A Study of Blood Vessels
Mike Clark, M.D.
Types of Blood Vessels
1. Arteries
2. Capillaries
3. Veins
Three Generic Circulations in the Body
1. Systemic – blood goes from left ventricle to Right Atrium
2. Pulmonary – blood goes from right ventricle through
lungs to left atrium
3. Hepatic Portal – venous circulation – drains blood from
portions of gastrointestinal tract (intestines) and takes it
to the liver
Schematic System Circulation
Figure 19.2
Pulmonary Circulation
Figure 19.18a
Hepatic Portal Circulation
Cross Section of Typical Blood Vessel
Figure 19.1b
Tunica interna (intima)
• composed of endothelium cells (simple
squamous) - these cells must be smooth
in order to not to activate the intrinsic
clotting cascade – additionally these cells
secrete various paracrine chemicals
• Basement membrane or basal lamina
• Small amount of loose connective tissue
• In some vessels have an internal elastic
lamina composed of elastin – particularly
in muscular arteries
Tunica Media
• Composed of various amounts of smooth
muscle depending on the blood vessel
type
• Composed of some loose connective
tissue
• Larger muscular arteries have an external
elastic lamina
Tunica Adventitia
• Outermost layer of blood vessels – composed of
fibroblasts, collagen and elastic fibers. This layer
becomes continuous with the connective tissue
elements surround the blood vessel – so the
vessel in held in place.
• Vasa Vasorum – in the walls of the larger thicker
blood vessels – the cells of the vessel wall itself
needs a blood supply – thus “a vessel to a vessel”.
Since veins generally have less oxygen than
arteries – the larger veins need more vasa
vasorum vessels than the larger arteries
• Note: larger thick lymphatic vessels also have
vasa vasorum vessels
Types of Blood Vessels
• Arteries
• Arterioles (resistance vessels)
• Capillary Bed (inclusive of capillaries) –
exchange vessels
• Post Capillary Venules – location where most
white blood cells leave circulation
(diapedesis)
• Venules
• Small, Medium and Large Veins (capacitance
vessels)
Figure 19.1
Arteries
• Artery – a blood vessel that transports blood away from the heart.
The arteries branch considerably as they get further from the heart
and the diameter gets smaller. There different types of arteries.
Types of Arteries
1. Elastic (Conducting) Arteries – arteries proximal to the heart that
can easily stretch and conduct blood from the heart ( aorta, common
carotids, subclavian, common iliac arteries and pulmonary trunk
2. Muscular (Distributive) Arteries –arteries with considerable
smooth muscle in the walls – thus can vasoconstrict and channel
(distribute) blood to organs that need it. The muscular arteries
include almost all of the arteries in the body besides those of the
elastic – these arteries are large, medium and small.
3. Arteriole – (resistance vessel) very, very tiny artery with a diameter
of 0.1mm or less – but considerable smooth muscle in the wall – can
perform considerable vasoconstriction (resistance).
Table 19.1 (1 of 2)
Figure 19.1a
Capillaries and Capillary Bed
• Capillaries (exchange vessels) are short length (0.25
μm – 1 μm) and thin diameter (10 μm - 30 μm) small
vessels. There walls are very thin and sometimes
porous (fenestrated, sinusoidal) – thus providing great
diffusive ability. The three anatomical types of capillaries
will be discussed later in this PowerPoint.
• True capillaries are generally located in capillary
beds. There are millions of capillary beds in the body.
Each population cells needs a capillary bed in order to
get oxygen and nutrients.
• Capillary beds contain metarterioles and
thoroughfare channels.
Table 19.1 (2 of 2)
Figure 19.4
Venules and Veins
• Vein (capacitance vessels) – a blood vessel that
returns blood back to the heart. As with arteries – there
are different types of veins.
