Vasculature Physiology Flashcards
When is turbulent flow likely to occur?
rate of flow becomes too great, makes a sharp turn, incurs obstruction, abnormal vessel walls, low viscocity and large diameter vessles
formation of what adds overall friction to turbulent flow?
eddy currents
what is the purpose of reynolds number?
indicates whether flow is likely to be laminar or turbulent
how is reynolds number calculated what is the significance of the critical value?
(velocity of flow x radius of vessel)/viscocity
above the critical value turbulence is likely
at what number will turbulence occur in branching but not smooth parts of a vessel?
200-400
at what number will turbulence definitely occur?
2000
what is a thixotropic fluid?
flow of fluid affects the viscocity of fluid
what causes the sounds heard in BP measurements?
the jetting of blood though a partially occluded vessel
what is laplaces law, how is it calculated and what is its significance?
distending pressure produces an opposing force or tension in the vessel wall
tension = distending pressure x radius
small radius normalises tension
why do aneurysms occurs?
walls of large arteries cannot constrict to normalise the tension produced by distending flow
what is the purpose of arterioles?
control regional distribution of blood
what is the purpose of metarterioles?
link arterioles to veins
formed of discontinuous smooth muscle cells
where are precapillary sphincters found?
where a true capillary branches from a metarteriole
what is hyperaemia?
regulation of blood flow controlled by local factors associated with metabolic activity of tissues
what is and when does reactive hyperaemia occur?
following occlusion of blood supply
blood flow increase 4-7x for a time proportional to time occluded
repays oxygen debt
what is and when does active hyperaemia occur?
increase in blood flow caused by increase in metabolic activity
mediated by large quantities of vasodilators which are the waste product of metabolism
what is flow autoregulation
change in flow in response to changes in arterial pressure
increase in pressure causes vasoconstriction to oppose flow
what mechanism mediates flow autoregulation
myogenic stretch response by stretch activated Ca2+ channels
what is vasomotion
the intermittent contraction of meta-arterioles and precapillary sphincters
what regulation of flow mechanism is related to response to injury
release of endothelium-1 by damaged endothelium cells
potent vasoconstriction to prevent bleeding
what is the role of NO
released during stress by endothelium to decrease resistance
how is NO synthesised by endothelial cells?
eNOS enzymes
ardinine and oxidation through reduction of inorganic nitrate
what hormone will trigger NO synthesis
angiotensin II - prevents excess vasoconstriction
how much CO is found in capillaries
5%
what are some local (metabolic) factors of vasodilation
adenosine,hydrogen ions, potassium
how is local blood flow regulated in the long term
change in physical size and number of blood vessels
name some hormonal vasocontrictors
adrenaline
angiotensin II
vasopressin
name some local vasoconstrictors
endothelin-1
myogenic stretch response
name some hormonal vasodilators
adrenaline
atrial naturetic peptide
name some local vasodilators
decrease in O2
NO
bradykinin
what are the different kinds of capillaries
fenestrated
continous
sinusoid or discontinuous
