Download Chapter 21: Blood Vessels and Circulation

Chapter 21:
Blood Vessels and Circulation
Primary sources for figures and content:
Marieb, E. N. Human Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.
Martini, F. H. Fundamentals of Anatomy & Physiology. 6 th ed. San Francisco: Pearson Benjamin Cummings,
2004.
The types of blood vessels,
their structures and functions.
6 Classes of Blood Vessels
1. Arteries:
–
–
carry blood away from heart
Branch and decrease in diameter
2. Arterioles:
–
–
Are smallest branches of arteries
Connect to capillaries
3. Capillaries:
–
–
are smallest blood vessels
location of exchange between blood and
interstitial fluid
6 Classes of Blood Vessels
4. Venules:
–
–
Smallest veins
collect blood from capillaries
5. Veins:
–
–
return blood to heart
Converge and increase in diameter
6. Anastomoses:
-
Bypass connection between vessels
The Largest Blood Vessels
• Attach to heart
• Pulmonary trunk:
– carries blood from right ventricle
– to pulmonary circulation
• Aorta:
– carries blood from left ventricle
– to systemic circulation
The Smallest Blood Vessels
• Capillaries
• Have small diameter and thin walls
• Chemicals and gases diffuse across
walls
The Anatomy of Blood Vessels
• Arteries, veins, and capillaries
• Have different functions
• Have different structures
Arteries and Veins
• Walls have 3 layers:
1. tunica intima
2. tunica media
3. tunica externa
The Tunica Intima/Tunica interna
• Is the innermost layer
• Includes:
– the endothelial cell lining
• Endothelium = simple squamous epitheliallike cells connected by tight junctions
– With basal lamina of loose connective tissue
containing elastic fibers (elastin)
• Arteries have internal elastic membrane
– extra layer of elastic fibers on the outer edge
Tunica Media
• Is the middle layer
• Contains smooth muscle cells in loose
connective tissue with sheets of elastin
– Binds to inner and outer layers
• Arteries have external elastic membrane
– extra layer of elastic fibers on the outer
edge
Tunica Externa/Tunica adventitia
• Is outer layer
• Contains collagen rich external connective
tissue sheath
• Infiltrated with nerve fibers and lymphatic
vessels
• Large vessels contain vasa vasorum
• Arteries = more collagen, scattered elastic fiber
bands
• Veins = extensive fiber networks, bundles of
smooth muscle cells
Vasa Vasorum
• Small arteries and veins
• Found:
– in walls of large arteries and veins
• Function:
– Supply cells of tunica media and tunica
externa
Structure of Vessel Walls
Figure 21-1
Structure of Blood Vessels
Figure 21-2
1. Arteries
• Designed to change diameter, elastic and
muscular, thick walls
– Tunica externa contains collagen
• Pressure
– Elasticity allows arteries to absorb pressure
waves that come with each heartbeat
• Contractility
– Arteries change diameter
– Controlled by sympathetic division of ANS
Vasoconstriction
and Vasodilation
• Vasoconstriction
– The contraction of arterial smooth muscle by
the ANS
• Vasodilatation
– The relaxation of arterial smooth muscle
– Enlarging the lumen
• Affect:
– afterload on heart
– peripheral blood pressure
– capillary blood flow
Artery Characteristics
• From heart to capillaries, arteries
change:
– from elastic arteries
– to muscular arteries
– to arterioles
Elastic Arteries
• Also called conducting arteries
• Diameter up to 2.5cm
• Elastin in all three tunics
– Elasticity evens out pulse force
• Stretch (ventricular systole) and
rebound (ventricular diastole)
• Not involved in systemic
vasoconstriction
Muscular Arteries
•
•
•
•
•
Also called distribution arteries
Are medium-sized (most arteries)
Transport blood to organs and tissues
Diameter 10mm – 0.3mm
More smooth muscle and less elastin in
tunica media than elastic arteries
• Involved in systemic vasoconstriction via
sympathetic stimulation
2. Arterioles
•
•
•
•
Also known as resistance vessels
Connect blood supply to capillary beds
Are small – diameters 300µm – 10µm
All three tunics thin with few elastic
fibers
• Involved in local vasoconstriction via
endocrine or sympathetic stimulation
Health Problems with Arteries
1. Aneurysm:
– Pressure of blood exceeds elastic capacity
of wall
– Causes bulge or weak spot prone to
rupture
– Caused by chronic high blood pressure or
arteriosclerosis
Health Problems with Arteries
2. Arteriosclerosis:
– Variety of pathological conditions
