lecture 9 - CVS 5: regulation of tissue blood flow Flashcards
what happens when arterioles vasodilate?
resistance decreases
blood flow increases
what happens when arterioles vasocontrict?
resistance increases
blood flow decreases
what is resistance controlled by?
vascular smooth muscle surrounding arteriole
capillaries don’t have smooth muscle
3 major physiological mechanisms that regulate arteriole radius
local control
hormonal control
neural control
local control
1) autoregulation of tissue blood flow
2) metabolic control of tissue blood flow
auto regulation of tissue blood flow
flow stays constant with increasing pressure - high flow rates damage vessels
intrinsic activity of smooth muscle - myogenic response
safety mechanism to prevent damage to blood vessels
darcys law
what is Darcy’s law?
flow = MAP / resistance
1) calcium moves into smooth muscle
2) activates contractile machinery - increased myogenic activity
3) constricts harder
metabolic control of tissue blood flow
metabolism derived vasodilators • increased CO2 • increased H+ - decreased pH • increases adenosine - breakdown of ATP • increased K+ • increased osmolarity • increased temp • decreased O2
smooth muscle has tone, what does this mean?
it is never fully relaxed or contracted
hormonal control
vasodilators • histamine • kinins • NO • adrenaline (beta2)
vasoconstrictors
• angiotensin II
• vasopressin
• adrenaline (alpha1)
role of adrenaline
can be a vasodilator or a vasoconstrictor depending on the receptors being expressed
NO and smooth muscle relaxation
- NO is a potent modulator of smooth muscle
- made in endothelial cells
- NO synthase stimulates NO production
- NO is short lived but has rapid diffusion across membrane to smooth muscle cells
- causes production of cGMP
- leads to smooth muscle reaction - increases blood flow
Ca++ has the opposite effect
what is angina?
feeling of pain/discomfort in the chest, left arm, back and jaw
how do you get angina?
symptom of chemicals being related and lack of sufficient nutrients
inability to supply efficient blood flow
how do you treat angina?
tablet under the tongue containing NO precursors
helps improve blood flow to the heart and reducing workload
only treats symptoms
regulation of smooth muscle function by adrenergic agonists
ACh binding
beta2 causes relaxation - cAMP production
alpha1 causes contraction - phospholipase C
neural control
sympathetic vasoconstrictor fibres
sympathetic vasodilator fibres
parasympathetic vasodilator fibres
sympathetic vasoconstrictor fibres
most widespread and most important
binding to alpha1 adrenergic receptors causes vasoconstriction - NE
blood vessels in the heart, lungs & liver don’t have many fibres but they have beta2 adrenergic receptors which cause relaxation - EP
can increase or decrease activity
sympathetic vasodilator fibres
work via NO generation in endothelial cells in skeletal muscle
sympathetic cholinergic - ACh
found in arterioles of skeletal muscle, external genitalia and sweat glands
parasympathetic vasodilator fibres
work via NO generation from endothelial cells
parasympathetic cholinergic
found in salivary glands
changes in CO at rest and during exercise
changes to meet oxygen demand
when exercising more blood is distributed to skeletal muscles and less to the GI tract, skin, kidney and brain
changes in BP and TPR at rest and during exercise
systolic pressure rises
diastolic remains constant
mean pressure doesn’t go up
• due to decrease in TPR
• modulates BP
