Phys- Regulation of Blood Pressure Flashcards
Describe baroreceptor stretch receptors
highly branched, enmeshed within the elastin matrix of the vessel wall
Name some things that infulence MAP
1.) Cardiac 2.) Systemic Nervous System 3.) Humoral 4.) Renal Fluid Volume control 5.) Local control
Reflex arc
feedback loops in which a stimulus is transmitted via afferent pathways to the central nervous system wher it gets processed and integrated to generate an appropriate output signal that is sent to the periphery via efferent pathway to an effector organ
Pressor Center Response to increased pressure
In response to increased pressure the pressor center causes a decrease in sympathetic output and passive vasodilation
Rate of baroreceptor firing is greatest during (systole/diastole) and decreases during (systole/diastole)
Greatest during systole (get burst of activity) and decreases during diastole
Medulla Oblongata
contains a number of important information receiving and integrating celnters for both the cardiovascular and respiratory systems. Stimulation results in specific effects
Which baroreceptors are tonically active (what does this mean)
Carotid baroreceptors (always firing)
relationship between arterial pressure and firing frequency in carotid baroreceptors
increased pressure causes distention and increased firing freqency (decreased pressure causes decreased fring frequency )
Cerebral cortex and regulation
1.) Emotional stimuli (extreme fear, anxiety, embarassment) can alter efferent output 2.) Painful stimuli can evoke powerful sympathetic stimulation that originates in the spinal cord
what is the driving force for tissue perfusion
arterial blood pressure
increased sympathetic activity to arterioles causes
ACTIVE vasoconstriction
Cardioinhibitory center
tonically active. Controls PARASYMPATHETIC (vagal output)
CO equation
CO= HR x SV
Pressor Center
TONICALLY ACTIVE. Controls peripheral resistance by controling sympathetic output. In face of increased pressure it causes a decrease in sympathetic output and passive vasodilation
Baroreflex negative feedback system
in response to DECREASED ARTERIAL PRESSURE the reflex acts to increase sympathetic activity - increase in caradiac output and causes peripheral vasoconstriction to raise pressure. In response to INCREASED ARTERIAL PRESSURE the reflex decreases sympathetic activity and increases sympathetic activity to decrease blood pressure
Why is the baroreflex considered superior to the other mechanisms that influence blood pressure
barorelflex mechanism responds most rapidly (within 15-20 seconds) and with a greater gain that other mechanisms
what is the pimary mechanism involved in regulating moment to moment changes in arterial blood pressure
Barorelflex
which “center” is not tonically active
Depressor center
Components of the baroreflex arc
1.) Baroreceptors in the carotid sinus, aortic arch, and other large thoracic arteries 2.) Afferent pathways in cranial nerves IX and X 3.) Medullary centers 4.) Efferent autonomic (sympathetic and parasympathetic) pathways 5.) Effector organs (heart, arterioles, and venules/veins
what is “effective circulating blood volume”
pressure in the system (blood pressure) that drives perfusion to the tissues
Response of hypothalamus to decreased arterial pressure
sends inhibitory signals to the nucleus ambiguous (cardioinhibitory center) and decreases vagal output
Aortic baroreceptor afferents
carried in the aortic nerve via the vagus nerve (CN X)
cardiostimulatory center
tonically active. Controls the sympathetic output of the heart (SA and AV nodes and ventricular myocardium)
define regultaion
maintanance at a CONSTANT level - the ability of the body to keep arterial pressure constant in the face of stress (eg: changes in body position or exertion)
Example of regulation and control
under normal circumstances mean arterial pressure is REGULATED at aprox 95 mmhg through reflexes that CONTROL cardiac output and peripheral resistance
tonic component of baroreceptor firing
depending on the magnitude of mean arterial pressure (average number of spikes over time) Static component
reflex
harwired involuntary response to a stimulus
what factors does the pressor center adjust to change MAP
Adjusts Total peripheral resistance (TPR) and Venous Capacitance
Response of capacitance vessels to baroreflex
change in effective circulating blood volume
Respone of the Resistance vessels to baroreflex
change peripheral vascular resistance through control of arteriole size (vascular resistance) - primarily under sympathetic control
