Ch 19 Circulation Physiology
Vascular system
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blood vessels
function :
• move blood
• exchange
nutrients
wastes
gases
H2O
blood vessels
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arteries
move blood away from heart
veins
move blood toward heart
capillaries
exchange
artery - arteriole - capillaries - venule - vein
blood vessel tissues
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endothelium
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smooth muscle
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thin, smooth inner lining
exchange
control blood flow
vasoconstriction
vasodilation
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elastic tissue
control blood pressure
stretch and recoil
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fibrous tissue
strength
physics of Blood Flow
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blood flow
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blood pressure BP
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force of blood against the vessel wall
R
viscosity V
V
R
blood vessel length
l
R
blood vessel diameter
d
R
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blood flow
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main factors
pressure
diameter *
 BP
 blood flow
 diameter
 blood flow
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mm Hg
BP difference moves blood (nature wants equil.)
resistance
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volume blood / time
ml / min
F=
ΔP/R
Δ Pr4(π) / nL(8)
vasoconstrict
 blood flow
vasodilate
 blood flow
Blood Pressure
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fluid pressure = force exerted by the pump
blood pressure = force exerted by heart
systolic BP
force from left ventricle (systole)
blood pushes blood
120+ mm Hg
diastolic BP force of elastic walls (recoil)
artery wall squeezes blood
80 mm Hg
pulse pressure
systolic BP - diastolic BP
120 - 80 = 40 mmHg
MAP
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mean arterial pressure
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ave. BP in a vessel
MAP = diastolic BP + (pulse press / 3)
80
(40 / 3)
= 93 mmHg
or, (2x diastolic BP + systolic BP)/3
due to: BP varies with stretch and recoil of elastic arteries
arterioles have little elasticity
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systolic BP = diastolic BP
no Pulse Pressure
BP drops
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BP drops throughout the circuit
capillary BP
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enter
35 mmHg
exit
15 mmHg
venous BP
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20 to 0 mmHg
venous BP
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rarely varies
venous return
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to R atrium
blood pressure
respiratory pump
inhaling
• decreases pressure in thoracic cavity
– vacuum
• increase pressure abdominal cavity
– squeezes abdominal veins
skeletal muscle pump
• muscles compress veins
• squeeze blood forward
• valves prevent backflow
maintanence of BP
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cardiac output
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CO = SV x HR
 CO
 BP
 SV and/or HR
 BP
peripheral resistance
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vasoconstriction
 BP
 viscosity
 BP
• polycythemia, anemia
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blood volume
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 volume
 BP
eg. osmolarity, blood loss
these compensate for each other to maintain optimum BP
regulation of BP
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receptors
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baroreceptors
chemoreceptors
neural control
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medulla and ANS
higher brain centers
chemical control
renal control
neural control of BP
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control peripheral resistance
alters blood distribution to organs
medulla
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arterioles
vasomotor centers
 BP
 BP
 vasomotor center
 S-ANS
vasodilation
 vasomotor center
 S-ANS
vasoconstriction
vasomotor tone
constant, moderate vasoconstriction
vasomotor fibers
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S-ANS
to smooth muscle of blood vessels
S-ANS to vessels in skin and organs
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norepinephrine
vasoconstrict
S-ANS to vessels to skeletal muscle
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acetylcholine
vasodilate
exercise - increase blood to skeletal muscles
w/o increase BP
BP reflex arc
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receptor
baroreceptors
sensory neuron
to medulla
integration
medulla – vasomotor center
motor neuron
S-ANS
effector
blood vessel smooth muscle
receptors
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baroreceptors
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pressure receptor
carotid sinus ; aortic arch
stretch
stim by  BP
inhibits vasomotor center
 S- ANS
 BP
chemoreceptors
carotid body ; aortic body
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stim by
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stim vasomotor center
 oxygen
 CO2 or  pH
 BP and speed blood flow
higher brain centers
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hypothalamus
limbic system
cerebral cortex
hormonal control
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epinephrine
 BP
 CO
some vasoconstriction
norepinephrine
 BP
vasoconstriction
ADH
 BP
 H2O reabsorption
aldosterone
 BP
 Na reabsorption
atrial natriuretic peptide  BP
renin-angiotensin
 Na excretion
vasodilation
 BP
vasoconstriction
 aldosterone, ADH
other chemical control
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from blood vessel wall
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local effects
endothelin
vasoconstriction (Ca entry)
prostaglandin
vasoconstricion
nitric oxide
major vasodilator
• stim by
acetylcholine, kinins, nitroglycerine
histamine
vasodilate
inflammation
bradykinins
vasodilate
inflammation
alcohol
vasodilate
inhibit ADH
nicotine
vasoconstrict
mimics NE
renal control
