L10 Flashcards
how is arterial pressure controlled
homeostatically
what is arterial pressure precisely regulated at
90mmHg
why do we need perfusion pressure
to overcome the resistance of arterioles
what does perfusion pressure enable
precise control of regional blood flow by manipulating only the regional resistance.
how is arterial blood pressure regulated
through a negative feedback loop
where are the sensors that detect blood pressure located
baroreceptors in the aortic arch and carotid sinus
how do baroreceptors work
they are collections of cells that detect stretch in the arterial walls.
an increases in stretch = an increase in pressure which causes an increase in the action potentials that those cells
fire.
this is the opposite for when there is a decrease in stretch therefore baroreceptors are tonically active
what is the afferent pathway for aortic baroreceptors
Aortic baroreceptors –>aortic nerve –> vagus (cranial nerve X)
what is the afferent pathway for carotid baroreceptors
Carotid baroreceptors – carotid sinus nerve – glossopharyngeal nerve
do the nerves associated with baroreceptors fire with systole and diastole
yes
each cardiac cycle distends the arterial wall therefore when you look at when the baroreceptors fire peak to peak = 1 cardiac cycle
what is blood pressure regulation important for
this is important for regulation short term changes in BP eg sitting to standing
what are bidirectional changes
long term
when nerve activity either increases or decreases because of changes in MABP
small change = small response
large change = large response
what is the integrator in the blood pressure regulation system
nucleus tracts solitarius (NTS) in the medulla
who does the NTS work
it receives afferent information from the B receptors
the NTS then takes this info, processes it and sends efferent signals to the heart and periphery to do things so that we can get BP back to normal
This involves pre and postganglionic nerves and both the sympathetic and parasympathetic NS
P = heart S= heart and vasculature
what is the baroreflex action in para and sympathetic NS
increase in pressure = increase in firing. the reflex via cardiovascular centre in the medulla causes an increase in parasympathetic outflow to the heart and a decrease in sympathetic outflow to the heart arterioles and veins
this leads to decreased contractility and vasodilation
opposite for decrease
what is an example of a hemostatic challenge
a haemorrhage
this is an escape of blood from a ruptured vessel
what are the 3 stages of restoration when you have a haemorrhage
baroreflex
cardiovascular volume restoration
total body volume restoration
when do the 3 stages of restoration occur after a haemorrhage
baroreflex = immediate
cardiovascular volume restoration = immediate
total body volume restoration = long term
what is the baroreflex (what happens in heart, veins and arterioles)
the baroreflex is rapid changes in para/simpathetic outflow to restore MABP towards the heart
the effect on the heart is increased HR and SV which leads to increases CO –> MABP
veins = venoconstriction, increases VR and EDV. this leads to in increases in CO –> increased MABP
arterioles = vasoconstriction –> increases TPR –> increases MABP
why do we have cardiovascular volume restoration
it takes 4 -8 weeks to fully replace RBC lost in a haemorrhage but we need to restore the volume
we do this via absorption of fluid from interstitial fluid
by capillaries to increase blood volume.
this happens because vasoconstriction causes decreases hydrostatic pressure which is the main driving force for fluid out of the cell
Reduced amount out and increased amount in
This is tissue specific. Most of the reabsorption in the skin and the gut as they have more a1 adrenergic receptors
how long does it take to restore blood volume after a haemorrhage
a few minutes only from redistribution of extracellular fluid
what is another name for total body volume restoration
Renin Angiotensin Aldosterone System
describe what happens in total body volume restoration
Reduced perfusion pressure (from a haemorrhage) stimulates the production of renin in the kidneys
The liver produces angiotensinogen
renin converts angiotensinogen to angiotensin 1 which is converted to angiotensin 2 which acts of the cardiovascular system to vasoconstrict
A2 also acts on the adrenal cortex to produce aldosterone which stimulates water and Na uptake in the kidney
what is the overall effect of total body volume restoration
it stimulates Na and H2O reabsorption in the kidney which decreases urine output and therefore increases total body H2O