Types of Veins
1. Post capillary venule – A tiny (15 μm – 20 μm) blood
vessel that has a wall as thin as the capillaries – this is
where most white blood cells leave the circulation
(diapedesis)
2. Small, medium (less than 1 cm) and large veins
Veins generally have a wider inside lumen diameter
than an artery – and have less smooth muscle in their
walls. It was this reason that veins easily stretch and
hold onto to more blood. Most of the blood (around
60%) in the body is located in the veins (high
capacitance) at any given time.
Table 19.1 (2 of 2)
Figure 19.1a
Secretions and receptors of Endothelial Cells
•Collagens Type II, IV, and V
•Lamin – type of intermediate filament
•Endothelin – causes vasoconstriction
•Nitric Oxide – (Endothelial Derived Relaxing Factor) has many
actions like vasodilation and keeps platelets off wall of blood
vessels
•Von Willebrand Factor – used to assist Clotting Factor VIII to
work
•Angiotensin Converting Enzyme – converts angiotensin I to
angiotensin II
•Enzymes that degrade Bradykinin, Serotonin, Prostaglandins,
Thrombin and Norepinephrine
•Can Bind Lipoprotein Lipase
1. Normally the intact endothelium produces
prostacyclin (PGI2)and Nitric Oxide, which
inhibit platelet aggregation. It also blocks
coagulation by the presence of
thrombomodulin and heparin-like
molecule on its surface membrane. These
two membrane-associated molecules
inactivate specific coagulation factors.
2. Injured endothelial cells release Von
Willebrand factor and tissue
thromboplastin and cease the production
and expression of inhibitors of coagulation
and platelet aggregation. They also release
endothelin, a powerful vasoconstrictor.
Factors Preventing Undesirable
Clotting
• Unnecessary clotting is prevented by
endothelial lining the blood vessels
• Platelet adhesion is prevented by:
– The smooth endothelial lining of blood vessels
– Heparin and PGI2 secreted by endothelial
cells
– Vitamin E quinone, a potent anticoagulant
Smooth Muscle
For an understanding of smooth muscle excitation- contraction please refer
To my PowerPoint Smooth Muscle Excitation Contraction under A&P II
Figure 9.25
Figure 9.26
Smooth muscle
like cardiac
muscle receives
some calcium
from the outside
of the cell for
contraction thus it too can be
slightly relaxed
by administering
calcium channel
blocker
medications.
Figure 9.27
Classes of Calcium Channel Blockers
1. Dihydropyridine calcium channel blockers are often used to
reduce systemic vascular resistance "-dipine".
Amlodipine (Norvasc)
Nifedipine (Procardia, Adalat)
2. Phenylalkylamine calcium channel blockers are relatively
selective for myocardium, reduce myocardial oxygen demand
and reverse coronary vasospasm, and are often used to treat
angina. They have minimal vasodilatory effects. Therefore, as
vasodilation is minimal with the phenylalkylamines, the major
mechanism of action is causing negative inotropy.
Phenylalkylamines are thought to access calcium channels
from the intracellular side, although the evidence is somewhat
mixed.
Verapamil (Calan, Isoptin)
Gallopamil (Procorum, D600
3. Benzothiazepine calcium channel blockers
are an intermediate class between
phenylalkylamine and dihydropyridines in their
selectivity for vascular calcium channels. By
having both cardiac depressant and vasodilator
actions, benzothiazepines are able to reduce
arterial pressure without producing the same
degree of reflex cardiac stimulation caused by
dihydropyridines.
Diltiazem (Cardizem)
Mathematical Analysis of the Circulatory System
1.
2.
3.
4.
5.
•
•
6.
7.
8.
9.
