1. chapter 5
The Cardiovascular System and Its Control

2. Learning Objectives
Review the structure and function of the heart, vascular system, and blood
Explore the role of the cardiovascular system in delivering oxygen and nutrients to active body tissues
Discover how the cardiovascular system removes metabolic waste from tissues

3. Major Cardiovascular Functions
Delivery of oxygen and other nutrients
Removal of carbon dioxide and other metabolic waste
Transport of hormones
Thermoregulation
Maintenance of acid–base balance and overall body fluid balance
Immune function

4. The Anatomy of the Human Heart

5. Myocardium—The Cardiac Muscle
Thickness varies according to the stress placed on chamber walls
Left ventricle is the most powerful of chambers and the largest chamber
With exercise training the size of the left ventricle increases
Intercalated disks in the myocardium allow impulses travel quickly in cardiac muscle and allow it to act as one large muscle fiber; all fibers in the heart contract together as one unit

6. Mechanism of Cardiac Muscle Contraction
Courtesy of Dr. Donna Korzick, Pennsylvania State University.

7. Structural and Functional Characteristics of Skeletal and Cardiac Muscle
Adapted, by permission, from K.L. Moore and A.F. Dalley, 1999, Clinically oriented anatomy, 4th ed. (Baltimore, MD: Lippincott, Williams, and Wilkins), 27.

8. Coronary Circulation

9. Cardiac Conduction System
Sinoatrial (SA) node
Atrioventricular (AV) node
AV bundle (bundle of His)
Purkinje fibers

10. Intrinsic Conduction System of the Heart

11. Extrinsic Control of the Heart
PNS acts through the vagus nerve, releasing ACh to decrease heart rate and force of cardiac contraction
Hyperpolarization of the conduction cells
Absence of vagal tone, HR = 100 beats/min
Maximal vagal tone, HR = beats/min
SNS increases rate of impulse generation and conduction speed, increasing heart rate and force of cardiac contraction
Maximal sympathetic stimulation, HR = 250 beats/min
Epinephrine and norepinephrine—released from the adrenal medulla as a result of sympathetic stimulation—increase heart rate

12. Relative Contribution of Sympathetic and Parasympathetic Nervous Systems to the Rise in Heart Rate During Exercise
Adapted from L.B. Rowell, Human Cardiovascular Control. Oxford University Press, 1993.

13. Heart Rate and Endurance Training
Resting heart rates in adults tend to be between 60 and 85 beats per min. However, extended endurance training can lower resting heart rate to 35 beats or lower. This lower heart rate is thought to be due to increased parasympathetic stimulation.

14. Electrocardiogram (ECG)
An ECG provides a graphical record of the electrical activity of the heart and can be used to aid clinical diagnoses

15. Cardiac Anatomy, Conduction, and Control
Key Points
The atria receive blood from the veins; the ventricles eject blood from the heart
The left ventricular myocardium is larger because it must produce more force than the other ventricles to pump blood to the systemic circulation
Cardiac tissue is capable of spontaneous rhythmicity and has its own conduction system
The SA node normally establishes heart rate
Heart rate and contractility can be altered by the PNS, SNS, and the endocrine system
The ECG is a recording of the heart’s electrical activity

16. Cardiac Arrhythmias Bradycardia: resting heart rate below 60 bpm
Tachycardia: resting heart rate above 100 bpm
Premature ventricular contractions (PVCs): skipped or extra beats from impulses originating outside the SA node
Ventricular tachycardia: three or more consecutive PVCs
Ventricular fibrillation: contraction of the ventricular tissue is uncoordinated and can result in cardiac death

17. Endurance Training vs. Pathological Bradycardia
The decrease in resting heart rate that occurs as an adaptation to endurance training is different from pathological bradycardia, an abnormal disturbance in the resting heart rate.

18. Cardiac Cycle
Defined as the mechanical and electrical events that occur during one heart beat (systole to systole)
Diastole is the relaxation phase during which the chambers fill with blood (T wave to QRS)
Systole is the contraction phase during which the chambers expel blood (QRS to T wave)

19. Wiggers Diagram
Figure 14.27, p. 433 from Human Physiology, 2nd ed. By Dee Unglaub Silverthorn. Copyright © 2001 Prentice-Hall, Inc. Reprinted by permission of Pearson Education, Inc.

