Download colloid osmotic pressures

Vascular physiology
Introduction
• The majority of body cells are not directly contact with the
external environment , but these cells must make exchanges with
this environment . e.g.O2 pickup and CO2 removal
• Blood vessels is passageway of substance transportation and bring
about the function of exchanging the substance
• All blood pumped by the right side of heart passes through the
lungs for O2 pickup and CO2 removal
• The blood pumped by the left side of the heart is parceled
out in various proportions to the systemic organs through a
parallel arrangement of vessels
• Advantages: each organ can be independently adjusted
without directly influencing blood flow through any other
organ
Distribution of cardiac output
at rest
This distribution of CO can be adjusted
as needed
Reconditioning organ – digestive organs,
kidneys and skin
Basic organization of the
cardiovascular system
the arterioles ,capillaries,
and venules are
collectively referred to
as he microcirculation
Blood vessels
• Arteries : carry blood from heart to tissue, elastic
vessels
• Arterioles: a small artery reaches the organ,
resistance vessels
• Capillaries: the smallest vessels , exchange vessels
• Venules: Capillaries rejoin to form Venules
• Veins : leave the organ and then unite to form larger
veins that empty blood into heart, capacitance vessels
• Microcirculation: Arterioles, Capillaries and
Venules
Blood flow
• Blood flow through vessels depends on the
pressure gradient and vascular resistance
Flow rate
• Flow rate is the volume of blood passing through per
unit of time
• Flow rate is directly proportional to the pressure
gradient and inversely proportional to vascular
resistance:
F = △P / R
Where
F = flow rate of blood through a vessel
△P = pressure gradient
R = resistance of blood vessels
F=△P / R = (P1-P2) / R
Flow rate ---
Pressure gradient
• The difference in pressure between the beginning
and end of a vessel – main driving force for the blood
flow
• The greater the pressure gradient forcing blood
through a vessel, the greater the rate of flow
through that vessel
e.g.
Relationship of flow to the pressure gradient in a vessel
Flow rate is directly proportional to △P , determined by the △P (difference)
between two ends of a vessel, not the absolute pressures
Flow rate --- Resistance
• Definition : A measure of the hindrance to blood flow through a
vessel caused by friction between the moving fluid and the
stationary vascular walls
•
F = △P / R
• Resistance increases, the △P must increase to maintain the
same flow rate.
• i.e. when the vessels offer more resistance to flow , the heart
must work harder to maintain adequate circulation
Flow rate --- Resistance
• Resistance to blood flow depends on
three factors:
--Viscosity of the blood
--Vessel length
--Vessel radius (important)
resistance --viscosity
• Viscosity refers to the friction developed between the
molecules of a fluid as they slide over each other during flow of
the fluid
• The greater the viscosity , the greater the resistance to flow.
the thicker a liquid , the more viscous it is.
viscosity of blood is determined by two factors:
(1) the concentration of plasma proteins
(2) the number of circulating red blood cells
(important)
At the normal situation , these two factors remain constant
resistance
• The greater the vessels surface area in contact with the
blood , the greater the resistance to flow.
