Blood Pressure regulation Flashcards
what is BP
the force exterted on the vessel walls as blood flows through
why do we need to maintain pressure
a minimum pressure (capillary hydrostatic pressure) is required to exhange substances across capillary networks
what are the 2 key determinants of BP?
BP = Caridac output x Total peripheral Resistance
what is the total peripheral resistance dependent on
arteriolar radius
cuz flow proportinal to r^4
what is autoregulation
regulating blood flow on a local level
for low levels of activity
what mechanisms need to be activated when doing vigorous exercise
central mechanisms that are under neural and endocrine control
when BP becomes low, what might be some chemical changes that take place?
decreased O2 (any availble o2 is used up)
increased metabolites
increased CO2
increased lactate
signals that there’s not enough local BF or BP and demands arent being met
Autoregulation of Blood flow: how is the disturbance in homeostasis counteracted
autoregulation
causes a local decrease in resistance
by relaxing precapillary sphincters (which is signalled by the inc in metabolites)
thus inc in BF
returns to homeostasis
see onenote
how does the sympathetic nervous system allow blood pressure to be increased (? in terms of cardiac output and total periph resis)
increases heart rate and strok volume
= increases cardiac output
increases vasoconstriction
= increases total periph resis
what occurs if autoregulation is insuffiecient and cant restore homeostasis
detected by baroreceptors and chemoreceptors
cardiovascular centres in the CNS (ie the medulla oblangata) are activated
short term and immediate increase in BP via activation of SNS
which increases CO and vasocontriction
see onenote for more detailed diagram
where are the baroreceptors located
aortic sinus (primarily detects changes in systemic circulation)
and
carotid sinus (primarliy detects changes in cerebral circulation)
what happens to baroreceptors when BP falls?
they’re inhibited
what are the 3 things that happens when baroreceptors are inhibited
-cardioaccelertory centre is activated
-cardioinhibitory centre is inhibited
= these lead to inc in HR and CO, by increasing the contractility
(so sympathetic is activated and parasymp is inhibited)
vasomotor centre is activated
= inc in vasoconstriction
all of this happens vice versa when BP rises
what hormone enhances the baroreceptor response
adrenaline and noradrenaline being released from the adrenal glands
where are the chemoreceptors located
in carotid bodies (detect changes in the blood)
in medulla oblangata (detects changes in the CSF)
what changes does the chemoreceptors in the carotid bodies detect when BP is low?
fall in pH
fall in O2
rise in CO2
what are the effects when carotid chemoreceptors detect these changes
the same effects caused whne barorecpetors are inhibted
what changes does the chemoreceptors in the medulla detects when BP is low?
rise in CO2 only (cuz O2 can’t acc cross the blood-brain barrier)
what are the effects when medulla chemoreceptors detect these changes
primary job is to activate the respiratory centre
to inc respiratory rate
also
vasodilation of cerebral vessels
inc blood flow to brain
basically makes sure the cardiovascular and respiratory resposnes are coordinated
when homeostasis still can’t be restored after this, then what happens
endocrine resposnse is stimulated
leading to long term events
via increasing blood volume and vasoconstriction
What is the RAAS
Renin Angiotensin Aldosterone System
what type of cells in the kidney detect a change in the BP
juxtaglomerular cells
what enzyme does the kindey secrete when it detects fall in BP?
Renin
what does renin do
converts angiotensinogen (a plasma protein produced by liver) into angiotensin 1 (which is actually inactive)
what enzyme is needed to activate angiotensin 1 and where is it produced
angiotensin converting enzyme
produced by cells in the lungs
converts angiotensin 1 to angiotensin 2
what does angiotensis 2 do
causes vasoconstriction - inc peripheral resistance
also stimulates the adrenal cells
to inc the steroid hormone aldosterone
what is aldosterone and what does it do
steroid hormone
acts on kidneys to inc amount of Na+ reabsorption
via activating Na K channels
when more Na reabsorbed, water is also reabsorbed
increases the blood volume
how is ADH involved in long term regulation of blood flow
anti-diuretic hormone (aka vasopressin)
released from pituitary
detects when blood vol low=
involved in vasoconstriction
also increases fluid retention
and inc the amount of water in the blood
stimulates thirst to increase blood volume further
how is erythropoeitin (Epo) involved in long term regulation of blood flow
detects fall in BP or O2
also is a vasoconstrictor
mainly stimulates production of RBC
thus increases blood vol
what in the heart can detect rise in BP
cardiac muscle cells in right atrium and ventricl
what is released when high BP is detected by the heart
natriuretic peptides
ANP - atrial natriuretic peptides (secreted by atria)
BMP - brain natriuretic peptide (secreted by ventricles jus has a stupid name)
but ANP is the main one
how does ANP affect the kidney
causes an increased Na+ loss
so increased water loss in urine - pee more
reduced thirst
decreased blood vol
(basically opposite to aldosterone)
how else does ANP lead to decrease in BP?
inhibts all those vasocondtricting hormones
e.g. ADH, aldosterone, NA and adrenaline
leading to peripheral vasodilation
and drop in BP
which 3 circulations need special consideration for local flow?
pulmonary
coronary
cerebral
how does the pulmonary circ differ in its blood flow regulation?
when O2 drops
instead of vasodilation to inc blood flow
arterioles will constrict in regions of low O2 to ‘shunt’ blood flow to the O2 rich areas
how does the cerebral circ differ in its blood flow regulation?
blood flow to brain must always be maintained (neurons are stupid and die vry quick if theres no blood supply)
so when there’s peripheral vasoconstriction, there will be vasodialtion of cerebral vessels to maintain its blood flow
how does the coronary circ differ in its blood flow regulation?
sympathetic activity doesnt lead to vasoconstriction like usual
there are special beta receptors which mean sympathetic stimulation causes vasodilation
so coronary blood flow is maintained