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alter blood volume to change BP
more long term
vs altering resistance
maintains blood volume (~ 5 L) and BP
by altering amount of urine
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 urine -  blood volume
 urine -  blood volume
 bl volume ( BP) -  urine -  blood volume
 bl volume ( BP) -  urine -  blood volume
measuring BP
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sphygmomanometer
stethoscope
auscultation
sounds of Korotkoff
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not heard when
blood flows freely
no blood flows
systolic pressure
1st sounds heard
diastolic pressure
sounds stop
hypotension
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below 100 / 60
orthostatic hypotension
chronic hypotension
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age
decreased viscosisty
Addison’s
decreased aldosterone
hypothyroid
hypertension
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above 140 / 90
normal
fever , exercise , emotion
primary (essential) hypertension
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contributing factors
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TX:
no cause
diet , weight , age
heredity , smoking , stress
diuretics
beta blockers
Ca channel blockers
ACE inhibitors
secondary hypertension
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other disorders
kidney
Cushing’s
Grave’s
Blood flow
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tissue perfusion
flow of blood through an organ
goals of blood flow :
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move blood
exchange
• exchange at tissue cells
– gases
– nutrient , wastes
• gas exchange at lung
• nutrient absorption from digestive tract
• blood filtering in kidney
velocity of blood flow
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slows as increase cross-sectional area
aorta – smallest area
fastest
capillaries
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greatest area
slowest
WHY?
local regulation of blood flow
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BP controlled systemically
blood flow to each organ controlled locally
= autoregulation
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varying resistance (diameter) of local arterioles
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metabolic
due to chemical changes
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myogenic
due to stretch of smooth muscle
metabolic autoregulation
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vasodilation of arterioles leading into capillaries
metabolic changes
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decreased O2 (hypoxia)
nitric oxide
H+ (low pH)
lactic acid
inflammatory chemicals
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histamine
kinins
myogenic autoregulation
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maintains local perfusion
stretch smooth muscle causes increased tone
 local BP (stretch) causes local vasoconstriction
 local BP (stretch) causes local vasodilation
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reactive hyperemia
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angiogenesis
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increased blood flow to area of occlusion
increased blood vessels if long term hypoxia
capillaries
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capillary beds
=
precapillary sphincters
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network of capillaries
smooth muscle
at root of each capillary
regulate flow into each capillary
local control
• increase flow if increase needs of tissues
capillary permeability
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holes
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clefts
spaces between cells of capillary
fenestrations
pores in cell walls of capillary
diffusion
O2 , CO2 , lipids
filtration
fluid forced through holes
capillary dynamics
hydrostatic pressure
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=
fluid pressure against a wall
= capillary Blood Pressure
HPc capillary hydrostatic pressure
HPif interstitial fluid hydrostatic pressure
~0
net force of fluid out of capillary = HP c – HPif = HPc
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arterial end
35 mmHg
venous end
15 mmHg
capillary dynamics 2
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colloid osmotic pressure
=
plasma proteins (albumin) in blood
pull of water into blood
=
concentration gradient
water follows particles
OP = 25 mmHg
=
osmosis
colloids
capillary dynamics 3
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net fluid pressure NFP
NFP = HP – OP
net flow = pressure out – pressure in
HP – OP =
arterial end:
venous end
10 mmHg
fluid out
-8 mmHg
fluid in
HP – OP =
blood flow to skeletal muscle
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exercise hyperemia
vasodilation
autoregulation
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vasodilation due to low O2
systemic vasoconstriction
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maintain BP and blood flow
blood flow to skin
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temperature regulation
hot
increase blood flow
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hypothalamus
decreased vasomotor stimulation
relax smooth muscle
vasodilation
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local
release nitric oxide = vasodilation
cold
decrease blood flow
blood flow to brain
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requires constant blood flow
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750 ml / min
high nutrient needs
low pH ; high CO2
vasodilation ; increase flow
low O2
vasodilation
high CO2 (hyperventilate)
depress brain activity
lose control of flow
 BP
vasodilate – to maintain flow
 BP
vasoconstrict – to prevent rupture
blood flow to lungs
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low pressure circuit
24 / 8
autoregulation reversed
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low O2
vasoconstrict
high O2
vasodilate
blood flow to heart
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coronary arteries
flow to myocardium during diastole only
low O2
vasodilation
exercise
vasodilation