• Surface area is determined by length and radius of the
vessel, (length remains constant , so the major
determinant of resistance to flow is the radius of vessel)
A given volume of blood comes into contact with much more of the surface area
of a small-radius vessel than of a large-radius vessel, resulting in greater
resistance
Resistance and radius
• The resistance is inversely proportional
to the fourth power of the radius
•
R∝1/r
4
double the radius decrease the resistance 16 times and
therefore increase flow through the vessel sixteenfold (at the
same pressure gradient)
Relationship of resistance and flow to the vessel radius
Same pressure gradient
Radius in vessel 2 = 2 times that of vessel 1
Resistance in vessel 2 =1/16 that of vessel 1
flow in vessel 2 = 16 times that of vessel 1
Resistance ∝ 1 / r 4
flow ∝ r 4
Poiseuille’s law
• The radius of arterioles is subject to regulate and is the
most important factor in the control of resistance to
blood flow
• The factors that affect the flow rate through a vessel
are integrated in Poiseuille’s law:
flow rate = π △P r 4 /
Where
8η L
η = viscosity
the flow rate is largely determined by vessel radius
Features of blood vessels
Vessel type
aorta
Number one
Large arteries
arterioles
several hundred
capillaries
half million
ten billion
Large vein
several hundred
Thick
2000μm
1000μm
20μm
1μm
500μm
Radius
12500μm
2000μm
30μm
3.5μm
5000 μm
Area
4.5cm
400 cm2
6000cm2
20cm2
Special Thick, highly elastic wall
features larger radius
functions Passageway from the
heart to the tissues;
serve as a pressure
reservoir
Highly muscular,
well-innervated
walls; small radius
Primary resistance
vessels; determine
the distribution of
CO
Vena cava
1500μm
40 cm2
Thin walled;
large cross
sectional area
two
30000μm
18 cm2
Highly distensible;
larger radius, thin
walled
Site of exchange;
determine the
distribution of ECF
between the
plasma and
interstitial fluid
Passageway to the
heart from the
tissues; serve as a
blood reservoir
Arteries
• Arteries (elastic properties) serve as rapid-transit
passageways to the tissues and as a pressure reservoir
• Pressure reservoir : providing the driving force for the
continued flow of blood to the tissues during cardiac relaxation
(elastic properties)
Elastin
fiber
The wall of the aorta in cross section,
it is common to all arteries
Arteries --- Pressure reservoir
• When the heart systole:
a greater volume blood enters the artery , only part of them
flow into smaller vessels, the left stored in the elastic artery,
then storing some of the pressure energy imparted by cardiac
contraction in their stretched walls
Heart contraction and emptying
the elastic arteries distend during cardiac systole as more blood is ejected
into them than drains off into the narrow high-resistance arterioles
downstream
Arteries --- Pressure reservoir
• When the heart relaxes:
no blood pumping, the stretched arterial walls passively recoil, the
recoil pushes the excess blood into the vessels downstream, make
the intermittent pump into continuous blood flow
Heart relaxing and filling
The elastic recoil of arteries during cardiac diastole continues driving the
blood forward when the heart is not pumping
Arterial blood pressure
• Arterial pressure fluctuates during the systole and diastole
• Blood pressure : the force exerted by the blood against a vessel
wall, depends on the volume of blood contained within the vessel
and the vessels’ compliance
• compliance：how easily they can be stretched
• Unit: K Pa, mm Hg, cm H2O
Arterial blood pressure
• Systole pressure: 80 - 120mm Hg
• during ventricular systole : a stroke volume of blood
enters the arteries while 1/3 blood enters the
arterioles (the maximum pressure exerted in the
arteries)
Arterial blood pressure
• Diastole pressure: 60 – 80 mm Hg
• during ventricular diastole : no blood enters
the arteries, while blood continues to leave,
driven by elastic recoil (the minimum
pressure exerted in the arteries)
• The blood pressure does not fall to 0 mm Hg, because the next
cardiac contraction occurs and refills before all the blood drains
off
Measurement of blood pressure
Direct measure technique
(invasive method)
Measurement of blood pressure
• Indirectly measurement
sphygmomanometry : pressure gauge , cuff
stethoscope
Indirectly measurement
technique (non-invasive)
Use of a sphygmomanometer in
determining blood pressure .
