• Answer questions about the functional
characteristics of blood, blood vessels and the
heart. This will be measured by lecture and
laboratory exams.
Outline
• Blood flow
• Vessel types
– Arteries
– Blood pressure
– Arterioles
– Capillaries
– Lymphatic system
– Veins
Outline
• Blood flow
– Flow, flow rate, pressure gradients
– Blood distribution, Poiselle’s law
Red and white blood cells within an arteriole.
Arteries branch into arterioles within organs
and deliver blood to the capillaries. SEM X6130.
Artery and Vein. A distributing artery (right)
and a medium-sized vein (left) surrounded
by connective tissue. Arteries and veins
are part of the extensive network of vessels
that make up the vascular system. SEM
X305.
Credit: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited
900019
Blood Flow
• Blood is constantly reconditioned so composition
remains relatively constant
• Reconditioning organs receive more blood than
needed for metabolic needs
– Digestive organs, kidneys, skin
– Adjust extra blood to achieve homeostasis
• Blood flow to other organs can be adjusted
according to metabolic needs
• Brain can least tolerate disrupted supply
100%
Lungs
Right side of heart Left side of heart
Distribution of Cardiac
Output at Rest
Digestive
system
(Hepatic portal
system)
Liver
Kidneys
Skin
Brain
21%
6%
20%
9%
13%
Heart
muscle
3%
Skeletal
muscle
15%
Bone
Other
5%
8%
Fig. 10-1, p. 344
Blood Flow
• Flow rate through a vessel (volume of blood passing
through per unit of time) is directly proportional to
the pressure gradient and inversely proportional to
vascular resistance
F = ΔP
R
F = flow rate of blood through a vessel
ΔP = pressure gradient
R = resistance of blood vessels
Blood Flow
• Pressure gradient is pressure difference between beginning
and end of a vessel
– Blood flows from area of higher pressure to area of lower
pressure
• Resistance is measure of opposition of blood flow through a
vessel
– Depends on three things
• Blood viscosity, vessel length, vessel radius
– Major determinant of resistance to flow is vessel’s radius
– Slight change in radius produces significant change in
blood flow
R is proportional to 1
r4
Relationship of
Resistance and Flow
to Vessel Radius
Vascular Tree
• Closed system of vessels
• Consists of
– Arteries
• Carry blood away from heart to tissues
– Arterioles
• Smaller branches of arteries
– Capillaries
• Smaller branches of arterioles
• Smallest of vessels across which all exchanges are made
with surrounding cells
– Venules
• Formed when capillaries rejoin
• Return blood to heart
– Veins
• Formed when venules merge
• Return blood to heart
Airway
Lungs
Air sac
Pulmonary
capillaries
Arterioles
Venules
PULMONARY
CIRCULATION
Pulmonary
artery
Basic Organization of
the Cardiovascular
System
Pulmonary
veins
Aorta
(major
systemic
artery)
Systemic
veins
SYSTEMIC
CIRCULATION
Tissues
Venules
For simplicity, only
two capillary beds within
two organs are illustrated.
Systemic
capillaries
Arterioles
Smaller arteries
branching off to
supply various tissues
Fig. 10-4, p. 349
Endothelium
Venous
valve
Elastin
fibers
Endothelium
Smooth
muscle
Smooth
muscle;
elastin
fibers
Elastin
fibers
Relative Thickness
of Layers in Wall
Large artery
Connective
tisssue coat
(mostly
collagen
fibers) Arteriole
Capillary
Connective
tisssue coat
(mostly
collagen
fibers)
Large vein
Endothelium
Elastin fibers
Smooth muscle
Collagen fibers
Table 10-1, p. 348
Outline
• Arteries
– “pressure reservoir”
– anatomy
Arteries
• Specialized to
– Serve as rapid-transit passageways for blood
from heart to organs
• Due to large radius, arteries offer little resistance to
blood flow
– Act as pressure reservoir to provide driving force
for blood when heart is relaxing
• Arterial connective tissue contains
– Collagen fibers
» Provide tensile strength
– Elastin fibers
» Provide elasticity to arterial walls
Arteries as a Pressure Reservoir
Outline
• Blood pressure
– Systolic/diastolic
– Measurements
• Pressure and pulse
– Mean arterial pressure
– Pressure abnormalities
Blood Pressure
• Force exerted by blood against a vessel wall
– Depends on
• Volume of blood contained within vessel
• Compliance of vessel walls how easily the vessel
distends when it fills with blood
• Systolic pressure
– Peak pressure exerted by ejected blood against
vessel walls during cardiac systole
– Averages 120 mm Hg
• Diastolic pressure
– Minimum pressure in arteries when blood is
draining off into vessels downstream
– Averages 80 mm Hg
Blood Pressure
• Can be measured indirectly using
sphygmomanometer and stethascope
– Sounds heard when determining blood pressure
