Download Cardiovascular System Blood Vessels Blood Vessel Structure

3/27/2016
Blood Vessels
• Delivery system of dynamic structures
• Closed system
Cardiovascular System
– Arteries
Blood Vessels
• Carry blood away from the heart
– Capillaries
• Contact tissue cells and directly serve cellular needs
– Veins
• Carry blood toward the heart
Venous system
Large veins
(capacitance
vessels)
Small veins
(capacitance
vessels)
Postcapillary
venule
Thoroughfare
channel
Arterial system
Heart
Common
carotid arteries
to head and
subclavian
arteries to
upper limbs
Capillary beds of
head and
upper limbs
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
Elastic arteries
(conducting
vessels)
Superior
vena cava
Aortic
arch
Aorta
Muscular arteries
(distributing
vessels)
RA
LA
RV
LV
Azygos
system
Thoracic
aorta
Venous
drainage
Lymphatic
Sinusoid
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary
sphincter
Capillaries
(exchange vessels)
Inferior
vena
cava
Arterial
blood
Capillary beds of
mediastinal structures
and thorax walls
Diaphragm
Abdominal
aorta
Inferior
vena
cava
Capillary beds of
digestive viscera,
spleen, pancreas,
kidneys
Capillary beds of gonads,
pelvis, and lower limbs
Figure 19.2
Figure 19.20
Blood Vessel Structure
Tunica intima
• Endothelium
• Subendothelial layer
Internal elastic lamina
Tunica media
(smooth muscle and
elastic fibers)
External elastic lamina
• Tissue layers
– Tunica intima
– Tunica media
– Tunica externa
Valve
Tunica externa
(collagen fibers)
Valve
Valve
Tunica
intima
Tunica
media
Lumen
Artery
Endothelial
Cell
Tunica
externa
(b)
Capillary
network
Lumen
Vein
Basement membrane
Endothelial cells
Capillary
Figure 19.1b
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Blood Vessel Structure
Blood Vessel Structure
Vasa vasorum nourishes outer layers of large vessels
Arteries of the head and trunk
Internal carotid artery
External carotid artery
Common carotid arteries
Vertebral artery
Subclavian artery
Brachiocephalic trunk
Aortic arch
Ascending aorta
Coronary artery
Thoracic aorta (above
diaphragm)
Celiac trunk
Abdominal aorta
Superior mesenteric artery
Renal artery
Gonadal artery
Common iliac artery
Inferior mesenteric artery
Internal iliac artery
(b) Illustration, anterior
view
Arteries
Arteries that supply
the upper limb
Subclavian artery
Axillary artery
• Transport blood from left ventricle to body
tissues
Brachial artery
Radial artery
Ulnar artery
– High pressure
Deep palmar arch
Superficial palmar arch
Digital arteries
Arteries that supply
the lower limb
External iliac artery
Femoral artery
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Arcuate artery
• Three groups
– Elastic (conducting)
– Muscular (distributing)
– Arterioles (resistance)
Figure 19.21b
Arteries
• Elastic arteries
– Near the heart
• Aorta and major branches
– Conducting arteries
• Conduct blood from the heart to medium-sized arteries
– Large and thick-walled
– Large lumen = low resistance
– Highly elastic
• Expand during systole & recoil during diastole
Table 19.1 (1 of 2)
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Arteries
• Muscular arteries
– Distributing arteries
Arteries
• Resistance arteries
– Smallest arterial vessels (arterioles)
• Distal to elastic arteries
• Deliver blood to body organs
– Thick tunica media with more smooth muscle
– Active in vasoconstriction
– Examples
• Lead to capillary beds
• Control valves to capillary beds
– Site of most vasodilation and vasoconstriction
Metarteriole
• Radial, femoral, brachial
Venule
Arteriole
Capillaries
• Exchange vessels
• Exceedingly thin walls – just a tunica intima
• Capillary beds
– Microcirculation
between arterioles
and venules
Capillaries
Capillaries
