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Chapter 6

Chapter 6. The Cardiovascular System and Its Control. The Cardiovascular System: Major Functions. Delivers O 2 , nutrients Removes CO 2 , other waste Transports hormones, other molecules Temperature balance and fluid regulation Acid-base balance Immune function. The Cardiovascular System.

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Chapter 6

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  1. Chapter 6 • The Cardiovascular System and Its Control

  2. 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

  3. 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

  4. 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

  5. Figure 6.1

  6. Figure 6.4

  7. 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)

  8. Intrinsic Control of Heart Activity: Cardiac Conduction System • 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

  9. Intrinsic Control of Heart Activity: Cardiac Conduction System • 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

  10. Figure 6.5

  11. Figure 3.1

  12. Figure 6.8

  13. Cardiac Terminology • Cardiac cycle • Stroke volume • Ejection fraction • Cardiac output (Q)

  14. 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

  15. Figure 6.9

  16. 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

  17. 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

  18. 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

  19. 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

  20. Figure 7.4

  21. 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

  22. Figure 6.11

  23. Figure 6.12

  24. Distribution of Venous Blood • At rest, veins contain 2/3 blood volume • High capacity to hold blood volume • Elastic, balloonlike vessel walls • Serve as blood reservoir • Venous reservoir can be liberated, sent back to heart and into arteries • Sympathetic stimulation • Venoconstriction

  25. Figure 6.14

  26. 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

  27. Figure 6.15

  28. Blood • 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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