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Pages 719-747
C h a p t e r
21
Blood Vessels and Circulation
Copyright © 2009 Pearson Education, Inc.,publishing as Pearson Benjamin Cummings
Basic circulatory route
Heart Arteries
ArteriolesCapillaries
Tissues
Venules
Veins
Vessel Structure
Brief Comparison of Arteries and Veins Blood flows away from heart in ___________________ Blood flows toward heart in ______________________
Arteries are thicker than veins:
Veins valves along their lengths Which vessels have the highest blood pressure?
Vessel Structure
Artery layers Tunica Externa
Connective tissue Anchors vessel
Tunica Media Smooth muscle External elastic membrane
Tunica Intima Simple squamous
endothelium Basement membrane Internal elastic membrane
Types of Arteries
Elastic Arteries (>1cm)Larger arteries such as aortaLess muscle and more elastic
tissueWhy do larger arteries have more elastic
tissue?
Muscular Arteries (0.1mm – 10mm)
Medium size to smaller arteries
More muscle, less elastic tissue
Vasoconstrict and vasodilate to
adjust blood flow
Types of Arteries
Smaller Vessels
ArteriolesSmallest arteries (10-100m)Deliver blood to capillariesLose tunica externaVasoconstrict and dilate to control blood
flow to capillaries
Types of Arteries
Smaller Vessels
Capillaries (4-10m) Tubes of endothelium
surrounded by basement membrane
Function in exchange of substances with tissues
Interconnect like a net to form capillary beds
Smaller Vessels
Venules (10–100m) Small veins Collect blood from
most capillaries Some smooth muscle Some exchange with
tissues
Capillaries and Associated Vessels
ArterioleCapillaries
Venule
Metarteriole Thoroughfare Channel
ArteriovenousAnastomosis
Anastomoses Union of two or more vessels Types
Arterial Venous Arteriovenous
Arterial anastomoses Ensures that arterial blockage does not totally interrupt
circulation Examples are arteries of heart, brain and extremities
Venous anastomoses increase collection of blood from a structure
Arteriovenous anastomoses act as capillary bypasses(as on previous slide)
Distribution of Blood
Venous circulation has more blood than arterial circulation Veins are thin and can expand to accept more blood If needed, veins can constrict and push more blood into
arteries. What might happen to require this? Pie chart shows how much blood is in different parts of
circulation.
Blood Pressure
Blood pressure (BP) is the force the blood
exerts against vessel walls
Difference in blood pressure (pressure gradient)
along vessels causes blood to flow
Blood flows from higher to lower pressure
Blood Pressure
Pressure is highest in the aorta and lowest in the vena cavae
Though blood pressure is in every blood vessel, most of our discussion will concern arterial blood pressure
The difference between pressure at the
heart and pressure at peripheral capillary
beds
Blood Pressure
Two factors affect blood pressureBlood flow
Amount of blood moving through vessels per unit of time What causes blood to flow? What can change blood flow
Resistance to blood flowBlood encounter friction and turbulence Resistance is a force that acts against blood flowFor blood to flow, blood pressure (BP) must
overcome this resistance
Blood Pressure
Blood Pressure FormulaBP Flow X Resistance
Flow causes BP, Flow causes BPR causes BP, R causes BP
Blood Pressure and Blood Flow
Factors in FlowCardiac Output (CO)
Amount of blood ejected by left ventricle in one minute
Recall that CO = Stroke Volume x Heart Rate
Blood volumeTotal amount of blood in bodyMore than 10% drop causes drop in BP
Flow and Blood PressureFlow indicated by redPressure indicated by blue
Blood Pressure and Blood Flow
Blood Pressure and Resistance
Factors That Affect ResistanceVascular Resistance
Vessel diameter and resistance Vasoconstriction increases resistance Vasodilation decreases resistance Which causes increased, and which causes
decreased arterial blood pressure? What word goes above each arrow below?
Blood Pressure and Resistance
Vasoconstriction and Resistance Black arrows indicate vasoconstriction
Blood Pressure and Resistance
Vascular ResistanceVessel Length and Resistance
Vascular resistance increasesDo you know why?
Blood Pressure and Resistance
Other Factors That Affect Resistance
Viscosity
Resistance caused by molecules and suspended
materials in a liquid
Whole blood viscosity is about five times that of
water
Does thicker blood increase or decrease
resistance?
