© 2012 Pearson Education, Inc. Figure 21-8 An Overview of Cardiovascular Physiology Cardiac Output Venous Return Regulation (Neural and Hormonal) Venous

© 2012 Pearson Education, Inc.

Figure 21-8 An Overview of Cardiovascular Physiology

Cardiac Output

Venous Return

Regulation(Neural and Hormonal)

VenousPressure

Arterial BloodPressure

PeripheralResistance

Capillary Pressure

Capillary exchange

Interstitial fluid


Pressure and Resistance

• Total capillary blood flow

• Equals cardiac output

• Is determined by

• pressure and resistance in the cardiovascular

system



• An Overview of Cardiovascular Pressures

• Systolic pressure

• Peak arterial pressure during ventricular systole

• Diastolic pressure

• Minimum arterial pressure during diastole

• Pulse pressure

• Difference between systolic pressure and diastolic pressure

• Mean arterial pressure (MAP)

• MAP = diastolic pressure + 1/3 pulse pressure


Figure 21-10a Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit

Vesseldiameter

(cm)

Vessel diameter


Figure 21-10b Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit

Total cross-sectional area of vessels

Cross-sectional

area(cm2)


Figure 21-10c Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit

Average blood pressure

Averageblood

pressure(mm Hg)


Figure 21-10d Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit

Velocity of blood flow

Velocityof blood

flow(cm/sec)


Figure 21-11 Pressures within the Systemic Circuit

Systolic

Pulsepressure

Diastolic

mm Hg

Mean arterialpressure



• Capillary Pressures and Capillary Exchange

• Vital to homeostasis

• Moves materials across capillary walls by

• Diffusion

• Filtration

• Reabsorption



• Diffusion

• Movement of ions or molecules

• From high concentration

• To lower concentration

• Along the concentration gradient



• Diffusion Routes

• Water, ions, and small molecules such as glucose

• Diffuse between adjacent endothelial cells

• Or through fenestrated capillaries

• Some ions (Na+, K+, Ca2+, Cl-)

• Diffuse through channels in plasma membranes



• Diffusion Routes

• Large, water-soluble compounds

• Pass through fenestrated capillaries

• Lipids and lipid-soluble materials such as O2 and

CO2

• Diffuse through endothelial plasma membranes

• Plasma proteins

• Cross endothelial lining in sinusoids



• Filtration

• Driven by hydrostatic pressure

• Water and small solutes forced through capillary wall

• Leaves larger solutes in bloodstream



• Reabsorption

• The result of osmosis

• Blood colloid osmotic pressure

• Equals pressure required to prevent osmosis

• Caused by suspended blood proteins that are too large to

cross capillary walls


Figure 21-12 Capillary Filtration

Capillaryhydrostatic

pressure(CHP) Amino acid

Blood protein

Glucose

Ions

Interstitialfluid

Hydrogenbond

Watermolecule

Small solutes

Endothelialcell 2

Endothelialcell 1



• Capillary Exchange

• 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

• Transition point between filtration and reabsorption

• Is closer to venous end than arterial end

• Capillaries filter more than they reabsorb

• Excess fluid enters lymphatic vessels



• Interplay between Filtration and Reabsorption

• Hydrostatic pressure

• Forces water out of solution

• Osmotic pressure

• Forces water into solution

• Both control filtration and reabsorption through

capillaries



• Net Hydrostatic Pressure

• Is the difference between

• Capillary hydrostatic pressure (CHP)

• And interstitial fluid hydrostatic pressure (IHP)

• Pushes water and solutes

• Out of capillaries

• Into interstitial fluid



• Net Colloid Osmotic Pressure

• Is the difference between

• Blood colloid osmotic pressure (BCOP)

• And interstitial fluid colloid osmotic pressure (ICOP)

• Pulls water and solutes

• Into a capillary

• From interstitial fluid



• Net Filtration Pressure (NFP)

• The difference between

• Net hydrostatic pressure

• And net osmotic pressure

NFP = (CHP – IHP) – (BCOP – ICOP)


Figure 21-13 Forces Acting across Capillary Walls

KEY

Arteriole

Filtration

CHP (Capillaryhydrostatic pressure)

Venule

BCOP (Blood colloidosmotic pressure)

NFP (Net filtrationpressure)

24 L/day 20.4 L/dayNo net fluidmovement

Reabsorption

35mmHg

25mmHg

25mmHg

25mmHg

25mmHg

18mmHg

NFP 10 mm Hg NFP 0 NFP 7 mm Hg

CHP BCOPFluid forced

out of capillary

CHP BCOPNo net

movementof fluid

BCOP CHPFluid movesinto capillary


Figure 21-14 Short-Term and Long-Term Cardiovascular Responses

Autoregulation

Local vasodilatorsreleased

HOMEOSTASISRESTORED

HOMEOSTASIS DISTURBED

HOMEOSTASIS

Local decreasein resistanceand increase inblood flow

Inadequatelocal bloodpressure andblood flow

Normalblood pressure

and volume

• Physical stress (trauma, high temperature)• Chemical changes (decreased O2 or pH, increased CO2 or prostaglandins)• Increased tissue activity

Autoregulation is dueto opening and closing precapillary sphinctersdue to local release ofvasodilator or vasoconstrictorchemicals from the tissue.

