This assignment is designed to expose learners to research of the cardiovascular system, its structure and function, and/or its relation to exercise performance.
Instructions:
No Chat GPT or any plagiarism 
Students will select a topic from Chapters 7 & 9 to investigate further.( Power Points are below)
Topic examples: heart rate variability, stroke volume, cardiac output, blood pressure, blood flow, cardiovascular drift, integrated cardiovascular response to exercise.
Refine your topic by considering what is of interest to you and how it can relate to exercise performance, cardiovascular function, or health in general.
For example, a topic of cardiac arrhythmia is quite broad and will pull up thousands or articles, so I will need to refine my search to a specific arrhythmia (atrial fibrillation). This is still broad, so I will refine my topic once more to create a research question/statement “atrial fibrillation effects on acute exercise performance”.

Find one peer-reviewed research article discussing your research statement/question. Utilize the CU library databases to facilitate your search. An original research article is best; this means the article includes an investigatory protocol in the Methods section. Meta-analyses are not ideal but will be acceptable for this assignment. Reviews and opinion articles should be avoided. If you need help of have questions do not hesitate to reach out. 

Once you find an article, ensure it is relatively recent (published after 2017) and you can obtain a PDF download of the article for free.

Read your article and be sure to take notes throughout your reading. You may need to read the article several times to fully understand what it is the researchers are investigating and discussing.
Write a one-page article summary of your selected peer-reviewed article. Be sure to include the important components of any peer-reviewed article (e.g. Purpose/purpose statement, methods & demographics, results/outcomes, discussion/conclusions).
Cardiorespiratory
Responses to
Acute Exercise
CHAPTER 9 Overview
• Cardiovascular responses to acute exercise
• Respiratory responses to acute exercise
• Recovery from acute exercise
Cardiovascular Responses
to Acute Exercise
• Increases blood flow to working muscle.
• Involves altered heart function, peripheral
circulatory adaptations:
– Heart rate
– Stroke volume
– Cardiac output
– Blood pressure
– Blood flow
– Blood
Cardiovascular Responses:
Resting Heart Rate (RHR)
• Normal ranges
– Untrained RHR: 60 to 80 beats/min
– Trained RHR: as low as 30 to 40 beats/min
– Affected by neural tone, temperature, altitude
• Anticipatory response: HR
just before start of exercise
– Vagal tone
– Norepinephrine, epinephrine
above RHR
Cardiovascular Responses:
Heart Rate During Exercise (1 of 2)
• Directly proportional to exercise intensity
• Maximal HR (HRmax): highest HR achieved in
all-out effort to volitional fatigue
– Highly reproducible
– Slight decline with age
– Estimated HRmax = 220 ? age in years
– For older adults:
• Better estimated HRmax = 208 ? (0.7 × age in years)
• Better estimated HRmax = 211 ? (0.64 × age in years)
(continued)
Cardiovascular Responses:
Heart Rate During Exercise (2 of 2)
• Steady-state HR: point of plateau, optimal
HR for meeting circulatory demands at a
given submaximal intensity
– If intensity increases, so does steady-state HR.
– Adjustment to new intensity takes 2 to 3 min.
• Steady-state HR basis for simple exercise
tests estimating aerobic fitness and HRmax
Figure 9.1
Figure 9.2
Cardiovascular Responses:
Heart Rate Variability
• Measure of HR rhythmic fluctuation
– Due to continuous changes in sympathetic and
parasympathetic balance
– At rest and during exercise
• Influenced by many factors
– Body core temperature, sympathetic nerve activity,
respiratory rate
– Analyzed with respect to frequency (spectral
analysis), not time
Cardiovascular Responses:
Stroke Volume (SV)
•
• Increases with intensity to 40%-60% VO2max
– Beyond this, plateau to exhaustion
– Possible exception: elite endurance athletes
• Maximal exercise SV ? double standing SV
• But maximal exercise SV only slightly
higher than supine SV
– Supine SV much higher than standing SV
– Supine end-diastolic volume (EDV) > standing EDV
Figure 9.3
Table 9.1 Importance of Stroke
? 2max
Volume in Determining ??O
Group
? 2max
??O
(ml/min)
HRmax
(beats/min)
SVmax
(ml/beat)
(a-v)O2max
(ml/100 ml)
Athletes
6,250
190
205
16
Normal subjects
3,500
195
112
16
Cardiac patients
1,400
190
43
17
Figure 9.5a
Figure 9.5b
Cardiovascular Responses:
Factors That Increase Stroke Volume
• ? preload: end-diastolic ventricular stretch
– ? stretch (i.e., ? EDV) ? ? contraction strength
– Frank-Starling mechanism
• ? contractility: inherent ventricle property
– ? norepinephrine or epinephrine ? ? contractility
– Independent of EDV (? ejection fraction instead)
• ? afterload: aortic resistance (R)
Cardiovascular Responses: Stroke
Volume Changes During Exercise
• ? preload at lower intensities ? ? SV
– ? venous return ? ? EDV ? ? preload
– Muscle and respiratory pumps, venous reserves
• Increase in HR ? ? filling time ? slight ?