Blood Pressure and Resistance
Turbulence Swirling action that disturbs smooth flow of liquid
Occurs in heart chambers and great vessels
Atherosclerotic plaques cause abnormal
turbulence
Blood Pressure Summary
Blood Pressure Summary
Blood Pressure
Types of Pressures
Blood pressure (BP or BHP )
Arterial pressure
Pressure in arterial system
Capillary hydrostatic pressure (CHP)
Pressure within the capillary beds
Venous pressure
Pressure in the venous system
Blood Pressure Measurements
BP measured in millimeters of mercuryWhat device is used?Where is it most often taken?Two pressure
Higher is _________________ pressureProduced by ___________________________
Lower is _________________ pressureProduced by ___________________________
Other Blood Pressures
Pulse pressure
Difference between systolic pressure and
diastolic pressure
Mean arterial pressure (MAP)MAP = diastolic pressure + 1/3 pulse pressure
Abnormal Blood Pressure
Normal = 120/80 Hypertension
Abnormally high blood pressure
Systolic140 or higher and diastolic 90 or higher
Prehypertension Systolic of 120-130 and diastolic of 80-89
Left untreated may become hypertension
Hypotension Abnormally low blood pressure
Systolic of 90 or less and diastolic of 60 or less
Pressure and Blood Flow
Elastic Rebound Arterial walls
Stretch during systole Rebound (recoil to original shape) during diastole Keep blood moving during diastole
Pressure and Blood Flow
Pressures in Small Arteries and Arterioles
Pressure and distance
MAP and pulse pressure decrease with distance
from heart
Blood pressure decreases with friction
Pulse pressure decreases due to elastic rebound
Pressure and Blood Flow
Figure 21–10 Pressures within the Systemic Circuit
Venous pressure and venous return
Venous pressure is lowCannot return blood to heart by itself Venous return aided by:
Venous valves Blood passes toward heart through successive one-way valves Compartmentalize blood to reduce pressure from gravity
Contraction of skeletal muscles Muscles squeeze blood past successive valves
Breathing Inhalation draws blood into the inferior vena cava Exhalation forces blood into right atrium
Blood Pressure and Veins
Venous Valve
•Calf muscle squeezes vein
•Venous valve open•Blood flows forward past valve
•Venous valve closed•Blood cannot flow back down leg
Which of the following is true?
(A) Blood flows from lower to higher pressure
(B) resistance causes blood pressure
(C) resistance causes blood pressure
(D) blood flow causes blood pressure
Question
The low number of a blood pressure reading occurs when the _______________.
(A) ventricle is pumping(B) ventricle is relaxing(C) AV valves are closed(D) SLvalves are open
Question
The mean arterial blood pressure for a BP of 120/75 is _____________.
(A) 80 mmHg(B) 90 mmHg(C) 95 mmHg(D) 100 mmHg
Question
Capillary Exchange
Vital to homeostasis
Moves materials between capillaries and
interstitial Fluid (IF) by:
Diffusion
Filtration
Reabsorption
Capillary Exchange
Diffusion
Movement of ions or molecules
From high concentration
To lower concentration
Along the concentration gradient
Capillary Exchange
Filtration
Driven by hydrostatic pressure
Water and small solutes forced through
capillary wall
Leaves larger solutes in bloodstream
Capillary Exchange
Reabsorption
Driven by osmosis
Blood colloid osmotic pressure (BCOP)
Equals pressure required to prevent osmosis
Caused by suspended blood proteins that are
too large to cross capillary walls
Capillary Exchange
Opposing pressures Capillary hydrostatic pressure (CHP) forces water
and solute out of capillaries Blood colloidal osmotic pressure (BCOP) draws
water and solute into capillaries Interstitial fluid hydrostatic pressure (IHP) opposes
CHP, but is negligible Interstitial fluid colloidal osmotic pressure (ICOP)
opposes BCOP, but is negligible
Capillary Exchange
CHP
BCOP
Blood in Capillary Interstitial Fluid (IF)
Opposing Pressures
IHP
ICOP
CHP pushes fluid out
BCOP pulls fluid in
Capillary Exchange
Mechanism of Filtration and Reabsorption On arteriole side of capillary, CHP BCOP – push pull
What happens? On venule side of capillary, BCOP CHP – pull push
What happens?