causing changes in walls that
decrease elasticity (“thickenings”)
• Focal calcification = smooth muscle
degenerates, replaced by calcium salts
• Atherosclerosis
3. Atherosclerosis: lipid deposits
Health Problems with Arteries
4. Stroke = cerebrovascular accident (CVA)
– Interruption of arterial supply to portion of
brain due to embolism or atherosclerosis
– Brain tissue dies and function is lost
3. Capillaries
• Only vessels with thin enough wall structure
to allow complete diffusion
– Designed to allow diffusion to/from the tissue
• Diameter 8 µm
– Consists of tunica intima only
– endothelium + basal lamina
• Human body contains 25,000 miles of
capillaries
Capillary Structure
Figure 21-4
Capillary Function
• Location of all exchange functions of
cardiovascular system
• Materials diffuse between blood and
interstitial fluid
Capillary Structure
• Endothelial tube, inside thin basal
lamina
• No tunica media
• No tunica externa
• Diameter is similar to red blood cell
Capillaries
Types of Capillaries
1. Continuous capillaries
-
Normal diffusion to all tissues except
epithelium and cartilage
Complete endothelium, tight junctions
Functions:
• Permit diffusion of: water, small solutes, lipidsoluble materials
• Block: blood cells and plasma proteins
• e.g., the blood–brain barrier
Types of Capillaries
2. Fenestrated capillaries
–
High volume fluids or large solute transfer
Pores/fenestrations span endothelium
Permit rapid exchange of water and larger
solutes between plasma and interstitial
fluid
Fenestrated Capillaries
• Are found in:
–
–
–
–
choroid plexus
endocrine organs
kidneys
intestinal tract
Sinusoids
• Areas in:
–
–
–
–
liver
spleen
bone marrow
endocrine organs
• Have gaps between adjacent
endothelial cells
Types of Capillaries
Sinusoids
3. Sinusoids
– Cell or large protein exchange
– Gaps between endothelial cells
– Permit free exchange of water and large
plasma proteins between blood and interstitial
fluid
– Phagocytic cells monitor blood at sinusoids
– Found: liver, bone marrow, lymphoid tissues
Capillary Networks
Figure 21-5
Capillaries Networks
• Organized into Capillary bed or
capillary plexus
• Connect 1 arteriole and 1 venule
• Not enough total blood to fill all
capillaries at once
– Flow through capillary bed must be
controlled based on need via precapillary
spincters
Capillary Sphincter
• Guards entrance to each capillary
• Opens and closes, causing capillary
blood to flow in pulses
Vasomotion
• Contraction and relaxation cycle of
capillary sphincters
– Spincter relaxed = flow in capillary bed
– Spincter constricted = capillary bed
empty, flow through anastomoses
• Causes blood flow in capillary beds to
constantly change routes
Structure of Blood Vessels
Figure 21-2
Veins vs. Arteries
• Are larger in diameter
• Have thinner walls
• Carry lower blood pressure
4. Veins
• Collect blood from capillaries in tissues and
organs
• Return blood to heart
• Can serve as blood reservoir
• Thin walls but large lumens
• Thin tunica media = little smooth muscle or
elastin
• Tunica externa = elastin and smooth muscle
• Tunica intima = valves to prevent back-flow
3 Vein Categories
1. Venules (5th type of vessel):
–
very small veins
•
–
–
Average diameter 20 µm
collect blood from capillary beds
Small venules lack tunica media
2. Medium-sized veins:
-
Diameter 2-9 mm
3. Large Veins:
-
Diameters up to 3 cm
Valves in the Venous System
Valves in tunica
intima insure one
way movement
Figure 21-6
Vein Valves
• Valves = Folds of tunica intima
• Prevent blood from flowing backward
• Pressure from heart drives blood flow in
arteries, but pressure in veins often too
low to oppose gravity
• Compression pushes blood toward heart
– Skeletal muscle movement required to
“squish” blood through veins
Health Problems with Veins
• Resistance to flow (gravity, obesity)
causes pooling above valves, veins
stretch out
– Varicose veins
– Hemorrhoids
Blood Reservoirs in
Venous System
• Venous system contains 65-70% total
blood volume
• Can constrict during hemorrhage to
keep volume in capillaries and arteries
near normal
6. Anastomoses
• Bypass routes between vessels
– Bypass the capillary bed
• Not present in retina, kidney, or spleen
• More common in veins
A cross section of tissue shows several small,
thin-walled vessels with very little smooth
muscle tissue in the tunica media. Which
type of vessels are these?