in EDV ? ? SV
• ? contractility at higher intensities ? ? SV
• ? afterload via vasodilation ? ? SV
Cardiovascular Responses:
•
Cardiac Output (Q)
•
• Q = HR × SV
•
• ? with ? intensity (plateau near VO2max)
• Normal values
•
– Resting Q ~5 L/min
•
– Untrained Q max ~20 L/min
•
– Trained Q max 40 L/min
•
• Q max a function of body size, aerobic fitness
Figure 9.6
Video 9.1
Cardiovascular Responses:
Fick Principle
• Calculation of tissue O2 consumption
depending on blood flow, O2 extraction
•
•
–
• VO2 = Q × (a-v)O2 difference
•
–
• VO2 = HR × SV × (a-v)O2 difference
Figure 9.7a
Figure 9.7b
Figure 9.7c
Cardiovascular Responses:
Blood Pressure (1 of 2)
• During endurance exercise, increase in
mean arterial pressure (MAP)
– Systolic BP ? proportional to exercise intensity
– Diastolic BP slightly ? or slightly ? (at max
exercise)
•
• MAP = Q × total peripheral resistance (TPR)
•
– Q ?, TPR ? slightly
– Muscle vasodilation versus sympatholysis
(continued)
Cardiovascular Responses:
Blood Pressure (2 of 2)
• Rate-pressure product = HR × SBP
– Related to myocardial oxygen uptake and
myocardial blood flow
• Resistance exercise ? periodic large
increases in MAP
– Up to 480/350 mmHg
– More common when using Valsalva maneuver
Cardiovascular Responses:
Blood Flow Redistribution (1 of 2)
• ? cardiac output ? ? available blood flow
• ? blood flow redirected to areas with
greatest metabolic need (exercising muscle)
• Blood shunted away from less active
regions by sympathetic vasoconstriction
– Splanchnic circulation (liver, pancreas, GI)
– Kidneys
(continued)
Cardiovascular Responses:
Blood Flow Redistribution (2 of 2)
• Local vasodilation permits additional blood
flow in exercising muscle.
– Local VD triggered by metabolic, endothelial
products
– Sympathetic vasoconstriction in muscle offset by
sympatholysis
– Local VD > neural VC
• As temperature rises, skin VD also occurs.
– ? sympathetic VC, ? sympathetic VD
– Heat loss permitted through skin
Figure 9.8a
Figure 9.8b
Cardiovascular Responses:
Cardiovascular Drift
• Associated with ? core temperature and
dehydration
• SV drift ?
– Skin blood flow ?
– Plasma volume ? (sweating)
– Venous return/preload ?
•
• HR drift ? to compensate (Q maintained)
Cardiovascular Responses:
Competition for Blood Supply
• Exercise and other demands for blood flow
•
create competition for limited Q .
– Exercise (muscles) + eating (splanchnic blood flow)
– Exercise (muscles) + heat (skin)
• Multiple demands may decrease muscle
blood flow.
