Regulation of arterial blood pressure Flashcards
diastolic pressure
lowest arterial pressure measured during a cardiac cycle and is the pressure in the arteries during ventricular relaxation when no blood is being ejected from the left ventricle
systolic pressure
highest arterial pressure measured during a cardiac cycle
it is the pressure in the arteries after blood has been ejected from the left ventricle during systole
dicrotic notch
blip in arterial pressure curve
produced when aortic valve closes
produces a brief period of retrograde flow from aorta back towards valve
briefly decreases aortic pressure below the systolic value
pulse pressure
difference between systolic and diastolic pressure
if all other factors are equal the magnitude of the pulse pressure reflects the volume of blood ejected from theft ventricle on a single beat or the stroke volume
mean arterial pressure
Pa
average pressure over a complete cardiac cycle
calculating Pa
DP + 1/3 pulse pressure
normal range of Pa
70-100 mmHg
what is blood flow through a vessel/series of vessels determined by?
pressure difference between 2 ends of the vessel
resistance of the vessel to blood flow
blood flow equation
Q= pressure difference/ resistance
total peripheral resistance
resistance of the entire systemic vasculature TPR or the systemic vascular resistance (SVR)
how can TPR be measured
by substituting cardiac output for flow and difference in pressure between the aorta and vena cava for the difference in pressure
what is blood flow to the tissues driven by
difference in pressure between arterial and venous sides of the circulation
what must mean arterial pressure be maintained at
high constant level
100mmHg
pressure in major artery to each organ
equal to Pa
because of the parallel arrangement of arteries off the aorta
how is the blood flow to each organ independently regulated
by changing the resistance of its arterioles through local control mechanism
MAP equatin
CO x SVR
Poiseuilles
R = nL/r^4 x 8/pi
R= resistance
n= viscosity
L= length
r= radius
half radius, resistance increases by 16 fold
R proportion to what
R proportional to 1/r^4
what are baroreceptors
mechanoreceptors
baroreceptors
arterial pressure cause stretch on the mechanoreceptors, changes membrane potential
sensitive to changes in pressure and rate of change of pressure
strongest stimulus that increase the rate of firing of the afferent nerves of the baroreceptors is a rapid increase in arterial pressure
carotid sinus baroreceptor
carried to brainstem on carotid sinus nerve
joins the glossopharyngeal nerve CN9
aortic arch baroreceptor
information carried to brainstem on Vagus nerve CN10
cranial nerve 9
acts on nucleus tractus solitarius
stimulare cardiac decelerator
parasympathetic
negative effect on SAN
firing decreases
heart rate decreases
cranial nerve 10
acts on nucleus tracts solitarius
inhibits cardiac accelerator and vasoconstrictor
sympathetic
positive effect on SAN and contractility in heart
positive effect on arterioles and veins
stimulus= high blood pressure
baroreceptors in carotid sinuses and aortic arch stimulated
peak impulses from baroreceptors, stimulate cardioinhibitory centre and inhibit vasomotor centre
decreased sympathetic impulses to heart causes decreased heart rate, decreased contractility and decreased CO
rate of vasomotor impulses allow vasodilation, decreased resistance
decreased CO and R return blood pressure to homeostatic range
stimulus= low blood pressure
baroreceptors in carotid sinuses and aortic arch are inhibited
impulses from baroreceptors activate cardioacceleratory centre and stimulate vasomotor centre
sympathetic impulses to heart cause increased HR, increased contractility and increased CO
vasomotor fibres stimulate vasoconstriction causing increased resistance
increased CO and R to return to homeostatic range
implications for damage to vital rogans
parallel vascular beds
sympathetic response, non uniform
F=P/R
consequences of prolonged vasoconstriction is ischaemic damage
sympathetic response non-uniform
vasoconstriction greatest in skeletal muscle
less in kidneys
least in gut
non in heart and brain
carotid sinus massage
massage of carotid sinus distends baroreceptors
increases vagal outflow to heart
slows SA firing and AV conduction
AVN conducts fewer action potentials through to the ventricles
less QRS complexes, ventricular rate slows down from dangerously high rates
examples of vagal manoeuvres
carotid sinus massage
diving reflex
valsalva manoeuvre
modified valsalva manoeuvre
valsalva manouevre
inhale deeply handheld breath
imagine chest and stomach muscles are very tight and bear down as though straining to initiate bowel movement
hold this position for short time, 10 seconds
breathe out forcibly to release the breath rapidly
resume normal breathing
how does the valsalva manoeuvre work
increased intrathoracic pressure increases blood flow from pulmonary circulation into the left atrium, increases left ventricular EDV and SV, compression of the aorta, increasing blood pressure
high intrathoracic pressure impedes venous return, decreasing SV and also blood pressure, in this period there is a baroreceptor-mediated increase in heart rate
when released, compression on the aorta is stopped and left ventricular filling pressures reduced temporarily as pulmonary vessels re-expand, blood pressure drop
VR restored, increases cardiac filling pressures and SV, increases bP, resulting in baroreceptor reflex-mediated bradycardia and subsequent fall in BP to normal levels
modified valsalva manoeuvre
SVT
S= strain, make 10cc of syringe move
V= venous return, passive leg raise
T= time, 15 seconds at each stage
renin-angiotensin 2-aldosterone system, RAAS
decrease in Pa activares RAAS
