Blood Flow and Pressure Flashcards
blood flow definition and equation
volume of blood that passes by a given point in a given unit of time
flow = ∆pressure/ resistance
what and why is the pressure difference between different venous systems
pressure highest in left ventricle, aorta and large arteries during systole lowest in right atrium
difference in pressure is important for maintaining blood flow
most blood is in veins during circulation
why is venous pressure low
the vessels are able to expand and compress in reaction to changes in blood flow
equation linking resistance, radius, length and viscosity of vessel
Resistance = 8lengthviscosity/pi*radius^4
explain laminar flow
blood travelling close to the vessel wall travels slower than blood in middle of vessel due to resistance at the edge of vessel. wider the vessel the less resistance and more conductance
Explain turbulent blood flow
up to a certain point as pressure increases flow increases linerally (laminar flow). after this point the rate of increase slows this is turbulent flow.
equation and meaning of reynold’s number (Re)
Re = vessel diameteraverage velocityblood density/blood viscosity
at Re>2000 vessel has turbulent flow
turbulent flow can increase risk of thrombosis
what is blood pressure
what does its nomenclature mean
equation for mean arterial blood pressure
the force exerted against vessel walls by blood
top number = systolic pressure
bottom number = diastolic pressure
both measured in mmHg
mean arterial blood pressure = diastolic pressure + (1/3 * difference between systolic and diastolic)
how does aorta maintain constant flow
aorta swells up and expands during ventricle systole to hold extra blood and during ventricle diastole the aorta contract to push out the extra blood to maintain a constant flow
Equations relating blood pressure, cardiac ouput and heart rate
blood pressure = cardiac output* total preipheral resistance
cardiac output = heart rate* stroke volume
TPR = resistance of systemic blood vessels
what happens when you stand up too quickly
significant amount of blood falls to your feet due to gravity resulting in decrease blood volume in upper body which can lead to further harmful effects
what are and where are they baroreceptors
specialised nerve endings with high expression in walls of aortic arch and right atrium both located on the vagus nerve and where the carotid sinus splits into internal and external carotid arteries.
what are mechanoreceptors
specialised sensory endings on the glossopharengeal nerves which detect stretching of the vessel wall to detect BP
what is a baroreflex
blood pressure directly correlates to frequency that baroreceptors fire action potentials
where do the impulses from baroreceptors go
go to various places in the brains then down the spinal chord to regulate vasoconstriction and to neurons of sympathetic nervous system to control kidneys and heart
what will change of blood pressure do and why
decrease in BP increases renal sympathetic activity and increases heart rate as heart rate is related to cardiac ouput and affects cardiac pressure. same goes in reverse
sympathetic and parasympathetic response
in low BP parasympathetic is inhibited in brainstem and sympathetic system fibres are activated in spinal chord this increases heart rate
arteries and arterioles vasoconstrict due to sympathetic by making adrenal medulla release adrenaline and noradrenaline as well as affecting smooth muscles to increase TPR which increases HR
role of renal sympathetic nerves
in glomerulus specialised cells called juxtaglomerular surround afferent arteriole and distal convoluted tubule are able to produce and release hormone renin
Renin-angiotensin-aldesterone system (RAAS)
macula densa cells sense low sodium or blood levels and cause juxtaglomerular cells to secrete renin
renin then binds to its active site, angiotensinogen which is continuously produced by the liver
this forms angiotensin 1 which is converted to its active form angiotensin 2 by ACE
angiotensin 2 has many function including promoting release of adesterone from adrenal gland
how does angiotensin 2 increase blood pressure
vascular walls have angiotensin 1 receptors and when angiotensin 2 binds to it, it vasoconstricts the vessel to increase TPR and blood pressure
how does angiotensin 2 increase thirst
it binds to angiotensin 1 recptors in the hypothalamus and vasopressin is secreted which acts as a neurotransmitter to increase thirst
this leads to increased blood and stoke volume
how and where does aldesterone maintain blood volume
works on collecting duct and distal convoluted tubules
it increases expression of epithelial Na+ channels which causes the influx of Na+ ions out of filtered fluid and into the cell
this creates an electochemical gradient and with anti-diuretic hormone increasing aqauporin expression this means more water can be absorbed to control blood content
how does Na+ reabsorption relate to cardiac output to affect blood pressure
aldesterone increases end diastolic volume which increases stroke volume then…
CO = HRSV so cardiac ouput increases and…
BP = COTRP so blood pressure increases
local regulation of blood pressure and flow
blood passing through vessels causes stress on walls which causes influx of Ca2+ into endothelial cells
this results in nitrous oxide diffusing into neighbouring smoot muscle cells
this activates K+ channels leading to K+ efflux and hyperpolarisation of cell membrane
it also closes Ca2+ channels which stops Ca2+ influx which vasodilates blood vessels which reduces blood pressure
treatment of hypertension
renin inhibitors, ACE inhibitors, angiotensin 2 receptor antagonists and mineralocorticoid receptor antagonists
side effect may include hyperkalaemia
treatment of hypertension in black patients
black patients are more sensitive to salt and so is a more likely cause of hypertension
black people also have lower levels of renin so renin antagnoists (and further antagnoists for its products) will be less affective