Cardiovascular Responses:
Blood Oxygen Content
–
• (a-v)O2 difference (mL O2/100 mL blood)
– Arterial O2 content ? mixed venous O2 content
– Resting: ~6 mL O2/100 mL blood
– Max exercise: ~16-17 mL O2/100 mL blood
• Mixed venous O2 ?4 mL O2/100 mL blood
– Venous O2 from active muscle ~0 mL
– Venous O2 from inactive tissue > from active muscle
– Increase in mixed venous O2 content
Figure 9.10
Cardiovascular Responses:
Plasma Volume
• Capillary fluid movement into and out of
tissue
– Hydrostatic pressure
– Oncotic, osmotic pressures
• Upright exercise ? ? plasma volume
– Compromise of exercise performance
– ? MAP ? ? capillary hydrostatic pressure
– Metabolite buildup ? ? tissue osmotic pressure
– Sweating further ? plasma volume
Figure 9.11
Cardiovascular Responses:
Hemoconcentration
• ? plasma volume ? hemoconcentration
– Fluid percentage of blood ?, cell percentage of
blood ?
– Hematocrit increase up to 50% (or even beyond)
• Net effects
– Red blood cell concentration ?
– Hemoglobin concentration ?
– O2-carrying capacity ?
Cardiovascular Responses:
Central Regulation
•
• What stimulates rapid changes in HR, Q ,
and blood pressure during exercise?
– Precede metabolite buildup in muscle.
– HR increases within 1 s of onset of exercise.
• Central command
– Higher brain centers
– Coactivation of motor and cardiovascular centers
Figure 9.12
Animation 9.12
For audio description use this link:
https://players.brightcove.net/901973548001/kplGlX8REA_default/index.html?videoId=6259868
186001
Cardiovascular Responses:
Integration of the Exercise Response
• Cardiovascular responses to exercise:
complex, fast, and finely tuned
• Priority: maintenance of blood pressure
– Blood flow can be maintained only if BP remains
stable.
– BP is prioritized before other needs (e.g., exercise,
thermoregulation).
Respiratory Responses:
Ventilation During Exercise (1 of 2)
• Immediate ? in ventilation
– Before muscle contractions
– Anticipatory response from central command
• Gradual second phase of ? in ventilation
– Driven by chemical changes in arterial blood
– ? CO2, H+ sensed by chemoreceptors
– Right atrial stretch receptors
(continued)
Respiratory Responses:
Ventilation During Exercise (2 of 2)
• Ventilation increase proportional to
metabolic needs of muscle
– At low exercise intensity, only tidal volume
– At high exercise intensity, rate also
• Ventilation recovery after exercise delayed
– Recovery takes several minutes.
– May be regulated by blood pH, PCO2, temperature.
Figure 9.14
Respiratory Responses:
Breathing Irregularities (1 of 3)
• Exercise-induced asthma
– Lower airway obstruction: coughing, wheezing, or
dyspnea
– More water evaporated from airway surface
– Disruption of airway epithelium and injury of
microvasculature
(continued)
Respiratory Responses:
Breathing Irregularities (2 of 3)
• Dyspnea (shortness of breath)
– Common with poor aerobic fitness
– Caused by inability to adjust to high blood PCO2, H+
– Fatigue in respiratory muscles despite drive to ?
ventilation
• Hyperventilation (excessive ventilation)
– Anticipation or anxiety about exercise
– ? PCO2 gradient between blood, alveoli
– ? blood PCO2 ? ? blood pH ? ? drive to breathe
(continued)
Respiratory Responses:
Breathing Irregularities (3 of 3)
• Valsalva maneuver: potentially dangerous
but accompanies certain types of exercise
– Close glottis
– ? intra-abdominal P (bearing down)
– ? intrathoracic P (contracting breathing muscles)
• Great veins collapsed by high pressures ?
•
? venous return ? ? Q ? ? arterial blood
pressure
Respiratory Responses:
Ventilation and Energy Metabolism
• Ventilation matching metabolic rate
• Ventilatory equivalent for O2
•
•
– VE/VO2 (L air breathed/L O2 consumed/min)
– Index of how well control of breathing is matched to
body’s demand for oxygen
• Ventilatory threshold
– Point where L air breathed > L O2 consumed
– Associated with lactate threshold and ? PCO2
Figure 9.15
Respiratory Responses:
Estimating Lactate Threshold
• Ventilatory threshold as surrogate
measure?