The pressure in the inflatable
cuff can be varied to prevent or
permit blood flow in the
underlying brachial artery
Indirectly measurement technique
Steps :
(1) Cuff is wrapped around the upper arm
(2) A stethoscope is placed over the brachial artery at the inside
bend of the elbow just below the cuff
(3) Inflating air into the cuff, until no sound is heard
when cuff pressure is greater than the pressure in the vessel,
the vessel is pinched closed so that no blood flows through it.
when blood pressure is greater than cuff pressure, the vessel is
open and blood flows through
(4) Let the air inside the cuff go, during which you can hear the
sound caused by blood flow
Laminar flow does
not create any sound
Turbulent flow can be heard
Pattern of sounds in relation to cuff pressure compared with blood
pressure
1. Cuff pressure > blood pressure .
No sound is heard
2. The first sound is heard at peak systolic pressure
3. Intermittent sounds are heard as blood pressure cyclically exceeds
cuff pressure
Pattern of sounds in relation to cuff pressure compared with blood
pressure
4. The last sound is heard at minimum diastolic pressure
5. Blood pressure exceeds cuff pressure through the cardiac cycle. No
sound is heard
Blood flow through the brachial artery in relation to
cuff pressure and sounds
When cuff pressure is greater
than 120 mm Hg :
No blood flows through the
vessel.
No sound is heard
When blood pressure is 120 / 80 mm Hg
Blood flow through the brachial artery in relation to
cuff pressure and sounds
When cuff pressure is between 120 and 80 mm
Hg:
Blood flow through the vessel is turbulent
whenever blood pressure exceeds cuff pressure
Intermittent sounds are heard as blood pressure
fluctuates throughout the cardiac cycle
When blood pressure is 120 / 80 mm Hg
Blood flow through the brachial artery in
relation to cuff pressure and sounds
When cuff pressure is between 120 and 80
mmHg:
The first sound can be heard is the indicative
of the systolic blood pressure
The last sound can be heard is the indicative
of the diastole blood pressure
When blood pressure is 120 / 80 mm Hg
Blood flow through the brachial artery in
relation to cuff pressure and sounds
When cuff pressure is less than 80 mmHg:
Blood flow through the vessel in smooth ,
laminar fashion
No sound is heard
The sound is not the heart sound
associated with valve closure
When blood pressure is 120 / 80 mm Hg
• In clinic practice , arterial blood pressure is expressed
as systolic pressure over diastolic pressure, with the
average blood pressure being 120 / 80 (120 over 80) mm
Hg
Pulse pressure
• The pulse can be felt on the surface of skin is due to
the difference systolic and diastolic pressures . This
difference is known as the pulse pressure.
• When the blood pressure is 120 / 80 mm Hg , pulse
pressure is 40 mm Hg (120 mm Hg – 80 mm Hg)
Mean arterial pressure (MAP)
• Mean arterial pressure is the main driving force
for blood flow
• MAP is an average pressure, not the halfway value
between systolic and diastolic pressure
e.g. with a blood pressure of 120 / 80 , MAP is not
100 mm Hg
Mean arterial pressure (MAP)
• At resting heart rate, about 2 / 3 of the cardiac
cycle is diastole and only 1 / 3 is systole. The MAP is
closer to diastole pressure.
Formula for MAP:
• MAP = diastole pressure + 1 / 3 pulse pressure
Pressure throughout
the systemic
circulation
Left ventricular pressure swings between a low pressure of 0 mm Hg to 120 mm Hg
Arterial blood pressure is of the same magnitude (systole:120 mmHg;
diastole:80mm Hg)
The pressure in arterioles drop sharply (the high resistance )
The pressure in capillaries, venules and veins decline at a slower rate, it is a
nonpulsatile
arterioles
• Arterioles are the major resistance vessels (reach the
organ)
• The high degree of arteriolar resistance causes a marked
drop in mean pressure.