• Two types
1. Continuous
•
•
•
Open junctions between adjacent endothelial cells
Most common
In skin & muscles
2. Fenestrated
•
•
Pores = permeable
Intestines, endocrine organs, kidneys
Capillaries
• Precapillary sphincters
– Cuff of smooth muscle fibers
– Acts as a valve to control blood flow into the
capillary
– Responds to local chemical conditions
– Vasomotor nerves (sympathetic)
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Precapillary
sphincters
Vascular shunt
Metarteriole
Capillaries
Thoroughfare channel
• Tissue capillary bed may be flooded with blood
or nearly completely empty
• Examples: GI tract after a meal; skeletal muscle
during exercise
True capillaries
Terminal arteriole
Postcapillary venule
(a) Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Figure 19.4
Continuous Capillaries
Continuous Capillaries
• Abundant in the skin and muscles
• Continuous capillaries of the brain
– Tight junctions connect endothelial cells
– Intercellular clefts
allow the passage of
fluids and small
solutes
– Tight junctions are complete, forming the bloodbrain barrier
– Carrier-mediated transport
Pericyte
Pinocytotic
vesicles
Red blood
cell in lumen
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Pinocytotic
Endothelial
vesicles
nucleus
(a) Continuous capillary. Least permeable, and
most common (e.g., skin, muscle).
Fenestrations
(pores)
Endothelial
nucleus
Intercellular
cleft
Basement membrane
Tight junction
Endothelial
cell
(b) Fenestrated capillary. Large fenestrations
(pores) increase permeability. Occurs in special
locations (e.g., kidney, small intestine).
Figure 19.3a
Figure 19.3b
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This is not in the Study Guide, just FYI
Capillaries
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Nucleus of
Incomplete
endothelial
basement
cell
membrane
(c) Sinusoidal capillary. Most permeable. Occurs in
special locations (e.g., liver, bone marrow, spleen).
• Functions
– Exchange area for blood and interstitial fluid
compartment
– Diffusion
• O2 and nutrients from the blood to tissues
• CO2 and metabolic wastes from tissues to the blood
Figure 19.3c
Veins
• Functions
– Collect blood from capillary beds
– “drain” organs and tissues of blood
• Become larger as they come closer to the heart
Veins of the head and trunk
Dural venous sinuses
External jugular vein
Veins that drain
the upper limb
Subclavian vein
Vertebral vein
Axillary vein
Internal jugular vein
Cephalic vein
Brachial vein
Basilic vein
Right and left
brachiocephalic veins
Superior vena cava
Great cardiac vein
Hepatic veins
Median cubital vein
Ulnar vein
Radial vein
Splenic vein
Digital veins
Veins that drain
the lower limb
Hepatic portal vein
Renal vein
Superior mesenteric
vein
Inferior vena cava
Inferior mesenteric vein
External iliac vein
Common iliac vein
Popliteal vein
Internal iliac vein
Posterior tibial vein
Femoral vein
Great saphenous vein
Anterior tibial vein
(b) Illustration, anterior
view. The vessels of the
pulmonary circulation
are not shown.
Small saphenous vein
Dorsal venous arch
Dorsal metatarsal veins
Figure 19.26b
Venules
• Formed when capillary beds unite
• Very porous
– Allow fluids and WBC’s into tissues
Copyright © 2010 Pearson Education, Inc.
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Veins
Pulmonary blood
vessels 12%
Systemic arteries
and arterioles 15%
•
•
•
•
Heart 8%
Capillaries 5%
Thinner walls, larger lumens than arteries
Blood pressure is lower than in arteries
Thin tunica media and a thick tunica externa
Capacitance vessels (blood reservoirs)
– Contain up to 60% of the blood supply
Systemic veins
and venules 60%
Figure 19.5
Blood Vessel Matching
1.
2.
3.
4.
5.