Discussion of Pressure
Discussion of Pressure in a pipe without an external
compression device (pressure in the blood vessels without the
heart) known as “Mean Circulatory Filling Pressure”. Discuss
unstressed and stressed blood volume
Discuss pressure in blood vessels with heart compression
Discuss Flow – velocity of flow versus rate of flow
Discuss Resistance –
resistance in pipes arranged in series versus those arranged in
parallel
Total Peripheral Resistance
Examine Diffusion Formula
Examine Capacitance (Compliance) Formula
Examine the Mean Arterial Pressure Formulas
Wall Tension
Formulas of importance
Flow = ∆P/ R, ∆P is the change in pressure from one area to
another (P1 – P2) – in the direction of flow, R is the resistance
(Note: pressure drops off as a fluid or gas passes further down
the pipe – thus the pressure in proximal area 1 (P1) is higher
than the pressure is distal area 2. The more pressure drop off
the more the flow. Also, the less the resistance the better the
flow.
• Rate of Flow = amount of gas or liquid/time (example
ml/min)
• Velocity of flow = amount of gas or liquid/time/cross sectional
area (another way of looking at it is Vf = rate of flow/cross
sectional area)
example of velocity of flow ml. /min per cm2
Note: Area of a circle (like the inside of a vessel ) = equals pi
(π) times the radius squared (π⋅r2), example ml. /min per cm2
Flow formula derived Ohm’s Law
Formulas of Importance
• Resistance –a force of impedance (holding
back) R = 8ηL/πR4 , η is viscosity of the gas or
liquid, L is the length of the vessel, and R is the
resistance raised to the 4th power
• Summation (∑) of Resistances – adding up the
resistors in flow arrangement a series arrange
• Resistors in series – one resistor in front of
another ∑ = R1 + R2 + R3 + ……
• Resistors in parallel – a pipe leads into a
branching set of pipes ∑ = 1/R1 + 1/R2 + 1/R3 +..
• Note: resistors in parallel give less total
resistance than those in series (think of the
capillary arrangement)
Total Peripheral Resistance (Systemic
Vascular Resistance)
• The TPR (SVR) is the summation (∑ ) of all the
resistors in the systemic (Left Ventricle – to Right
Atrium) circulation. Some of the blood vessel resistors
are in series (R1 + R2 + R3 + ……) and some are in
parallel (1/R1 + 1/R2 + 1/R3 )– thus the two different
formulas must be used.
• Since R is raised to 4th power it numerically is the most
significant contributor to Total Peripheral Resistance –
thus vasoconstriction and vasodilation are the most
important contributors to TPR.
• Alternate calculations are Total Pulmonary Resistance
which is resistance in the pulmonary circulation – as
well as other organ and circulatory resistances can be
calculated
Formulas of Importance
Diffusion – net movement of certain particles from a region of
high concentration of those certain particles to region of low
concentration of those certain particles
D = A x Dc /t (Co – Ci)
• A is the area of the membrane being diffused through, Dc is
the diffusion coefficient, t- is the thickness of the membrane
being diffused through, Co – Ci is the concentration
difference between the o (outside) and I (inside) of the
container
• The diffusion coefficient = solubility coefficient divided by the
square root of the molecular weight of the substance diffusing
(this applies more to gases)
• Analysis- the greater the area and/or diffusion coefficient –
the faster the rate of diffusion. The more the concentration
difference the faster the rate of diffusion. However, the
thicker the membrane to diffuse through the slower the rate
of diffusion.
Formulas of Importance
• Capacitance (Compliance) C – is the ease at
which a container can stretch to accommodate
increased volumes of gases or liquids.
C = ∆V/∆P,
• ∆P is change in pressure, and ∆V is change in
volume
• The more volume change without a change in
pressure (due to compression of atoms and
molecules in a minimally stretchable container)
the greater the capacitance (compliance)
• Thus a balloon would have greater capacitance
(compliance) that a leather container.
Laminar Flow Versus Turbulent Flow
Laminar flow, sometimes known as streamline flow, occurs
when a fluid flows in parallel layers, with no disruption between
the layers. It is the opposite of turbulent flow. In nonscientific
terms laminar flow is "smooth," while turbulent flow is "rough."