• The advantages of the marked drop pressure :
(1) Establishment of pressure gradient (MAP is from 93 to 37 mm Hg)
(2) converting the pulsatile systolic-to-diastolic pressure into the
nonfluctuating pressure in the capillaries
arterioles
• The radius (resistance) of arterioles can be adjusted independently ,
which have two function:
(1) To variably distribute the cardiac output , according to the body’s
momentary need (intrinsic control)
(2) To help regulate arterial blood pressure (extrinsic control)
Mechanism of adjustment independently
1. Arteriolar walls structure:
(1) very little elastic connective tissue
(2) thick layer of smooth muscle is sensitive to local chemical change and
a few of circulating hormone (richly innervated by sympathetic nerve)
2. Arteriolar smooth muscle displays a state of vascular tone :
(1) myogenic activity (partial constriction)
(2) sympathetic fiber supplying the most arterioles continually release
NE
Normal arteriolar tone
Vasodilation
Myogenic activity
Oxygen decrease
Vasoconstriction
Caused by Myogenic activity
Oxygen increase
CO2 decrease
Sympathetic
stimulation ,vasopressin
CO2 increase
Sympathetic
stimulation
Histamine release
Heat
Intrinsic control (local control ) of
arteriolar radius
• Local control of arteriolar radius determined the
distribution of cardiac output so that blood flow is
matched with the tissues’ metabolic needs
• The amount of the CO received by each organ is
determined by the number and caliber of the arterioles
supplying that area
Local control
caliber of the arterioles
The distribution of CO
Constant pressure in pipe (MAP)
From pump
No flow
Moderate flow
large flow
Distribution of the
cardiac output at
rest and during
moderate exercise
Total cardiac output is 5000
Total cardiac output is
12500
Extrinsic control of arteriolar radius
• Extrinsic control of arteriolar radius is primarily
important in the regulation of arterial blood pressure
• Two types :
-- neural influences (sympathetic nerve is the most
important)
sympathetic nerve supply arteriolar smooth muscle everywhere in the systemic
circulation except in the brain
-- humoral influences
Extrinsic control of arteriolar radius
Changes in arteriolar resistance bring about changes in
MAP
F = △P / R
F: flow of the blood is equal to the cardiac output (Looking at the
circulatory system as a whole )
△P : the pressure gradient for the entire systemic circulation is the
MAP (for systemic circulation is 93 mm Hg，pulmonary circulation is 15)
R: total peripheral resistance is caused by arteriolar resistance
(arterioles are the primary resistance vessels)
△P = F x R ------- MAP = cardiac output x total peripheral
resistance
Pressure at end of systemic
circulation = 0 mm Hg
Pressure at beginning of systemic
circulation = MAP (93 mm Hg)
The pressure gradient in
the systemic circulation
Extrinsic control of arteriolar radius
△P = F x R
MAP = cardiac output x total peripheral
resistance
So the total peripheral resistance influences the MAP
immensely
Local control and extrinsic control for
arterioles’ radius
Local control is more important than extrinsic control
when maintaining the blood flow. (e.g. active heart or
skeletal muscle)
Extrinsic control (sympathetic role) is maintenance the
driving force for blood flow
note: Brain is an exception (blood vessels have no α receptor),
entirely controlled by local mechanism
Parasympathetic nerve supply to the arterioles of the penis and
clitoris--erection
Arteriolar smooth muscle adrenergic receptors
Receptor type
characteristic
Location of the
receptor
Chemical mediator
that binds with the
receptor
α
β2
All arteriolar smooth
muscle except in the
brain
Arteriolar smooth
muscle in the heart and
skeletal muscle
Norepinephrine from
sympathetic fibers and
the adrenal medulla
Epinephrine from the
adrenal medulla (greater
affinity of this receptor)
Epinephrine from the
adrenal medulla (less
affinity of this receptor)
Arteriolar smooth
muscle response
vasoconstriction
vasodilation
Total peripheral resistance
Blood viscosity
Arteriolar radius
Number of RBC
Local control
Local metabolic
changes in O2, CO2
(matching blood
flow with metabolic
needs)
Concentration of
plasma proteins
Extrinsic control
Sympathetic activity
(exert vasoconstrictor
effect)
Major factor affecting arteriolar radius
Factors affecting
total peripheral
resistance
Capillaries
• Capillaries are ideally suited to serve as sites of
exchange
• Structure : one layer of endothelial cell
•
no smooth muscle or connective tissue
• Function : transfer the substances between blood and
tissue (diffusion and no carrier-mediated process)
Capillary anatomy
Photograph of a capillary bed. The
capillaries are so narrow that the
RBC must pass through single file
7um
A cross section of a capillary (the
capillary wall consists of a single
layer of endothelial cells) 1um
No smooth muscle cell and
connective tissue
features in capillary bed
They minimize diffusion distances while maximizing surface area
and time available for exchange
1. Short distance : the rate of exchange increase
Thin capillary wall :1μm (the diameter of human hair 100μm)
small capillary diameter :7μm
no tissue cell is farther than 100μm from a capillary
2. Large area : the rate of exchange increase
number :10 -14 billion
d area: 600 m2
The structure determined the capillary are ideally suited to enhance
diffusion in accordance with Fick’s law of diffusion
factor
Concentration gradient of substance (ΔC)
Permeability (P)
Surface area of membrane (A)
Molecular weight of substance (MW)
Distance (thickness) (ΔX)
Rate of diffusion
features in capillary bed
3.