6.
a.
b.
c.
d.
e.
f.
Pump
Resistance vessels, site of most vasodilation and vasoconstriction
Exchange sites
Pressure reservoirs, conducting vessels
Blood reservoirs
Distributing vessels
Venous Blood Pressure
• Low pressure
– Due to cumulative effects of peripheral resistance
• Working against gravity
Veins
Arterioles
Capillaries
Heart
Elastic arteries
Muscular arteries
– Valves
– Skeletal muscle action
– Thoracic pressure changes
Venous Valves
Valve (open)
Contracted
skeletal
muscle
Valve (closed)
Vein
Direction of
blood flow
Figure 19.7
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Varicose Veins
• Incompetent valves
Blood Flow
• Blood flow is involved in
– Pregnancy
– Obesity
– Long periods of standing
– Hemorrhoids
– O2 delivery
– Removal of wastes
– Gas exchange (lungs)
– Absorption of nutrients (digestive tract)
– Urine formation (kidneys)
Blood Flow
• Perfusion
Blood Flow
•
– Rate of blood flow per given volume of tissue
• Blood flow (F)
– Volume of blood flowing through a vessel, an organ, or tissue
in a given period
• Measured as ml/min
• Varies widely through individual organs
– Based on needs
Blood Flow
F= Δ P
R
• Relationship between blood flow, blood
pressure, and resistance
– If ∆P increases, blood flow speeds up
– If R increases, blood flow decreases
• R is more important in influencing local blood
flow
– Changed by altering blood vessel diameter
F= Δ P
R
o F = Blood flow
o ΔP = Difference in pressure between two points
o R = Resistance
Blood Pressure
• Blood pressure (BP)
– Force per unit area exerted on the wall blood vessel
by the blood
– Expressed as the height of a column of mercury
(mmHg)
–P=HxD
• P = pressure
• H = height of column
• D = density of material in the column
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Blood Pressure
Blood Pressure
• Systolic pressure
• Factors influencing blood pressure
– Pressure exerted during ventricular contraction
– Top number
– Cardiac output (CO)
– Peripheral resistance (PR)
– Blood volume
• Diastolic pressure
– Lowest level of arterial pressure
– Bottom number
• Average value = 120/80
• Pulse pressure
– Difference between systolic and diastolic pressure
Blood Pressure
Systolic pressure
• Basic concepts
Mean pressure
– The pumping action of the heart generates blood
flow
– Pressure results when flow is opposed by resistance
Diastolic
pressure
• Systemic pressure
– Highest in the aorta
– Declines throughout the pathway
– Is close to 0 mmHg in the right atrium
• The steepest drop occurs in arterioles
Figure 19.6
Arterial Blood Pressure
• Reflects two factors of the arteries close to the
heart
– Elasticity
– Volume of blood forced into them at any time
• Blood pressure near the heart is pulsatile
Arterial Blood Pressure
Mean arterial blood pressure (MABP)
Pressure that propels blood to tissues
Represents average blood pressure
MABP = diastolic pressure + 1/3 pulse pressure
Pulse pressure and MABP both decline
with increasing distance from the heart
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Hypertension
• “Silent Killer”
– Resting systolic >140 mmHg and/or diastolic >90 mmHg
• Causes
– Loss of flexibility in vessel walls
• Results
–
–
–
–
Capillary Blood Pressure
• Not pulsatile
• 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
Heart failure
Renal failure
Stroke
Increased risk of aneurysm
Peripheral Resistance
• The opposition to blood flow exerted by vessel
walls
– The result of friction
• Influenced by 3 factors
– Blood viscosity
– Blood vessel length
– Blood vessel radius
Peripheral Resistance
• Vessel length
– The farther fluid travels = more cumulative friction
Peripheral Resistance
• Viscosity = a fluid’s resistance to flow
• Blood viscosity influenced by…
– Albumin
– Erythrocytes
Peripheral Resistance
• Vessel radius
– Most significant factor
– Vasoconstriction and vasodilation
