Transcript Document

Blood Vessels-Chps. 14-19
Powered by the pumping action of the heart
Heart
ArteriesElastic
muscular
Arterioles
Capillaries
Venules
veins
• Transporting nutrients and oxygen to the tissues
• Transporting waste products away from the tissues
• Transporting hormones
Lecture outline
I. Review anatomy of vessels
A. Arteries
B. Elastic
C. Muscular
D. Arterioles- resistance vessels
E. Capillaries- exchange vessels
F. Veins- capacitance vessels
II. Ohm’s law is flow = change in
pressure/ resistance
A. Blood Flow
i. Laminar vs. turbulent
B. Pressure- blood pressure
i. Mean arterial pressure (MAP)
ii. Central venous pressure
iii. Pulse pressure
C. Resistance
i. Factors of resistancePoiseuille’s law
III. Getting to know “Flow” better
A. Velocity
B. Control of flow
i. Autoregulation
ii. Nervous system
iii. Endocrine-kidney (unit 4)
IV. Exchange of extracellular fluid- the
microcirculation
A. Starling Forces
i. Capillary hydrostatic pressure
ii. Interstitial hydrostatic pressure
iii. Capillary colloid osmotic
pressure
iv. Interstitial colloid osmotic
pressure
B. Lymphatic drainage
C. Causes of edema
2
• Branch and diverge
• Blood away from heart
• Walls have 3 tunics
Arteries
– Tunica intima-simple
squamous endothelium
– Tunica media-circular
sheets of smooth muscle
(vasodilation and
vasoconstriction- diameter
controlled by local factors
and sympathetic NS)
– Tunica adventitiaconnective tissue with
collagen and elastin in
longitudinal arrangement
3
Arteries
• Elastic- largest arteries near
heart
– Low resistance
– More elastin interspersed with
the tunica media
– Can distend and recoil back
to pump blood (maintain
blood pressure)
• Muscular– Supply organs
– Can regulate diameter of
artery to control blood supply
to organ
– Thick tunica media with more
smooth muscle
– External and internal elastic
lamina.
4
Arterioles
• Smallest arteries“resistance arteries”
• THICK tunica media- little
compliance
• Diameter controlled by
local factors (intrinsic) and
sympathetic division
(extrinsic) and long-term
factors (hormones)
• Metarterioles- just
upstream of capillary beds.
• Precapillary sphincterscontrols blood reaching
capillary bed.
5
Capillaries
• Smallest blood vessels
• Single layer of endothelial
cells and basal lamina
• Renew interstitial fluid- pick
up wastes, drop off nutrients,
etc.
• Most cells only 20-30 µm
away
• Over 10 billion of them.
6
Types of Capillaries
•
Continuous
– Most common and least
permeable
– Intercellular clefts and
transcellular cytosis allows for
exchange of molecules
– Abundant in skin and muscle
•
Fenestrated
– “Holes” in the endothelial
membrane
– Found in kidney
•
Sinusoidal/ discontinuous
– Most permeable and least
common
– Big ‘holes” in endothelial
membranes
– Big clefts between cells
– Liver, spleen, and bone marrow
especially
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Veins
• Volume reservoir- “capacitance vessels” (60-70%)
of blood
• Have vasomotor control.
• Valves in abdominal veins prevent backflow
• Skeletal muscle “pump” and respiratory pump
9
Vascular Distensibility= is the fractional increase in
volume for each mmHg rise in pressure times original volume- veins are
8x more distensible
0 mmHg
Artery
Vein
100 mmHg
100 ml
800 ml
In hemodynamics, it’s more valuable to know the total quantity of blood that can be
stored in a given portion of the circulation for each mmHg pressure rise.
10
Capacitance = increase in volume/increase in pressure
The capacitance of veins is 24 times that of arteries.
Ohm’s Law
• Q=P/R
• Flow (Q) through a blood
vessel is determined by:
• 1) The pressure
difference (P) between
the two ends of the
vessel
– Directly related to flow
• 2) Resistance (R) of the
vessel
– Inversely related to flow
• Can you rearrange the
equation above and solve
for P? Solve for R?
11
Blood Flow (L/min)
• Blood flow is the quantity of
blood that passes a given
point in the circulation in a
given period of time.
• Unit of blood flow is usually
expressed as milliliters (ml) or
Liters (L) per minute.