Slow blood flows : adequate time for
exchange , the rate of exchange increase
speed of flow is inversely proportional to
the total cross-sectional area (6000 cm2 )
velocity of flow
≠
flow rate
Flow rate:refers to the volume of blood flowing
through a given segment of the circulatory
system per unit of time
Velocity of flow:refers to the linear speed with
which blood flows forward through a given
segment of the circulatroy system.
Relationship between total cross-sectional area and velocity of flow
flow rate is the same at all levels of the circulatory system
Three dark area represent equal volume of water
Comparison of blood flow and
velocity of flow in relation to
total cross-sectional area
The blood flow rate is the same at all
level of the vessel
The velocity of flow is inversely
proportional to the total cross-sectional
area
velocity of flow
flow rate
_____
=
total cross-sectional
area of vessels at
that level
Why isn’t capillaries the resistance vessels ,
even which have smaller radius than arterioles?
1. capillaries’ tremendous total cross-sectional area
2. Capillary caliber cannot be adjusted
substances exchanges across the capillary wall
Lipid-soluble substance, such
as O2 and CO2 , can pass
through the endothelial cells
by dissolving
This pore permit passage of
water-soluble substances . e.g.
ions ,glucose and amino acid
The large, non - lipid - soluble
substances are exclude from
passage of the pore . e.g.
proteins
brain:pores are nonexistent
liver:big enough for protein
though
Structure of capillary bed
Metarteriole : surround by wisps of
smooth muscle cell (SMC) ；
thoroughfare channel
Precapillary sphincters: SMC
no nerve innervated
high myogenic tone
sensitive to local metabolic changes
control the blood flow (like
arterioles)-stopcock
Capillaries : no SMC , no the
function of regulating of blood flow
Capillary bed
• Many capillaries are not open under resting conditions.
(determined by the metabolic activity)
• e.g. 10% of the capillaries in resting muscle are open at any
moment . When the metabolic activity is changed , the extent of
the capillaries opening is more ，result in more blood flow to
muscles
• Blood flow through a particular tissue (a constant blood
pressure ) is regulated by
• (1) the degree of resistance offered by the arterioles in the
organ (controlled by sympathetic nerve and local factor)
• (2) the number of open capillaries (controlled by action of local
metabolic factors on precapillary sphincters)
Complementary action of precapillary
sphincters and arterioles in adjusting
blood flow through a tissue in response
to changing metabolic needs
The function of capillary bed
– substance exchange
The substance exchange
across the capillary walls
Exchange between blood
and the tissue cells
are not made directly.
Interstitial fluid acts
as the go-between
Interstitial fluid acting
as an intermediary
between blood and cells
step1:Diffusion between
cell and interstitial fluid:
• Passive transport:
simple diffusion
facilitated diffusion
Active transport:
carrier-mediated transport
vesicular transport
step2:Diffusion between
capillary and interstitial fluid:
• largely passive transport:
simple diffusion
facilitated diffusion
active transport:
limited vesicular transport
substances exchanges across the capillary wall
Lipid-soluble substance, such
as O2 and CO2 , can pass
through the endothelial cells
by dissolving
This pore permit passage of
water-soluble substances . e.g.