– Flow is proportional to fourth power of radius
• Alteration of radius profoundly affects blood flow
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Poiseuille’s Law
• Formula representing the factors influencing flow
F = ΔPπr4
8 nL
Poiseuille’s Law
• Blood flow is directly proportional to pressure
gradient and vessel radius
F = ΔPπr4
8 nL
F= flow
ΔP = pressure gradient
r4 = vessel radius
n = viscosity
L = vessel length
Poiseuille’s Law
• Blood flow is inversely proportional to vessel
length and blood viscosity
F = ΔPπr4
8 nL
Regulation of Peripheral Resistance
Local control
Localized hypoxia
Metabolites (CO2, lactic acid, adenosine)
Regulation of Peripheral Resistance
• Local control
– Arterioles vary diameters = autoregulation
• A response to the chemical composition of the blood
– Faster flow = faster removal of wastes
Regulation of Peripheral Resistance
• Local control
– Precapillary sphincters
• Respond to local stimuli and vasoactive hormones
– Endothelial cells & platelets
Acidic pH
• Vasodilators
– NO, prostacyclin
Inhibit smooth muscle
• Vasoconstrictors
– Endothelians, seratonin, thromboxane A2
Vasodilation
Increased blood flow
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Intrinsic mechanisms
(autoregulation)
Peripheral Resistance
Extrinsic mechanisms
• Distribute blood flow to individual
organs and tissues as needed
• Maintain mean arterial pressure (MAP)
• Redistribute blood during exercise and
thermoregulation
Amounts of:
Sympathetic
pH
O2
Metabolic
Amounts of:
• During muscle activity, blood flow increases in direct
proportion to the metabolic activity
• Blood flow can increase 10× or more during physical activity
Epinephrine,
norepinephrine
CO2
K+
• Example of autoregulation
– Blood flow to skeletal muscles
α Receptors
β Receptors
controls
Nerves
Angiotensin II
Hormones
Prostaglandins
Antidiuretic
hormone (ADH)
Adenosine
Nitric oxide
Atrial
natriuretic
peptide (ANP)
Endothelins
Myogenic
Stretch
controls
Dilates
Constricts
Figure 19.15
Peripheral Resistance
• Neural control
Brain
Heart
– Directed by ANS via sympathetic innervation
Skeletal
muscles
• Vascular smooth muscle lacks parasympathetic input
Skin
Kidney
Abdomen
Other
Total blood
flow at rest
5800 ml/min
Total blood flow during strenuous
exercise 17,500 ml/min
Figure 19.13
Peripheral Resistance
Neural control
Vasomotor center in medulla = primary control center
Integrates input from 3 ANS reflex circuits
Baroreflex
Chemoreflex
Ischemic reflex
Peripheral Resistance
• Baroreflex
– Baroreceptors (pressure receptors) in
• Carotid sinuses
• Aortic arch
– Example: Blood pressure increases
• Inhibitory signals are sent to the
vasomotor center
• Stimulatory signals are sent to
the cardioinhibitory center (which acts
through which nerve?)
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Peripheral Resistance
3 Impulses from baroreceptors
stimulate cardioinhibitory center
and inhibit vasomotor
center.
4a Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
2 Baroreceptors
in carotid sinuses
and aortic arch
are stimulated.
• Chemoreflex
4b Rate of
vasomotor impulses
allows vasodilation,
causing R
1 Stimulus:
Blood pressure
(arterial blood
pressure rises above
normal range).
5 CO and R
return blood
pressure to
homeostatic range.
Homeostasis: Blood pressure in normal range
5 CO and R
return blood pressure
to homeostatic range.
4b Vasomotor
fibers stimulate
vasoconstriction,
causing R
– Excitatory or inhibitory signals to vasomotor
center
– Chemorecetors detect low blood pH, O2 levels
and high CO2 levels
– Chemoreceptors are located in the
• Carotid bifurcation
• Aortic arch
• Large arteries of the neck
2 Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
4a Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
3 Impulses from baroreceptors stimulate
cardioacceleratory center and stimulate vasomotor center.