Laminar Flow is a quiet smooth flow through blood vessels –
whereas turbulent flow makes a noise as it flows – the more
turbulent the flow the louder the noise.
Turbulent flow produces murmur like sounds in the heart.
A Bruit is the unusual sound that blood makes when it rushes
past an obstruction (called turbulent flow) in an artery when the
sound is auscultated with the bell portion of a stethoscope. A
related term is "vascular murmur", which should not be
confused with a heart murmur.
Note- that once laminar flow hit the obstruction (like blood wall
atherosclerotic plaque – it converted to turbulent flow.
Reynolds number (Re) is the ratio of inertial forces to viscous forces and is given by
the formula:
Re = ρVD/μ
where ρ = density of the fluid, V = velocity, D = pipe diameter, and μ = fluid viscosity.
Reynolds number is used to determine whether a flow will be laminar or turbulent. If Re
is high (>2100), inertial forces dominate viscous forces and the flow is turbulent; if Re
number is low (<1100), viscous forces dominate and the flow is laminar.
Determining if flow is Laminar
versus Turbulent
The Reynolds number is used to determine
whether a flow will be laminar or turbulent.
Reynolds number (Re) is the ratio of inertial
forces to viscous forces and is given by the
formula:
Re = ρVD/μ
where ρ = density of the fluid, V = velocity, D = pipe diameter,
and μ = fluid viscosity.
If Re is high (>2100), inertial forces dominate viscous forces
and the flow is turbulent; if Re number is low (<1100), viscous
forces dominate and the flow is laminar.
Mean Arterial Pressure
It is defined as the average arterial pressure during a
single cardiac cycle.
MAP (SYSTEMIC) = CO X TPR (SVR)
MAP (SYSTEMIC) is the average pressure in the
systemic circulation (Left Ventricle to Right Atrium).
Thus MAP (pulmonic) can be calculated also as
well as other circulations.
CO is the cardiac output = heart rate x stroke volume
(stroke volume is End Diastolic Volume – End
Systolic Volume)
TPR (SVR) is the total resistance in the systemic
circulation
MAP (SYSTEMIC) = CO X TPR (SVR)
• This formula is an excellent one to use to understand
pressures in the blood vessels. It can explain hypertensive
pressures, normotensive pressures and hypotensive
pressures. However, it cannot be actually calculated in that
the TPR cannot be calculated. TPR in involves calculating
the radius of the blood vessels at each millimeter along the
circulation – the human body has approximately 60,000
miles of blood vessels – thus this is impossible to calculate.
• The algebraic formula used to calculate MAP is
MAP = DBP + 1/3 (SBP – DBP)
DBP is the Diastolic Blood Pressure, and SBP is the Systolic
Blood Pressure
SBP – DBP is the Pulse Pressure
MAP = DBP + 1/3 (SBP – DBP)
Systolic Blood Pressure – occurs during Ejection Contraction Time
The Diastolic Blood Pressure has more weight (significance) in this
formula – because during one cardiac cycle there is more time
spent in diastole in the blood vessels than is systole. The actual
way MAP is calculated by the computer (arterial line) is using
differential Calculus. Differential calculus exactly calculates the
area under a curve.
Blood Vessel Wall Tension
• Tension = Pressure inside vessel x r/ 2
• r is radius of the vessel
• Interpretation: For a given blood pressure, increasing the
radius of the blood vessel leads to a linear increase in
tension. This implies that large arteries must have thicker
walls than small arteries in order to withstand the level of
tension.
Arteries
1. Elastic (Conducting) Arteries – first vessels to leave heart –
act as a second pump – since the heart is an intermittent
pump. (Aorta, Common Carotids, Subclavian, Common
iliacs and pulmonary trunk)
2. Muscular (Distributive) Arteries
arteries with considerable smooth muscle in the walls – thus can vasoconstrict and
channel (distribute) blood to organs that need it. The muscular arteries include
almost all of the arteries in the body besides those of the elastic – these arteries are
large, medium and small.
