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Arteries
AWAY
Branch
Typically oxygenated.
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Capillaries
Smallest.
Most abundant.
How many??
Why?
Exchange
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Veins
TOWARDS
Converge.
Typically deoxygenated.
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3 Layers of the Vascular Wall
Tunica interna
Tunica media
Tunica externa.
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Tunica Interna/Intima
Lining.
Endothelium.
Supported by loose CT.
Only layer in capillaries.
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Tunica Media
Primarily smooth muscle plus elastic fibers.
Most prominent layer in arteries.
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Tunica Media
Smooth muscle tone
Regulated by:
Metabolites
Hormones
Sympathetic vasomotor
neurons.
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Vasomotor neurons constantly release NE onto TM smooth
muscle. What does the NE do?
Why have a constant release?
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Increased NE release by a vasomotor neuron causes:
Tunica media smooth muscle tone to:
Vessel diameter to:
Resistance to blood flow in the vessel to:
Blood flow thru the vessel to:
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This gentleman has fatty plaques in his lower
leg arteries.
How do you think they affect blood flow?
How does that relate to his facial
expression?
His doctor recommends that the sympatheticnerves to those arteries be cut.
Why?
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Tunica Externa/Adventitia
Primarily collagen
Function?
Most prominent
layer in veins
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Elastic Arteries
Aorta and major branches.
Act as AUXILIARY PUMPS.
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Regional distribution
Significant layer
Muscular Arteries
http://www.vetmed.wsu.edu/VAn308/_vti_bin/shtml.dll/muscular.htm/map8/2/2019 Blood Flow Images
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Smallest.
May or may not have an externa.
Highly innervated by vasomotor neurons.
Arterioles
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Regulation of blood pressure and flow.
Easy to change the diameter.How would you do it?
Why would you want to?
Arterioles
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Capillaries
Smallest.
Thin walls
Billions
Function?
Almost everywhere.
C i ill i
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Continuous capillaries
Most common and least permeable.
No endothelial holes
Intercellular clefts.
Abundant in
F t t d ill i
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Fenestrated capillaries
Endothelial holes
Intercellular clefts
Found in
Si id l ill i
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Sinusoidal capillaries.
Most permeable and least common.
Big endothelial holes
Intercellular clefts.
Can have macrophages in theirlining. Why?
Found in
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Why are capillaries organized into beds?
What tissues will have high densities of capillary beds?
Wh t d ill hi t d ?
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What determines whether the
sphincters are open or closed?
What do precapillary sphincters do?
Vascular shunt vs.
True capillaries
If i
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If you were running,
1. Precapillary sphincters in your biceps femoris would
2. Precapillary sphincters in your large intestine would
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Veins
All 3 tunics.
TE is the largest.
Thin walls
Large lumens.
Low resistance
High compliance
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Veins
Smooth muscle toneprevents too muchdistention.
Capacitance vessels/Bloodreservoirs.
65%
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Veins
Low pressure vessels.
Contain valves.
What do they do?
Where are they needed?
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Venous Sinuses
Thin-walled veins made of endothelium only.
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Blood Flow
Volume per time.
Flow thru systemic circuit = cardiac output.
Flow to individual organs varies.
How is this achieved?
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Blood Pressure
Force per unit area exerted on
the vessel wall by blood.
Millimeters of mercury (mmHg).
All vessels
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Resistance
Opposition to flow
Measure of friction.
Peripheral resistance.
Direction!
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While this guy is running,
- the resistance of the arterioles
of his quadriceps needs to
- the resistance of arterioles inhis colon needs to
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Sources of Resistance
Blood viscosity.
Total vessel length.
Vessel radius.
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Viscosity
Viscosity resistance.
Can you drink one of these with
a straw?
What makes it challenging?
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What are the major contributors to blood
viscosity?
Does viscosity change often in a healthyperson?
An increase in plasma EPO will cause
resistance to
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Total Vessel Length
Length resistance.
Does total vessel length change in a normal person?
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Which tube has greater intrinsic resistance?
A B
As total vessel length increases, resistance will
As total vessel length decreases, blood flow will
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Vessel Radius
(1/radius4
) resistance
Does vessel radius change in a normal healthy
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Does vessel radius change in a normal healthyperson?
Which vessels?
How is the change achieved?
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Which tube has the greater intrinsic resistance?
What layer of the vessel wall has the greatest effect on
vessel resistance?
a. Interna
b. Media
c. Externa
A B
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Resistance (length)(viscosity)
(radius)4
Whi h t b h th LEAST i t ?
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Which tube has the LEAST resistance?
Which tube has the GREATEST resistance?
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FLOW PRESSURE GRADIENTRESISTANCE
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As resistance decreases, flow will
As the pressure gradient increases, flow will
Which does the heart influence more: pressure
gradient or resistance?
Bl d P
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Blood Pressure
Why do all blood vessels have a BP?
Which vessel do we usually care about?
Where is systemic BP the highest?
Where is systemic BP the lowest?
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Arterial Blood Pressure Model
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What would happen to AP if the amount of blood
pumped into the arteries increased?
Thus, arterial pressure varies directly with
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What would happen to AP if the resistance in the
arterioles went up?
Thus, arterial pressure varies directly with
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What would happen to AP if there was more blood
in the entire system?
Thus, arterial pressure varies directly with
Systolic Blood Pressure
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Systolic Blood Pressure
Diastolic Blood Pressure
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Diastolic Blood Pressure
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P l
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What creates it?
How/Where do you measure it?
Whats its relationship to heart rate?
Pulse
Pulse Pressure
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Pulse Pressure
Change in arterial pressure caused by ventricular
systole.
Varies directly with
PP = SBPDBP.
Mean Arterial Pressure (MAP)
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Mean Arterial Pressure (MAP)
Arterial BP fluctuates. Why?
MAP is the pressure driving blood flow.
MAP is a weighted average of SBP and DBP.
Mean Arterial Pressure (MAP)
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MAP = DBP + SBP
MAP = DBP + PP
Mean Arterial Pressure (MAP)
Capillary Blood Pressure
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Capillary Blood Pressure
Low BP.
Why is this good? (Think about the structure of a
capillary.)
Venous Blood Pressure
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Venous Blood Pressure
Even lower BP.
Very small gradient.
What is responsible for venous return?
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What is responsible for venous return?
Remaining force imparted by ventricular systole.
Gravity.
Skeletal muscle pump.
Respiratory pump.
Venomotor action.
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Skeletal Muscle Pump
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Skeletal Muscle Pump
Deep InspirationRespiratory Pump
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Thoracic volume will
Pressure in thoracic cavity will
Blood flow into thoracic veins and
towards the heart will
Deep InspirationRespiratory Pump
Pressure in thoracic veins will
Venomotor Tone
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Venomotor Tone
An increase in sympathetic activity causes:
NE release on the TM of medium/large veins to
Venous pressure to
Venous return to
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