Peripheral Resistance
• Medullary Ischemic Reflex
– Triggered by low perfusion of the medulla
Hypoxia and hypercapnia (high blood CO2) of the
brain
Peripheral Resistance
• Hormonal controls
– Angiotensin II
• Generated by kidney release of renin
• Causes vasoconstriction
– Atrial natriuretic peptide/factor
• Causes blood volume and blood pressure to decline
• Causes generalized vasodilation
Vasoconstriction in extremities
Blood flow directed to head and upper body
Peripheral Resistance
Activity of
muscular
pump and
respiratory
pump
• Hormonal controls cont.
Release
of ANP
Conservation
of Na+ and
water by kidney
Fluid loss from
hemorrhage,
excessive
sweating
Crisis stressors:
exercise, trauma,
body
temperature
Blood volume
Blood pressure
Blood pH, O2,
CO2
Bloodborne
chemicals:
epinephrine,
NE, ADH,
angiotensin II;
ANP release
Dehydration,
high hematocrit
Body size
– Antidiuretic hormone (ADH, vasopressin)
Blood
volume
• Causes intense vasoconstriction in cases of extremely low
BP
Venous
return
– Epinephrine
• Causes generalized vasoconstriction and increases cardiac
output
Stroke
volume
Baroreceptors
Chemoreceptors
Activation of vasomotor and cardiac
acceleration centers in brain stem
Heart
rate
Cardiac output
Diameter of
blood vessels
Blood
viscosity
Blood vessel
length
Peripheral resistance
Initial stimulus
Physiological response
Result
Mean systemic arterial blood pressure
Figure 19.11
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Fluid Shifts Between Capillaries and
Tissue
Arterial system
Venous system
Large veins
(capacitance
vessels)
Heart
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
• Capillaries allow plasma and solutes to pass into interstitial space
interstitial or extracellular fluid (ECF)
– Facilitates exchange of resources & wastes between
cells & plasma
– Dynamic equilibrium
– Imbalances?
– Exceptions?
Small veins
(capacitance
vessels)
Elastic arteries
(conducting
vessels)
Muscular arteries
(distributing
vessels)
Lymphatic
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary sphincter
Sinusoid
Postcapillary
venule
Thoroughfare
channel
Capillaries
(exchange vessels)
Figure 19.2
Regulation of ECF Movement
• Hydrostatic and osmotic pressure
– Hydrostatic “pushes” and osmotic “sucks”
– 4 types
Arteriole
Venule
Interstitial fluid
Capillary
Net HP—Net OP
(35—0)—(26—1)
Capillary hydrostatic pressure
Interstitial osmotic pressure
Move water out of
the vascular system
Interstitial hydrostatic pressure
Capillary osmotic pressure
Move water into
the vascular system
Net
HP
35
mm
Net
OP
25
mm
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
Net HP—Net OP
(17—0)—(26—1)
Net
HP
17
mm
Net
OP
25
mm
NFP is ~8 mm Hg;
fluid moves in
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HPc)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HPif)
• Pushes fluid into capillary
• 0 mm Hg in this example
OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OPc)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OPif)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Figure 19.17
Regulation of ECF Movement
• Hydrostatic
– Capillary hydrostatic pressure (HPc)
• Capillary blood pressure
• Tends to force fluids through the capillary walls
• Is greater at the arterial end (35 mm Hg) of a bed than at
the venous end (17 mm Hg)
– Interstitial hydrostatic pressure (HPif)