• Overall flow in the circulation
of an adult is 5 liters/min
which is the cardiac output.
• CO= HR X SV
• 70 b/min x 70 ml/beat
=4900ml/min
12
Characteristics of Blood
Flow
• Blood usually flows in streamlines with each layer
of blood remaining the same distance from the
wall, this type of flow is called laminar flow.
– When laminar flow occurs, the velocity of blood in
the center of the vessel is greater than that toward
the outer edge creating a parabolic profile.
Laminar flow
Blood Vessel
13
Laminar Vs. Turbulent Blood Flow
Causes of turbulent blood flow:
• high velocities
• sharp turns in the circulation
• rough surfaces in the circulation
• rapid narrowing of blood vessels
Turbulent flow
• Laminar flow is silent, whereas turbulent flow tend to cause murmurs.
• Murmurs or bruits are important in diagnosing vessels stenosis, vessel shunts, and
cardiac valvular lesions.
14
Effect of Wall Stress on Blood Vessels
Turbulent flow increases resistance and wall stress
Nitric oxide released by endothelial cells to reduce the stress
Aortic Aneurysm
Atherosclerosis
15
Blood Pressure—
The driving force
• Blood pressure (hydrostatic
pressure) is the force
exerted by the blood against
any unit area of vessel wall.
Stephen Hales
1733
• Measured in millimeters of
mercury (mmHg). A pressure
of 100 mmHg means the
force of blood was sufficient
to push a column of mercury
100mm high.
• All vessels have it – but
we’re usually addressing
arteries when we refer to it.
16
Ejected Blood
contracted
When the LV contracts more blood enters the
arterial system than gets pushed onward.
This causes the arteries to stretch and
pressure within them to rise. The highest
pressure achieved is known as the systolic
pressure.
17
Recoil of the elastic artery
relaxed
As the LV relaxes, the stretched arterial walls recoil
and push the contained blood onward through the
system. As they recoil, the amount of blood
contained decreases as does pressure. The lowest
pressure achieved just before the next contraction is
the diastolic pressure.
18
Mean Arterial Pressure (MAP)
FLOW = arterial - venous pressure (P)
resistance (R)
• Is an average, but not a simple
arithmetic average
• Heart spends longer in diastole
than systole
• Value is significant- why?
• The difference between the mean
arterial pressure and the pressure
in the venous system drives the
blood through the capillary beds.
• MAP= .4 (systolic) + .6 (diastolic)=
96mmHg
• Venous pressure is about 2mmHg
100 mmHg
A
0 mmHg
R = .1mmHg/ml/min
FLOW = 1000 ml/min
100 mmHg
B
20 mmHg
R = .1mmHg/ml/min
FLOW = 800 ml/min
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Central Venous Pressure
•
Pressure in the right atrium is called
central venous pressure.
•
determined by the balance of the heart
pumping blood out of the right atrium
and flow of blood from the large veins
into the right atrium.
•
normally 0 mmHg, but can be as high as
20-30 mmHg.
More vigorous heart contraction (lower
CVP).
Less heart contraction (higher CVP)
Factors that increase CVP:
increased blood volume
increased venous tone (peripheral
pressure)
dilation of arterioles
decreased right ventricular function
Skeletal and respiratory pumps
•
•
•
Figure 15-9; Guyton and Hall
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Arterial Pulsations and Pulse Pressure
• The height of the pressure pulse is the
systolic pressure (120mmHg), while the
lowest point is the diastolic pressure
(80mmHg).
• The difference between systolic and diastolic
pressure is called the pulse pressure
(40mmHg). Systolic Pressure
}
Pulse Pressure
Diastolic Pressure
21
Factors Affecting Pulse Pressure
• Stroke volume —increases in
stroke volume increase pulse
pressure, conversely decreases
in stroke volume decrease
pulse pressure.
• Arterial compliance —decreases in
compliance increases pulse
pressure; increases in compliance
decrease pulse pressure.
Figure 15-5; Guyton and Hall
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Stroke
volume
Cardiac
output
Systolic Pressure
}
Pulse Pressure
Mean
Pressure
Total
Peripheral
resistance
Stroke
volume
Diastolic
Pressure
Time
HR x SV = CO = MAP/ TPR
MAP= (0.4 SP) + (0.6 DP)
PP= SP- DP
Arterial
compliance
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Damping of Pulse
Pressures in the
Peripheral Arteries
What’s an anatomical reason for
why the pressure fluctuation
disappears here?
