Pages 719-747 C h a p t e r 21 Blood Vessels and Circulation Copyright © 2009 Pearson Education,...

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?


Vasoconstriction and Resistance Black arrows indicate vasoconstriction


Vascular ResistanceVessel Length and Resistance

Vascular resistance increasesDo you know why?


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?


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

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


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


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


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


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:


Myogenic ReflexSudden in blood pressure causes

vasoconstrictionExamples:


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?


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


= Sensory input = Motor output


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


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:


Figure 21–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses


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


Figure 21–15 The Chemoreceptor Reflexes


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


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 ____________________________


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 ____________________________

________________________________________


Longer Term Hormonal Regulation

Angiotensin II

Responds to fall in renal blood pressure

Stimulates

Aldosterone production

ADH production

Thirst

Cardiac output

Peripheral vasoconstriction


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


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 _________________________

_____________________________________


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


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:


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


Exercise, Cardiovascular Fitness, and Health

Regular moderate aerobic exercise

Lowers total blood cholesterol levels

Improves heart function

Some improvement in blood pressure


The Cardiovascular Response to Bleeding

(hemorrhaging)

Entire cardiovascular system adjusts to

Maintain blood pressure

Restore blood volume


Short-Term Maintenance of Blood Pressure Sympathetic Division of ANS stimulates

_________________________________________________

_________________________________________________

venoconstriction improves venous return

Hormones

Epinephrine, ADH and Angiotensin II

Cause ________________________________________________

______________________________________________________


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

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