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BIOC33H3 Lecture Notes - Baroreceptor, Carotid Sinus, Common Carotid Artery

Biological Sciences
Course Code
Stephen Reid

of 12
BIOC34 Lec 8. Jan 29/14
oMon. March 3 @ 5pm
Blood flow (slide 32 lec 7)
oChange in P/ resistance to blood flow
oFlow = ∆P/R
CO = blood pumped per minute
All CO flows through systemic circuit
CO - Flow (ml/min)
MAP - Venous pressure = MAP
MAP drives blood flow in systemic circulation
MAP = ∆P
oMajor factors affecting:
Vessel radius
o2 things to keep in mind when talking about blood flow/BP regulation
BP regulation = overall body phenomena
Blood flow can be regulated
Blood flow within the systemic and pulmonary circuits is in parallel
oBlood does not go from one organ to the next
Each organ receives fully oxygenated blood
Independent regulation of blood flow to each organ
oDistribution of blood flow to various organs under different conditions of rest and
oWithin both systemic and pulmonary circuit, blood flow is parallel - each organ is
receiving oxygenated blood from an artery coming from left hand side of heart
oGoing from rest to exercise  blood flow distribution changes
oMost notably, skeletal muscle and skin which received low blood flow at rest,
blood flow increases during exercise
Skeletal muscle is involved in powering exercise and skin is site of
thermal regulation
oWhen exercising, metabolic rate increases and heat increases blood flow to skin
is enhanced and heat can dissipate to environment
oOrgans such as liver, gut, kidneys which receive high volumes of blood during
rest receive less during exercise
oBrain and heart are protected; blood flow is kept constant or higher
oWith heart, proportion of blood flow is constant but because blood flow is 5x
higher during exercise, it is receiving more blood than when under rest
oThough the proportion drops in the brain, amount of blood flow is enhanced
because lower proportions are going into brain but absolute values are higher
Resistance within a parallel circuit
oTotal resistance of a network of parallel vessels is less than the resistance of the
vessel having the lowest resistance
Parallel arrangement of vessels greatly reduces resistance to blood flow
With many parallel vessels, changing the resistance of a small number of
these vessels will have little effect on total resistance for the segment
Local (intrinsic) control of blood flow
oIndependent regulation flow to organs by vasoconstriction or vasodilation of
blood vessels (small arteries, arterioles) that are leading to the various organs
oHave a small arteriole and venule on the other side
Rings of smooth muscle on arterioles - not much smooth muscle on
oPossible to contract smooth muscle, causing it to squeeze in on blood vessel,
increasing resistance and reducing flow
oIf smooth muscle is relaxed, blood vessel diameter increases, resistance decreases
and flow increases
oVascular smooth muscle is control of local blood flow - acted on by hormones 
Ad, NAd from sympathetic nervous system or adrenal glands
oCan have local factors exerting effects - low oxygen, high CO2 causes
oMyogenic smooth muscle - high pressures cause smooth muscle to stretch and in
response to stretch, it contracts
oHappens in brain and kidneys
oRegulation of oxygen and CO2 is simple - if oxygen goes down in EC fluid, blood
flow goes up and if CO2 goes up, blood flow also goes up
Local Changes in Metabolism (O2)
o1. Steady state O2 delivery to tissues
Rate of O2 consumption = rate of O2 delivery
oIncreasing metabolic rate, tissues use more oxygen; as they use oxygen, gradient
for oxygen movement into EC fluid is enhanced, tissue oxygen decreases and
oxygen will diffuse into tissues where it is used in the mitochondria
Get reductions of oxygen in EC fluid as oxygen consumption increases
Mismatch of use and delivery from cardiovascular system
Local changes in Metabolism (O2)
o2. Increase in metabolic rate
o3. O2 consumption by the tissues increases
oDirect effect on vascular smooth muscle, decrease in oxygen levels in EC fluid
causes rings of smooth muscle to relax; no longer constricting; vessel dilates,
diameter increases and enhancement in blood flow
oBefore we get an enhancement in blood flow  ischemia: insufficient blood flow
is being met for metabolic demands
oVascular smooth muscle dilates, oxygen delivery has increased
oKeep in mind: change in oxygen in EC fluid; not changes within blood itself
oxygen levels in blood remain constant
oCardiovascular/respiratory system want to maintain oxygen uptake and CO2
secretion in the lungs; blood remains constant
oSee a similar thing in metabolically active tissues in CO2 production; CO2
produced in excess is removed
o(s42) Increase in metabolic rate - CO2 levels are greater on production side than
removal side - see direct effect of CO2 on blood vessels
oHigh levels of CO2 work on smooth muscles and cause vessels to dilate