S2W4 L1- Circulatory Physiology- Regulation of MAP- Al Benson Flashcards
Mean arterial pressure
CO x total peripheral resistance
two factors that increase CO
increased SV
increased HR
two factors which increase HR
decreased parasymp impulses
increased symp impulses and adrenal medulla hormones
two factors which increase SV
increased symp impulses and adrenal medulla hormones
increased venous return
4 factors which increase venous return
increase blood vol
skeletal muscle pump
resp pump
vasoconstriction
3 factors which increase systemic vascular resistance
increased blood viscosity
increased total blood vessel length
decreased blood vessel radius
a factor which increases total blood vessel length
increased body size- obesity
a factor which increases blood viscosity
polycythaemia- increased number of rbc
where is the CV centre located
medulla oblongata
what are the CV centre inputs
higher brain centres
( cerebral cortex, limbic system, hypothalamus)
proprioceptors
baroreceptors
chemoreceptors
what are the CV centre outputs
vagus nerve -> heart
cardiac accelerator nerve->
heart
vasomotor nerves -> blood vessels
effect of increased frequency of impulses from vagus nerve to heart
decreased HR
effect of increased frequency of impulses from cardiac accelerator nerve to heart
increase HR and contractility
effect of increased frequency of impulses from vasomotor nerve to blood vessels
vasoconstriction
how are baroreceptors excited
increased atrial pressure, increased distending pressure on atrial wall, increased stretch
where are baroreceptors located
adeventitial layer of arterial walls in carotid sinus and aortic arch
what afferent projections do barorrecptors have and where to
IX and X cranial nerves projections to CV centre
what is the response when baroreceptors are activated
increase in MAP, increase parasymp stim of afferent, decrease symp stim of afferent, decrease SA node rate of firing, decrease ventricular myocardial contraction
what is baroreflex an example of
negative homeostasis feedback loop
respone of orthostasis
decrease MAP, decrease baroreceptor stim,
CV centre decreases vagal outflow to heart and increases symp outflow in cardiac and vasomotor nerves
what is cerebral perfusion
delivery of blood to neural tissue in brain
first response of orthostasis
MAP decreases. baroreceptor stimulation decreases
why does baroreceptor stimulation decrease during orthostasis
decreased pulse pressure and decreased carotid sinus pressure (gravity)
what is the response of the CV centre when orthostasis causes decreases baroreceptor stimulation
decreases vagal outflow to heart and increases sympathetic outflow in cardiac and vasomotor nerves
what is the result of the CV centre responses to orthostasis
increase in HR, increase cardiac contractility, limiting fall in cardiac output by 20%, TPR increases by 30-40%, overall MAP increases 10-15mmHg above supine level
what is responsible for the long term regulation of MAP
cardiopulmonary stretch receptors and hormonal influences
two types of cardiopulmonary stretch receptors
atrial and pulmonary stretch receptors
difference between atrial baroreceptors and cardiopulmonary stretch receptors
cardiopulmonary receptors respond to lower pressures
primary role of cardiopulmonary stretch receptors
regulate blood volume
when stimulation of cardiopulmonary stretch receptors is decreased, what is initiated
reflex release of antidiuretic hormone (e.g ADH & vasopressin) from hypothalamus
two ways which ADH increase blood volume
increases reabsorption of fluid from renal tubules
reduces rate of glomerular filtration by constricting afferent renal arteries
another effect of ADH
vasoconstrictor effect particularly in splanchnic circulation increasing TPR
where are chemoreceptors located
carotid aortic bodies
3 things that stimulate chemoreceptors
hypoxia
hypercaprea
acidosis
what does stimualtion of chemoreceptos lead to
sympathetically mediated peripheral vasoconstriction
overall effect of chemorecpetors
increase CO2
increase TPR
increase MAP
what is the most important long term determinant of BP
blood volume
what cells in the kidney detect low blood volume or low renal blood flow
juxtaglomerular cells
what is released when juxtoglomerular cells detect low BV and low renal blood flow
renin enzyme
action of renin enzyme
angiotensinogen-> angiotensin I
three actions of angiotensin II
increase thirst
vasoconstriction
adrenal gland releases abosterone
action of abosterone on kidney
salt/ water retention
causes BP to rise
what NS is the adrenal medulla an extension of
the sympathetic NS
when is adrenaline and noradrenaline released
in response to stimulation of sympathetic preganglionic fibres
effects of adrenaline
increase CO mediated by B adrenoceptors causing increase in MAP
effect of noradrenaline
vasoconstriction via alpha receptors, increased total peripheral resistance
Atrial Natiueretic Peptide (ANP) action
vasodilation
promotes Na+ excretion in kidneys
reduces MAP
NO action
causes local vasodilation