set of responses attempt to increase Pa back to normal
most important: effect of aldosterone to increase renal Na+ reabsorption
increase Na+ absorption, total body Na+ content increases, increases ECF volume and blood volume
increases in blood volume produce an increase in venous return and cardiac output produces increase in Pa
direct effect of angiotensin 2 to constrict arterioles, increasing TPR and contributing to increase in Pa
what does renin do
convert angiotensinogen to angiotensin 1
angiotensin
converted to angiotensin 2
by ACE
in lungs and kidneys
angiotensin 2
using AT1 R
causes increased vasoconstriction, increases TPR
increase thirst
increases Na+, H+ exchange, increases Na+ reabsorption, increases ECF volume
increased aldosterone, increased Na+ reabsorption, increased ECF volume
all increase Pa towards normal
angiotensin 2 other route
using ACE 2
Ang 1-7
Ang 1-7
using MasR
leads to vasodilation
regulatory mechanisms
peripheral chemoreceptors
central chemoreceptors
antidiuretic hormone
cardiopulmonary (low pressure) baroreceptors
peripheral chemoreceptors
for O2 in carotid bodies, near bifurcation of common carotid and aortic bodies
have high blood flow, chemoreceptors primarily sensitive to decrease in partial pressure of O2
chemoreceptors sensitive to increases in partial pressure CO2 and decreases in pH, particularly when simultaneously decreased
reponse of peripheral to decreased arterial P O2 greater than when P CO2 is increased or pH decreased
central chemoreceptors
Cushing reaction shows how cerebral chemoreceptors maintain cerebral flow
intracranial pressure increases there is compression of cerebral arteries, decreased perfusion of the brain
immediate PCO2 increase and pH decrease as CO2 generated from brain tissue not adequately removed by blood flow
medullary chemoreceptors respond to these changes by directing increase in sympathetic outflow to blood vessels
increase TPR and increase Pa
central chemoreceptors
Cushing reaction shows how cerebral chemoreceptors maintain cerebral flow
intracranial pressure increases there is compression of cerebral arteries, decreased perfusion of the brain
immediate PCO2 increase and pH decrease as CO2 generated from brain tissue not adequately removed by blood flow
medullary chemoreceptors respond to these changes by directing increase in sympathetic outflow to blood vessels
increase TPR and increase Pa
ADH
secreted by posterior lobe of pituitary gland
regulates body fluid osmolarity and regulation of arterial blood pressure
has 2 receptors V1 and V2
V1
in vascular smooth muscle
cause vasoconstriction of arterioles and increased TPR
V2
principal cells of renal collecting ducts
involved in water reabsorption in collecting ducts and maintenance of body fluid osmolarity
types of stimuli for ADH secretion
increases in serum osmolarity
decreases in blood volume and blood pressure
cardiopulmonary baroreceptors
located in veins, atria and pulmonary arteries
sense changes in blood volume/fullness of vascular system
located on venous side of circulation, where most of blood volume is held
increase in blood volume, resulting increase in venous and atrial pressure detected by cardiopulmonary baroreceptors
return blood volume to normal by increasing excretion of Na+ and water
response to haemorrhage the baroreceptor reflex
decreases Pa
produces decreased stretch on the baroreceptors and decreased firing rate of the carotid sinus nerve
information is received in the nucleus tracts solitaires of the medulla
produces coordinated decrease in parasympathetic activity and increase in sympathetic activity
heart rate, contractility increase causing increased CO
increased arteriole constriction producing increase in TPR
increased constriction of the vieins so decreased unstressed volume and increased venous return
response to haemorrhage renin-angiotensin 2-aldosterone
increase in angiotensin 2
increased TPR
increased aldosterone
increased Na+ reabsorption
increased blood volume
Response to haemorrhage in capillaries
decreased Pc
increased fluid absorption
increased blood volume
what is the diving reflex
when cold water stimulates the sensory receptors of the trigeminal nerve and receptors in the nasopharynx and oropharynx
results in 3 changes
1. Apnoea, whilst apnoea changing concentrations of o2 and CO2 in blood stimulate chemoreceptors, increasing vagal drive and decreasing heart rate
2. bradycardia, intense vagal inhibition decreases the slope of the pacemaker action potential and decreased oxygen consumption
3. peripheral vasoconstriction in splanchnic, renal and skeletal muscle vascular bed the strong sympathetically mediated vasoconstriction increases TPR allowing blood pressure to be maintained despite profound bradycardia
decrease in MAP/Pa causes what
decrease in renal perfusion pressure
causes release of renin from JG cells into plasma
what does renin catalyse
conversion of plasma angiotensinogen to angiotensin 1
angiotensin 1 conversion
in the lungs and the kidneys by ACE into angiotensin 2
what is angiotensin 2
agonist at AT 1 receptors
a GPCR
angiotensin 2 presence on tissues
arterioles, causes vasoconstriction
adrenal cortex, induces release of aldosterone
proximal convoluted tubules, stimulates increased Na+/H+ exchange increasing reabsorption of Na+
aldosterone on DCT
increases expression of ENaCs on apical membrane and sodium pump on basolateral membrane
CNS:Ang2 stimulates
hypothalamus to increase thirst and water intake
pituitary gland to release ADH which reduces water loss by up regulating aquaporins in th CD of the kidney
blood pressure increases because of what
increased TPR
increased sodium reabsorption to increased ECF volume to increased BP
increased water retention to increased body fluid
