Cardiovascular System: Vessels
Chapter 20 – Lecture Notes
to accompany
Anatomy and Physiology: From Science to Life
textbook by
Gail Jenkins, Christopher Kemnitz, Gerard Tortora
Chapter Overview
20.1 Arterial Blood Flow Overview
20.2 Capillaries
20.3 Venules and Veins
20.4 Capillary Exchange
20.5 Blood Flow
20.6 Blood Pressure Regulation
20.7 Pulse
20.8 Systemic and Pulmonary Circuits
Essential Terms
artery
 blood vessel carrying blood away from the
heart
vein
 vessel carrying blood toward the heart
capillaries
 smallest vessels that function in exchange of
nutrients and wastes between blood and
body cells
Introduction
Blood vessels transport materials
throughout body



carry nutrients to cells
carry wastes away for excretion
From heart to






arteries to
arterioles to
capillaries to
venules to
veins to heart
Concept 20.1
Arteries
Arteries
Two main types

elastic arteries
muscular arteries


Three coats

tunic interna


tunica media


elastic fibers and smooth muscle fibers
tunic externa



endothelium, basement membrane, internal elastic
lamina
elastic and collagen fibers
Innervated by sympathetic fibers of ANS
Figure 20.1ab
Figure 20.1c
Figure 20.1d
Figure 20.1e
Elastic Arteries
largest diameter
highest proportion of elastic fibers in tunica
media
help propel blood onward while ventricles
are relaxing





stretch with surge of blood
recoil when pressure decreases
Figure 20.2
Muscular Arteries


medium-sized arteries
tunica media has more smooth muscle and
fewer elastic fibers than elastic arteries



adjust blood flow
capable of greater vasoconstriction and
vasodilation
most named arteries are muscular arteries
Arterioles





muscular arteries divide into smaller arteries
smaller arteries divide into arterioles
arterioles feed capillaries
tunics minimize as they near capillary beds
regulate resistance


contraction of smooth muscle increases
resistance
can significantly affect blood pressure
Figure 20.3
Concept 20.2
Capillaries
Capillaries







microscopic vessels that connect arterioles to
venules
exchange vessels
fed by metarterioles
found near almost every cell in the body
number varies with metabolic activity of
tissue they serve
center vessel is thoroughfare channel
all others have precappillary sphincters that
can constrict and restrict flow
Figure 20.3
Three Capillary Types
From least leaky to most leaky
1.
continuous
2.
fenestrated
3.
sinusoids
If blood passes from one capillary network to
another through a vein
–
vein is called portal vein
–
second network is called portal system
Figure 20.4a
Figure 20.4b
Figure 20.4c
Concept 20.3
Venules and Veins
Venules



capillaries unite to form venules
drain into veins
tunica interna and tunica media
Veins






venules unite to form veins
return blood to the heart
tunica interna, media, and externa
thinner than arteries
many have valves to prevent back flow
low pressure system
Figure 20.5
Veins






venules unite to form veins
return blood to the heart
tunica interna, media, and externa
thinner than arteries
many have valves to prevent back flow
low pressure system
Table 20.1
Blood Reservoirs


about 64% of blood is in systemic veins and
venules at any given moment
brain stem can vasoconstrict these vessels
allowing greater blood flow to skeletal
muscles
Figure 20.6
Concept 20.4
Capillary Exchange
Capillary Exchange
exchange mechanisms include




diffusion
transcytosis
bulk flow
Hydrostatic pressure influences exchange
Blood colloid osmotic pressures helps blood
retain fluid in vessels



resisted by interstitial fluid osmotic pressure
Figure 20.7
Filtration and Reabsorption
filtration


pressure driven movement of fluid and solutes
FROM blood into interstitial fluid
reabsorption


pressure driven from interstitial fluid INTO blood
vessels
net filtration pressure (NFP)


difference between filtration pressure and
reabsorption pressure is
Figure 20.7
Concept 20.5
Blood Flow
Blood Pressure
hydrostatic pressure exerted by blood on
walls of blood vessel
measured in mm Hg
systolic blood pressure




highest pressure attained in arteries during
systole
diastolic blood pressure


lowest pressure during diastole
mean arterial pressure



average of systolic and diastolic pressures
useful when considering blood flow
Figure 20.8
Vascular Resistance
opposition to blood flow due to friction between
blood and walls of vessels
increase in resistance increases BP
decrease in resistance decreases BP
Systemic vascular resistance depends on three
things
size of lumen




