Download 3b CardioII-Vasculature

Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Blood Vessels: The Vascular System
Venous system
Large veins
(capacitance
vessels)
Small veins
(capacitance
vessels)
Postcapillary
venule
Thoroughfare
channel
Arterial system
Heart
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
Elastic arteries
(conducting
vessels)
Muscular arteries
(distributing
vessels)
Lymphatic
Sinusoid
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary sphincter
Capillaries
Figure 19.2
(exchange vessels)
Layers of Blood Vessels
Tunica intima
• Endothelium
• Subendothelial layer
Internal elastic lamina
Tunica media
(smooth muscle under
Valve
control of symp. n.s. and
elastic fibers)
External elastic lamina
Tunica externa
(fibrous connective: collagen fibers)
Lumen
Artery
(b)
Capillary
network
Capillary
Lumen
Vein
Basement membrane
Endothelial cells
Figure 19.1b
Differences Between Blood Vessel Types
 Walls of arteries are the
thickest, while lumen is
smaller in diameter
 Walls of veins are thinner,
while lumens of veins are
larger
 Walls of capillaries are only
one cell layer thick to allow
for exchanges between blood
and tissue
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Arteries, Compared
Elastic Arteries

Large thick-walled arteries with elastin in all
three tunics

Aorta and its major branches

Large lumen offers low-resistance

Act as pressure reservoirs—expand and recoil as
blood is ejected from the heart
Muscular Arteries

Distal to elastic arteries; deliver blood to body
organs

Have thick tunica media with more smooth
muscle

Active in vasoconstriction
Arterioles

Smallest arteries

Lead to capillary beds

Control flow into capillary beds via
vasodilation and vasoconstriction
Table 19.1 (1 of 2)
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Capillaries and Capillary Beds
Venous system
Large veins
(capacitance
vessels)
Small veins
(capacitance
vessels)
Postcapillary
venule
Thoroughfare
channel
Arterial system
Heart
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
Elastic arteries
(conducting
vessels)
Muscular arteries
(distributing
vessels)
Lymphatic
Sinusoid
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary sphincter
Capillaries
Figure 19.2
(exchange vessels)
Capillaries
 Found in all tissues except for cartilage,
epithelia, cornea and lens of eye
 Three structural types
1. Continuous capillaries
2. Fenestrated capillaries
3. Sinusoidal capillaries (sinusoids)
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
• Tight junctions are complete, forming
the blood-brain barrier
Pericyte
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Endothelial
nucleus
Pinocytotic
vesicles
(a) Continuous capillary. Least permeable, and
most common (e.g., skin, muscle).
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)
Pinocytotic
vesicles
Red blood
cell in lumen
Fenestrations
(pores)
Endothelial
nucleus
Basement membrane
Tight junction
Intercellular
cleft
Endothelial
cell
(b) Fenestrated capillary. Large fenestrations
(pores) increase permeability. Occurs in special
locations (e.g., kidney, small intestine).
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
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Incomplete
basement
membrane
Nucleus of
endothelial
cell
(c) Sinusoidal capillary. Most permeable. Occurs in
special locations (e.g., liver, bone marrow, spleen).
Figure 19.3c
Capillary Beds

Interwoven networks of capillaries form the
microcirculation between arterioles and venules

Consist of two types of vessels
1. Vascular shunt (metarteriole—thoroughfare
channel):
o
Directly connects the terminal arteriole and a
postcapillary venule
2. True capillaries
o
10 to 100 exchange vessels per capillary bed
o
Branch off the metarteriole or terminal arteriole
Blood Flow Through Capillary Beds
Precapillary
sphincters
Terminal arteriole
Vascular shunt
Metarteriole
Thoroughfare channel
True capillaries
Postcapillary venule
Low O2, high
CO2, high pH,
low nutrients,
hot external
temperatures,
relaxation
(a) Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
High O2, low
pH, nutrients,
low CO2, cold
external
temperatures,
fight or flight
conditions
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Figure 19.4
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Venules and Veins
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
Table 19.1 (2 of 2)
Veins

Adaptations that ensure
return of blood to the heart
1.
Large-diameter lumens
offer little resistance
2.
Valves prevent backflow
of blood
o