Higher CHP on arteriole side pushes water and solute from capillary into interstitial fluid = _______________
Higher BCOP on venule side pulls water and solute from interstitial fluid into capillary = _______________
Capillary Exchange Diagram
BCOP (pull)25 mmHg
CHP (push)(18 mmHg)
BCOP (pull)(25 mmHg)
Filtration
CHP (push)(35 mmHg)
Reabsorption
Blood Capillary
Lymph Capillary
Interstitial Fluid
Interstitial Fluid
Arterial End Venule End
Summary of Capillary Filtration and Reabsorption
At arterial end of capillaryFluid moves out of capillary Into interstitial fluid
At venous end of capillaryFluid moves into capillaryOut of interstitial fluid
Capillaries filter more than they reabsorbExcess fluid enters lymphatic vessels
Capillary Exchange
Capillary Dynamics Hemorrhaging
Reduces CHP and NFP
Increases reabsorption of interstitial fluid (recall of fluids)
Dehydration Increases BCOP
Accelerates reabsorption
Increase in CHP or decrease in BCOP Fluid moves out of blood
Builds up in peripheral tissues (edema)
Which of the following causes capillary filtration?
1 BCOP>CHP2 CHP>BCOP3 CHP=BCOP4 vasoconstriction
Question
Cardiovascular Regulation
Cardiovascular regulation changes blood
flow to a specific area
At an appropriate time
In the right area
Without changing blood pressure and blood
flow to vital organs
Cardiovascular Regulation
Controlling Cardiac Output and Blood Pressure
Autoregulation
Causes immediate, localized homeostatic adjustments
Neural mechanisms
Respond quickly to changes at specific sites
Endocrine mechanisms
Direct long-term changes
Cardiovascular Regulation
Autoregulation Local regulation within tissues
Assures proper blood flow into capillaries Tissues regulate blood flow to meet their needs Changes in blood pressure, blood chemistry, and blood temperature
cause An increase in capillary blood flow by
_________________________________________ A decrease in capillary blood flow by
_________________________________________ Myogenic Reflex Sudden in blood pressure causes arterial vasoconstriction Examples:
Cardiovascular Regulation
Myogenic ReflexSudden in blood pressure causes
vasoconstrictionExamples:
Cardiovascular Regulation
Neural Mechanism Motor (output) to heart and blood vessels
Cardiovascular Centers (CV) of the medulla oblongata Cardiac Centers
CAC increases HR and cardiac output CIC decreases HR and cardiac output
Vasomotor Centers Decrease blood flow to most organs by causing
widespread _________________________________ Increase blood flow to brain and skeletal muscles by
causing ____________________________________ What effect does widespread vasoconstriction have on
arterial blood pressure?
Cardiovascular Regulation
Sensory Adjustments in cardiac output and vasomotor regulationFor CV centers of medulla oblongata to
make proper adjustments, must be input from different sensory sensors
________________ sense changes in blood pressure
________________ sense changes in certain blood chemicals
Cardiovascular Regulation
= Sensory input = Motor output
Cardiovascular Regulation
Reflex Control of Cardiovascular Function
Cardiovascular centers monitor arterial blood
Baroreceptor reflexes:
respond to changes in blood pressure
Chemoreceptor reflexes:
respond to changes in chemical composition, particularly
pH and dissolved gases
Cardiovascular Regulation
Baroreceptor Reflexes Stretch receptors in walls of
Carotid sinuses: maintain blood flow to brain Aortic sinuses: monitor start of systemic circuit Right atrium: monitors end of systemic circuit
When blood pressure rises, CV centers Decrease cardiac output Cause peripheral vasodilation:
When blood pressure falls, CV centers Increase cardiac output Cause peripheral vasoconstriction:
Cardiovascular Regulation
Figure 21–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses
Cardiovascular Regulation
Chemoreceptor Reflexes
Respond to changes in CO2, O2 and pH
Peripheral chemoreceptors in carotid bodies and aortic
bodies monitor blood
Central chemoreceptors below medulla oblongata
Monitor cerebrospinal fluid
Control respiratory function
Control blood flow to brain
Cardiovascular Regulation
Figure 21–15 The Chemoreceptor Reflexes
Cardiovascular Regulation
Higher Brain Centers
Thought processes and emotional states
can elevate blood pressure by cardiac
stimulation and vasoconstriction
What occurs when blood pressure increases?