– Sounds are distinct from heart sounds associated
with valve closure
Pressure-recording
device
Stethoscope
Inflatable
cuff
Fig. 10-8a, p. 344
Blood
Pressure
Show animation
Pulse Pressure
• Pressure difference between systolic and diastolic
pressure
• Example
– If blood pressure is 120/80, pulse pressure is 40
mm Hg (120mm Hg – 80mm Hg)
• Pulse that can be felt in artery lying close to surface
of skin is due to pulse pressure
Mean Arterial Pressure
• Average pressure driving blood forward into tissues
throughout cardiac cycle
• Formula for approximating mean arterial pressure
Mean arterial pressure = diastolic pressure + ⅓ pulse pressure
At 120/80, mean arterial pressure = 80 mm Hg +
⅓ (40 mm Hg) = 93 mm Hg
Pressure in various vessels
Systolic pressure
120
110
Mean pressure
100
Pressure (mm Hg)
90
80
Diastolic
pressure
70
60
50
40
30
20
10
0
Left
ventricle
Large
arteries
Arterioles Capillaries
Venules and veins
Fig. 10-9, p. 352
Outline
• Arterioles
– Resistance vessels
– Vasoconstriction and vasodilation
– Regulation of arteiolar diameter
• Local factors
• Endothelial cells, nitric oxide
Arterioles
• Major resistance vessels
• Radius supplying individual organs can be adjusted
independently to
– Distribute cardiac output among systemic organs,
depending on body’s momentary needs
– Help regulate arterial blood pressure
Arterioles
• Mechanisms involved in adjusting arteriolar
resistance
– Vasoconstriction
• Refers to narrowing of a vessel
– Vasodilation
• Refers to enlargement in circumference and radius of
vessel
• Results from relaxation of smooth muscle layer
• Leads to decreased resistance and increased flow
through that vessel
Arteriolar Vasoconstriction and Vasodilation
Arterioles
• Only blood supply to brain remains constant
• Changes within other organs alter radius of vessels
and adjust blood flow to organ
• Local chemical influences on arteriolar radius
– Local metabolic changes
– Histamine release
• Local physical influences on arteriolar radius
– Local application of heat or cold
– Chemical response to shear stress
– Myogenic response to stretch
Magnitude and Distribution
Of the Cardiac Output at Rest
and During Moderate Exercise
Arterioles
• Specific local chemical factors that produce
relaxation of arteriolar smooth muscle
– Decreased O2
– Increased CO2
– Increased acid
– Increased K+
– Increased osmolarity
– Adenosine release
– Prostaglandin release
Arterioles
•
•
Local vasoactive mediators
– Endothelial cells
• Release chemical mediators that play key role in locally regulating arteriolar
caliber
• Release locally acting chemical messengers in response to chemical
changes in their environment
• Among best studied local vasoactive mediators is nitric oxide (NO) causes
releaxation of arteriolar smooth muscle (vasodilation)
Specific local chemical factors that produce relaxation of arteriolar smooth muscle
– Decreased O2
– Increased CO2
– Increased acid
– Increased K+
– Increased osmolarity
– Adenosine release
– Prostaglandin release
Arterioles
•
Extrinsic control
– Accomplished primarily by sympathetic nerve influence
– Accomplished to lesser extent by hormonal influence over arteriolar
smooth muscle
•
Cardiovascular control center
– In medulla of brain stem
– Integrating center for blood pressure regulation
•
Other brain regions also influence blood distribution
– Hypothalamus
• Controls blood flow to skin to adjust heat loss to environment
•
Hormones that influence arteriolar radius
– Adrenal medullary hormones
• Epinephrine and norepinephrine
– Generally reinforce sympathetic nervous system in most organs
• Vasopressin and angiotensin II
– Important in controlling fluid balance
Outline
• Capillaries
– Exchange and anatomy
– Pressures driving diffusion
Capillaries
• Thin-walled, small-radius, extensively branched
• Sites of exchange between blood and surrounding
tissue cells
– Maximized surface area and minimized diffusion
distance
– Velocity of blood flow through capillaries is
relatively slow
• Provides adequate exchange time
– Two types of passive exchanges
• Diffusion
• Bulk flow
• Factors affecting diffusion
– Ficks law of diffusion
– Slow blood velocity
– Permeability
– Metarterioles and precapillary sphincters
– Exchanges
• Blood to interstitial fluid to cell
– Passive
– Active
– Bulk Flow
• Ultrafiltration
• reabsorption
Table 3-1, p. 62
Fig. 10-16, p. 355
Glucose
O2
CO2
Plasma
Interstitial
fluid
Facilitated
diffusion
by carrier
Glucose + O2
CO2 + H2O + ATP
Tissue cell
Fig. 10-21, p. 366
Bulk Flow
• Bulk flow occurs when protein-free plasma filters out of
the capillary, mixes with the interstitial fluid and then is
reabsorbed.
