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8/12/2019 Cardiovascular Physiology 4 - Gomez MD.pdf
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BLOOD VESSELS
VEINS
ARTERIES
CAPILLARIES
PULMONARY CIRCULATION
SYSTEMIC CIRCULATION
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Marieb, Human Anatomy and Physiology, 7thedition
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ARTERIES
transport blood
under high pressure
high velocity flow 8x less distensible
than veins
transport blood awayfrom the heart
carry oxygenated
blood
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TYPES OF ARTERIES
ELASTIC ARTERIES
(LARGE-SIZED)
MUSCULAR ARTERIES
(MEDIUM-SIZED)
RESISTANCE ARTERIES
(SMALL-SIZED)
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ELASTIC ARTERIES
a.k.a. large-sized
arteries or conducting
arteries
elastic tissue and
smooth muscle
pulsatile flow pressure fluctuations
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MUSCULAR ARTERIES
a.k.a. medium-sized
arteries or distributing
arteries
(+) elastic tissue and
smooth muscle
pulsatile flow
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RESISTANCE ARTERIES
a.k.a. small-sized
arteries
elastic tissue and
smooth muscle
pulsatile flow
stopcocks (controlconduits) of the
vascular system
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CAPILLARIES Made up of single layer of
endothelial cells and
basement membrane
(-) smooth muscle and (-)
elastic tissue
Contain tight junctions,
fenestrations (pores),
intercellular cleft and and
pericytes
Total area exceeds 6300 m2and
1 m thick
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CONTINUOUS CAPILLARIES
FENESTRATED CAPILLARIES
SINUSOIDAL CAPILLARIES
TYPES OF CAPILLARIES
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Hydraulic conductivity of capillaries in
various parts of the body(Ganong, Medical Physiology 2001)
Organ Conductivity Type of Endothelium
Brain (except CVO) 3
Skin 100Skeletal muscle 250 Continuous
Lungs 340
Heart 860
GIT (intestinal mucosae) 13,000 Fenestrated
Kidney (glomerulus)
Liver
Bone marrow
Endocrine glands Sinusoidal
Lymphoid tissue
(Marieb, Human Anatomy and Physiology)
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VEINS
Transport blood
under low pressure.
8x more distensiblethan arteries
transport blood
towards the heart
carry deoxygenated
blood.
Great veins no valves, thin and easily
distended
Venules no valves, walls slightly
thicker than capillaries
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Basic Theory of Circulatory Function Rate of blood flow to each tissues is
almost always precisely controlled in
relation to the tissue needs. The cardiac output is controlled mainly
by the sum of all the local tissue flows.
In general, the arterial blood pressure iscontrolled independently of either local
blood flow control of cardiac output
control
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Structural and Functional Differences of Various
Blood Vessels
Lumen Diameter and Wall Thickness
Vessel Lumen Diameter Wall Thickness
Aorta 2.5 cm 2 mm
Medium-sized 0.4 cm 1 mm
Arteriole 30.0 m 20 m
Capillary 5.0 m 1 m
Venule 20.0 m 2 m
Vein 0.5 cm 0.5 mm
Great vein 3.0 cm 1.5 mm
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Vessel % of blood
volume
Systemic 84 %
Arteries 13 %
Arteriole 1-2 %
Capillary 5 %
Veins 64 %(54 %)
Pulmonary/Heart 16 %
Lungs 9 %
Heart 7 %
BLOOD DISTRIBUTION
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Total Cross Sectional Area
Vessel Areas (cm2)
aorta 2.5
medium-sized 20.0arterioles 40.0
capillaries 2500.0
venules 250.0veins 80.0
great veins 8.0
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Pressure
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Blood Flow Velocity
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Resistance to Blood Flow
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Vascular Distensibility
1 ml= ----------------------------
1mmHg X 10 ml
= 0.1 per mmHg or 10 mmHg
Systemic and pulmonary circulationdistensibility
Veins > Arteries
Vein DistensibilitySystemic veins = Pulmonary veins
Arterial DistensibilityPulmonary > Systemic
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Vascular Compliance / Capacitance
Vascular Compliance = Distensibility X Volume
Guyton, Medical Physiology, 11thedition
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HEMODYNAMICS
study of physical properties that
govern blood flow through the blood
vessels and the heart.
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BLOOD FLOW
means the quantity
of blood that passes a
given point in thecirculation in a given
period of time.
usually expressed in
ml/min or L/min
(cm3/min).
