Cardiovascular mechanisms Flashcards
what are capillaries the site of
Exchange of gas, nutrients and water between blood and tissues
what blood vessels contain majority of blood volume during rest
veins
what is afterload
the stress in the wall of the left ventricle during ejection or the end load against which the heart contracts to eject blood
how is MAP calculated using CO
CO x SVR
how is SVR regulated
by vascular smooth muscles in blood vessels
vasocontriction of vascular smooth muscle causes what
increases MAP and SVR
vasodilation of vascular smooth muscle causes what
decreases SVR and MAP
what are vascular smooth muscles controlled by
extrinsic and intrinsic mechanisms
where through pathway of blood through circulation is the biggest drop in pressure
when blood travels from arterioles to capillaries
what is resistance to blood flow directly proportional to
blood viscosity and length of blood vessel
what is resistance to blood flow indirectly proportional to
the radius of blood vessel to the power 4
what is the resistance to blood flow mainly controlled by
via vascular smooth muscle through changes in the radius of arterioles
what nerves supply vascular smooth muscles
sympathetic nerve fibres
what is the neurotransmitter for sympathetic nerve fibres and what receptors do they act on
noradrenaline, alpha receptors
what is the vasomotor tone
due to continuous release of noradrenaline vascular smooth muscles are partially constricted at rest
what does increased sympathetic discharge cause
increases the vasomotor tone
where is vasculature innervated with parasympathetic nerve fibres
penis and clitoris only
what does adrenaline acting on alpha receptors do
causes vasoconstriction
what does adrenaline acting on beta 2 receptors do
causes vasodilatation
when are alpha receptors predominant
skin, gut and kidney arterioles
where are B2 receptors predominant
cardiac and skeletal muscle arterioles
what do B2 receptors in muscle arterioles help to achieve
strategic redistribution of blood e.g. during exercise
what are two other hormones that affect vascular smooth muscle (and what do they do)
Angiotensin II: causes vasoconstriction
Antidiuretic hormone (vasopressin): causes vasoconstriction
what are Angiotensin II and Antidiuretic hormone (vasopressin) important in controlling
the intermediate control of blood pressure
what do the intrinsic control mechanisms of VSM match to what
the blood flow of their tissue to their metabolic needs
what can the extrinsic control mechanisms over-ride
extrinsic control mechanisms
what do intrinsic control mechanisms include
LOCAL chemical and physical factors
what is the main way local blood flow is controlled
local intrinsic control mechanisms
what can local metabolic changes within an organ influence
the contraction of arteriolar smooth muscles
name the local metabolic factors causing relaxation of arteriolar smooth muscles (6)
Decreased local PO2
Increased local PCO2
Increased local [H+] (decreased pH)
Increased extra-cellular [K+]
Increased osmolality of ECF
Adenosine release (from ATP)
what does relaxation of arteriolar smooth muscles result in
vasodilatation and metabolic hyperaemia
what us hyperaemia
excess of blood in a vessel
In addition to metabolites what other local chemicals released within an organ influence the contraction of arterial and arteriolar smooth muscles
local humoral agents
what can the release of local humoral agents be caused by
tissue injury or inflammation
give three examples of local humoral agents that cause relaxation of ASM
Histamine
Bradykinin
Nitric Oxide (NO)
describe the release if NO
continuously released by endothelial cells of arteries and arterioles
what are local humoral agents classed as as a mechanisms
intrinsic control mechanisms of VSM (chemical)
how is NO produced
by the vascular endothelium from the amino acid L-arginine through enzymatic action of Nitric Oxide Synthase (NOS)
what is the role of NO
is a potent vasodilator which is important in the regulation of blood flow and maintenance of vascular health
what is the duration of life of NO
few seconds
what causes the release of calcium in vascular endothelial cells and what does this cause (WHAT IS THIS CALLED)
FLOW DEPENDANT NO FORMATION
Shear stress on vascular endothelium, as a result of increased flow- subsequent activation of NOS (which will produce NO from L-arginine )