– Excess lactic acid + sodium bicarbonate
– Result: excess sodium lactate, H2O, CO2
– Lactic acid, CO2 accumulated simultaneously
• Refined to better estimate lactate threshold
– Anaerobic threshold
•
•
•
•
– Monitoring of both VE/VO2 and VE/VCO2
Figure 9.16
Respiratory Responses:
Limitations on Performance (1 of 2)
• Ventilation normally not limiting factor
•
– Respiratory muscles account for 10% of VO2, 15% of
•
Q during heavy exercise.
– Respiratory muscles are very fatigue resistant.
• Airway resistance and gas diffusion
normally not limiting factors at sea level
• Restrictive or obstructive respiratory
disorders possibly limiting
(continued)
Respiratory Responses:
Limitations on Performance (2 of 2)
• Exception: elite endurance-trained athletes
exercising at high intensities
– Ventilation possibly limiting
– Ventilation–perfusion mismatch
– Exercise-induced arterial hypoxemia (EIAH)
Respiratory Responses:
Acid–Base Balance (1 of 2)
• Metabolic processes produce H+ ?
pH.
• H+ + buffer ? H-buffer
• At rest, body is slightly alkaline.
– 7.1 to 7.4
– Higher pH = alkalosis
• During exercise, body is slightly acidic.
– 6.6 to 6.9
– Lower pH = acidosis
(continued)
Figure 9.17
Respiratory Responses:
Acid–Base Balance (2 of 2)
• Physiological mechanisms control pH.
– Chemical buffers include bicarbonate, phosphates,
proteins, hemoglobin.
– ? ventilation helps H+ bind to bicarbonate.
– Kidneys remove H+ from buffers, excrete H+.
• Active recovery facilitates pH recovery.
– Passive recovery: 60 to 120 min
– Active recovery: 30 to 60 min
Table 9.2 Buffering Capacity
of Blood Components
Buffer
Slykes*
%
Bicarbonate
18.0
64
Hemoglobin
8.0
29
Proteins
1.7
6
Phosphates
0.3
1
Total
28.0
100
*Milliequivalents of hydrogen ions taken up by each liter of blood from pH 7.4 to 7.0.
Table 9.3 Blood and Muscle pH and Lactate
Concentration 5 min After a 400 m Run
Muscle
Runner
Time (s)
pH
Lactate
Blood
pH
(mmol/kg)
Lactate
(mmol/L)
1
61.0
6.68
19.7
7.12
12.6
2
57.1
6.59
20.5
7.14
13.4
3
65.0
6.59
20.2
7.02
13.1
4
58.5
6.68
18.2
7.10
10.1
Average
60.4
6.64
19.7
7.10
12.3
Figure 9.18
Recovery From Acute Exercise:
Cardiovascular Variables
• Postexercise hypotension (aerobic)
– Driven by peripheral vasodilation.
– Can last for several hours.
– Histamine is an important mediator of this response.
• Postexercise hypotension (resistance)
– Driven by decreased cardiac output.
The Cardiovascular
System and Its Control
CHAPTER 7 Overview
• The heart
• Vascular system
• Blood
Cardiovascular System:
Major Functions
• Delivers O2 and nutrients
• Removes CO2 and other waste
• Transports hormones and other molecules
• Supports temperature balance and controls
fluid regulation
• Maintains acid–base balance
• Regulates immune function
Cardiovascular System
• Includes three major circulatory elements:
1. Pump (heart)
2. Channels or tubes (blood vessels)
3. Fluid medium (blood)
• Heart generates pressure to drive blood
through vessels.
• Blood flow must meet metabolic demands.
Heart
• Four chambers
– Right and left atria (RA, LA): top, receiving
chambers
– Right and left ventricles (RV, LV): bottom, pumping
chambers
• Pericardium
• Pericardial cavity
• Pericardial fluid
Figure 7.1
Animation 7.1
For audio description use this link:
https://players.brightcove.net/901973548001/kplGlX8REA_default/index.html?videoId=6259866
649001
Blood Flow Through the Heart
• Right heart: pulmonary circulation
– Pumps deoxygenated blood from body to lungs
– Superior, inferior vena cavae ? RA ? tricuspid
valve ? RV ? pulmonary valve ? pulmonary
arteries ? lungs
• Left heart: systemic circulation
– Pumps oxygenated blood from lungs to body
– Lungs ? pulmonary veins ? LA ? mitral valve ?