response of cardiostimulatory center to increased pressure
decrease sympathetic outflow leading to decreased heart rate, contractility, and conduction velocity
Depressor Center
NOT TONICALLY ACTIVE. Inhibits pressor center
what is responsible for short term blood pressure (seconds, minutes, hours)
Cardiovascular system
Role of Hypothalamus in regulation of blood pressure
1.) recieves input from low pressure baroreceptors in the right artrium and pulmonary artery. Hypothalamus sends signals to the the cardiostimulayory and cardioinhibitory centers to alter sympathetc and parasympathetic activity 2.) Thermoregulation
Baroreceptor adaptation
afferent output resets in the face of chronic change in pressure. EX: in the face of chronically elevated pressure (early stages of hypertension) the baroreceptors will have a lower sensitivity at a given blood pressure. Sensitivity curve shifts to the right so that NOW the baroreceptor is most sensitive at the NEW mean. Adaptation occurs over hours to days
Aortic baroreceptor threshold
100-110 mmhg (not as sensitive as carotid baroreceptors)
define sensitivity in terms of baroreceptors
number of impulses per mmHg
decreased sympathetic activity to arterioles causes
PASSIVE vasoconstriction
which “center” acts through parasympathetic output
cardioinhibitory center
what is responsible for long term regulation of arterial blood pressure
Kidney
Thermoregulation and arterial pressure
changes in core body temperature can alter the regional distribution of blood flow which can compromise regulation of arterial pressure
define control
change in the activity level of a given system (ex: changing cardiac output, peripheral vascular resistance)
what are the five components of the reflex arc
1.) Receptor 2.) Afferent Pathway 3.) Central integrator 4.) Efferent pathway 5.) Effector organ
Carotid Sinus barorecptors threshold
50-60 mmhg (most sensitive and effective baroreceptors)
Response of medulla to baroreflex
release of epinephrine
Where is the sensitivity of baroreceptors the greatest? What is the significance of this?
90-100 mmHg (the normal mean arterial pressure) Allows Baroreceptors to be very responsive to small changes in arterial pressure
what modulates the activity of the pressor center
Depressor center (inhibits the pressor center)
How does changing Vascular capacitance help to maintain blood pressure
constriction of smooth musle in large capacitance veins and an increase in the “effective” circulating blood volume that can help maintain blood pressure
response of cardioinhibitory center to decreased pressure
decreased pressure results in decreased vagal output and increased heart rate
response of cardiostimulatory center to decreased pressure
increase sympathetic outflow to increase heart rate, contractility and conduction velocity
which “centers” act to change peripheral resistance
1.) Pressor center 2.) Depressor center
Carotid baroreceptor afferents
carried in the carotid sinus nerve via CN IX (glossipharyngeal)
Response of the heart to baroreflex
changes in cardiac output via changes in heart rate and contractility (which influences stroke volume)
Baroreflex receptor type
stretch receptors - changes in transmural pressure elicits an action potential (stretch determines firing frequency)
components involed in maintaining short term blood pressure
Integration of: 1.) Cardiac output 2.) Peripheral vascular resistance 3.) effective circulating blood volume
Location of baroreceptors
1.) Carotid Sinus (bilaterally) 2.) Aortic arch and other large vessels of the throrax
response of cardioinhibitory center to increased pressure
increaed pressure results in increased vagal output leading to decreased heart rate, decreased afferent input
examples of effector organs in the reflex arc
Heart, vessels, respiratory muscle, kidney, GI mucosa, sweat glands
Phasic component of baroreceptor firing
reflects the rate of change of pressure (burst pattern) Dynamic component
Depressor response to increased arterial pressure
Increaed inhibition of th pressor center to cause decreased sympathetic outflow resulting in passive vasodilation
Baroreceptor sensitivity zone
50-200 mmHg
Mean Arterial pressure equation
MAP = CO X TPR
Nucleus tractus solitarius
caudal medulla that receives afferent information and relays it to the four control centers.
Afferents from baroreceptors travel where?
to the nucleus tractus solitarius of the medulla
which “centers” act to change cardiac output
1.) Cardiostimulatory center 2.) Cardioinhibitory center