• Important in regulating the distribution of ECF between
plasma and interstitial fluid to help maintain arterial blood
pressure.
• Depends on two processes:
– Ultrafiltration occurs when pressure inside the capillary exceeds
pressure outside and fluid is pushed out through the pores.
– Reabsorption occurs when inward-driving pressures exceed outward
pressures and net movement of fluid back into the capillaries occurs.
• Bulk flow occurs because of differences in the:
– Hydrostatic pressure (pushes fluid out of the capillary bed)
– Colloid osmotic pressures between plasma and interstitial fluid.
– Plasma colloid osmotic pressure draws fluid back into the capillary bed.
FORCES AT ARTERIOLAR
END OF CAPILLARY
FORCES AT VENULAR
END OF CAPILLARY
Net exchange pressure = (Pc + PIF) – (Pp + PIF)
• Outward pressure
• Inward pressure
11 mm Hg
(ultrafiltration)
Net outward pressure
of 11 mm Hg =
Ultrafiltration pressure
From arteriole
All values are given in mm Hg.
Pc
Pp
PIF
PIF
Interstitial
fluid
Initial
lymphatic
vessel
9 mm Hg
(reabsorption)
To venule
• Outward pressure
• Inward pressure
Net inward pressure
of 9 mm Hg =
Reabsorption pressure
Blood capillary
Capillary blood pressure
Plasma colloid osmotic pressure
Interstitial fluid hydrostatic pressure
Interstitial fluid colloid osmotic pressure
Fig. 10-22, p. 367
Arteriole
Smooth muscles
Precapillary
sphincter
Metarteriole
Myogenic tone
Stopcock
Local metabolic
changes
Capillary
Venule
Fig. 10-19, p. 357
Capillaries
• Narrow, water-filled gaps (pores) lie at junctions
between cells
• Permit passage of water-soluble substances
• Lipid soluble substances readily pass through
endothelial cells by dissolving in lipid bilayer barrier
• Size of pores varies from organ to organ
Capillaries
• Under resting conditions many capillaries are not
open
• Capillaries surrounded by precapillary sphincters
• Contraction of sphincters reduces blood flowing into
capillaries in an organ
• Relaxation of sphincters has opposite effect
• Metarteriole
– Runs between an arteriole and a venule
Systemic
circulation
Lymphatic
System
Lymph node
Pulmonary
circulation
Initial
lymphatics
Lymph vessel
Valve
Blood
capillaries
Veins
Arteries
Heart
Lymph
node
Initial
lymphatics
(a) Relationship of lymphatic system to circulatory system
Blood
capillaries
Fig. 10-25, p. 369
Lymphatic System
•
•
•
•
•
Extensive network of one-way
vessels
Provides accessory route by
which fluid can be returned
from interstitial to the blood
Initial lymphatics
– Small, blind-ended terminal
lymph vessels
– Permeate almost every
tissue of the body
Lymph
– Interstitial fluid that enters a
lymphatic vessel
Lymph vessels
– Formed from convergence
of initial lymphatics
– Eventually empty into
venous system near where
blood enters right atrium
– One way valves spaced at
intervals direct flow of
lymph toward venous outlet
in chest
Lymphatic System
• Functions
– Return of excess filtered fluid
– Defense against disease
• Lymph nodes have phagocytes which destroy bacteria
filtered from interstitial fluid
– Transport of absorbed fat
– Return of filtered protein
elephantiasis
Outline
• Veins
– Capacitance vessels
– Regulation of pressure and flow
– Venous return
Veins
• Venous system transports blood back to heart
• Capillaries drain into venules
• Venules converge to form small veins that exit
organs
• Smaller veins merge to form larger vessels
• Veins
– Large radius offers little resistance to blood flow
– Also serve as blood reservoir
Pulmonary
vessels
9%
Systemic arteries
13%
Systemic arterioles
2%
Heart
7%
Systemic capillaries
5%
Systemic veins
64%
Capacitance!
Fig. 10-27, p. 364
Veins
• Factors which enhance venous return
– Driving pressure from cardiac contraction
– Sympathetically induced venous vasoconstriction
– Skeletal muscle activity
– Effect of venous valves
– Respiratory activity
– Effect of cardiac suction
Skeletal muscle pump
Fig. 10-29, p. 366
Standing
Walking
Heart
Thigh
150 cm
Calf
34 cm
Foot
100
mm Hg
Foot vein supporting
column of blood 1.5 m
(150 cm) in height
Venous
pressure
in foot
27
mm Hg
Foot vein supporting
column of blood
34 cm in height
Fig. 10-31, p. 367
Vein
Open venous valve
permits flow of
blood toward heart
Contracted
skeletal muscle
Closed venous valve
prevents backflow
of blood
Stepped art
Fig. 10-32, p. 368
Factors that Influence Venous Return
summary