• Pressure of fluid within intercellular spaces
• Constantly enters lymphatic drainage
• Averages 0 mmHg
Regulation of ECF Movement
• Osmotic
– Interstitial fluid osmotic pressure (OPif)
• The osmotic pressure force created by interstitial solutes
• Low (~1 mm Hg), due to low protein content
– Capillary colloid osmotic pressure (OPc)
• Created by non-diffusible plasma proteins, which draw
water toward themselves
• ~26 mm Hg
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Regulation of ECF Movement
Regulation of ECF Movement
• The movement of fluid between the
extracellular compartments is driven by a
pressure gradient
• Net Filtration Pressure (NFP)
– Comprises all the forces acting on a capillary bed
– Most influenced by capillary hydrostatic pressure
NFP = (HPc - HPif) - (Opc - OPif)
Regulation of ECF Movement
• Arterial NFP
– Arterial end of a capillary bed = hydrostatic forces
dominate
Arteriole
Venule
Interstitial fluid
• Fluid moves out
• NFP = (35-0) – (26-1) = 10 mm Hg
Capillary
Net HP—Net OP
(35—0)—(26—1)
Net HP—Net OP
(17—0)—(26—1)
HP = hydrostatic pressure
• Due to fluid pressing against a wall
• “Pushes”
• In capillary (HPc)
• Pushes fluid out of capillary
• 35 mm Hg at arterial end and
17 mm Hg at venous end of
capillary in this example
• In interstitial fluid (HPif)
• Pushes fluid into capillary
• 0 mm Hg in this example
• Venous NFP
– Venous end of a capillary bed = osmotic forces dominate
• Fluid moves in
• NFP = (17-0) – (26-1) = -8 mm Hg
• Excess fluid
Net
HP
35
mm
Net
OP
25
mm
NFP (net filtration pressure)
is 10 mm Hg; fluid moves out
– Returned to the blood via the lymphatic system
Filtration=
fluid moves out
Net
HP
17
mm
Net
OP
25
mm
NFP is -8 mm Hg;
fluid moves in
OP = osmotic pressure
• Due to presence of nondiffusible
solutes (e.g., plasma proteins)
• “Sucks”
• In capillary (OPc)
• Pulls fluid into capillary
• 26 mm Hg in this example
• In interstitial fluid (OPif)
• Pulls fluid out of capillary
• 1 mm Hg in this example
Reabsorption=
fluid moves in
Figure 19.17
Venous system
Large veins
(capacitance
vessels)
Small veins
(capacitance
vessels)
Arterial system
Edema
Heart
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Arteriovenous
anastomosis
Elastic arteries
(conducting
vessels)
• Occurs when filtration greatly exceeds
reabsorption
Muscular arteries
(distributing
vessels)
– Abnormal increase in interstitial fluid volume
Lymphatic
capillary
Arterioles
(resistance vessels)
Terminal arteriole
Metarteriole
Precapillary sphincter
Sinusoid
Postcapillary
venule
Thoroughfare
channel
Capillaries
(exchange vessels)
Figure 19.2
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Venous Blood Pressure
• Changes little during the cardiac cycle
• Low pressure due to cumulative effects of
peripheral resistance
• Central venous pressure
Venous Return
• Venous hydrostatic pressure relatively low
• Returning blood to heart requires adaptations
– Pressure at the point where vena cava enter heart
– Average = 4.6 mm Hg
21_09
Mechanisms of Venous Return
1. Thoracic pump
• Pressure changes created during breathing move blood
toward the heart by squeezing abdominal veins as
thoracic veins expand
2. Cardiac Suction
• During atrial systole, movement of AV valves enlarges
atria = lower pressure = increasing pressure gradient
between vena cava
3. Muscular pump
• Contraction of skeletal muscles “milk” blood toward the
