پاورپوینت به زبان انگلیسی Blood Vessels

Blood Vessels

Blood Vessels
Delivery system of dynamic structures that begins and ends at the heart
Arteries: carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of a fetus
Capillaries: contact tissue cells and directly serve cellular needs
Veins: carry blood toward the heart

Large veins
(capacitance
vessels)
Large
lymphatic
vessels
Arteriovenous
anastomosis
Lymphatic
capillary
Postcapillary
venule
Sinusoid
Metarteriole
Terminal arteriole
Arterioles
(resistance vessels)
Muscular arteries
(distributing
vessels)
Elastic arteries
(conducting
vessels)
Small veins
(capacitance
vessels)
Lymph
node
Capillaries
(exchange vessels)
Precapillary sphincter
Thoroughfare
channel
Lymphatic
system
Venous system
Arterial system
Heart

Structure of Blood Vessel Walls
Arteries and veins
Tunica intima, tunica media, and tunica externa
Lumen
Central blood-containing space
Capillaries
Endothelium with sparse basal lamina

Tunica media
(smooth muscle and
elastic fibers)
Tunica externa
(collagen fibers)
Lumen
Artery
Lumen
Vein
Internal elastic lamina
External elastic lamina
Valve
(b)
Endothelial cells
Basement membrane
Capillary
network
Capillary
Tunica intima
• Endothelium
• Subendothelial layer

Tunics
Tunica intima
Endothelium lines the lumen of all vessels
In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present

Tunics
Tunica media
Smooth muscle and sheets of elastin
Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels

Tunics
Tunica externa (tunica adventitia)
Collagen fibers protect and reinforce
Larger vessels contain vasa vasorum to nourish the external layer

Elastic (Conducting) 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 (Distributing) Arteries and Arterioles
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

Capillaries
Microscopic blood vessels
Walls of thin tunica intima, one cell thick
Pericytes help stabilize their walls and control permeability
Size allows only a single RBC to pass at a time

Capillaries
In all tissues except for cartilage, epithelia, cornea and lens of eye
Functions: exchange of gases, nutrients, wastes, hormones, etc.

Capillaries
Three structural types
Continuous capillaries
Fenestrated capillaries
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

Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Endothelial
nucleus
Tight junction
Pinocytotic
vesicles
Pericyte
Basement
membrane
(a) Continuous capillary. Least permeable, and
most common (e.g., skin, muscle).

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)

Figure 19.3b
Red blood
cell in lumen
Intercellular
cleft
Fenestrations
(pores)
Endothelial
cell
Endothelial
nucleus
Basement membrane
Tight junction
Pinocytotic
vesicles
(b) Fenestrated capillary. Large fenestrations
(pores) increase permeability. Occurs in special
locations (e.g., kidney, small intestine).

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

Figure 19.3c
Nucleus of
endothelial
cell
Red blood
cell in lumen
Endothelial
cell
Tight junction
Incomplete
basement
membrane
Large
intercellular
cleft
(c) Sinusoidal capillary. Most permeable. Occurs in
special locations (e.g., liver, bone marrow, spleen).

Capillary Beds
Interwoven networks of capillaries form the microcirculation between arterioles and venules
Consist of two types of vessels
Vascular shunt (metarteriole—thoroughfare channel):
Directly connects the terminal arteriole and a postcapillary venule

Capillary Beds
True capillaries
10 to 100 exchange vessels per capillary bed
Branch off the metarteriole or terminal arteriole

Blood Flow Through Capillary Beds
Precapillary sphincters regulate blood flow into true capillaries
Regulated by local chemical conditions and vasomotor nerves

Figure 19.4
(a) Sphincters open—blood flows through true capillaries.
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Precapillary
sphincters
Metarteriole
Vascular shunt
Terminal arteriole
Postcapillary venule
Terminal arteriole
Postcapillary venule
Thoroughfare channel
True capillaries

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

Artery
Vein
(a)

Heart 8%
Capillaries 5%
Systemic arteries
and arterioles 15%
Pulmonary blood
vessels 12%
Systemic veins
and venules 60%