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BLOOD FLOW
( P1 - P2)F = ------------------
R
where,
F = flow
P1
P2 = pressure difference or gradient ofblood between two points of the vesselR = resistance to flow ( vascular
resistance)
pressure differencebetween two ends of
the vessel (arterialend minus venous
end)
impediment to bloodflow in a vessel.
cannot be measureddirectly
expressed in R units
The overall blood flow in
the total circulation in a
resting adult is 5,000 ml.(Cardiac Output)
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Methods for measuring blood flow
(Flowmeters) Electromagnetic Flowmeters
Ultrasonic Doppler Flowmeters
Fick Principle
Indicator Dilution Method
Clearance Principle
Plethysmography
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POISEUILLES EQUATION
P . r4
F -----------------
. Lwhere,
F = flow
P = pressure difference between
two ends of the vessel = viscosityr4 = radius
L = length of the tube
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Since flow (F) is equal to pressure
difference (P) divided by resistance (R)
. LR ------------
r4
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Determinants of vascular resistance Radius of the blood vessel
depends on the degree of vasoconstriction
Viscosity of the blood depends mainly on hematocrit (% of volume
of blood occupied by the RBC
amount of protein in the blood
Hyperimmunoglobulin D, E and M resistance of the cell to deformation
(Hereditary Spherocytosis)
Length of the blood vessel
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EFFECT OF CHANGES IN BLOOD VESSEL RADIUS
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EFFECT OF CHANGES IN BLOOD VESSEL LENGTH
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Shear Stress and Shear rate
Shear Stress
Force created by flowing blood on the
endothelium that is parallel to the long axisof the vessel
Equal to viscosity X shear rate
Shear rate Rate at which axial velocity from the vessel
wall towards the lumen
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Resistance in Series vs Resistance in Parallel
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CONDUCTANCE
Measure of blood
flow through avessel for a given
pressure difference
1
C = --------------------------
RESISTANCE
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F
F = V . A or V = ------
A
where;
F = flowV = mean velocity
A = cross-sectional area of the blood vessel
FLOW, VELOCITY AND AREA
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BERNOULLIS PRINCIPLE
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Laminar vs. Turbulent F low
Laminar flow (Streamline flow)
silent flow
characterized by concentric layer of blood moving inparallel down the length of a blood vessel.
Turbulent flow
flow that that creates sound
probability is also related to the diameter of thevessel and viscosity of the blood
can be expressed by
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Conditions that can result to
turbulent flowa) When blood flow becomes too great.
b) When there is obstruction in a vesselc) When it makes a sharp turn.
d) When it passes over a rough surface
Turbulent flow in proximal aorta and
pulmonary arterya) High velocity of blood flow
b) Pulsatile nature of blood flowc) Sudden change in vessel diameter
d) Large vessel diameter
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p . D . V
Re = ----------------
where,
Re = Reynolds number
p = density of the fluid
D = diameter of the tubeV = velocity of flow
= viscosity of the fluid
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LAW OF LAPLACE
T = Pr
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BLOOD PRESSURE force exerted by the
blood per unit area of
the vessel wall(pressure is exerted
equally in all
directions).
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Blood Pressure in the Various
Parts of the Systemic Circulation
Mean Blood Pressure
average pressure in any segment of the
cardiovascular system during cardiac cycle.
Arterial Blood Pressure
blood pressure in the arterial side of the vascular
system conveniently written as systolic pressureover diastolic pressure ( N.V. 100 -130 / 70 -
90 mmHg )
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Arterial Blood Pressure
Systolic pressure
highest pressure attained in the aorta as a result of the
ejection of blood by the ventricle.(N.V. 100 - 120 mmHg )
Diastolic pressure
is the lowest pressure which the gradient of fall reachesduring the resting or diastolic phase of the heart.
( 70 - 80 mmHg)
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Pulse Pressure
is the difference between the systolic and
diastolic pressure. (SPDP = 40 mmHg)
factors that affect pulse pressure (SV/C) Stroke volume
Compliance of arterial tree
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Mean Arterial Blood Pressure represents the average pressure attained inthe arterial system during the cardiac cycle.
MAP = Diastolic Pressure + 1/3 pulse pressure
Diastolic Pressure + ( Systolic Diastolic pressure )
MAP= -----------------------------------------
3
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Arterial Blood Pressure
ABP = CO X TPR
CO ABPTPR ABP
CO = SV X HR
EDV - ESV
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ABP = CO X TPR
SV X HR
EDV - ESV
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RESISTANCE
. LR ------------
r4
a) viscosity hematocrit
amount of protein in the blood
b) lengthc) radius
vasoconstriction /vasodilatation
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EDVSV CO ABP ESV
Blood viscosity
Vessel length TPR ABP
Vessel radius
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Methods of Measuring Blood PressureA. Direct Method
B. Indirect Method
a) Auscultatory Methodb) Palpatory Method
increased pressure ----------- HYPERTENSION
decreased pressure ----------- HYPOTENSION
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