Integration if the Cardiovascular Mechanisms Flashcards
What are the arteries
passage of blood from heart to tissues
what are the arterioles
major resistance vessels
what are capillaries
site of gas exchange of gas, nutrients and water between blood and tissues
what are veins
capacitance vessels
passageways of blood from tissues to heart
contain most of blood volume under resting conditions
what must venous return provide
heart with sufficient blood to pump
Regulation of heart rate
autonomic nervous system
regulation of stroke volume
pre-load
myocardial contractility
cardiac output =
HR x SV
mean arterial blood pressure =
CO x systemic vascular resistance (SVR)
MAP =
DBP + 1/3 pulse pressure
Main site of systemic vascular resistance
arterioles
contraction of vascular smooth muscles =
vasoconstriction
increase SVR and MAP
relaxation of vascular smooth muscle =
vasodilation
decrease SVR and MAP
vascular smooth muscles are controlled by what type of mechanisms
extrinsic
intrinsic
resistance to blood flow = directly proportional to
blood viscosity
length of blood vessels
resistance to blood flow = indirectly proportional to
radius of blood vessel
resistance to blood flow is mainly controlled by
vascular smooth muscles through changes in the radius of the arterioles
what’s involved in extrinsic control of VSM
nerves and hormones
explain nerves as an extrinsic control of vascular smooth muscle
B.P. regulation Baroreceptor reflux sympathetic nerves neurotransmitter = noradrenaline acting on a receptors vasomotor tone
explain vasomotor tone
partially constricted at rest
caused by - tonic discharge of sympathetic nerves
releases - noradrenaline
increased sympathetic tone will _______ vasomotor tone resulting in _____
increase
vasoconstriction
explain hormones as an extrinsic control of vascular smooth muscle
adrenaline
acting on a receptor = vasoconstriction
B2 recepetor = vasodilation
where are a receptors found
skin
gut
kidney arterioles
where are B2 receptors found
cardiac
skelteal muscle
name hormones which affect vascular smooth muscle
angiotensin 2
antidiuretic hormone
angiotensin 2 causes
vasoconstriction
antidiuretic hormone causes
vasoconstriction
what does intrinsic control of vacsuclar smooth muscle match
blood flow if different tissues to heir metabolic needs
chemical and physical factors
chemical local metabolites
influence contraction
list factors causing relaxation of arterial smooth muscles
decreased PO2 increased PCO2 increased H+ increase K+ increased osmolarity adenosine release
relaxation of vascular smooth muscles results in
vasodilation
metabolic hyperaemia
humoral agents cause vasodilation
histamine
bradykinin
nitric oxide
key features of nitric oxide
continuously produced vascular endothelium
potent vasodilator
flow dependent - no formation
receptor stimulated - no formation
humoral agents causing vasoconstriction
serotonin
thromboxane A2
leukotrienes
endothelin (potent vasoconstrictor)
explain endothelian
important in maintenance of vascular health
damage caused - high BP high cholesterol diabetes smoking
endothelial produced vasodilator are -
anti-thrombotic
anti-inflammatory
anti-oxidants
endothelial produced vasoconstrictors are
pro-thrombotic
pro-inflammatory
pro-oxidants
physical intrinsic control of VSM
temp
myogenic response
sheer stress
cold temp cuases
vasoconctstriction
warm temp causes
vasodilation
myogenic response explain
MAP rises - constrict
MAP falls - dilate
myogenic response important in
brain
kidneys
local control of SVR immediate or delayed
immediate
overrides nervous control
list factors influencing incresedvenous return
increased venomotor tone
increased skeletal muscle pump
increased blood volume
increased respiratory pump
increased venous return leads to
increased arterial pressure
increases EDV
increased stroke volume
increased venomotor tone leads to
increased venous return, SV and MAP
venous smooth muscles are supplied by what
sympathetic nerve fibres
stimulation of sympathetic nerve fibres
venous constriction - venous valves - blood driven to RA
what increases venous return to the heart
increasing rate and depth of breathing
muscle activity
acute CVS response to exercise
sympathetic increases
HR, SV = CO increases
vasomotor nerves = reduce flow to kidneys + gut (vasoconstriction)
skeletal + cardiac muscle = vasodialtion
blood flow to skeletal + cardiac muscle = increase
increased CO = increased systolic BP decreased SVR decreased DBP
explain how sympathetic stimulation increases heart rate
increases rate of firing of SA node
decreases AV nodal delay
(also increases force of contraction)
sympathetic stimulation on pacemaker cells
slope increases
potential reached quicker
frequency increases
positive chronotropic effect
sympathetic nerve stimulation on ventricular contraction
contractility of heart given EDV rises
Frank-Starling curve to left
chronic CVS response to exercise
regular - reduce B.P.
multifactorial
e.g. reduction in sympathetic tone and noradrenaline levels