A. arteries
B. capillaries
C. arterioles
D. veins
Why are valves located in veins, but
not in arteries?
A. venous blood pressure is lower
B. venous blood pressure is higher
C. venous walls are more muscular
D. venous lumens are larger
Where in the body would you find
fenestrated capillaries?
A. absorptive areas of intestine
B. filtration areas of kidney
C. choroid plexus of brain
D. all of the above are correct
Blood Distribution
Figure 21-7
The mechanisms that regulate
blood flow through arteries,
capillaries, and veins.
Physiology of Circulation
Figure 21-8
Physiology of Circulation
• Blood flow = volume of blood flowing through a
vessel in given period
– Total body flow = Cardiac output
• Blood Pressure = force per unit area exerted on
vessel by blood (mmHg)
– Blood flows from high pressure  low
• Resistance = opposition to blood flow, friction
– Incr. blood viscosity = incr. resistance
– Incr. vessel length = incr. resistance
– Decr. Vessel diameter = incr. resistance
Factors that influence blood
pressure and its regulation.
Pressure
• Pressure (P)
– The heart generates P to overcome
resistance
– Absolute pressure is less important than
pressure gradient
• The Pressure Gradient (P)
– The difference between pressure at the
heart and pressure at peripheral capillary
beds
Force (F)
• Is proportional to the pressure
difference (P)
• Divided by R
Vascular Resistance
• Adult vessel length is constant
• Vessel diameter varies by vasodilation
and vasoconstriction
• R increases exponentially as vessel
diameter decreases
Vasoconstriction and
Vasodilation
• Vasoconstriction
– Decr. Flow
– Incr. Blood Pressure
– Incr. Resistance
• Vasodilation
– Incr. Flow
– Decr. Blood Pressure
– Decr. Resistance
Pressure
• Blood pressure changes throughout
body
– Greatest in arteries leaving heart, lowest
in veins returning to heart
• Person’s BP measured at arteries near
heart
– Systolic pressure/diastolic pressure (from
ventricles, squeeze/rest)
– “Normal” = 110/70 mmHg
Vessel Diameter
and Cardiac Pressure
Figure 21-9a
Pressures in the Systemic Circuit
Figure 21-10
Pressures in the
Systemic Circuit
• Systolic pressure:
– peak arterial pressure during ventricular
systole
• Diastolic pressure:
– minimum arterial pressure during diastole
• Pulse pressure:
– difference between systolic pressure and
diastolic pressure
Abnormal Blood Pressure
• Hypertension:
–
–
–
–
Arterial pressure > 150/90 mmHg
abnormally high blood pressure
Causes incr. workload for heart
Untreated = enlarged left ventricle
requires more O2 heart can fail
• Hypotension:
– abnormally low blood pressure
Blood Pressure
• As arteries branch, area for blood
increases, pressure decreases and
becomes constant
• Blood at arterioles ~35mmHg 
capillaries  Blood at venules ~18mmHg
• Pressure continues to decline as veins
increase diameter
In a healthy individual, where would the
blood pressure be greater, at the aorta or
at the inferior vena cava?
A. aorta
B. inferior vena cava
While standing in the hot sun, Sally
begins to feel light headed and faints.
Explain.
A. Blood has pooled in her lower limbs.
B. Cardiac output has decreased,
sending less blood to the brain.
C. Sweating has reduced blood volume.
D. All of the above have occurred.
The mechanisms
and pressures involved
in the movement of fluids
between capillaries and
interstitial spaces.