3. Arterioles (Resistance Vessels)
• very, very tiny artery with a diameter of 0.1mm or less –
but considerable smooth muscle in the wall – can
perform considerable vasoconstriction (resistance).
4. Capillary and Capillary Bed
• True capillary (three types) continuous,
fenestrated and sinusoidal – degree of
permeability makes the difference
• Metarteriole – tiny blood vessel with space
intermittent smooth muscle in its wall – generally
its entrance is guarded by a precapillary
sphincter
• Precapillary sphincter – valve type structure
comprised of surrounding smooth muscle at the
entrance of metarterioles and true capillaries
• Thoroughfare channels – anatomic structure
with very low resistance and not guarded by a
precapillary sphincter – leads to venules
Capillaries are the exchange (diffusion) vessels. There are millions of capillary beds in
the body. Each population cells needs a capillary bed in order to get oxygen and
nutrients.
The true capillary and the associated capillary bed are excellent for diffusion because (1)
they have very thin walls (2) a large cross sectional area to diffuse through and (3) the
large cross sectional area slows the velocity of flow (4) they are narrow in diameter (10
μm - 30 μm) therefore less distance from lumen to membrane. Because they are narrow
in diameter – this could significantly increase the resistance – but the parallel
arrangement reduces this.
D = A x Dc /t (Co – Ci)
Capillary
• The the peripheral circulation of the whole body has
about 10 billion capillaries with a total surface area
estimated to be 500 -700 square meters (about 1/8th the
surface area of a football field). It is rare for any
functional cell of the body to be more than 20 – 30
micromillimeters from a capillary – definitely no more
than 100 micromillimeters.
Blood Flow Through Capillaries
• Vasomotion
– Slow and intermittent flow
– Reflects the on/off opening and closing of
precapillary sphincters
Parallel arrangement of vessels reduces resistance.
R = 1/R1 + 1/R2 + 1/R3
Capillary bed has very slow
velocity of flow due to its large
cross sectional area.
Figure 19.13
Capillaries
The three anatomical types of capillaries differ in the
degree of permeabilities
Three anatomical types
1. Continuous capillaries (least permeable)
2. Fenestrated capillaries (medium permeability)
3. Sinusoidal capillaries (sinusoids) – very
permeable
Continuous capillary
Fenestrated capillary
Sinusoidal Capillary
Figure 19.3
Continuous Capillaries
• Abundant in the skin and muscles
– Tight junctions connect endothelial cells
– Intercellular clefts allow the passage of fluids and
small solutes
• Continuous capillaries of the brain & Thymus
– Tight junctions are complete, forming the bloodbrain barrier and in the thymus Gland- forming the
blood-thymic Barrier
– In brain the capillaries are surrounded by
astrocytes and in the thymus surrounded by
reticular epithelial cells
Continuous capillary
Least permeable capillaries found in skin and muscles. Blood – Brain barrier
and Blood- Thymic Barrier have even less permeability.
Figure 19.3a
Fenestrated Capillaries
• Some endothelial cells contain pores
(fenestrations)
• More permeable than continuous
capillaries
• Function in absorption or filtrate formation
(small intestines, endocrine glands, and
kidneys)
Fenestrated Capillary
Have more permeability – found in small intestine and endocrine
glands, kidneys
Figure 19.3b
Sinusoidal Capillaries
• Fewer tight junctions, larger intercellular
clefts, large lumens
• Usually fenestrated
• Allow large molecules and blood cells to
pass between the blood and surrounding
tissues
• Found in the liver, bone marrow, spleen
Sinusoidal Capillary
Have considerable permeability – found in liver, spleen, bone marrow and adrenal
medulla
Figure 19.3c
What routes do
substances enter
and exit the
capillaries?
1. Diffusion through
the endothelial cells
(transcellular) - transudative
2. Diffusion between
the endothelial cells
(exudative)
3. Movement through
the fenestra
4. Movement using
pinocytotic
Vesicles
(pinocytosis).
