feedback control with cardiovascular system Flashcards
what is blood pressure?
outward pressure exerted by blood on blood vessel walls
what is systolic blood pressure?
-pressure exerted by blood on the walls of the aorta and systemic arteries when the heart CONTRACTS
-normal 120 mmHg (resting)
what is diastolic blood pressure?
pressure exerted by blood on the walls of the aorta and systemic arteries when the heart RELAXES
-normal 80 mmHg (resting)
what is normal systolic range?
90-120 mmHg
what is normal diastolic range
60-80 mmHg
what is hypertension (what are the numerical values)?
-high blood pressure
-clinical bp 140/90 mmHg
-day time average 135/85 mmHg or higher
what is pulse pressure?
different between systolic and diastolic blood pressures
-normal range 30-50 mmHg
what is mean arterial blood pressure?
average arterial blood pressure during a single cardiac cycle (contraction/relaxation)
what occurs during a normal cardiac cycle?
diastolic period is twice as long as the systolic period
how is MAP calculated?
-MAP = [(2 x Diastolic) + Systolic] / 3 OR
MAP = Diastolic + (pulse pressure/3)
what is the normal range of MAP?
70-105 mmHg
what is the least amount of MAP needed and why?
-at least 60 mmHg
-needed to perfuse vital organs (brain/heart/kidney)
why can the MAP not be too high?
-damages blood vessels (brain/kidney/eyes)
-extra strain on the heart
what is hypotension?
-low blood pressure
-bp less than 90/60 mmHg
what kind of mechanism does the CV system use?
negative feedback mechanism
what are the sensors of the CV system
baroreceptors
what are baroreceptors sensitive to?
pressure/stretch
what do baroreceptors do?
when they detect stretch/pressure they send an impulse to the control centre (medulla)
what happens when firing rate of baroreceptors increases?
-MAP increases
what do baroreceptors regulate?
MAP
what is the control centre of the CV system?
the medulla
what does the medulla do?
receives afferent signals and sends instructions to the effectors (heart and blood vessels)
what are the 2 types of baroreceptors?
-aortic baroreceptors
-carotid baroreceptors
what is the nucleus tracts solitaries (NTS)?
1st synapse site for all CV system afferents in the medulla
what are the effectors of the CV system?
-heart
-blood vessels
do baroreceptors respond to acute or chronic changes
-ONLY acute
-firing rate will decrease if high blood pressure is sustained
what varies in the heart as an effector?
-heart rate
-stroke volume
what varies in the blood vessels as an effector?
systemic vascular resistance
how CAN MAP be calculated in relation to negative feedback?
MAP = Cardiac Output (CO) x Systemic Vascular Resistance (SVR)
how is cardiac output (CO) calculated?
CO = Stroke Volume (SV) x Heart Rate (HR)
what is cardiac output (CO)?
volume of blood pumped by each ventricle of the heart per minute
what is stroke volume?
volume of blood pumped by each ventricle of the heart per heartbeat
what is systemic vascular resistance?
the sum of all resistance in the systemic circulation (everything BUT lungs)
how ELSE CAN MAP be calculated in relation to negative feedback? (3 factors)
MAP = SV x HR x SVR
how can MAP be regulated?
increasing/decreasing:
-heart rate
-stroke volume
-systemic vascular resistance
what is autorhythmicity?
hearts capability to beat rhythmically without external stimuli
what is the heart modified by?
Autonomic (”involuntary”) Nervous system (ANS)
what is the sympathetic division?
-simulation of the vagus nerve accelerates heart rate (tachycardia)
-Noradrenaline acts on B1 receptors
what is the parasympathetic division?
-simulation of the vagus nerve slows the heart rate (bradycardia)
-Acetylcholine acts on muscarinic M2 receptors
how is stroke volume regulated?
-sympathetic nerves
-stimulation increases force of contraction
how is heart rate increases
-sympathetic stimulation
- noradrenaline acts on β1 receptors
how is the systemic vascular resistance regulated?
vascular smooth muscles - sympathetic nerve fibres
what are the main resistance vessels
arterioles
what happens when there is a contraction of vascular smooth muscles?
-vasoconstriction
-increases SVR and MAP
what happens when there is a relaxation of vascular smooth muscles?
-vasodilation
-decreases SVR and MAP
what happens when there’s an increase in BP
-barorecptors discharge increases
-send impulse to medulla
-decrease in sympathetic activity
-increase in vagal (parasympathetic) activity
→decreases HR
→decreases SV (ventilation)
(both cause decrease in CO)
-decrease in sympathetic constrictor tone
→vasodilation
→decreases SVR This brings blood pressure back to normal (decreases BP)
what happens when there’s a decrease in BP
-barorecptors discharge is low
-send impulse to medulla
-increase in sympathetic activity
-decrease in vagal (parasympathetic) activity
→increase HR
→increases SV (venoconstriction)(both cause increase in CO)
-increase in sympathetic constrictor tone
→vasoconstriction
→increases SVR
This brings blood pressure back to normal (increases BP)
what is vasomotor tone?
tonic discharge of sympathetic nerves
why are vascular smooth muscles partially constricted at rest?
continuous release of noradrenaline → because of tonic discharge
what happens if there an increase in sympathetic discharge?
increase the vasomotor tone→ vasoconstriction
what happens if there an decrease in sympathetic discharge?
decrease the vasomotor tone→ vasodilation
is there any significant parasympathetic innervation of arterial smooth muscles?
no, except in penis and clitoris
arterial and arteriolar smooth muscles are mainly supplied by….
sympathetic nerves