• The intensity of pulsations
becomes progressively less in the
smaller arteries.
• The degree of damping is
proportional to the resistance of
small vessels and arterioles and the
compliance of the larger vessels.
•Elastic arteries:
• large radii, low resistance, some
pressure reservoir
•Muscular arteries
•Smaller radii
•Little more resistance
•More pressure reservoir
•Arterioles
•Thick tunica media vs. radius
•major pressure reservoir
Figure 15-6; Guyton and Hall
24
Blood Pressure Profile in the Circulatory
System
Pulmonary veins
Capillaries
Large veins
40
Small veins
60
Venules
80
Capillaries
Pressure
(mmHg)
100
Pulmonary arteries
120
20
0
Systemic
Pulmonary
Circulatory pressure- averages 100mmHg
Arterial blood pressure-100-35mmHg
Capillary pressure- 35mmHg at beginning and 10-15mmHg at end
Venous pressure-15-0mmHg
•Large pressure drop across the arteriolar-capillary junction
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Resistance
R = ΔP = mmHg
Q ml/min
• Resistance is the impediment
to blood flow in a vessel.
• Can not be measured directly
How Would a Decrease in Vascular Resistance Affect
Blood Flow?
FLOW =
Conversely,
P
RESISTANCE
FLOW =
P
RESISTANCE
Therefore, flow and resistance are inversely related!
26
Resistance makes a difference for the two
sides of the heart!
• Let’s say the CO (flow) is roughly
100ml/sec (easier math).
• To calculate systemic resistance vs.
pulmonary resistance we need to
know pressure differences.
• Pulmonary resistance is 16-2/100
• Systemic resistance is 100/100
• So, CO is same on each side of
heart (has to be!), but right side
generates less pressure due to lower
resistance (1/7th than systemic).
100 mmHg
16
mmHg
2mmHg
0mmHg
R = ΔP = mmHg
Q ml/min
27
Factors of Resistance
Poiseuille’s Law =
Q =_Pr4
8l
• Blood viscosity
• Total vessel length
• Vessel diameter
• Resistance 
(length)(viscosity)
(radius)4
28
Viscosity
• What are the major
contributors to blood
viscosity?
• As viscosity
increases, resistance
will…
• An increase in plasma
EPO will cause
resistance to…
Figure 14-11; Guyton and Hall
Figure 14-12; Guyton and Hall
29
Total Vessel Length
• Longer the vessel.....more
opportunity for resistance.
Radius
30
So, lets review:
Blood Flow is volume flowing/time
• Ohm’s Law
• Blood Flow (Q) = Δ P/ R
Blood flow in center is fastestbecause that is the area of least
resistance
P1
P2
• Increase pressureincrease blood flow
• Decrease
resistanceincrease blood flow
• Increase
resistancedecrease blood
flow
ΔP= P1-P2
•
•
•
As resistance decreases, flow will…
As the pressure gradient increases, flow will…
Which does the heart influence more: pressure gradient
or resistance?
–
–
–
–
Vessel diameter
Viscosity
length
Turbulence (usually
result of an occlusion
reducing vessel
diameter unevenly)
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Flow (amount of blood/time) MUST
be the same through vessels in
series!
If a pipe’s diameter changes over its length, a fluid will flow through
narrower segments faster than it flows through wider segments
because the volume of flow per second must be constant throughout
the entire pipe.
Flow (volume/time) vs. velocity (distance/time) are NOT synonyms!
32
If capillaries have such a small diameter,
why is the velocity of blood flow so slow?
Aorta >Arterioles> Small veins >Capillaries
We need slow blood flow in the capillaries—the exchange vessels
33
Control of blood flow through
vessels- Why is this important?
• Perfusion vs. ischemia vs.
hypoxia vs. anoxia vs.
infarction
• Tissue Perfusion
Dependent on:
– Cardiac output
– Peripheral resistance
– Blood pressure
• Regulation of perfusion
dependent on:
– Autoregulation (Acute, local,
intrinsic)
– Neural mechanisms (acute)
– Endocrine mechanisms (longterm)
http://www.flometrics.com/services/artery/
34
Autoregulation  the automatic adjustment of blood flow to
each tissue in proportion to the tissue’s requirements at any
instant even over a wide range of arterial pressures
Working
Muscle
Tissue
active hyperemia:
when tissues
become active,
blood flow
increases.
