Transcript Vessels and Circulation - SCF Faculty Site Homepage

Chapter
21
Blood Vessels
and Circulation
Pages 719-747
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Basic circulatory route
Veins
Venules
Heart
Capillaries
Tissues
Arteries
Arterioles
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



Tunica Media



Connective tissue
Anchors vessel
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 aorta
 Less muscle and more elastic

tissue
 Why do larger arteries have more elastic
tissue?
Types of Arteries

Muscular Arteries (0.1mm – 10mm)

Medium size to smaller arteries

More muscle, less elastic tissue

Vasoconstrict and vasodilate to
adjust blood flow
Smaller Vessels

Arterioles
Smallest arteries (10-100m)
 Deliver blood to capillaries
 Lose tunica externa
 Vasoconstrict and dilate to control blood
flow to capillaries

Types of Arteries
Smaller Vessels

Capillaries (4-10m)



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 (10–100m)




Small veins
Collect blood from
most capillaries
Some smooth muscle
Some exchange with
tissues
Capillaries and Associated Vessels
Arteriole
Capillaries
Metarteriole
Thoroughfare Channel
Venule
Arteriovenous
Anastomosis
Anastomoses

Union of two or more vessels

Types




Arterial anastomoses



Arterial
Venous
Arteriovenous
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 pressure

Blood flow




Amount of blood moving through vessels per unit of time
What causes blood to flow?
What can change blood flow
Resistance to blood flow
Blood encounter friction and turbulence
 Resistance is a force that acts against blood flow
 For blood to flow, blood pressure (BP) must
overcome this resistance

Blood Pressure

Blood Pressure Formula

BP  Flow X Resistance
 Flow causes BP, Flow causes BP
 R causes BP, R causes BP

Blood Pressure and Blood Flow

Factors in Flow

Cardiac Output (CO)

Amount of blood ejected by left ventricle in one
minute


Recall that CO = Stroke Volume x Heart Rate
Blood volume
Total amount of blood in body
 More than 10% drop causes drop in BP

Blood Pressure and Blood Flow

Flow and Blood Pressure
Flow indicated by red
 Pressure indicated by blue

Blood Pressure and Resistance

Factors That Affect Resistance

Vascular 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 Resistance

Vessel Length and Resistance

Vascular resistance increases

Do 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


Capillary hydrostatic pressure (CHP)


Pressure in arterial system
Pressure within the capillary beds
Venous pressure

Pressure in the venous system
Blood Pressure Measurements
BP measured in millimeters of mercury
 What device is used?
 Where is it most often taken?
 Two pressure


Higher is _________________ pressure


Produced by ___________________________
Lower is _________________ pressure

Produced 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 low
Cannot return blood to heart by itself
 Venous return aided by:


Venous valves



Contraction of skeletal muscles


Blood passes toward heart through successive one-way valves
Compartmentalize blood to reduce pressure from gravity
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 open
•Blood flows forward past valve
•Calf muscle squeezes vein
•Venous valve closed
•Blood cannot flow back down leg
Venous Valve
Question
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
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
Opposing Pressures
CHP
BCOP
Blood in Capillary
IHP
CHP pushes fluid out
ICOP
 BCOP pulls fluid in
Interstitial Fluid (IF)
Capillary Exchange

Mechanism of Filtration and Reabsorption

On arteriole side of capillary, CHP  BCOP – push  pull


On venule side of capillary, BCOP  CHP – pull  push



What happens?
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
Filtration
Lymph Capillary
Reabsorption
Interstitial Fluid
CHP (push)
(35 mmHg)
BCOP (pull)
(25 mmHg)
Arterial End
Blood Capillary
BCOP (pull)
25 mmHg
CHP (push)
(18 mmHg)
Interstitial Fluid
Venule End
Summary of Capillary Filtration and Reabsorption



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
Capillaries filter more than they reabsorb

Excess 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)
Question
Which of the following causes capillary
filtration?
1 BCOP>CHP
2 CHP>BCOP
3 CHP=BCOP
4 vasoconstriction
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


Neural mechanisms


Causes immediate, localized homeostatic adjustments
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 Reflex
Sudden  in blood pressure causes
 vasoconstriction
 Examples:

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 regulation

For 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
Question
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
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:
Angiotensinogen
Renin from Kidneys
Angiotensin I
ACE
Angiotensin II






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
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.
Question





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
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:


Venous return increases:


Increasing circulation
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
Clinical Terms

Deep Venous Thrombosis

Phlebitis

Phlebotomist

Venipuncture