Most abundant in veins of
the limbs
Venous sinuses: flattened
veins with extremely thin
walls (e.g., coronary sinus
of the heart and dural
sinuses of the brain)
One-way valves in veins prevent backflow
where positive pressure is at a mininum
Most of the Blood is in Veins and Venules
Pulmonary blood
vessels 12%
Systemic arteries
and arterioles 15%
Heart 8%
Capillaries 5%
Systemic veins
and venules 60%
Figure 19.5
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
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Pulse
 Pulse – pressure
wave of blood
 Monitored at
“pressure points”
where pulse is
easily palpated
Figure 11.16
Physiology of Circulation: Definition of Terms
 Blood flow
• Volume of blood flowing through a vessel, an organ, or the entire circulation
in a given period, measured in ml/min
 Blood pressure (BP)
• Force per unit area exerted on the wall of a blood vessel by the blood,
expressed in mm Hg
• Measured as systemic arterial BP in large arteries near heart
 Peripheral Resistance
• Opposition to flow; a measure of the amount of friction blood encounters
• Generally encountered in the peripheral systemic circulation
• Three important sources of resistance
o Blood viscosity (relatively constant)
o Total blood vessel length (relatively constant)
o Blood vessel diameter (Resist. varies inversely with the fourth power of vessel
radius (e.g., if the radius is doubled, the resistance is 1/16 as much)
Local Blood Pressures
Systemic pressure
• Highest in the aorta, declines throughout the pathway; 0 mm Hg in the right atrium
Arterial pressure
 Reflects two factors of the arteries close to the heart
• Elasticity (compliance or distensibility)
• Volume of blood forced into them at any time
 Blood pressure near the heart is pulsatile
o Systolic pressure: pressure exerted during ventricular contraction
o Diastolic pressure: lowest level of arterial pressure
o Pulse pressure = difference between systolic and diastolic pressure
 Mean arterial pressure (MAP): pressure that propels the blood to the tissues
MAP = diastolic pressure + 1/3 pulse pressure
 Pulse pressure and MAP both decline with increasing distance from the heart
Capillary blood pressure
 Low capillary pressure is desirable; low pressure forces filtrate into interstitial spaces
Venus blood pressure - near zero
Comparison of Blood Pressures
Blood pressure results when flow is opposed by resistance
Disease causing blood
pressure change
Arteriosclerosis:
Hardening of the artery
walls and decrease of
elasticity, restricting flow
and increasing blood
pressure.
Atherosclerosis: A specific
type of arterosclerosis
where arteries are clogged
by an accumulation of
plaques: cholesterol
particles (lipoproteins), fat,
calcium, cellular waste and
other substances.
Factors Aiding Venous Return
1.
Respiratory “pump”:
pressure changes created
during breathing move blood
toward the heart by
squeezing abdominal veins
as thoracic veins expand
2. Muscular “pump”:
contraction of skeletal
muscles “milk” blood toward
the heart and valves prevent
backflow
3.
Vasoconstriction of veins
under sympathetic control
Measuring Arterial Blood Pressure


Measurements by health professionals
are made on the pressure in large arteries
•
Systolic – pressure at the peak of
ventricular contraction
•
Diastolic – pressure when ventricles
relax
Pressure in blood vessels decreases as the
distance away from the heart increases
Listen for the sounds of Kortokoff
Normal BP is 120/75-80
Blood pressure
animation online
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure
Variations in Blood Pressure
 Human normal range is variable
• Normal
o 110-140 mm Hg systolic
or just 120/70
o 70-80 mm Hg diastolic
• Hypotension
o Low systolic (below 110 mm HG)
o Often associated with illness or physical conditioning
• Hypertension
o High systolic (above 140 mm HG)
o Can be dangerous if it is chronic
o Caused by many things, including a high saturated fat and/or
salty diet, little exercise, & chronic stress
Cardio System II: Vasculature and Pressure
 Blood Vessel Anatomy
• Arteries and arterioles
• Capillaries (3 types)
• Veins and venules
 Pulse and Pressure Points
 Blood Pressure
• Factors Regulating
Blood Pressure