Veins
Adaptations that ensure return of blood to the heart
Large-diameter lumens offer little resistance
Valves prevent backflow of blood
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)

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

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 as ml/min
Equivalent to cardiac output (CO) for entire vascular system
Relatively constant when at rest
Varies widely through individual organs, based on needs

Physiology of Circulation: Definition of Terms
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 the heart
The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

Physiology of Circulation: Definition of Terms
Resistance (peripheral resistance)
Opposition to flow
Measure of the amount of friction blood encounters
Generally encountered in the peripheral systemic circulation
Three important sources of resistance
Blood viscosity
Total blood vessel length
Blood vessel diameter

Resistance
Factors that remain relatively constant:
Blood viscosity
The “stickiness” of the blood due to formed elements and plasma proteins
Blood vessel length
The longer the vessel, the greater the resistance encountered

Resistance
Frequent changes alter peripheral resistance
Varies inversely with the fourth power of vessel radius
E.g., if the radius is doubled, the resistance is 1/16 as much

Resistance
Small-diameter arterioles are the major determinants of peripheral resistance
Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance
Disrupt laminar flow and cause turbulence

Relationship Between Blood Flow, Blood Pressure, and Resistance
Blood flow (F) is directly proportional to the blood (hydrostatic) pressure gradient (P)
If P increases, blood flow speeds up
Blood flow is inversely proportional to peripheral resistance (R)
If R increases, blood flow decreases: F = P/R
R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter

Systemic Blood Pressure
The pumping action of the heart generates blood flow
Pressure results when flow is opposed by resistance
Systemic pressure
Is highest in the aorta
Declines throughout the pathway
Is 0 mm Hg in the right atrium
The steepest drop occurs in arterioles

Systolic pressure
Mean pressure
Diastolic
pressure

Arterial Blood 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

Arterial Blood Pressure
Systolic pressure: pressure exerted during ventricular contraction
Diastolic pressure: lowest level of arterial pressure
Pulse pressure = difference between systolic and diastolic pressure

Arterial Blood 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
Ranges from 15 to 35 mm Hg
Low capillary pressure is desirable
High BP would rupture fragile, thin-walled capillaries
Most are very permeable, so low pressure forces filtrate into interstitial spaces

Venous Blood Pressure
Changes little during the cardiac cycle
Small pressure gradient, about 15 mm Hg
Low pressure due to cumulative effects of peripheral resistance

Factors Aiding Venous Return
Respiratory “pump”: pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand
Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow
Vasoconstriction of veins under sympathetic control

Valve (open)
Contracted
skeletal
muscle
Valve (closed)
Vein
Direction of
blood flow

Maintaining Blood Pressure
Requires
Cooperation of the heart, blood vessels, and kidneys
Supervision by the brain

Maintaining Blood Pressure
The main factors influencing blood pressure:
Cardiac output (CO)
Peripheral resistance (PR)
Blood volume

Maintaining Blood Pressure
F = P/PR and CO = P/PR
Blood pressure = CO x PR (and CO depends on blood volume)
Blood pressure varies directly with CO, PR, and blood volume
Changes in one variable are quickly compensated for by changes in the other variables

Cardiac Output (CO)
Determined by venous return and neural and hormonal controls
Resting heart rate is maintained by the cardioinhibitory center via the parasympathetic vagus nerves
Stroke volume is controlled by venous return (EDV)

Cardiac Output (CO)
During stress, the cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation
ESV decreases and MAP increases

Venous return
Exercise
Contractility of cardiac muscle
Sympathetic activity
Parasympathetic
activity
Epinephrine in blood
EDV
ESV
Stroke volume (SV)
Heart rate (HR)
Cardiac output (CO = SV x HR
Activity of respiratory pump
(ventral body cavity pressure)
Activity of muscular pump
(skeletal muscles)
Sympathetic venoconstriction
BP activates cardiac centers in medulla
Initial stimulus
Result
Physiological response