Capillary Exchange
• Vital to homeostasis
• Functions to feed tissues and remove
wastes
• Due to filtration and diffusion
• Dependent on good blood flow and
pressure
• Moves materials across capillary walls by:
1. Diffusion
2. Filtration
3. Reabsorption
1. Diffusion
• Movement of ions or molecules:
– from high concentration to lower
concentration
1. Small ions transit through endothelial cells
– e.g. Na+
2. Large ions & small organics pass between
endothelial cells
– E.g. glucose, amino acids
3. Lipids pass through endothelial membrane
– e.g. steroid hormones
1. Diffusion
4. Large water soluble compounds diffuse at
fenestrated capillaries
– e.g. in intestine
5. Large plasma proteins diffuse only at sinusoids
– e.g. in liver
2. Filtration
• The removal of large solutes through a porous
membrane
• Pressure forces substances through membrane
• Blood hydrostatic pressure in capillaries drives
water and solutes out of plasma to tissues
– 24L/day
• Most recollected by osmosis (plasma proteins)
back into capillary
– filtered at arteriole end
– absorbed at venule end
2. Filtration
• 3.6 L/day flows through interstitial spaces,
recollected by lymphatic system
– Accelerates distribution of nutrients
– Flushes out toxins and pathogens
• Will be removed/detoxified by immune
cells in lymphatic system
3. Reabsorption
• The result of osmosis
Hydrostatic pressure:
– forces water out of solution
Osmotic pressure:
– forces water into solution
**Both control filtration and reabsorption
through capillaries
Forces Across Capillary Walls
Figure 21-12
Net Hydrostatic Pressure
• The difference between:
– capillary hydrostatic pressure (CHP)
– and interstitial fluid hydrostatic pressure
(IHP)
• Pushes water and solutes:
– out of capillaries
– into interstitial fluid
Net Colloid Osmotic Pressure
• The difference between:
– blood colloid osmotic pressure (BCOP)
– and interstitial fluid colloid osmotic
pressure (ICOP)
• Pulls water and solutes:
– into capillary
– from interstitial fluid
Capillary Exchange
• At arterial end of capillary:
– fluid moves out of capillary
– into interstitial fluid
• At venous end of capillary:
– fluid moves into capillary
– out of interstitial fluid
Edema
• Buildup of fluid in the tissues, due to
too much diffusion or filtration, not
enough osmosis, or blocked lymphatics
KEY CONCEPT
• Total peripheral blood flow equals cardiac
output
• Blood pressure overcomes friction and elastic
forces to sustain blood flow
• If blood pressure is too low:
– vessels collapse
– blood flow stops
– tissues die
• If blood pressure is too high:
– vessel walls stiffen
– capillary beds may rupture
Cardiovascular Regulation
Cardiovascular Regulation
• Flow, BP, and resistance must be controlled
to insure delivery of nutrients and removal
of wastes in tissues
• Changes blood flow to a specific area:
– at an appropriate time and area
– without changing blood flow to vital organs
• 3 Regulatory Mechanisms
1. Autoregulation
2. Neural Mechanism
3. Hormonal Regulation
1. Autoregulation
1. Autoregulation
– causes immediate, localized homeostatic
adjustments
– Single capillary bed: action at a
precapillary sphincter
1. Autoregulation
1. Autoregulation
– Local vasodilators: (increase blood flow)
• Incr. CO2 or decr. O2
• Lactic acid, Incr. K+ or H+
• Inflammation: histamine, NO
• Elevated temperature
– Local vasoconstrictors: (decrease blood flow)
• Prostaglandins
• Thromboxanes
• Endothelins
2. Neural Mechanisms
1. Cardiovascular (CV) centers:
– cardiac and vasomotor centers of medulla
oblongata
– adjust cardiac output and peripheral resistance
– Cardiac Center
• Cardioacceleratory center: sympathetic = incr. CO
• Cardioinhibitory center: parasympathetic = decr. CO
– Vasomotor Center
• Sympathetic = NE = vasoconstriction
2. Neural Mechanisms
2. Baroreceptor reflexes:
• Respond to changes in blood pressure
• Trigger cardiovascular center
3. Chemoreceptor reflexes:
• Respond to changes in blood and CSF
CO2 and O2, pH
• Trigger respiratory and cardiac center
3. Hormonal Regulation
1. Antidiuretic Hormone (ADH)
– From pituitary gland in response to low blood
volume
– Causes vasoconstriction and water conservation
at kidney
2. Angiotensin II
– From kidney in response to low BP
– Causes:
• Na+ retention and K+ loss at kidney
• Stimulates release of ADH, stimulates thirst,
Stimulated CO
• Stimulates arteriole constriction
3. Hormonal Regulation
3. Erythropoietin
– From kidney in response to low O2
– Stimulates production and maturation of RBCs
4. Atrial Natriuretic Peptides (ANP)
– From atria in response to stretching
– Causes:
• Increase Na+ and H2O loss at kidney
• Reduced Thirst
• Blocks ADH release
• Stimulates vasodilation
KEY CONCEPT
• Cardiac output cannot increase
indefinitely
• Blood flow to active vs. inactive tissues
must be differentially controlled
• This is accomplished by autoregulation,
neural regulation, and hormone
release
Cardiovascular Response to
Hemorrhages
• Short term (aimed at incr. BP and incr.