Figure 19.15
Capillary Exchange of Respiratory
Gases and Nutrients
• Diffusion of
– O2 and nutrients from the blood to tissues
– CO2 and metabolic wastes from tissues to the blood
• Lipid-soluble molecules diffuse directly through
endothelial membranes (Transudative)
• Water-soluble solutes pass through clefts and
fenestrations (Exudative)
• Larger molecules, such as proteins, are actively
transported in pinocytotic vesicles or caveolae
Understanding the significance of the capillary
Slide 1
As you should be aware of – the blood circulation,
unlike the lymphatic circulation, is a continuous loop –
a continuous set of pipes from the heart and back to
the heart.
The purpose of the bloodstream is to act as a
transportation system -transporting good fresh
materials to the tissue cells and picking up the tissue
cells’ waste so as to transport these substances to
the organs (kidneys, sweat glands, etc) that can
excrete them from the body.
Understanding the significance of the capillary
Slide 2
The entrance into and out of the bloodstream
for the fresh substances and waste is by simple
diffusion. Diffusion (Diffusion Equation) occurs
best through a barrier that is thin (the capillary
wall). If blood goes into a pipe that is thin – it
will unload its fresh products there and pickup
waste there – it has no choice but to do this- it
does not have a brain that gives it a choice
where to pickup and deliver substances– just
wherever the wall is thin enough. Thus the
blood cannot enter a thin walled pipe unless it
is ready to unload and load substances.
Understanding the significance of the capillary
Slide 3
Therefore, if the cells in the toe (for example)
need some fresh substances and/or need to
unload waste – the blood going to the toe
should not enter a thin walled pipe (capillary)
till it gets to the toe. Thus the blood needs to
stay in the thicker walled pipes (arteries,
arterioles) on the way to the toe capillaries
(thin walled) – unload the fresh stuff and pick
up the waste – then again enter a thick
walled pipe (veins) till it gets to the area
where it will unload the waste.
Understanding the significance of the capillary
Slide 3
In our continuous loop circulation - the
capillaries act as the exchange vessels. All
the other blood vessels from the heart
(arteries and arterioles) and back to the heart
(venules and veins) are conduit vessels
(hallways) getting the blood to the main area
of work for the bloodstream – the capillaries where all the fresh materials needed for
tissue cells exits the bloodstream and all of
the waste enters the bloodstream.
Net Filtration Pressure
The next slide will explain how water enters and leaves the
capillaries.
There are many substances that enter and leave the capillaries
(gases, nutrients, hormones, etc.) using simple diffusion – but net
filtration pressure only explains how water enters and exits the
capillaries.
Starling’s Law of the Capillaries states that the amount of water
exiting the capillary should equal the amount of water reentering
the capillary.
If more water exits the capillary than reenters – edema occurs in
that area. On the other hand if more enters that leaves that area
becomes dehydrated.
Net Filtration Pressure Calculation
NFP = (Amount of Fluid out of capillary) – (Amount of Fluid
Reentering capillary)
NFP is generally calculated at two locations – at the arteriolar
end of the capillary (water exit location) and at the more distal
venous end of the capillary (water reentry into capillary
location)
------------------------------------Forces out of capillary are (1) Hydrostatic (water) pressure of
the blood – which is the mean arterial pressure (average
blood pressure) – this pressure pushes water out of the
capillary and (2) osmotic Pressure of the surrounding tissue
fluids – sucking the water out of the blood vessels.
Forces into capillary are (1) Hydrostatic (water) pressure of
the surrounding tissue fluids – pushing water into the
capillary and (2) osmotic pressure of the blood – sucking
water back into the capillary.