Tissue temp. rises
Tissue CO2 levels rise
Tissue O2 levels fall
Arterioles
serving tissue
vasodilate and
precapillary
sphincters relax
Lactic acid levels rise
Aka: intrinsic
metabolic
vasodilation
Increased blood
flow to tissue
CO2 removed
Now arterioles
will
vasoconstrict
and
precapillary
sphincters
contract
Lactic acid removed
Heat removed
O2 delivered
35
Autoregulation of Blood Flow to specific
tissues
• Vasodilator agents
Histamine
Nitric oxide
Elevated temperatures
Potassium/hydrogen ions
Lactic acid
Carbon dioxide
Adenosine/ ADP
• Vasoconstrictors
Norepinephrine and
epinephrine
Angiotensin
Vasopressin (ADH)
Thromboxane
36
Other ways to ultimately change blood flow throughout the body is to change
Pressure and Resistance
Arterial Pressure = Cardiac Output x Total Peripheral Resistance
Short term BP control- nervous
37
Long Term BP control- hormonal
Brain Centers involved in Short
Term BP Control
• Vasomotor
– Adjusts peripheral
resistance by adjusting
sympathetic output to the
arterioles
• Cardioinhibitory- transmits
signals via vagus nerve to
heart to decrease heart rate.
(parasympathetic)
• Cardioacceleratory/
contractility-sympathetic
output
38
Vasomotor control: Sympathetic Innervation
of Blood Vessels
• Sympathetic nerve fibers
innervate all vessels except
capillaries and precapillary
sphincters (precapillary
sphincters follow local control)
• Innervation of small arteries
and arterioles allow
sympathetic nerves to increase
vascular resistance.
Figure 18-2; Guyton and Hall
• Large veins and the heart are
also sympathetically innervated.
39
Anatomy of the Baroreceptors
• spray type nerve endings located in
the walls of the carotid bifurcation
called the carotid sinus and in the
walls of the aortic archpressoreceptors that respond to
stretch.
• Signals from the carotid sinus are
transmitted by the glossopharyngeal
nerves .
• Signals from the arch of the aorta are
transmitted through the vagus into the
NTS.
• Important in short term
regulation of arterial pressure.
– They are unimportant in long term
control of arterial pressure because
the baroreceptors adapt.
Figure 18-5; Guyton and Hall
40
Response of the Baroreceptors to
Arterial Pressure
Figure 18-7; Guyton and Hall
Constrict
Common Carotids
Pressure at
Carotid Sinuses
Arterial Pressure
Constrictors
•
Baroreceptors respond to changes in arterial
pressure.
•
As pressure increases the number of impulses
from carotid sinus increases which results in:
1) inhibition of the vasoconstrictor
2) activation of the vagal center
41
Figure 18-5; Guyton and Hall
Functions of the Baroreceptors
• Maintains relatively constant pressure despite
changes in body posture.
Supine
Standing
Decrease
Venous return
Sympathetic
Nervous Activity
Decrease
Cardiac Output
Vasomotor
Center
Sensed By
Baroreceptors
Decrease
Arterial Pressure
42
BP rises
Detected by
baroreceptors in
aortic arch &
carotid sinus
Info sent to cardiac
and vasomotor
centers
Decreased
vasomotor
activity
Decreased NE
release on
arterioles
Vasodilation
Decreased PR
Increased
cardioinhibitory
activity
Increased vagus
activity
Decreased
BP
Increased ACh
release on heart
Decreased
cardioacceleratory
activity
Decreased CO
Decreased NE
release on heart
Decreased SV
and HR
Carotid and Aortic
Chemoreceptors
• Chemoreceptors are chemosensitive
cells sensitive to oxygen lack, CO2
excess, or H ion excess.
• Chemoreceptors are located in carotid
bodies near the carotid bifurcation and
on the arch of the aorta.
• Activation of chemosensitive receptors
results in excitation of the vasomotor
center.
O2
CO2
pH
Figure 18-5; Guyton and Hall
Chemoreceptors
VMC
Sympathetic
activity
BP
44
Nervous control also found in the heartBainbridge Reflex
• Prevents damming of blood in veins, atria and
pulmonary circulation.