heart and valves prevent backflow
4. Gravity
• Helps with return of blood from superior regions
Mechanisms of Venous Return
• Circulatory shock
– Definition = CO is insufficient to meet the metabolic
demands of the tissues
– Cardiogenic shock
• Heart’s ability to pump blood is impaired
– Other types of shock
• Due to low venous return (LVR)
Types and Causes of LVR Shock
1. Hypovolemic shock
– Most common form of shock
– Result of blood loss
•
•
Direct losses: hemorrhage, trauma, burns, bleeding ulcers
Indirect losses: fluids other than blood lost
–
Burns and dehydration
– Hypovolemic shock
– Vascular shock
» Neurogenic shock
» Septic shock
» Anaphylactic shock
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2. Vascular shock
– Body retains normal blood volume but blood
accumulates in extremities
Chemoreceptors activated
(by ↓ in blood pH)
Activation of
respiratory centers
Cardioacceleratory and
vasomotor centers activated
Sympathetic nervous
system activated
ADH
released
Neurons
depressed
by ↓ pH
Central
nervous system
depressed
widespread vasodilation
Kidney
↓ Renal blood flow
Adrenal
cortex
Bacterial endotoxin simulates vasodilation
Following allergic reaction
Sudden release of histamine
changes
Brain
Intense vasoconstriction
(only heart and brain spared)
Renin released
Angiotensin II
produced in blood
c) Anaphylactic shock
•
•
Hypothalamus activated
(by ↓ pH and ↓ blood pressure)
Baroreceptor firing reduced
(by ↓ blood volume and pressure)
b) Septic shock
•
Signs and symptoms
Result
Major effect Minor effect
↑Heart rate
Usually follows spinal cord trauma
Physiological response
1. Inadequate tissue perfusion
resulting in ↓ O2 and nutrients to cells
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
a) Neurogenic shock
•
Initial stimulus
Acute bleeding (or other events that cause
blood volume loss) leads to:
Types and Causes of LVR Shock
Aldosterone
released
massive vasodilation and permeability
↑ Rate and
depth of
breathing
Tachycardia,
weak, thready
pulse
Kidneys retain
salt and water
Skin becomes
cold, clammy,
and cyanotic
Water
retention
↓ Urine output
Thirst
Restlessness
(early sign)
Coma
(late sign)
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops. ↓ BP is a late sign.
CO2 blown
off; blood
pH rises
Figure 19.18
Pathways of Blood Circulation
• Complete circuits begin and end at heart
• A double pump with 2 pathways
– Pulmonary circulation
– Systemic circulation
Systemic Circulation
• Carries oxygen rich blood to all parts of the body
• Subdivisions
– Coronary circulation
• Supplies myocardium
– Hepatic-portal circulation
• Directs blood from spleen, stomach, pancreas, gallbladder, and
intestines to the liver via portal vein
– Organs of digestion and recycling – materials are substantially
metabolized in the liver before reaching general circulation
– Jaundice
• Portal systems
– 2 capillary beds
Inferior vena cava
(not part of hepatic
portal system)
Hepatic veins
Liver
Hepatic portal
vein
Gastric veins
Spleen
Inferior vena cava
Splenic vein
Pulmonary Circulation
• Carries oxygen poor blood from heart to
alveolar surface of lungs and oxygen rich blood
back to the heart
Right gastroepiploic
vein
Inferior
mesenteric vein
Small intestine
Superior
mesenteric vein
Large intestine
Rectum
(c) The hepatic portal circulation.
Copyright © 2010 Pearson Education, Inc.