ions ,glucose and amino acid
The large, non - lipid - soluble
substances are exclude from
passage of the pore . e.g.
proteins
The substances exchanges of capillaries
The large non-soluble molecules
must be exchange in
endocytotic-exocytotic vesicles
The substance exchange across the
capillary walls
• The means for the exchanges between blood and
surrounding tissues across the capillary walls
• (1) passive diffusion down concentration gradients
(for exchange of individual solutes)
• (2) bulk flow, a volume of protein - free plasma
actually filters out of the capillary , mixes with the
surrounding interstitial fluid ,and is subsequently
reabsorbed. (in contrast to the discrete diffusion of
individual solutes down concentration gradients)
The substance exchange --- diffusion
• Diffusion : individual solute cross primarily by diffusion down
concentration gradients (glucose , amino acid , ion). This process
repeat itself continuously
Independent exchange of individual
solutes down their own concentration
gradients across the capillary wall
The substance exchange --- bulk flow
• Bulk flow:determining the distribution of the ECF volume
between the vascular and interstitial fluid compartments
• Ultrafiltration : when pressure inside the capillary exceeds
pressure outside, fluid is pushed out through the pores.
• Reabsorption : when inward driving pressures exceed
outward pressures across the capillary wall, the fluid will
move into the capillaries through the pores.
• bulk flow occurs because of differences
in the hydrostatic and colloid osmotic
pressures between the plasma and
interstitial fluid.
• (pressure differences exist elsewhere in the
circulatory system, only the capillaries have
pores that allow fluids to pass )
The substance exchange --- bulk flow
• Review
• Osmosis: water diffuse down its own concentration gradient
from the area of higher water concentration (lower solute
concentration) to the area of lower water concentration (higher
solute concentration). This net diffusion of water is known as
osmosis
The substance exchange --- bulk flow
• Hydrostatic (fluid) pressure
Water moves from side 1
to 2
solute unable to move from
side 2 to 1
Water concentration not equal and solute concentration not equal
Tendency for water to diffuse by osmosis into side 2 is exactly balanced by
opposing tendency for hydrostatic pressure difference to push water into
side 1
Osmosis ceases
Opposing pressure necessary to completely stop osmosis is equal to osmotic
pressure of solution
The substance exchange --- bulk flow
• The osmotic pressure related directly to the
concentration of nonpenetrating solute (plasma
protein).
The higher solute concentration , the greater
osmotic pressure of solution
• colloid osmotic pressure
• crystal osmotic pressure
bulk flow
• Bulk flow is responsible for the formation of interstitial fluid.
• Four forces influence fluid movement across the capillary wall:
• (1) capillary blood pressure (Pc) :
definition : the hydrostatic pressure exerted on the inside of the capillary
walls by the blood.
direction of the force : force fluid out of the capillaries into the
interstitial fluid.