Control of Blood Pressure
Short-term neural and hormonal controls
Counteract fluctuations in blood pressure by altering peripheral resistance
Long-term renal regulation
Counteracts fluctuations in blood pressure by altering blood volume

Short-Term Mechanisms: Neural Controls
Neural controls of peripheral resistance
Maintain MAP by altering blood vessel diameter
Alter blood distribution in response to specific demands

Short-Term Mechanisms: Neural Controls
Neural controls operate via reflex arcs that involve
Baroreceptors
Vasomotor centers and vasomotor fibers
Vascular smooth muscle

The Vasomotor Center
A cluster of sympathetic neurons in the medulla that oversee changes in blood vessel diameter
Part of the cardiovascular center, along with the cardiac centers
Maintains vasomotor tone (moderate constriction of arterioles)
Receives inputs from baroreceptors, chemoreceptors, and higher brain centers

Short-Term Mechanisms: Baroreceptor-Initiated Reflexes
Baroreceptors are located in
Carotid sinuses
Aortic arch
Walls of large arteries of the neck and thorax

Short-Term Mechanisms: Baroreceptor-Initiated Reflexes
Increased blood pressure stimulates baroreceptors to increase input to the vasomotor center
Inhibits the vasomotor center, causing arteriole dilation and venodilation
Stimulates the cardioinhibitory center

Baroreceptors
in carotid sinuses
and aortic arch
are stimulated.
Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Impulses from baroreceptors stimulate
cardioacceleratory center (and inhibit cardioinhibitory
center) and stimulate vasomotor center.
CO and R
return blood
pressure to
homeostatic range.
CO and R
return blood pressure
to homeostatic range.

Rate of
vasomotor impulses
allows vasodilation,
causing R
Vasomotor
fibers stimulate
vasoconstriction,
causing R

Sympathetic
impulses to heart
cause HR,
contractility, and
CO.

Stimulus:
Blood pressure
(arterial blood
pressure falls below
normal range).
Stimulus:
Blood pressure
(arterial blood
pressure rises above
normal range).
3
2
1
5
4a
4b
Homeostasis: Blood pressure in normal range
4b
3
2
1
5
4a

Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
1
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid
sinuses and
aortic arch are
stimulated.
Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
2
1
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid
sinuses and
aortic arch are
stimulated.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
2
3
1
Homeostasis: Blood pressure in normal range

Sympathetic
impulses to heart
cause HR,
contractility,
and CO.
Baroreceptors
in carotid
sinuses and
aortic arch are
stimulated.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
2
3
1
4a
Homeostasis: Blood pressure in normal range

Sympathetic
impulses to heart
cause HR,
contractility,
and CO.
Rate of
vasomotor impulses
allows vasodilation,
causing R
Baroreceptors
in carotid
sinuses and
aortic arch are
stimulated.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
2
3
1
4b
4a
Homeostasis: Blood pressure in normal range

Sympathetic
impulses to heart
cause HR,
contractility,
and CO.
CO and
R return
blood pressure
to homeostatic
range.
Rate of
vasomotor impulses
allows vasodilation,
causing R
Baroreceptors
in carotid
sinuses and
aortic arch are
stimulated.
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
2
3
1
4b
4a
5
Homeostasis: Blood pressure in normal range

Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
1
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
2
1
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioacceleratory center
(and inhibit cardioinhibitory center)
and stimulate vasomotor center.
Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
2
3
1
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioacceleratory center
(and inhibit cardioinhibitory center)
and stimulate vasomotor center.
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
2
3
1
4a
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioacceleratory center
(and inhibit cardioinhibitory center)
and stimulate vasomotor center.
Vasomotor
fibers stimulate
vasoconstriction,
causing R
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
2
3
1
4b
4a
Homeostasis: Blood pressure in normal range

Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
Impulses from baroreceptors
stimulate cardioacceleratory center
(and inhibit cardioinhibitory center)
and stimulate vasomotor center.
CO and R
return blood
pressure to
homeostatic
range.
Vasomotor
fibers stimulate
vasoconstriction,
causing R
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
Stimulus:
Blood pressure
(arterial blood
pressure falls
below normal
range).
2
3
1
4b
4a
5
Homeostasis: Blood pressure in normal range

Rate of
vasomotor impulses
allows vasodilation,
causing R
Vasomotor
fibers stimulate
vasoconstriction,
causing R

Sympathetic
impulses to heart
cause HR,
contractility, and
CO.

