolateral medulla is responsible for?
Vasculature repsonse
The dorsal motor nucleus of the vagus and nucleus ambiguous is responsible for?
Cardiac response
Baroreceptors send signals to the medulla, which is considered the?
Control center
Stretch of receptors decreases firing rate of which neurons?
Afferent neurons - send the signal to the medulla
Efferents are both?
Parasympathetic (vagus) and sympathetic
What parts of the brain do the afferents travel to?
Cerebral cortex and hypothalamus
Mean arterial blood pressure (MABP) =
HR x SV x TPR
What is the baroreceptor reflex working to maintain?
MABP
TPR is dependent on?
Sympathetic stimulation of arterioles
SV is dependent on?
- Sympathetic stimulation of heart
- Preload
HR is dependent on?
- Sympathetic (increases)
- Parasympathetic (decreases)
Increased frequency of stimulation increases what?
Strength of AP
How is the aortic sinus different from the carotid?
- Higher threshold for activation
- Continues to respond above saturation
- Less sensitive to rate, less effected by decreases
The increase or decrease in firing rate of these receptor neurons is proportional to?
The change in pressure
How does the sympathetic nervous system affect the firing rate of baroreceptors?
Decreases firing rate
Sympathetic NS does what to arterioles and veins; via which receptor?
Constriction via α receptors
Sympathetic NS does what to HR and contractility; via which receptor?
Increases via β receptors
Parasympathetic NS affects the firing rate of baroreceptors how?
Increases firing rate
Which nerve is part of the parasympathetic NS and signals to the SA node, atria and ventricles; via what receptor?
Vagus nerve using muscarinic receptors
What is the affect of the parasympathetic NS on blood vessels?
Indirect vasodilation (via stimulation of NO release)
How does HTN affect baroreceptors?
Will cause them to adjust their set-point to the new condition. Makes it so that the body can still respond to changes.
How does RAAS help control BP?
Regulation blood volume
For longer term adjustments to changes in BP what kind of response is invoked?
A hormonal response
The hormonal response is invoked and begins how quick and building for how long?
Begins within minutes and can build over a period of days or longer if needed
Renin is secreted by, in response to?
Secreted by the kidney in a response to a drop in BP and by sympathetic stimulation
Stimulation of what receptor also increases the release of renin?
β1-adrenergic receptor by sympathetic NS
What does renin do in the blood?
Causes Angiotensinogen to be converted to Angiotensin I (inactive)
What must occur to angiotensin I to become active; where?
Must be converted to Angiotensin II in the lungs (and kidneys)
What part of the kidney secretes Renin?
Juxtaglomerular (JG) cells in walls of renal afferent arterioles
Angiotensin II causes the secretion of what 2 things?
1) Aldosterone from the adrenal cortex
2) ADH (Vasopressin)
What does aldosterone do?
Leads to Na+ and H2O retention by kidney
Aldosterone causes an increase in?
Blood volume, preload/stroke volume, CO, and therefore BP
What is the affect of ADH (vasopressin)?
Reduces urine production (fluid retention) and increases TPR
How does angiotensin II affect arterioles; binds to?
Binds to AT1 receptors and causes global vasoconstriction of arterioles
Angiotensin II affect on the hypothalamus?
Increases thirst
What do ACE inhibitors do?
Prevent the conversion of angiotensin I to angiotensin II in lungs
Side effect of ACE inhibitors?
Cough because of a buildup of bradykinin (Angiotensin II breaks down bradykinin)
How can arteriolar angiotensin II receptors be blocked pharmacologically?
Using angiotensin receptor blockers (ARBs)
BP =
BP = CO x TPR
*CO = SV x HR
Vasopressin (ADH) acts via which receptors, found where?
V1 receptors (smooth muscle) - increase TPR
V2 receptors (collecting ducts) - fluid retention
Vasopressin (ADH) is secreted in response to what 3 things?
1) Angiotensin II
2) Increased osmolarity of blood
3) Atrial receptors in presence of low preload
What are the 3 forms of natriuretic peptides?
1) Atrial (ANP)
2) Brain (BNP)
3) C-type (CNP)
When are natriuretic peptides secreted?
During excessive preload of atria and ventricles
What 3 things do natriuretic peptides cause?
1) Arteriolar dilation - decreases TPR
2) Increase fluid loss - decreases preload
3) Inhibits renin - decreases both TPR and preload
Natriuretic peptides protect against?
Overdilation and overstretching of cardiac chambers
Cerebral ischemia causes?
Increased sympathetic outflow from vasomotor center
Why would you want increased sympathetic outflow during cerebral ischemia?
Sympathetic outflow = vasoconstriction = protective if BP is dropping and there will not be enough to adequately perfuse the brain
Cushing reflex is in response to?
Increased intracranial pressure - compresses cerebral arteries and reduces perfusion
What is the triad for the Cushing Reflex; cause for each?
1) HTN (sympathetic drive to increase blood flow to brain)
2) Bradycardia (baroreceptors sensing increased BP)
3) Irregular respiration (impaired brain stem function)
In response to increased blood volume - increased preload, what 4 things occur?
1) Increases secretion of ANP
2) Decrease ADH secretion
3) Renal vasodilation
4) Increased HR
Anticipation at what part of the brain causes the changes before exercise?
Cerebral cortex - central command response
What is the central command response to the anticipation of exercise?
1) Increased sympathetic output/decreased parasympathetic
2) Increased HR/contractility/stroke volume
3) Increased venous return (preload)
4) Vasoconstriction (slight increase in MAP)
What orchestrates the peripheral response (local) in exercising skeletal muscle; importance?
- Active hyperemia due to an increase in local metabolites (K+, lactate, and adenosine)
- Most important mechanism of control during exercise
The central command during exercise causes vasoconstriction of?
Splanchnic (gut) and renal arterioles
What 2 things causes an increase in venous return during exercise?
1) Contraction of skeletal muscle around the veins has a mechanical (squeezing) action
2) Activation of the sympathetic nervous system
produces venoconstriction.
What triggers the anticipatory affect produced by the central command before exercise?
Triggered by muscle mechanoreceptors
Vasoconstriction will not occur where during exercise?
Skeletal muscle, coronary and cerebral circulation
What happens to TPR during exercise?
An overall decrease in TPR due to vasodilation of skeletal muscle