Flow)
– Blood flow to brain kept constant while other
systems adjust, can compensate for ~20%
blood loss
1. Incr. cardiac output = trigger peripheral
vasoconstriction to incr. BP
2. Venoconstrict to moblize venous reserve to incr.
blood volume
3. Release NE, ADH, Angiotensin II to incr. BP
Cardiovascular Response to
Hemorrhages
• Long term (aimed at restoring normal
blood volume after hemorrhage)
1.
2.
3.
4.
Recall fluid from interstitial spaces
Release Incr. ADH for fluid retention at kidney
Increase thirst
Release EPO to Incr. RBCs
Shock
• Low BP and inadequate blood flow
• Due to:
–
–
–
–
Loss of > 30% blood volume
Damage to heart
External pressure on heart
Extensive vasodilation
• Result in:
– Hypotension, rapid weak pulse clammy skin,
confusion
– Incr. heart rate
– Decr. urine production and blood pH
*Body focuses on supplying blood to brain at expense
of other tissues
Circulatory Collapse
• Blood flow stops completely as muscles
in vessels no longer contract due to
lack of oxygen
• Results in no blood flow = death
Aging and the
Cardiovascular System
1. Decreased hematocrit
2. Increased blood clots (thrombus)
formation
3. Blood-pools in legs
–
due to venous valve deterioration
4. Reduction in max Cardiac output
5. Increased arteriosclerosis
A blockage of which branch from the
aortic arch would interfere with
blood flow to the left arm?
A. left common carotid artery
B. left subclavian artery
C. brachiocephalic trunk
D. right common carotid artery
Why would a compression of the
common carotid arteries cause a person
to lose consciousness?
A. Because it would cause a reflexive decrease
in heart rate and blood pressure.
B. Because cerebral arteries would dilate in
response to pressure.
C. Because increased blood pressure would
occur at the carotid sinus.
D. Because rapid fall in blood flow to the
brain would occur.
Whenever Tim gets angry, a large vein
bulges in the lateral region of his neck.
Which vein is this?
A. superior vena cava
B. brachiocephalic vein
C. internal jugular vein
D. external jugular vein
A blood sample taken from the umbilical cord
contains a high concentration of oxygen and
nutrients and a low concentration of carbon
dioxide and waste products. Is this a sample from
an umbilical artery or from the umbilical vein?
A. umbilical artery
B. umbilical vein
SUMMARY
• 3 types of blood vessels:
– arteries
– veins
– Capillaries
• Structure of vessel walls
• Differences between arteries and veins
• Atherosclerosis, arteriosclerosis, and plaques
• Structures of:
– elastic arteries
– muscular arteries
– arterioles
SUMMARY
• Structures of capillary walls:
– continuous
– Fenestrated
• Structures of capillary beds:
– precapillary sphincters
– Vasomotion
• Functions of the venous system and valves
• Distribution of blood and venous reserves
• Circulatory pressures:
– blood pressure
– capillary hydrostatic pressure
– venous pressure
SUMMARY
• Resistance in blood vessels:
– viscosity
– turbulence
– Vasoconstriction
• The respiratory pump
• Capillary pressure and capillary exchange:
– osmotic pressure
– net filtration pressure
• Physiological controls of cardiovascular system:
– autoregulation
– neural controls
– hormonal controls