Regulation of blood pressure Flashcards
cardiac output?
blood flow in volume/time
CO = (equation)
heart rate (bpm) X stroke volume (volume of blood per beat)
systole?
contraction
diastole?
relaxation
end systolic volume? (ESV)
volume of ventricle at end of contraction
end diastolic volume (EDV)?
volume of ventricle just before contraction (i.e. end of filling)
stoke volume = (equation)
EDV - ESV
mean blood pressure is controlled by?
controlled by changing total peripheral resistance and or cardiac output
cardiac output is controlled by?
by sympathetic and para sympathetic nerves which effect heart rate and force of contraction
TPR controlled by?
by nervous and chemical means to effect constriction/dilation of arterioles and venules due to elasticity
TPR?
total peripheral resistance
P = (blood pressure equation)
= CO x TPR
cardiac output X total peripheral resistance
arterial blood pressure measured in?
in mm Hg
Systolic blood pressure (SBP)
maximum arterial blood pressure during heart contraction (i.e. systole)
Average 90-120 mm Hg in humans
Diastolic blood pressure (DBP)?
minimum arterial blood pressure during heart relaxation (i.e. diastole)
Average 60-80 mm Hg in humans
mean arterial pressure?
the mean pressure over the entire cardiac cycle
it usually is not equal to the mean of the SBP and DBP as the systolic and diastolic phases of the cardiac cycle are not the same duration
Average: 95mm Hg in humans
the vessels of small mammals are very small so…
so they have high resistances
As a result, their heart rates are much higher than large mammals (hamster HR = 400 beats/min, whale = 20)
the smaller the animal … the larger the animal…
smaller = higher HR
larger = lower HR
why is it important to maintain blood pressure within a range?
ensure adequate perfusion of vital organs
why is the process of balancing blood pressure required?
daily activities, physiological situations, food - they all cause changes in the body
what types of regulation is there for blood pressure?
short term regulation
long term regulation
baroreceptors?
found in arterial wall increase their AP firing rate in response to increased stretch (as by increased pressure)
thus a decrease in pressure actually decreases baroreceptor firing, which in turn increases contraction force
the most important baroreceptors are found where?
in the carotid artery (in the carotid bodies) and the aortic arch (in the aortic bodies)
the net results of baroreceptors is?
response to mechanical stress
net result is vasodilation, decrease HR, decrease contractility etc. all of which tend to restore arterial pressure to normal
carotid sinus baroreceptors detect?
detect changes in pressure to the brain
aortic arch baroreceptor detect?
detect changes in pressure to the body
what are the sensors if the blood pressure falls?
aortic arch and carotid sinus due to baroreceptors present here
effectors of baroreceptor reflex?
constriction of veins and arterioles
increased stroke volume
increased heart rate
THEREFORE
increased peripheral resistance and cardiac output and thus increased blood pressure
neural integration of baroreceptor reflex?
nucleus tractus solitarius
vasoconstriction, cardiac stimulation, cardiac inhibition
postral hypertension?
sitting down too long and stand up and feel dizzy
so when sitting - blood circulating in body is the same as when standing up however when sitting down for prolonged amounts of time, the venous return (how much blood goes back into heart) is quicker when sitting
Stand up to quickly - so venous return decreases therefore cardiac output decreases as does blood flow and blood pressure so baroreceptors react - feel dizzy
what is nucleus tractus solitarius?
relay centre in brain and receives information to do with heart
what are peripheral chemoreceptors?
(found in carotid and aortic bodies) and central chemoreceptors (in medulla oblongata) are stimulated by low arterial 02, high arterial co2 and low arterial pH
activation of chemoreceptors produces?
peripheral vasoconstriction
increased lung ventilation (except when under water)
in some cases, decreased HR
coronary artery baroreceptors respond to?
to arterial pressure but more sensitive than carotid and aortic ones
veno-atrial mechanoreceptors?
respond to changes in central blood volume
- lie down, lift your legs and cause peripheral vasodilation
unmyelinated mechanoreceptors?
respond to distension of heart
ventricular ones during systole; atrial ones during inspiration
apart from chemo and baro - what are the other stretch receptors?
coronary artery baroreceptors
veno-atrial mechanoreceptors
unmyelinated mechanoreceptors
if decline in blood pressure last more than a few mins - what gets involved and why?
THE KIDNEY
rechannelling of blood occurs to vital organs and kidneys give up blood supply for other organs
When this takes longer than expected, the drop in pressure is sensed by specialised cells in the kidneys
Activation of the RAAS occurs
decrease in perfusion is sensed by?
JGA in the macula densa (modified cells in glomerular capillary)
AIMED AT INCREASING BP
renin is?
it is released by JG cells
it is Renin cleaves Angiotensinogen - Angiotensin I
AIMED AT INCREASING BP
what does ACE do?
converts angiotensin I to angiotensin II by angiotensin converting enzyme in the lungs
AIMED AT INCREASING BP
angiotensin II is a major vasoactive product and what does it result in?
causes vasoconstriction
stimulates release of aldosterone from adrenal gland
Stimulate release of ADH pituitary gland
AIMED AT INCREASING BP
Clinical value of knowing RAAS system?
ACE inhibitors - managing hypertension
feline hypertension very common