what is receptor stimulated NO formation
when chemical stimuli induce NO formation
describe the path of NO
diffuses from endothelium into the adjacent smooth muscle cells
what does NO do when in smooth muscle cells
activates the formation of cGMP that serves as a second messenger for signalling smooth muscle relaxation
give four examples of humoral agents which cause contraction of arteriolar smooth muscles resulting in VASOCONSTRICTION
Serotonin
Thromboxane A2
Leukotrienes
Endothelin
describe endothelin
is a potent vasoconstrictor released from endothelial cells
what is the production of endothelin caused by
various agents which cause vasoconstriction
what can damage endothelium
high blood pressure, high cholesterol, diabetes and smoking
describe endothelial produced vasodilators
anti-thrombotic, anti-inflammatory, anti-oxidants
describe endothelial produced vasoconstrictors
are pro-thrombotic, pro-inflammatory, pro-oxidants
what are the three physical control mechanisms of VSM
temperature, myogenic response, sheer stress
what does myogenic response stop
changes in blood affecting the brain and the kidneys
describe the action of myogenic response if MAP increases
resistance vessels automatically constrict to limit flow
describe the action of myogenic response if MAP falls
resistance vessels automatically dilate to increase flow
what creates sheer stress and what does it cause
Dilatation of arterioles causes sheer stress in the arteries upstream to make them dilate. This increases blood flow to metabolically active tissues
what is the autoregulation of cerebral blood flow
myogenic response
what else is cerebral blood flow controlled by
Sympathetic nerve stimulation
what four factors increase venous return
increased;
venomotor tone, skeletal muscle pump,
blood volume, respiratory pump
what pressure does increased venous return increase
atrial pressure
how does increased venous return affect EDV
increases it
how does increased venous return affect SV
increases it (starling curve)
describe the respiratory pump
Descend of diaphragm when breathing increases abdominal pressure and decreases intrathoracic pressure which decreases pressure in RA which creates a bigger pressure gradient therefore increasing venous return
what type of vessels are veins
capacitance vessels
what nerve fibres are venous smooth muscles supplied with
sympathetic
what does increased venomotor tone lead to (3)
increased;
venous return, SV and MAP
what does invrease vasomotor tone do (2)
increased;
SVR and MAP
how does skeletal muscle activity affect venous return and how
increased activity increases venous return as large veins in limbs lie between muscle which pump blood when they constrict
what affects blood volume (2)
fluid shifts across capillaries and salt & water balance
what happens to sympathetic nerve activity during exercise
increases
what happens to HR and SV during exercise
increases
what is the action of sympathetic vasomotor nerves during exercise
reduce flow to kidneys & gut - vasoconstriction
what overcomes vasomotor drive in skeletal and cardiac muscle during exercise and casuing what
metabolic hyperaemia, vasodilation
in proportion to what during exercise does blood flow increase
metabolic activity
what do the increases in CO during exercise do to systolic BP
increase it
what does the metabolic hyperaemia do to SVR and DBP
decreases them
why does DBP decrease during exercie
as muscle bed big tissue so has lot of vasodilatation
what is the effect of sympathetic stimulation on the heart
increases HR by increasing SA node firing and decreasing nodal delay and increases force of contraction
what does sympathetic stimulation do to the slope of pacemaker potential
decreases it, positive chronotropic effect
what is the effect of sympathetic nerve stimulation on ventricular contraction
Peak ventricular pressure rises - contractility of heart at a given EDV rises
what is the effect of sympathetic nerve stimulation on the frank starling curve
shifted to the left
what does regular aerobic exercise help to reduce
BP
what might chronic cardiovascular responses to regular exercise include (6)
Reduction in sympathetic tone and noradrenalile levels
Increased parasympathetic tone to the heart
Cardiac remodeling
Reduction in plasma renin levels, reduces BP
Improved endothelial function: more vasodilators less vasoconstrictors
less arterial stiffening- therefore decrease BP