Start


Figure 21-14 Short-Term and Long-Term Cardiovascular Responses

Central Regulation

Stimulation ofreceptors sensitiveto changes insystemic bloodpressure orchemistry

Endocrine mechanisms

HOMEOSTASISRESTORED

Neuralmechanisms

Activation ofcardiovascularcenters

Stimulationof endocrineresponse

Long-term increasein blood volumeand blood pressure

Short-term elevation of blood pressure bysympatheticstimulation of theheart and peripheralvasoconstriction

Central regulation involves neuroendocrine mechanisms that control the total systemic circulation. This regulation involves both the cardiovascular centers and the vasomotor centers.

If autoregulation is ineffective


Figure 21-15 Baroreceptor Reflexes of the Carotid and Aortic Sinuses

Responses to IncreasedBaroreceptor Stimulation

Baroreceptorsstimulated

HOMEOSTASISDISTURBED

Rising bloodpressure

Cardioinhibitorycenters stimulated

Cardioacceleratorycenters inhibited

Vasomotor centersinhibited

Decreasedcardiacoutput

Vasodilationoccurs

HOMEOSTASISRESTORED

Blood pressuredeclines

HOMEOSTASIS

Normal rangeof bloodpressure

Start


Figure 21-15 Baroreceptor Reflexes of the Carotid and Aortic Sinuses

HOMEOSTASIS

Normal rangeof bloodpressure


HOMEOSTASISRESTORED

Falling bloodpressure

Blood pressurerises

Baroreceptorsinhibited

Vasoconstrictionoccurs

Increasedcardiacoutput

Vasomotor centersstimulated

Cardioacceleratorycenters stimulated

Cardioinhibitorycenters inhibited

Responses to DecreasedBaroreceptor Stimulation

Start


Figure 21-16 The Chemoreceptor Reflexes

Increasing CO2 levels,

decreasing pHand O2 levels

Respiratory centers inthe medulla oblongatastimulated

Respiratory rateincreases

Increased cardiacoutput and bloodpressure

Cardioacceleratorycenters stimulated

Cardioinhibitorycenters inhibited

Respiratory Response

CardiovascularResponses

Effects onCardiovascular Centers

Vasomotor centersstimulated

Vasoconstrictionoccurs

Normal pH, O2,

and CO2 levels in

blood and CSF

HOMEOSTASIS

Elevated CO2 levels,

decreased pH and O2

levels in blood and CSF


Start

Decreased CO2 levels,

increased pH and O2

levels in blood and CSF

HOMEOSTASISRESTORED

Reflex Response

Chemoreceptorsstimulated


Figure 21-17a The Hormonal Regulation of Blood Pressure and Blood Volume

HOMEOSTASIS

Factors that compensate fordecreased blood pressure andvolume

Increased red bloodcell formation

Thirst stimulated

Antidiuretic hormonereleased

Angiotensin II Effects

Combined Short-Termand Long-Term Effects

Endocrine Responseof Kidneys

Renin release leadsto angiotensin IIactivation

Erythropoietin (EPO)is released

Increased cardiacoutput andperipheralvasoconstriction

Sympathetic activationand release of adrenalhormones E and NE

Long-term

Short-term

Increasedbloodpressure

Increasedbloodvolume

Decreasing bloodpressure and

volume

StartBlood pressureand volume fall

HOMEOSTASISDISTURBED HOMEOSTASIS

RESTORED

Normal bloodpressure and

volume

Blood pressureand volume rise

Aldosterone secreted

Angiotensin II


Figure 21-17b The Hormonal Regulation of Blood Pressure and Blood Volume

HOMEOSTASIS

Factors that compensate forincreased blood pressure andvolume

Increasing bloodpressure and

volume

HOMEOSTASISRESTORED

Declining bloodpressure and

volume

Normalblood pressure

and volume


Rising bloodpressure and

volume

Natriureticpeptides releasedby the heart

Increased water loss inurine

Reduced thirst

Inhibition of ADH,aldosterone, epinephrine,and norepinephrinerelease

Peripheral vasodilation

Reduced bloodvolume

CombinedEffects

Increased Na loss inurine

Responses to ANPand BNP


Table 21-2 Changes in Blood Distribution during Exercise


21-4 Cardiovascular Adaptation

Table 21-3 Effects of Training on Cardiovascular Performance

Subject Heart Weight (g)

Stroke Volume (mL)

Heart Rate (BPM)

Cardiac Output (L/min)

Blood Pressure (systolic/ diastolic)

Nonathlete (rest) 300 60 83 5.0 120/80

Nonathlete (maximum)

104 192 19.9 187/75

Trained athlete (rest)

500 100 53 5.3 120/80

Trained athlete (maximum)

167 182 30.4 200/90*

*Diastolic pressures of athletes during maximum activity have not been accurately measured.


Figure 21-18 Cardiovascular Responses to Hemorrhaging and Blood Loss

Normal bloodpressure and

volume

Extensive bleedingreduces bloodpressure andvolume


Responsescoordinated by theendocrine system

Responsesdirected by thenervous system

Falling bloodpressure and

volume

Long-Term Hormonal Response

ADH, angiotensin II, aldosterone,and EPO released

Blood pressureand volume rise

HOMEOSTASISRESTORED

Cardiovascular Responses

Peripheralvasoconstriction;mobilization ofvenous reserve

Increasedcardiacoutput

Elevationof bloodvolume

Stimulation ofbaroreceptors andchemoreceptorsPain, stress,

anxiety, fear

Higher Centers

Stimulation ofcardiovascularcenters

Generalsympatheticactivation

HOMEOSTASIS

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© 2012 Pearson Education, Inc. Figure 21-8 An Overview of Cardiovascular Physiology Cardiac Output Venous Return Regulation (Neural and Hormonal) Venous