LV ? aortic valve ? aorta
Myocardium (1 of 2)
• Myocardium is cardiac muscle.
• LV has the most myocardium.
– Must pump blood to entire body.
– Has the thickest walls (hypertrophy).
– LV hypertrophies with both exercise and disease.
– But exercise adaptations and disease adaptations
differ greatly.
(continued)
Myocardium (2 of 2)
• Has only one fiber type (like type I).
– High capillary density
– High number of mitochondria
– Striations
• Cardiac muscle fibers are connected by
intercalated disks.
– Desmosomes hold cells together.
– Gap junctions rapidly conduct action potentials.
Myocardium Versus Skeletal Muscle
• Skeletal muscle cells
– Large, long, unbranched, multinucleated
– Intermittent, voluntary contractions
– Ca2+ released from SR
• Myocardial cells
– Small, short, branched, one nucleus
– Continuous, involuntary rhythmic contractions
– Calcium-induced calcium release
Figure 7.2
Figure 7.3
Myocardial Blood Supply
• Right coronary artery
– Supplies right side of heart
– Divides into marginal and posterior interventricular
• Left (main) coronary artery
– Supplies left side of heart
– Divides into circumflex and anterior descending
• Atherosclerosis ? coronary artery disease
Figure 7.4
Intrinsic Control of Heart Activity:
Cardiac Conduction System (1 of 3)
• Spontaneous rhythmicity: Special heart
cells generate and spread electrical signal.
– Sinoatrial (SA) node
– Atrioventricular (AV) node
– AV bundle (bundle of His)
– Purkinje fibers
• Electrical signal spreads via gap junctions.
– Intrinsic heart rate (HR) would be 100 beats/min.
– Observed in heart transplant patients (no neural
innervation).
(continued)
Intrinsic Control of Heart Activity:
Cardiac Conduction System (2 of 3)
• SA node initiates contraction signal.
– Made of pacemaker cells in upper posterior RA wall.
– Signal spreads from SA node via RA/LA to AV node.
– Stimulates RA, LA contraction.
• AV node delays, relays signal to ventricles.
– Located in RA wall near center of heart.
– Delay allows RA, LA to contract before RV, LV.
– Relays signal to AV bundle after delay.
(continued)
Intrinsic Control of Heart Activity:
Cardiac Conduction System (3 of 3)
• AV bundle relays signal to RV, LV.
– Travels along interventricular septum.
– Divides into right and left bundle branches.
– Sends signal toward apex of heart.
• Purkinje fibers send signal into RV, LV.
– Form terminal branches of right and left bundle
branches.
– Spread throughout entire ventricle wall.
– Stimulate RV, LV contraction.
Figure 7.5
Extrinsic Control of Heart Activity:
Parasympathetic Nervous System
• Reaches heart via vagus nerve (cranial
nerve X).
• Carries impulses to SA, AV nodes.
– Releases acetylcholine, hyperpolarizes cells.
– Decreases HR, force of contraction.
• Decreases HR below intrinsic HR.
– Intrinsic HR is 100 beats/min.
– Normal resting HR (RHR) is 60 to 100 beats/min.
– Elite endurance athlete have 35 beats/min.
Extrinsic Control of Heart Activity:
Sympathetic Nervous System
• Opposite effects of parasympathetic.
• Carries impulses to SA, AV nodes.
– Releases norepinephrine, facilitates depolarization.
– Increases HR, force of contraction.
– Endocrine system can exert similar effect
(epinephrine, norepinephrine).
• Increases HR above intrinsic HR.
– Determines HR during physical, emotional stress.
– Maximal possible HR is 250 beats/min.
Figure 7.6
Extrinsic Control of Heart Activity:
Effects of Endurance Training
• Endurance training reduces resting HR.
