Chapter 6 Review Questions ESS 435 Spring 2021 (1)
Folke
Chapter6PowerPointwithaudio.pptxThe Cardiovascular System and Its Control
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The Cardiovascular System: Major Functions
Delivers O2, nutrients
Removes CO2, other waste
Transports hormones, other molecules
Temperature balance and fluid regulation
Acid–base balance
Immune function
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The Cardiovascular System
Three major circulatory elements
1. A pump (heart)
2. Channels or tubes (blood vessels)
3. A fluid medium (blood)
Heart generates pressure to drive blood through vessels
Blood flow must meet metabolic demands
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The 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
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Figure 6.1
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Animation 6.1
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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
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Intrinsic Control of Heart Activity: Cardiac Conduction System
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): 100 beats/min
Observed in heart transplant patients (no neural innervation)
(continued)
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Intrinsic Control of Heart Activity: Cardiac Conduction System (continued)
SA node: initiates contraction signal
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
In RA wall near center of heart
Delay allows RA, LA to contract before RV, LV
Relays signal to AV bundle after delay
(continued)
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Intrinsic Control of Heart Activity: Cardiac Conduction System (continued)
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
Terminal branches of right and left bundle branches
Spread throughout entire ventricle wall
Stimulate RV, LV contraction
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Figure 6.5
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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: 100 beats/min
Normal resting HR (RHR): 60 to 100 beats/min
Elite endurance athlete: 35 beats/min
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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 have similar effect (epinephrine, norepinephrine)
Increases HR above intrinsic HR
Determines HR during physical, emotional stress
Maximum possible HR: 250 beats/min
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Terminology of Cardiac Function
Cardiac cycle
Stroke volume
Ejection fraction
Cardiac output (Q•)
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Cardiac Cycle
All mechanical and electrical events that occur during one heartbeat
Diastole: relaxation phase
Chambers fill with blood
Twice as long as systole
Systole: contraction phase
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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 ejected
At end, blood in ventricle = end-systolic volume (ESV)
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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)
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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): percent of EDV pumped
SV / EDV = EF
60 mL/100 mL = 0.6 = 60%
Clinical index of heart contractile function
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Cardiac Output (Q•)
Total volume of blood pumped per minute
Q• = HR x SV
RHR ~70 beats/min, standing SV ~70 mL/beat
70 beats/min x 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 ~5 L
Total blood volume circulates once every minute
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The Vascular System
Arteries: carry blood away from heart
Arterioles: control blood flow, feed capillaries
Capillaries: site of nutrient and waste exchange
Venules: collect blood from capillaries
Veins: carry blood from venules back to heart
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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
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General Hemodynamics
Blood flow: required by all tissues
Pressure: force that drives flow
Provided by heart contraction
Blood flows 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
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General Hemodynamics: Blood flow = DP/R
Easiest way to change flow change R
Vasoconstriction (VC)
Vasodilation (VD)
Diverts blood to regions most in need
Arterioles: resistance vessels
Control systemic R
Site of most potent VC and VD
Responsible for 70 to 80% of P drop from LV to RA
(continued)
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Distribution of Blood
Blood flows to where needed most
Often, regions of metabolism blood flow
Other examples: blood flow changes after eating, in the heat
At rest (Q• = 5 L/min)
Liver, kidneys receive 50% of Q•
Skeletal muscle receives ~20% of Q•
During heavy exercise (Q• = 25 L/min)
Exercising muscles receive 80% of Q• via VD
Flow to liver, kidneys decreases via VC
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Figure 6.11
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Return of Blood to the Heart
Upright posture makes venous return to heart more difficult
Three mechanisms assist venous return
One-way venous valves
Muscle pump
Respiratory pump
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Figure 6.14
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Animation 6.14
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Blood
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)
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Blood (continued)
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: <1%)
Platelets (<1%)
Hematocrit = total percent of volume composed of formed elements
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Red Blood Cells
No nucleus, cannot reproduce
Replaced regularly via hematopoiesis
Life span ~4 months
Produced and destroyed at equal rates
Hemoglobin
Oxygen-transporting protein in red blood cells (4 O2 / hemoglobin)
Heme (pigment, iron, O2) + globin (protein)
250 million hemoglobin/red blood cells
Oxygen-carrying capacity: 20 mL O2 / 100 mL blood
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Blood Viscosity
Thickness of blood (due to red blood cells)
Twice as viscous as water
Viscosity as hematocrit
Plasma volume must as red blood cells
Occurs in athletes after training, acclimation
Hematocrit and viscosity remain stable
Otherwise, blood flow or O2 transport may suffer
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