1.

larger lumen less resistance
blood viscosity
2.

thinner blood less resistance
vessel length
3.

shorter length less resistance
Venous Return
mechanisms that “pump” blood from lower
body to heart
skeletal muscle pump

1.
figure 20.9

respiratory pump
2.
during inhalation the diaphragm moves
downward increasing pressure in abdominal
cavity and decreasing pressure in thoracic
cavity

–
abdominal veins are compressed and blood forced
upward
Figure 20.9
Velocity of Blood Flow
Inversely related to cross-sectional area of
vessel



slowest where area is greatest
velocity slows as blood moves into larger veins
Circulation time



time required for a drop of blood to pass from
right atrium through pulmonary and systemic
circulation back to right atrium
normally about 1 minute
Figure 20.10
Concept 20.6
Blood Pressure
Regulation
Cardiovascular Center
in medulla oblongata
controls neural and hormonal negative
feedback systems
input



from cerebral cortex, limbic system and
hypothalamus
sensory receptors



proprioceptors, baroreceptors, chemoreceptors
output

ANS sympathetic & parasympathetic neurons
vasomotor nerves throughout body



especially skin and abdominal visceral
Figure 20.11
Neural Regulation of BP
Baroreceptor Reflexes

pressure sensitive sensory receptors in


aorta, internal carotid arteries in neck and chest
two most important



carotid sinus reflex (BP in brain)
aortic reflex (BP in ascending arch of aorta)
if pressure drops



sympathetic stimulation increases
parasympathetic stimulation decreases
Chemoreceptor Reflexes


monitor carbon dioxide, oxygen gas, pH
Figure 20.12
Figure 20.13
Hormonal Regulation of BP
Renin-angiotensin-aldosterone system


Epinephrine and norepinephrine




endocrine response
sympathetic nervous system
ADH
ANP
Table 20.2
Autoregulation of BP
tissue level automatic regulation of BP to
match metabolic needs
Two general types of stimuli




physical changes
chemicals
Concept 20.7
Measuring
Pulse and BP
Pulse





alternate expansion and recoil of arteries
rate same as heart rate
strongest close to heart
faintest most distally
may be felt in any artery that lies near the
surface of body and runs over a bone or other
firm structure
Blood Pressure



measured in mm Hg using
sphygomanometer
when pressure in cuff exceeds systolic
blood pressure sounds cut off
as pressure is released sounds return when
pressure in cuff is equal to systolic pressure
and disappears again as it is equalized with
diastolic blood pressure
Figure 20.15
Concept 20.8
Systemic and Pulmonary
Circulation
Figure 20.16
Circulatory Routes
anastomosis

union of two or more arteries that supply the
same body region
provide collateral circulation



alternate routes for blood to reach a tissue or organ
end arteries


arteries that do not anastomose
Concept 20.9
Pulmonary Circulation
Pulmonary Circulation








heart to lungs and back again
heart to pulmonary trunk to
right and left pulmonary arteries
to lungs (arteries, arterioles, capillaries
surrounding alveoli, to venules to
pulmonary veins to
left atrium
blood leaves the heart deoxygenated and
returns oxygenated
resistance is very low in pulmonary circuit
(low pressure system)
Figure 20.17a
Figure 20.17b
Concept 20.10
Systemic Circulation
Systemic Circulation



all arteries and arterioles that carry blood
containing oxygen and nutrients from left
side of heart throughout the body and back
to the right atrium via vena cava
leaves through aorta
returns through superior and inferior vena
cava or coronary sinus
Figure 20.18a
Figure 20.18b
Figure 20.18c
Figure 20.24
Table 20.3 pt 1
Table 20.3 pt 2
Figure 20.20a
Figure 20.20b
Figure 20.20c
Figure 20.20d
Table 20.4 pt 1
Table 20.4 pt 2
Table 20.4 pt 3
Figure 20.21a
Figure 20.21b
Table 20.5
Figure 20.22a
Figure 20.22b
Figure 20.22c
Figure 20.22d
Figure 20.22e
Table 20.6 pt 1
Table 20.6 pt 2
Figure 20.23a