• Increase in atrial pressure increases heart
rate.
• Stretch of atria sends signals to VMC via
vagal afferents to increase heart rate and
contractility.
Atrial
Stretch
Vagal
afferents
Vasomotor
Center
Heart rate
Contractility
45
The Microcirculation-chapter
16
• Important in the transport of nutrients to
tissues.
• Site of waste product removal.
• Over 10 billion capillaries with surface
area of 500-700 square meters perform
function of solute and fluid exchange.
Figure 16-1;
Guyton and Hall
46
Most substances are
exchanged via diffusion
Concentration
differences
across capillary
enhances
diffusion.
47
Determinants of Net Fluid Movement across
Capillaries-Starling forces
Figure 16-5; Guyton and Hall
• Capillary hydrostatic pressure (Pc)-tends to force fluid
outward through the capillary membrane.
(30 mmHg arterial; 10mmHg venous- average 17.3mmHg)
• Interstitial fluid hydrostatic pressure (Pif)- opposes filtration
when value is positive (but it’s not positive-- due to
lymphatic drainage! – 3mmHg).
48
Determinants of Net Fluid Movement across
Capillaries-Starling forces
Figure 16-5; Guyton and Hall
• Plasma colloid osmotic pressure ( c)- opposes filtration
causing osmosis of water inward through the membrane
– Colloid osmotic pressure of the blood plasma. (28mmHg)
– 75% from albumin; 25% from globulins
• Interstitial fluid colloid pressure ( if) promotes filtration by
causing osmosis of fluid outward through the membrane
– Colloid osmotic pressure of the interstitial fluid. (8mmHg)
– 3gm%
49
Net Forces in Capillaries
Filtration= Kf X (Pc- Pif - c + if)
mmHg
Mean forces tending to move fluid outward:
Mean Capillary pressure
Negative interstitial free fluid pressure
Interstitial fluid colloid osmotic pressure
TOTAL OUTWARD FORCE
17.3
3.0
8.0
28.3
Mean force tending to move fluid inward:
Plasma colloid osmotic pressure
TOTAL INWARD FORCE
28.0
28.0
Summation of mean forces:
Outward
Inward
NET OUTWARD FORCE
28.3
28.0
0.3
Net filtration pressure of .3 mmHg which causes a net filtration rate of
2ml/min for entire body (2-4 liters/day!)
50
If capillary BP is greater than capillary
OP, there will be net movement of fluid
out of the capillary.
Capillary BP
Filtration
Pressure
Capillary OP
Reabsorption
If capillary BP is less than capillary OP, there will be net movement of
fluid into the capillary.
Arterial end
Venous end
Distance along the capillary
Filtration= Kf X (Pc- Pif - c + if)
• Lymphatic vessels collect
lymph from loose connective
tissue
– Fluid flows only toward the
heart
– Collect excess tissue fluid
and blood proteins and
carry to great veins in the
neck
– All three tunics
– NO pump!
– Valves!
• contains plasma, water,
ions, sugars, proteins,
gases, amino acids- is
colorless, but low in protein
compared to blood
• Lymph can contain
hormones, bacteria, viruses,
cellular debris, traveling
cancer cells, macrophages
2ml/min Excess
tissue fluid is
returned to the
blood vessels via the
lymphatic system!
52
Causes of Edema
• Excessive accumulation of tissue
fluid.
• Edema may result from:
– High arterial blood pressure.
– Venous obstruction.
– Leakage of plasma proteins
into interstitial fluid.
– Valve problems
– Cardiac failure
– Decreased plasma protein.
– Obstruction of lymphatic
drainage. ElephantiasisWuchereria bancrofli
I would see your homework packet and study page 303 of Guyton and Hall!
53
Unbalanced Ventricular Output
54
Unbalanced Ventricular Output
55
Hypertension
 ISF
formation
 capillary BP
Starvation
Lack of
dietary
protein
Histamine
 capillary
permeability
 in
plasma
albumin
Vasodilation
 capillary
OP
 ISF
formation
 capillary BP
 ISF
formation
56
Burn/crush
injury
 capillary
permeability
Backup of blood in
pulmonary circuit
Cap OP
 pulmonary
capillary BP
 ISF
formation
 ISF
formation
L. Ventricle
failure
Decreased blood
flow in systemic
circuit
 systemic
capillary BP
 ISF
formation
57