Arteriole
Venule
Interstitial fluid
Net HP—Net OP
(35—0)—(26—1)
Net
HP
35
mm
Capillary
Net
OP
25
mm
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
Net HP—Net OP
(17—0)—(26—1)
Net
HP
17
mm
Net
OP
25
mm
NFP is ~8 mm Hg;
fluid moves in
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HPc)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HPif)
• Pushes fluid into capillary
• 0 mm Hg in this example
OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OPc)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OPif)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Figure 19.17
Net Filtration Pressure is a calculation for fluid transfer into and out of capillaries
Figure 19.16
• NFP (arterial end) = (35 mm Hg + 1mm Hg) - (26 mmHg + 0) = 10 out
• NFP (venous end) = (17 mmHg + 1 mmHg) – (26 mm Hg + 0) = 8 in
• At the arterial end of a bed, hydrostatic forces dominate (fluids
flow out) and at the venous end forces dominate back into
blood vessel – however more fluid does exit than comes back
in – the role of the lymphatics is to correct that amount.
The lymphatics return the
excess fluid to the circulation.
Now hopefully, you can understand
that if the lymphatics are blocked
in a certain area of the body, that
area will swell (edema).
Venules, Veins
• Vein (capacitance vessels) – a blood
vessel that returns blood back to the heart.
As with arteries – there are different types
of veins.
• By the time the blood has reached the
veins it is fairly devoid of pressure – so the
dependent veins (veins below the heart)
need external compression to bring blood
back to heart – they also need valves.
Venules
• Formed when capillary beds unite
• Very porous; allow fluids and WBCs into
tissues
• Postcapillary venules consist of
endothelium and a few pericytes
• Larger venules have one or two layers of
smooth muscle cells
Veins
• Formed when venules converge
• Have thinner walls, larger lumens
compared with corresponding arteries
• Blood pressure is lower than in arteries
• Thin tunica media and a thick tunica
externa consisting of collagen fibers and
elastic networks
• Called capacitance vessels (blood
reservoirs); contain up to 65% of the blood
supply
C = ∆V/∆P
Pulmonary blood
vessels 12%
Systemic arteries
and arterioles 15%
Heart 8%
Capillaries 5%
Systemic veins
and venules 60%
Veins are our
capacitance
vessels – they
contain most of
the blood in the body
at any given time.
Figure 19.5
Little to no pressure in veins – so hard to get venous return to
In the dependent body areas.
Figure 19.5
Need external compression
and valves to assist blood
back to the heart in the
dependent body areas (areas
of the body below the heart)
If blood cannot come
back to the heart get
“venous stasis”.
This could lead to Deep
Venous Thrombosis or
Varicose Veins.
Figure 19.6
Differences Between Arteries
and Veins
Arteries
Veins
Delivery
Blood pumped into single
systemic artery—the aorta
Blood returns via
superior and interior
venae cavae and the
coronary sinus
Location
Deep, and protected by tissues
Both deep and superficial
Pathways
Fairly distinct
Numerous
interconnections
Supply/drainage
Predictable supply
Usually similar to
arteries, except dural
sinuses and hepatic
portal circulation
Vascular Anastomoses
• Interconnections of blood vessels
• Arterial anastomoses provide alternate
pathways (collateral channels) to a given
body region
– Common at joints, in abdominal organs, brain,
and heart
• Vascular shunts of capillaries are
examples of arteriovenous anastomoses
• Venous anastomoses are common
• End Artery – when only one artery goes to
an area (kidney for example) no collateral
THE PULSES
Pulse
• The pulse rate generally is the same as the
heart rate – thus normal resting pulse rate is
between 60 and 100.
• The pulse pressure is the difference
between the systolic blood pressure and the
diastolic pressure – generally equal to slightly
greater than 40 mmHg. Various conditions
can lower or elevate the pulse pressure. Low
blood volume can decrease pulse pressure,
exercise may temporarily elevate pulse
pressure and stiffness of major arteries may
consistently elevate the pulse pressure.