20. Stroke Volume and Cardiac Output
Stroke Volume (SV)
Volume of blood pumped per contraction
End-diastolic volume (EDV)—volume of blood in ventricle just before contraction
End-systolic volume (ESV)—volume of blood in ventricle just after contraction
SV = EDV – ESV
Cardiac Output (Q)
Total volume of blood pumped by the ventricle per minute
Q = HR  SV . .

21. Ejection Fraction (EF)
Proportion of blood pumped out of the left ventricle with each beat
EF = SV / EDV
Averages 60% at rest

22. Calculation of Stroke Volume, Ejection Fraction, and Cardiac Output

23. The Vascular System
Arteries
Arterioles
Capillaries
Venules
Veins

24. Blood Pressure
Systolic blood pressure (SBP) is the highest pressure within the vascular system generated during cardiac contraction
Diastolic blood pressure (DBP) is the lowest pressure within the vascular system when the heart is relaxed
Mean arterial pressure is the average pressure
MAP = 2/3 DBP + 1/3 SBP
MAP = DPB + [0.33 (SBP - DBP)]

25. General Hemodynamics
Blood flows from a region within the vessel of high pressure to a region within the vessel with lower pressure (pressure gradient)
Pressure gradient across the entire cardiovascular system = 100 mmHg
Blood vessels and the blood itself provide resistance to blood flow
Resistance to blood flow = [ηL / r4],
η = viscosity of the blood
L = length of the vessel
r4 = radius of the vessel to the 4th power

26. Blood Flow = Δpressure / resistance
Changing Blood Flow
Blood Flow = Δpressure / resistance
Blood flow can change by either changing pressure or resistance or a combination of the two
Changing resistance has a larger effect on blood flow because of the fourth power mathematical relationship between vascular resistance and vessel radius
Vasoconstriction: radius of the vessel decreases, decreasing blood flow
Vasodilation: radius of the vessel increases, increasing blood flow

27. Pressure Changes Across the Systemic Circulation

28. Distribution of Cardiac Output at Rest and During Heavy Exercise
Reprinted, by permission, from P.O. Åstrand et al., 2003, Textbook of work physiology: Physiological bases of exercise, 4th ed. (Champaign, IL: Human Kinetics), 143.

29. Intrinsic Control of Blood Flow
Stimuli to increase local blood flow
Metabolic factors
increased oxygen demand
increases in metabolic by-products
inflammatory chemicals
Endothelium released factors
Nitric oxide
Prostaglandins
Endothelium-derived hyperpolarization factors (EDHF)
Myogenic responses

30. Intrinsic Control of Blood Flow
Figure courtesy of Dr. Donna H. Korzick, Pennsylvania State University.

31. Extrinsic Neural Control
Accomplished by the sympathetic nervous system through vasoconstriction

32. Blood Distribution Within the Vasculature When the Body Is at Rest

33. Integrative Control of Blood Pressure
Blood pressure is maintained and controlled by the autonomic nervous system
Receptors that modify blood pressure control through the cardiovascular control centers:
Baroreceptors: stretch receptors in the aortic arch and carotid arteries that are sensitive to changes in blood pressure
Chemoreceptors: chemical receptors that relay information about the chemical environment
Mechanoreceptors: receptors that sense changes in muscle length and tension

34. Return of Blood to the Heart
Valves in the veins
The muscle pump
The respiratory pump

35. Return of Blood to the Heart: The Muscle Pump

36. Control of Blood Flow Key Points
Blood is distributed throughout the body based on the needs of individual tissues
Redistribution of blood is controlled locally by the release of chemical substances, which cause vasodilation
Extrinsic neural control of blood flow distribution is accomplished through vasoconstriction through the sympathetic nervous system
Blood returns to the heart through veins, assisted by valves, the muscle pump, and respiratory pump

37. Functions of the Blood Important to Exercise
Transportation
Temperature regulation
Acid–base (pH) balance

38. Composition of Whole Blood

39. Hematocrit Ratio of formed elements to the total blood volume
White blood cells are involved in the immune response
Blood platelets are cell fragments that help blood coagulation
Red blood cells carry oxygen to tissues with the help of hemoglobin

40. Blood Viscosity Thickness of the blood
The more viscous, the more resistant to flow
Higher hematocrits result in higher blood viscosity

41. Blood
Key Points
Blood is about 55% to 60% plasma and 40% to 45% formed elements
Oxygen is transported primarily by binding to hemoglobin in red blood cells
As blood viscosity increases, so does resistance to blood flow