– Autonomic neural hypothesis:
• Shift in autonomic neural balance
– Intrinsic rate hypothesis:
• Change in inherent cardiac pacemaker rate
Electrocardiogram (ECG)
• ECG: recording of heart’s electrical activity
– 10 electrodes, 12 leads
– Different electrical views
– Diagnostic tool for coronary artery disease
• Three basic phases
– P wave: atrial depolarization
– QRS complex: ventricular depolarization
– T wave: ventricular repolarization
Figure 7.7
Cardiac Arrhythmias
• Bradycardia (pathological vs. exercise
induced)
• Tachycardia (pathological vs. exercise
induced)
• Premature ventricular contraction
• Atrial flutter, fibrillation
• Ventricular tachycardia
• Ventricular fibrillation
Terminology of Cardiac Function
• Cardiac cycle
• Stroke volume
• Ejection fraction
•
• Cardiac output (Q )
Cardiac Cycle
• All mechanical and electrical events
occurring during one heartbeat
• Diastole: relaxation phase
– Chambers fill with blood.
– Lasts twice as long as systole.
• Systole: contraction phase
Cardiac Cycle: Ventricular Systole
• QRS complex to T wave.
• 1/3 of cardiac cycle.
• Contraction begins.
– Ventricular pressure rises.
– Atrioventricular valves close (heart sound 1, “lub”).
– Semilunar valves open.
– Blood is ejected.
– At end, blood in ventricle = end-systolic volume
(ESV).
Cardiac Cycle: Ventricular Diastole
• T wave to next QRS complex.
• 2/3 of cardiac cycle.
• Relaxation begins.
– Ventricular pressure drops.
– Semilunar valves close (heart sound 2, “dub”).
– Atrioventricular valves open.
– Fill 70% passively, 30% by atrial contraction.
– At end, blood in ventricle = end-diastolic volume
(EDV).
Figure 7.8
Stroke Volume, Ejection Fraction
• Stroke volume (SV): volume of blood
pumped in one heartbeat
– During systole, most (not all) blood ejected
– EDV ? ESV = SV
– 100 mL ? 40 mL = 60 mL
• Ejection fraction (EF): % of EDV pumped
– SV/EDV = EF
– 60 mL/100 mL = 0.6 = 60%
– Clinical index of heart contractile function
•
Cardiac Output (Q)
• Total volume of blood pumped per minute
•
• Q = HR × SV
– RHR ~70 beats/min, standing SV ~70 mL/beat
– 70 beats/min × 70 mL/beat = 4,900 mL/min
– Use L/min (4.9 L/min).
• Resting cardiac output ~4.2 to 5.6 L/min
– Average total blood volume is ~5 L.
– Total blood volume circulates once every minute.
Figure 7.9a
Figure 7.9b
Figure 7.9c
Pumping Action of Heart
During Exercise
• Functional syncytium: pumping of the heart
as one unit
• Torsional contraction: increased
contractility during intense exercise to
enhance left ventricle filling
– Systole: Heart twists gradually, storing energy like a
spring.
– Diastole: Abrupt untwisting allows atrial filling
(dynamic relation).
Video 7.1
Vascular System
• Arteries: Carry blood away from heart.
• Arterioles: Control blood flow, feed
capillaries.
• Capillaries: Provide site for nutrient and
waste exchange.
• Venules: Collect blood from capillaries.
• Veins: Carry blood from venules back to
heart.
Blood Pressure
• Systolic pressure (SBP)
– Highest pressure in artery (during systole)
– Top number, ~110 to 120 mmHg
• Diastolic pressure (DBP)
– Lowest pressure in artery (during diastole)
– Bottom number, ~70 to 80 mmHg
• Mean arterial pressure (MAP)
– Average pressure over entire cardiac cycle
– MAP ? 2/3 DPB + 1/3 SBP
General Hemodynamics
• Blood flow: required by all tissues
• Pressure: force that drives flow
– Provided by heart contraction
– Blood flow from region of high pressure (LV,
arteries) to region of low pressure (veins, RA)
– Pressure gradient = 100 mmHg ? 0 mmHg
= 100 mmHg
• Resistance: force that opposes flow
– Provided by physical properties of vessels
– R = [hL/r4] ? radius most important factor
General Hemodynamics:
Blood Flow = DP/R (1 of 2)
• Easiest way to change flow ? change R
– Vasoconstriction (VC)
– Vasodilation (VD)
– Diversion of blood to regions most in need
• Arterioles: resistance vessels
– Control of systemic R
– Site of most potent VC and VD
– Responsible for 70%-80% of P drop from LV to RA
(continued)
General Hemodynamics:
Blood Flow = DP/R (2 of 2)
•
• Blood flow: Q
• DP
– Pressure gradient that drives flow
– Change in P between LV/aorta and vena cava/RA
• R
– Affected by small changes in arteriole radius
– VC, VD
Figure 7.10
Distribution of Blood
• Blood flow to sites where most needed
– Often, regions of ? metabolism ? ? blood flow
– Other examples: after eating, in the heat
•
• At rest (Q = 5 L/min)
•
– Liver, kidneys receive 50% of Q .