value: at the arteriolar end is 37 mm Hg , at the venular end is 17 mmHg
bulk flow
• (2) Plasma-colloid osmotic pressure (πp)
definition: a force cause by the colloidal
dispersion of plasma protein
direction of force : encourage fluid
movement into the capillaries (protein
concentration gradients )
value : 25 mmHg
bulk flow
(3) interstitial fluid hydrostatic
pressure (Pif)
definition: the pressure exerted on the
outside of the capillary wall by the interstitial
fluid
direction of force : force fluid
movement into the capillaries
value : 1 mmHg
bulk flow
• (4) interstitial fluid-colloid osmotic pressure (πif)
• definition: a force cause by the colloidal dispersion
of plasma protein in the interstitial fluid
• direction : encourage fluid movement out of the
capillaries
• value : 0 mm Hg
• note：normally the πif does not contribute
significantly to bulk flow)
bulk flow
•
The net exchange at a given point across the capillary wall can be
calculated using the following equation:
• net exchange pressure = (Pc +πif) - (πp + Pif)
•
outward pressure
inward pressure
•
A positive net exchange pressure (when the outward pressure exceeds
the inward pressure) represent an ultrafiltration pressure (11 mm Hg)
•
A negative net exchange pressure (when the inward pressure exceeds
the outward pressure) represent a reabsorption pressure (9 mm Hg)
Force at arteriolar
end
Ultrafiltration occurs at the
beginning of the capillary
Force at venular
end of capillary
Reabsorption occurs at
the end of the capillary
Bulk flow across the capillary wall (ultrafiltration and reabsorption )
Schematic representation of ultrafiltration and reabsorption as a
result of imbalances in the forces acting across the capillary wall
Net filtration and net reabsorption along the vessel length
The inward pressure remains constant throughout the length of the capillary whereas the
outward pressure progressively declines
In the first half of the vessel, progressively diminishing quantities of fluid are filtered out
In the last half of the vessel, progressively increasing quantities of fluid are reabsorbed
Bulk flow
• The significance of bulk flow:
the amount of substance exchange across the capillary wall by
bulk flow is extremely small compared to the much larger
transfer of solutes by diffusion
significance: regulating the distribution of ECF between the
plasma and interstitial fluid. (temporary mechanism)
e.g. by hemorrhage the plasma volume is reduced and the blood
pressure falls. Now the filtration reduced and reabsorption
increased.
Where is the extra filtered fluid ?
On average, the net ultrafiltration pressure starts at
11mmHg at the beginning of the capillary, whereas the
net reabsorption pressure only reaches 9mmHg by
the vessel’s end.
Lymphatic system
• lymphatic system is an accessory route
by which interstitial fluid can be
returned to the blood
Lymphatic system--structure
• overlapping endothelial cells--valvelike
Lymphatic system
•
•
•
•
return of excess filtered fluid
defense against disease
transport of absorbed fat
return of filtered protein
clinical point:
• edema—swelling of the tissues because of
excess interstitial fluid
1 Reduced concentration of plasma proteins
kidney disease;
reduced synthesis of plasma proteins as a result of liver
disease;
a diet deficient in protein;
clinical point:
• edema—swelling of the tissues because
of excess interstitial fluid
2.Increased permeability of the capillary
walls
tissue injury or allergic reaction
clinical point:
• edema—swelling of the tissues because
of excess interstitial fluid
3.Increased venous pressure-congestive
heart failure
congestive heart failure
clinical point:
• edema—swelling of the tissues because
of excess interstitial fluid
4.Blockage of lymph vessels—filariasis
elephantiasis mosquito-borne parasitie
worm
veins
• Vein serve as a blood reservoir as well as passageways back to the heart
• Structure and feature :
-- large radius (low resistance) ;
-- more collagen fibers, less elastin fibers,
-- smooth muscle little inherent myogenic tone
highly
distensible
-- venous smooth muscles is abundantly supplied with sympathetic nerve
fiber
-- capacitance vessels (storage capacity, at rest more than 60%)
veins
Percentage of total blood volume in different
parts of the circulatory system at rest
Venous return
central venous pressure: pressure
within right atrial and big vein in
thoracic cavity
significance: detact CVP in case
overload as injecting .
Venous return
• Venous return : the volume of blood entering each atrium per
minute from the veins (the venous capacity affect it)
• Venous return caused by pressure gradient (determined by
cardiac contraction ):
At the beginning of vein , mean pressure average 17 mm Hg .
The atrial pressure is near 0 mm Hg.