(A) baroreceptor stimulation heat rate, and vasoconstriction
(B) baroreceptor stimulation heat rate, and vasoconstriction
(C) baroreceptor stimulation heat rate, and vasodilation
(D) baroreceptor stimulation heat rate, and vasodilation
Question
Cardiovascular Regulation
Hormones and Cardiovascular Regulation
Hormones can have short-term and long-term effects
on cardiovascular regulation
For example, epinephrine (E) and norepinephrine
(NE) from adrenal gland can quickly stimulate cardiac
output and peripheral vasoconstriction
This results in ____________________________
Cardiovascular Regulation
Longer Term Hormonal Regulation Antidiuretic Hormone (ADH)
Released by pituitary gland Reduces water loss by kidneys ADH responds to
Low blood volume High plasma osmotic concentration Circulating angiotensin II
This results in ____________________________
________________________________________
Cardiovascular Regulation
Longer Term Hormonal Regulation
Angiotensin II
Responds to fall in renal blood pressure
Stimulates
Aldosterone production
ADH production
Thirst
Cardiac output
Peripheral vasoconstriction
Cardiovascular Regulation
Angiotensin formation:
Aldosterone secretion by adrenal glands salt retention ADH secretion water retention Thirst water intake Water and salt cardiac output (CO) peripheral vasoconstriction peripheral resistance CO and peripheral resistance blood pressure
Angiotensinogen Angiotensin I
Angiotensin II
ACE
Renin from Kidneys
Cardiovascular Regulation
Longer Term Hormonal Regulation Erythropoietin (EPO)
Released at kidneys
Responds to low blood pressure, low O2 content in blood
Stimulates red blood cell production
This results in _________________________
_____________________________________
Cardiovascular Regulation
Figure 21–16a The Hormonal Regulation of Blood Pressure and Blood Volume.
Which of the following maintains adequate blood pressure to the brain when a person stands up?
(A) stimulation of carotid baroreceptors with reflex slowing of the heart and vasodilation
(B) stimulation of carotid baroreceptors with reflex slowing of the heart and vasoconstriction
(C) stimulation of carotid baroreceptors with reflex speeding-up of the heart and vasoconstriction
(D) stimulation of carotid baroreceptors with reflex slowing of the heart and vasodilation
Question
Cardiovascular Adaptation
Blood, heart, and cardiovascular system
Work together as unit
Respond to physical and physiological
changes (for example, exercise, blood loss)
Maintains homeostasis
Cardiovascular Adaptation
The Cardiovascular Response to Exercise
Light exercise Extensive vasodilation occurs:
Increasing circulation
Venous return increases: With muscle contractions
Cardiac output rises: Due to rise in venous return (Frank–Starling principle)
and atrial stretching:
Cardiovascular Adaptation
The Cardiovascular Response to Exercise Heavy exercise
Activates sympathetic nervous system Cardiac output increases to maximum:
about four times resting level
Restricts blood flow to “nonessential” organs (e.g., digestive system)
Redirects blood flow to skeletal muscles, lungs, and heart
Cardiovascular Adaptation
Cardiovascular Adaptation
Exercise, Cardiovascular Fitness, and Health
Regular moderate aerobic exercise
Lowers total blood cholesterol levels
Improves heart function
Some improvement in blood pressure
Cardiovascular Adaptation
Cardiovascular Adaptation
The Cardiovascular Response to Bleeding
(hemorrhaging)
Entire cardiovascular system adjusts to
Maintain blood pressure
Restore blood volume
Cardiovascular Adaptation
Short-Term Maintenance of Blood Pressure Sympathetic Division of ANS stimulates
_________________________________________________
_________________________________________________
venoconstriction improves venous return
Hormones
Epinephrine, ADH and Angiotensin II
Cause ________________________________________________
______________________________________________________
Cardiovascular Adaptation
Long-Term Restoration of Blood Volume
Recall of fluids from interstitial spaces
Aldosterone and ADH promote fluid retention
and reabsorption
Thirst increases
Erythropoietin stimulates red blood cell
production
Clinical Terms
Hypertension
Aneurysm
Stroke (CVA or brain attack
Claudication
Deep Venous Thrombosis
Phlebitis
Phlebotomist
Venipuncture
Clinical Terms