Short-Term Mechanisms: Baroreceptor-Initiated Reflexes
Baroreceptors taking part in the carotid sinus reflex protect the blood supply to the brain
Baroreceptors taking part in the aortic reflex help maintain adequate blood pressure in the systemic circuit

Short-Term Mechanisms: Chemoreceptor-Initiated Reflexes
Chemoreceptors are located in the
Carotid sinus
Aortic arch
Large arteries of the neck

Short-Term Mechanisms: Chemoreceptor-Initiated Reflexes
Chemoreceptors respond to rise in CO2, drop in pH or O2
Increase blood pressure via the vasomotor center and the cardioacceleratory center
Are more important in the regulation of respiratory rate (Chapter 22)

Influence of Higher Brain Centers
Reflexes that regulate BP are integrated in the medulla
Higher brain centers (cortex and hypothalamus) can modify BP via relays to medullary centers

Short-Term Mechanisms: Hormonal Controls
Adrenal medulla hormones norepinephrine (NE) and epinephrine cause generalized vasoconstriction and increase cardiac output
Angiotensin II, generated by kidney release of renin, causes vasoconstriction

Short-Term Mechanisms: Hormonal Controls
Atrial natriuretic peptide causes blood volume and blood pressure to decline, causes generalized vasodilation
Antidiuretic hormone (ADH)(vasopressin) causes intense vasoconstriction in cases of extremely low BP

Long-Term Mechanisms: Renal Regulation
Baroreceptors quickly adapt to chronic high or low BP
Long-term mechanisms step in to control BP by altering blood volume
Kidneys act directly and indirectly to regulate arterial blood pressure
Direct renal mechanism
Indirect renal (renin-angiotensin) mechanism

Direct Renal Mechanism
Alters blood volume independently of hormones
Increased BP or blood volume causes the kidneys to eliminate more urine, thus reducing BP
Decreased BP or blood volume causes the kidneys to conserve water, and BP rises

Indirect Mechanism
The renin-angiotensin mechanism
 Arterial blood pressure  release of renin
Renin production of angiotensin II
Angiotensin II is a potent vasoconstrictor
Angiotensin II  aldosterone secretion
Aldosterone  renal reabsorption of Na+ and  urine formation
Angiotensin II stimulates ADH release

Arterial pressure
Baroreceptors
Indirect renal
mechanism (hormonal)
Direct renal
mechanism
Sympathetic stimulation
promotes renin release
Kidney
Renin release
catalyzes cascade,
resulting in formation of
ADH release
by posterior
pituitary
Aldosterone
secretion by
adrenal cortex
Water
reabsorption
by kidneys
Blood volume
Filtration
Arterial pressure
Angiotensin II
Vasoconstriction
( diameter of blood vessels)
Sodium
reabsorption
by kidneys
Initial stimulus
Physiological response
Result

Activity of
muscular
pump and
respiratory
pump
Release
of ANP
Fluid loss from
hemorrhage,
excessive
sweating
Crisis stressors:
exercise, trauma,
body
temperature
Bloodborne
chemicals:
epinephrine,
NE, ADH,
angiotensin II;
ANP release
Body size
Conservation
of Na+ and
water by kidney
Blood volume
Blood pressure
Blood pH, O2,
CO2
Dehydration,
high hematocrit
Blood
volume
Baroreceptors
Chemoreceptors
Venous
return
Activation of vasomotor and cardiac
acceleration centers in brain stem
Heart
rate
Stroke
volume
Diameter of
blood vessels
Cardiac output
Initial stimulus
Result
Physiological response
Mean systemic arterial blood pressure
Blood
viscosity
Peripheral resistance
Blood vessel
length

The end

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