The factors that influences venous return
(1) Driving pressure impart by the cardiac contraction. (primary
factors)
(2) sympathetic activity
(3) skeletal muscle activity
(4) the effect of venous valves
(5) respiratory activity
(6) effect of cardiac suction
Influencing the pressure
gradient between the veins
and the heart
(secondary factors)
The factors that influences
venous return
• Effect of sympathetic activity on venous return
• Mobilizing the stored blood : sympathetic stimulation produces venous
vasoconstriction , which elevates venous pressure
• Decreasing venous capacity: venous return increase , the contractility of
heart increase, the cardiac output increase
the different outcomes of vasoconstriction in arterioles and veins:
Arteriolar vasoconstriction increase the resistance and reduces flow (less
blood can enter and flow through a narrowed arteriole)
venous Vasoconstriction decrease the capacity and increases flow (narrowing
of veins squeezes out more of the blood that is already present in the veins)
The factors that influences
venous return
• Effect of skeletal muscle activity on venous return
(1) When skeletal muscle contract, veins are
compressed, decreased the venous capacity , increase
the venous return
•Skeletal pump: one way extra blood
stored in the veins is returned to the
heart during exercise
Skeletal pump enhancing the venous return
The factors that influences venous
return
• (2) Skeletal muscle pump counters the effect of
gravity on the venous system
-- Gravity force:
• When a person is lying down , the gravity force is
uniform (no need consider it)
• When a person stands up, the gravity force is not
uniform (the pressure caused by cardiac contraction
and the weight of the column of blood )
90 mm Hg caused by gravitational
effect
10 mm Hg caused by pressure imparted
by cardiac contraction (friction loss)
Pressure=100 mm Hg
P=90mmhg
Effect of contraction of the skeletal
muscles (as in walking ) completely empties
given vein segments, interrupting the
column of blood that must be supported by
the lower veins
The factors that influences venous return
• Effect of venous valves on venous return
Blood can only be driven forward
because the large veins are
equipped with one-way valves
spaced at 2 to 4cm intervals.
Venous valves play a role in
conteracting gravitational effect
by minimizing the backflow of
blood and temporarily supporting
portions of the column of blood
The factors that influences venous return
• Effect of respiratory activity on venous return
as a result of respiratory activity, the pressure inside the chest
averages 5 mm Hg less than atmospheric pressure.
between the lower veins and the chest veins , there is a pressure
gradient
The factors that influences venous return
• Effect of cardiac suction on venous return
• During the contraction , the amount of blood pumping increase , the
venous return increase
• During the relaxation , increasing the vein-to-atria pressure
gradient, venous return enhanced
Regulation of blood pressure
• mean blood pressure is closely regulated (not too high or too low)
• When blood pressure is too low, there is no adequate blood flow
to tissue
• When blood pressure is too high, the workload of heart
increased and the risk of small blood vessels damage or rupture
increased
• MAP=CO X total peripheral resistance
• indicates the determinants of MAP
MAP=DP+1/3pulse pressure
Blood pressure regulation
• Two types:
• Long-term mechanism: related to the regulation of urine
formation and thirst (requiring minutes to days) (humoral
regulation)
• Short-term mechanism: related to the regulation of CO
and total peripheral resistance (within seconds) -Baroreceptor reflex (nervous regulation)
Mean arterial blood pressure
Cardiac output
Heart rate
Total peripheral resistance
Stroke volume
Arteriolar radius
Blood viscosity
RBC
Parasympath
-etic activity
sympath-etic activity
and epinepherine
Effective circulatory
Blood volume
Respirato
-ry activity
Venous
return
Cardiac
suction
Skeletal muscle activity
Local
control
Sympathetic
activity and E
Extrinsic
control
Vasopre
-ssin
Factors influence the BP
• Stroke volume: SV increase, the blood amount in the
artery increase during systole, systole pressure increase
and diastole almost remain constant or increase less
(resistance and HR constant) pulse pressure increase
The systolic pressure change mainly reflect the change
of SV
Factors influence the BP
• Total peripheral resistance : R increase (CO constant) ,
the velocity of the blood flow to tissue decrease, the blood
amount left in the artery increase (during diastole) ,
diastole pressure increase largely , pulse pressure decrease .
• So diastolic pressure change mainly reflect the change of
total peripheral resistance
Factors influence the BP
• Heart rate : HR increase (SV and total peripheral
resistance constant) , the diastole shortening , so blood flow
to down-stream tissue decrease, the left blood in artery
more than before, so diastolic pressure increase largely ,
pulse pressure decrease