Strengths of Palpable Pulse
•
•
•
•
•
0 = Absent
1 = Barely palpable
2 = Easily palpable
3 = Full
4 = Aneurysmal or Bounding pulse
Pulse
• The pulse represents the tactile arterial
palpation of the heartbeat (whether normal
or abnormal)
• The pulse may be palpated in any place
that allows an artery to be compressed
against a bone such as at the neck
(carotid artery), at the wrist (radial
artery), behind the knee (popliteal
artery), on the inside of the elbow
(brachial artery), and near the ankle joint
(posterior tibial artery).
Figure 19.11
Pulse
• Pressure waves generated by cardiac systole
move the artery walls, which are pliable and
compliant. These properties form enough to create
a palpable pressure wave.
• The Heart Rate may be greater or lesser than the
Pulse Rate depending upon physiologic demand.
In this case, the heart rate are determined by
auscultation or audible sounds at the heart apex,
in which case it is not the pulse. The pulse deficit
(difference between heart beats and pulsations at
the periphery) is determined by simultaneous
palpation at the radial artery and auscultation at
the heart apex.
Pulse Pressure
The alternating
expansion (ejection
contraction) and contraction
(diastole)
of the arteries during
a heart beat causes
the pulse.
The further an artery
is away from the heart –
the less the alternating
Expansion and contraction –
due to resistance – the
magnitude of the pulse will
The pulse pressure is the
difference
between the systolic blood
pressure
and the diastolic blood
pressure
Abnormal Pulses
1. Pulsus alternans - a physical finding with
arterial pulse waveform showing alternating
strong and weak beats. It is almost always
indicative of left ventricular systolic
impairment, and carries a poor prognosis.
2. Pulsus bigeminus - a cardiovascular
phenomenon characterized by groups of two
heartbeats close together followed by a
longer pause. The second pulse is weaker
than the first. It is caused by premature
contractions ventricular contractions (PVCs).
3. Pulsus bisferiens, a sign where, on
palpation of the pulse, a double peak per
cardiac cycle can be appreciated. Bisferious
means striking twice. Classically, it is
detected when aortic prolapse with
regurgitation exists in association with aortic
stenosis, but may also be found in isolated
but severe aortic regurgitation , and
hypertrophic obstructive cardiomyopathy
(idiopathic hypertrophy of heart muscle).
4. Pulsus tardus et parvus, (slow-rising
pulse) a sign where, upon palpation, the
pulse is weak/small (parvus), and late
(tardus) relative to its usually expected
character. It is seen in aortic valve stenosis.
5. Pulsus paradoxus is an exaggeration of
the normal variation during the inspiratory
phase of respiration, in which the blood
pressure declines as one inhales and
increases as one exhales. It is a sign that
is indicative of several conditions
including cardiac tamponade, pericarditis,
chronic sleep apnea, and obstructive lung
disease (e.g. asthma, COPD).
Blood Pressure Control
See Blood Pressure Control
PowerPoint
TAKING A BLOOD PRESSURE
See the PowerPoint
Blood Pressure Determination
Shock
See Shock PowerPoint
Hypertension
See Hypertension PowerPoint
Serum Lipid Transfer
See PowerPoint on
Serum Lipid Transport
Anatomy of the Circulatory System
Figure 19.18a
Figure 19.18b
Figure 19.19
Figure 19.20a
Figure 19.20b
Figure 19.21a
Figure 19.21b
Figure 19.21c, d
Figure 19.21d
Figure 19.22a
Figure 19.22b
Figure 19.23a
Figure 19.23b
Figure 19.23c
Figure 19.23d
Figure 19.24a
Figure 19.24b, c
Figure 19.25a
Figure 19.25b
Figure 19.26a
Figure 19.26b, c
Figure 19.26b
Figure 19.26c
Figure 19.27a
Figure 19.27b
Figure 19.28a
Figure 19.28b
Figure 19.28c
Figure 19.29a
Figure 19.29b, c