factors affecting blood flow Flashcards
what do beta 2 agonists do?
induce bronchodilation by binding to beta 2 receptors in the lungs, activating adenyl cyclase to relax bronchial smooth muscle
what condition is characterised by narrowing/blockage of arteries, leading to reduced blood and oxygen flow to specific part of the body which is then damaged?
critical limb ischaemia
what condition is characterised by the interruption or blockage of heart blood supply by a build up of fatty substances in coronary arteries?
coronary artery disease
what factors affect blood flow?
. length of tube
. viscosity of liquid flowing through tube
. pressure gradient across length of tube
. cross sectional area of tube
where is blood at its highest pressure?
leaving heart
what may increase blood viscosity?
dehydration
state the poiseuille equation
Q = delta P x pi x radius^4 / 8 x n x l
what is ‘Q’ equal to in poiseuille’s equation?
volumetric flow rate
what is ‘delta P’ equal to in poiseuille’s equation?
pressure change/difference
what is ‘l’ equal to in poiseuille’s equation?
length of tube
what is ‘n’ equal to in poiseuille’s equation?
viscosity
what are the assumptions associated with poiseuille’s equation?
. blood flow is laminar
. flow is non-pulsative
. flow is through a uniform straight pipe
what may cause deep vein thrombosis?
immobility, dehydration
how may you reduce the risk of deep vein thrombosis?
moving, staying hydrated, wearing compression socks
what is flow determined by?
. pressure gradient
. resistance
. branching
what happens to blood flow and resistance as branching increases down arterial tree (arteries - arterioles - capillaries)
resistance increases and blood flow is reduced
what is the function of slowed blood flow in capillaries?
allows more time for substance exchange
in what areas is blood flow slowest?
areas with largest cross-section
which areas have the largest cross-section?
capillaries
blood flows from high pressure to low pressure, which vessels are carry blood at high pressure and which carry blood at low pressure?
artery - high
veins - low
what happens to blood flow as blood exits capillaries into veins?
increases
do veins have a small or large pressure gradient?
small
what percentage of blood do veins hold at any one time?
70%
which structure promotes venous return?
skeletal muscle pump
which process aids venous return?
respiratory movement
which hormone produced by sympathetic nerves constricts veins, increasing venous return to the heart?
noradrenaline
what effect does noradrenaline opreoduced by sympathetic nerves have on the blood low to the heart?
increases
what is the term for venous return to the right ventricle?
preload
what are the effects of an increased preload?
heart has to work harder to pump blood out
what 2 conditions may increased preload cause?
heart failure, coronary artery disease
what class of drugs can be used to decrease preload
nitrates
what effect do nitrates have on vessels?
vasodilation
what effect does nitrates have on venous pressure?
decreased
what effect do nitrates have on cardiac output?
decreased
changes in oxygen/CO2/celluar metabolites can dilate arterioles, increasing organ blood flow, what is this known as?
active hyperaemia
what does blocking blood flow induce?
reactive hyperaemia
what is the name of the biological process which maintains blood flow?
flow autoregulation