•
– Skeletal muscle receives ~20% of Q .
•
• Heavy exercise (Q = 25 L/min)
•
– Exercising muscles receive 80% of Q via VD.
– Flow to liver, kidneys decreases via VC.
Figure 7.11
Intrinsic Control
of Blood Flow (1 of 2)
• Ability of local tissues to constrict or dilate
arterioles that serve them
• Alteration of regional flow based on need
• Three types of intrinsic control
– Metabolic
– Endothelial
– Myogenic
(continued)
Intrinsic Control
of Blood Flow (2 of 2)
• Metabolic mechanisms (VD)
– Buildup of local metabolic by-products
– ? O2
– ? CO2, K+, H+, lactic acid
• Endothelial mechanisms (mostly VD)
– Substances secreted by vascular endothelium
– Nitric oxide (NO), prostaglandins, EDHF
• Myogenic mechanisms (VC, VD)
– Local pressure changes causing VC, VD
– ? P ? ? VC, whereas ? P ? ? VD
Figure 7.12
Extrinsic Neural Control of Blood Flow
• Upstream of local, intrinsic control
• Redistribution of flow at organ, system level
• Sympathetic nervous system innervating
smooth muscle in arteries and arterioles
– Baseline sympathetic activity ? vasomotor tone
– ? Sympathetic activity ? ? VC
– ? Sympathetic activity ? ? VC (passive VD)
Local Control of Muscle Blood Flow
• Increase of blood flow to exercising muscle
to match its metabolic demand
– Local alteration of blood flow
– Improved extraction at the tissue level
• Functional sympatholysis
– Inhibition of sympathetic vasoconstriction by
reducing vascular responsiveness to ?-adrenergic
receptor activation
Distribution of Venous Blood
• At rest, veins contain 2/3 of blood volume.
– High capacity to hold blood volume
– Elastic, balloonlike vessel walls
– Blood reservoir
• Venous reservoir can be liberated, sent
back to heart and into arteries.
– Sympathetic stimulation
– Venoconstriction
Figure 7.14
Integrative Control of Blood Pressure
• Blood pressure maintained by autonomic
reflexes
• Baroreceptors
– Sensitive to changes in arterial pressure
– Afferent signals from baroreceptor to brain
– Efferent signals from brain to heart, vessels
– Adjustment of arterial pressure back to normal
• Also, chemoreceptors, mechanoreceptors
in muscle
Return of Blood to the Heart
• Upright posture makes venous return to
heart more difficult.
• Venous return is assisted by three
mechanisms.
– One-way venous valves
– Muscle pump
– Respiratory pump
Figure 7.15
Animation 7.15
For audio description use this link:
https://players.brightcove.net/901973548001/kplGlX8REA_default/index.html?videoId=6259866
147001
Blood (1 of 2)
• Three major functions
– Transportation (O2, nutrients, waste)
– Temperature regulation
– Acid–base (pH) balance
• Blood volume: 5 to 6 L in men, 4 to 5 L in
women
• Whole blood = plasma + formed elements
(continued)
Blood (2 of 2)
• Plasma (55%-60% of blood volume)
– Can decrease by 10% with dehydration in the heat.
– Can increase by 10% with training, heat acclimation.
– 90% water, 7% protein, 3% nutrients, ions, etc.
• Formed elements (40%-45% of blood volume)
– Red blood cells (erythrocytes: 99%)
– White blood cells (leukocytes: