Control of blood pressure Flashcards
define blood pressure
force exerted by blood against a vessel wall
what can BP be influenced by?
physiological factors; physical factors
what are the physiological factors that influence BP?
Heart rate (HR) Stroke volume (SV) Cardiac output = HR x SV Peripheral resistance (i.e. vascular tone)
what are the physical characteristics that influence BP?
Blood volume Elastic characteristics (i.e. distensibility)
types of cardio control?
neural and hormonal (humoral)
what parts of the brain influence neural control?
cortex, responsible for CV function during times of emotional stress; hypothal, modulation neuronal activity; medulla, contains afferent fibres baroreceptors, chemoreceptors and stretch receptors;
what cell bodies does the medulla contain how are they active?
Medulla contains cell bodies for the sympathetic,
parasympathetic (vagal) and efferent nerves
These cell bodies within the medulla, where parasympathetic (vagal) fibers originate, are tonically active even under resting conditions, resulting in a resting heart rate lower than the intrinsic firing rate of the sinoatrial pacemaker
how does the parasym NS modulate the CV?
ACh released from postgang fibres which produces negative chronotropy (HR), dromotropy (conduction velocity), and inotropy (contractility); The negative inotropic effects by parasympathetic is more evident in the atria than in the ventricles
Effects of sympathetic innervation on cardiovascular function
NEpi produces tachycardia and vasoconstriction; not a big influence on HR; removal of symp innervation causes vasodilation and hypotension; Sympathetic activation increases chronotropy, dromotropy, and inotropy in the heart which are mediated by the norepinephrine release
what are the sensors for blood pressure?
baroreceptors, (stretch receptors?)
where are baroreceptors located?
They are located in the carotid sinus (at the bifurcation of the external and internal carotid arteries) and in the aortic arch
baroreceptors are always firing; but when the vessel walls stretches they fire more
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Firing of baroreceptors cause the inhibitory effect on sympathetic system and excitatory effect on parasympathetic (increase in ACh), thereby resulting in decrease in blood pressure & heart rate
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what are the major humoral factors of CV modulation?
catecholamines (NE and E); Renin-Angiotensin-Aldosterone system; atrial natriuretic peptide; vasopressin (aka ADH)
where are teh catcholamines released from?
adrenal medulla
how much NE and E are released?
80% E, 20% NE when stimulation by the sympathetic NS
how do catechols. influence blood pressure
direct stimulation of myocytes in ventricles (increase force of contraction via β1-receptor)
increases HR (both automaticity and conduction velocity) mediated by β1-receptor
vasoconstriction in resistance vessels and veins (α-receptor)
Both the β-receptors and α-receptors are adrenergic receptors (adrenoceptors)
review slide 14 of nov 28
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what are the components of blood pressure?
systolic pressure; diastolic pressure; pulsatile pressure; mean arterial pressure
what is systolic pressure?
upper limit of the periodic oscillations of the BP causes by ventricular systole; usually 120 mmHg
what is diastolic pressure?
min pressure within the
arteries during ventricular diastole; around 80 mmHg
what is pulsatile pressure?
difference between SP and DP: PP = SP -DP
what is mean arterial pressure?
It is the average pressure in the arteries
over time
Can be approximated by the following formula:
mAP = DP + 1/3 PP
= DP + 1/3 (SP - DP)
Or, = 1/3 SP + 2/3 DP
HOWEVER, this equation cannot be used for people who suffer from tachycardia