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Fetal Circulation
Fetal Circulation
• Oxygen and nutrients obtained from maternal
blood
– Respiratory and digestive systems not yet functional
– Blood oxygenated in placenta
• Attached to uterine wall by cotyledons (contain placental
villi)
• Waste carried from fetus by umbilical arteries
– Extensions of the internal iliac arteries
• Nutrient rich blood enters fetal circulation by umbilical
vein
Fetal Circulation
– Continuation of the umbilical
vein under liver
– Drains into inferior vena cava
– Allows blood to bypass the liver
– Functionally closes minutes
after birth
– Structurally closes in term
infants in 3-7 days
Fetal Circulation
• Foramen ovale
– Opening between right and left atria
lungs
– Blood routed to aorta
• Ductus venosus
• Foramen ovale
bypasses fetal
– First breath after birth decreases pulmonary pressure
– Left atrial pressure exceeds right and forces foramen
ovale closed
– May remain open
• Patent foramen ovale or ASD
• “Hole in the heart”
• May be surgically closed
Fetal Circulation
• Ductus arteriosis
– Connects pulmonary artery with descending thoracic
aorta
– Also aids in bypassing lungs
Fetal Circulation
• Ductus arteriosis
– Failure to close at birth = patent ductus arteriosis
– Leads to pulmonary hypertension
and congestive heart failure
– NSAIDs are administered to
force closure
• Why NSAIDs MUST be
avoided in late pregnancy
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Fetus
Aortic arch
Fetal Circulation
Superior vena cava
Ductus arteriosus
Ligamentum arteriosum
Pulmonary artery
Pulmonary veins
Heart
Lung
Foramen ovale
Fossa ovalis
Liver
Ductus venosus
Ligamentum venosum
Placenta
Left atrium
Umbilical vein
Aorta
Hepatic portal vein
Umbilical vein
Ductus venosus
Ligamentum teres
Inferior vena cava
Umbilicus
Abdominal aorta
Common iliac artery
Umbilical arteries
Internal
iliac arteries
Foramen ovale
Inferior vena cava
Medial umbilical ligaments
Urinary bladder
Right atrium
Umbilical cord
Right ventricle
Placenta
High oxygenation
Moderate oxygenation
Low oxygenation
Very low oxygenation
(a)
Ductus arteriosis
Umbilical
arteries
Placenta
Pulmonary artery
Figure 28.14a
Categories for Blood Pressure
Levels in Adults
(Ages 18 Years and Older)
Hypertension
Blood Pressure Level (mmHg)
• “Silent Killer”
– Produces few symptoms
• Major cause of heart failure, stroke & kidney
failure
• Resting systolic above?
• Resting diastolic above?
Hypertension
• Arteries are stretched
– Tears endothelium = exposes muscle = focal point
for atherosclerosis = worsens hypertension
• Remember atherosclerosis?
– Emboli may lodge in narrowed vessel
– Clots may form on roughened endothelium
– Long-standing belief that high lipid, high cholesterol
diets contribute are being called into question
Category
Systolic
Normal
< 120
and
< 80
Prehypertension
120-139
or
80-89
Diastolic
High Blood Pressure
Stage 1
Hypertension
140–159
or
90–99
Stage 2
Hypertension
160
or
100
Renal Hypertension
• Blood flow to kidneys is reduced
– Leads to thickening of arterioles
respond as
though BP were reduced
Angiotensin II produced
aldosterone released
• Increases blood volume and BP
– Worsens existing hypertension
result
kidney failure may
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Hypertension
• Primary hypertension
– 90% of hypertensive conditions
– Cause unknown
– Contributing factors include
• Genetics
• Obesity
» Adipose tissue extensively vascularized
» 10 miles per pound!!
» Means increased peripheral vascular resistance
• Smoking
» Nicotine = coronary vasoconstrictor
Hypertension
• Secondary hypertension
– 10% of cases
– Due to identifiable disorders
• Kidney disease
• Atherosclerosis
• Endocrine disorders
– Hyperthyroidism
– Cushing’s disease
– Polycythemia
• Diet
» Salt = water retention
higher blood volume
» Mineral deficiencies (Mg, K, Ca)
• Deep venous thrombosis (DVT)
• Affects mainly the veins in the lower leg and the thigh
• It involves the formation of a clot (thrombus) in the larger veins of the area
This picture shows a red and swollen thigh and leg caused by a
blood clot (thrombus) in the deep veins in the groin
which prevents normal return of blood from the leg to the heart.
• Can be caused by any condition that restricts venous return in the lower
extremities
• Cause in 1/3 of cases is unknown
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