CHAPTER
21 BLOOD VESSELS AND HEMODYNAMICS
I.STRUCTURE
OF BLOOD VESSELS
A. Types of vessels
1. Large Arteries
2. Arterioles (small
arteries)
3. Capillaries
4. Venules (small veins)
5. Veins
B. Blood flows from heart via arteries
(1) to 5 above
C. Composition of wall of arteries and
veins
1. lumen - inside of vessel
2. tunica intima
a. endothelium
b. large vessels
have subendothelial layer of
loose connective
tissue
3. tunica media
a. smooth muscle
and elastin arranged in circles
1.
innervation for vasomotor tone
2. also
respond to substances produced
by endothelial cells
4. tunica adventitia
a. loosely woven
collagen fibers
b. nerve fibers,
lymphatic vessels,
blood
vessels - vasa vasorum
D. Arteries
1. carries blood away from
heart
2. oxygenated blood except
pulmonary and fetal circulation
3. resistance vessels
4. types
a. elastic
arteries
1. more
elastin
2. large
diameter
3. keeps
blood under continuous pressure
by
expanding and recoiling and generates
the ARTERIAL PULSE
b. muscular
arteries
1.
farther from heart
2. more
smooth muscle
c. arterioles
1.
smallest arteries
2. most
resistance
3.
vasoconstrict and vasodilate to change
diameter
E. Capillaries
1. smallest vessels
2. RBCs pass through single
file
3. only has tunica intima
4. types
a. continuous
capillaries
1.
junctions between endothelial cells
are
tight or gap
b. fenestrated
capillaries
1. many
pores
2. more
permeable
3.
kidney
5. capillary beds
a. networks at
tissue level
b. pre and post
capillary sphincters to regulate blood flow and
filtration
F. Veins
1. return blood generally
deoxygenated to heart
2. larger than corresponding
artery
3. walls thicker nearer to
heart
4. types
a. venules
1.
junction of capillaries on return
2.
smallest veins
3.
permeability changes occur here
b. veins
1.
thinner walls than arteries
2.
larger lumen
3.
capacitance vessels
4. low
blood pressure in venous system
5. valves to prevent
backflow
a. varicose veins
result from
incompetent valves
6. venous sinuses
a. pool blood
b. flat thin wall
spaces
7. anastomoses or
collaterals
a. alternate
vessels
b. more in veins
than arteries
therefore less
likely to have problems from
occlusion of veins
II.
CIRCULATORY PHYSIOLOGY
A. Terminology
1. BLOOD FLOW (BF)
a.volume of blood
flowing in vessel,organ, etc
2. BLOOD PRESSURE (BP)
a.force exerted on
vessel wall measure in mmHg
Why Hg instead of water?
3. RESISTANCE (R)
a.opposition to
flow
b. TOTAL
PERIPHERAL RESISTANCE (TPR)
1. most resistance in small vessels in periphery
of body
c. properties
contributing to resistance
1.
viscosity
2.
vessel diameter
3.
vessel length
d. resistance most
important factor influencing
blood flow
B. Systemic BP
1. closer to heart, higher
pressure is
2. mechancal energy (from
contraction of heart)
transferred to
blood as kinetic energy
3. pressure highest in aorta
so blood moves from
aorta to other
arteries at lower pressure
4. 120 mmHg at time blood is
ejected into aorta
a. this is
SYSTOLIC arterial blood pressure
5. 80 mmHg at lowest
pressure in aorta
a. this is when
ventricle is relaxing or
DIASTOLIC
arterial blood pressure
b. more important
since it is pressure
that heart has to
work against
6. normal 120/80
7. MEAN ARTERIAL BLOOD
PRESSURE
a. value between two
b. MABP= DABP +
1/3(SABP -DABP)
c. SABP-DABP =
pulse pressure
1.
pressure that drives blood through body 8.
Venous Return
a. factors that
affect return of blood to heart
since low pressure
1.
valves
2.
skeletal muscle
3.
respiration
a.
pressures change in abdominal and
thoracic
cavity that create a pressure
gradient
to move blood from high pressure
to low
pressure
9. BP=CO X TPR
a. CO= SV X HR
b. TPR=1/r4
radius increases resistance deceases
(inversely proportional)
c. blood volume
affects BP
1.
decrease blood volume, decrease BP
d. regulation of
blood pressure
1.
baroreceptors
2.
chemoreceptors
3.
vasomotor center-medulla
4.
autonomic control center-hypothalmus
5. norepinephrine, epinephrine
6.
regulate by reflexs
7.
hormones
a.
thyroxine
b.
ADH, aldosterone
8.
factors that alter vasomotor tone
a.
endothelial cells
e. measure BP
1.
auscultatory method
a.
brachial artery
b. sphygmomanometer and
stethoscope
2. apply
pressure greater than systolic BP
3. no
pulse
4.
reduce pressure
5.
listen for tap = Systolic BP
6.
reduce pressure
7. no
sound = diastolic BP
f.
hypotension
1. less
than normal BP
2.
orthostatic hypotension
g. hypertension
1.
essential - unknown etiology 90%
2.
nonessential or secondary hypertension
10%
- renal disease, hyperthyroidism,etc
3.
normal to increase with age due
to loss
of elastin in arteries
4.
hardening of arteries or plaques can
increase
BP
5.
danger of stroke
D. Blood flow
1. regional vascular beds
cerebral
circulation
coronary
pulmonary
messentary
renal
skeletal muscle
skin
2. some beds have a more
constant blood supply
and others vary widely with need
a. cerebral and
coronary
1.
constant blood flow needed
3. exercising muscle
a. increase blood
flow, shunts from messentary
4. low resistance in
pulmonary circulation
a. BP here is
25/10
5. cross-sectional area of
vessels
a. velocity in vessels is inversely related to area- more
area slower flow
b. most area in
capillaries
6. BP regulation
a. vasomotor tone
b. constriction,
dilation
c. local factors
d. autoregulation
7. reactive hyperemia
a. increase in
blood flow to area that
had blood flow cut
off (ischemia)
E. Microcirculation
1. capillaries and small
vessels
2. delivery of
nutrients,removal of waste
3. process of diffusion and
filtration
at capillaries
4. driving force for
filtration
5. lymphatics return the
filtered fluid back into circulation
hydrostatic pressure (HP)
from column of blood pushes
fluid out osmotic pressure (OP) sucking in
arteriole
end of cap. cap. venule end of cap.
HP=32mmHg
push out HP=15
push out
OP=25
pull in OP=25 pull in
interstial
fluid: HP=0
OP=3mmHG
pull to interstium
What
is the net filtration pressure over the area of the capillary from the
arteriole end and venule end of capillary? Is net effect in favor of filtration
or reabsorption? Hint: Consider pressure driving fluid into capillary as a
negative number and pressures taking fluid out of capillary as positive, then
sum all pressures.
This
is Starling's Law of the Capillary
F. Circulatory Shock
1. inadequate circulation of
blood
2. hemorrhage
3. vasodilation of all
vascular beds can
result in drop in
BP
4. compensatory responses to
the drop in BP
a. increase HR
b. increase BV
c. increase thirst
d. decrease
urination
e. increase
respiration