Cardiovascular Physiology

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CON T E N T S

C H A P T E R 1

OVERVIEW OF THE CIRCULATION

AND BLOOD 1

The Circulatory System 1

Blood 5

Erythrocytes 5

Leukocytes 6

Lymphocytes 7

Blood Is Divided into Groups by Antigens

Located on Erythrocytes 7

Summary 9

Case 1-1 9

C H A P T E R 2

EXCITATION: THE CARDIAC

ACTION POTENTIAL . 11

Cardiac Action Potentials Consist of Several

Phases 11

The Principal Types of Cardiac Action

Potentials Are the Slow and Fast

Types 12

Ionic Basis of the Resting

Potential 13

The Fast Response Depends Mainly on

Voltage-Dependent Sodium

Channels 15

Ionic Basis of the Slow Response 24

Conduction in Cardiac Fibers Depends on

Local Circuit Currents 25

Conduction of the Fast Response 25

Conduction of the Slow Response 27

Cardiac Excitability Depends on the

Activation and Inactivation of Specific

Currents 27

Fast Response 27

Slow Response 28

Effects of Cycle Length 28

Summary 29

Case 2-1 29

C H A P T E R 3

AUTOMATICITY: NATURAL

EXCITATION OF THE HEART . 31

The Heart Generates Its Own Pacemaking

Activity 31

Sinoatrial Node 32

Ionic Basis of Automaticity 34

Overdrive Suppression 35

Atrial Conduction 36

Atrioventricular Conduction 37

Ventricular Conduction 39

An Impulse Can Travel Around a Reentry

Loop 41

Afterdepolarizations Lead to Triggered

Activity 42

Early Afterdepolarizations 43

Delayed Afterdepolarizations 43

Electrocardiography Displays the Spread of

Cardiac Excitation 44

Scalar Electrocardiography 44

Dysrhythmias Occur Frequently and

Constitute Important Clinical

Problems 47

Altered Sinoatrial Rhythms 47

Atrioventricular Transmission Blocks 48

Premature Depolarizations 48

Ectopic Tachycardias 49

Fibrillation 49

Summary 51

Case 3-3 52

C H A P T E R 4

THE CARDIAC PUMP 55

The Gross and Microscopic Structures of the

Heart Are Uniquely Designed for Optimal

Function 55

The Myocardial Cell 55

Structure of the Heart: Atria, Ventricles,

and Valves 60

The Force of Cardiac Contraction Is

Determined by Excitation-Contraction

Coupling and the Initial Sarcomere Length

of the Myocardial Cells 63

Excitation-Contraction Coupling Is

Mediated by Calcium 63

Mechanics of Cardiac Muscle 65

The Sequential Contraction and Relaxation of

the Atria and Ventricles Constitute the

Cardiac Cycle 69

Ventricular Systole 70

Echocardiography Reveals Movement of

the Ventricular Walls and of the

Valves 73

The Two Major Heart Sounds Are

Produced Mainly by Closure of the

Cardiac Valves 74

The Pressure-Volume Relationships in the

Intact Heart 75

Passive or Diastolic Pressure-Volume

Relationship 75

Active or End-Systolic Pressure-Volume

Relationship 77

Pressure and Volume during the Cardiac

Cycle: The P-V Loop 77

Preload and Afterload during the Cardiac

Cycle 77

Contractility 78

The Fick Principle Is Used to Determine

Cardiac Output 79

Summary 89

Case 4-1 90

C H A P T E R 5

REGULATION OF THE

HEARTBEAT 91

Heart Rate is Controlled Mainly by the

Autonomic Nerves 91

Parasympathetic Pathways 92

Sympathetic Pathways 93

Higher Centers Also Influence Cardiac

Performance 97

Heart Rate Can Be Regulated via the

Baroreceptor Reflex 97

The Bainbridge Reflex and Atrial

Receptors Regulate Heart Rate 98

Respiration Induces a Common Cardiac

Dysrhythmia 99

Activation of the Chemoreceptor Reflex

Affects Heart Rate 101

Ventricular Receptor Reflexes Play a

Minor Role in the Regulation of Heart

Rate 102

Myocardial Performance Is Regulated

by Intrinsic Mechanisms 102

The Frank-Starling Mechanism Is an

Important Regulator of Myocardial

Contraction Force 103

Changes in Heart Rate Affect Contractile

Force 107

Myocardial Performance Is Regulated by

Nervous and Humoral Factors 110

Nervous Control 110

Cardiac Performance Is Also Regulated by

Hormonal Substances 113

Summary 116

Case 5-1 117

C H A P T E R 6

HEMODYNAMICS 119

Velocity of the Bloodstream Depends on

Blood Flow and Vascular Area 119

Blood Flow Depends on the Pressure

Gradient 120

Relationship Between Pressure and Flow

Depends on the Characteristics of the

Conduits 122

Resistance to Flow 125

Resistances in Series and in Parallel 126

Flow May Be Laminar or Turbulent 127

Shear Stress on the Vessel Wall 128

Rheologic Properties of Blood 129

Summary 133

Case 6-6 134

C H A P T E R 7

THE ARTERIAL SYSTEM . 135

The Hydraulic Filter Converts Pulsatile Flow

to Steady Flow 135

Arterial Elasticity Compensates for the

Intermittent Flow Delivered by the

Heart 137

The Arterial Blood Pressure Is Determined by

Physical and Physiological Factors 140

Mean Arterial Pressure 140

Cardiac Output 142

Peripheral Resistance 142

Pulse Pressure 144

Stroke Volume 144

Arterial Compliance 145

Total Peripheral Resistance and Arterial

Diastolic Pressure 146

The Pressure Curves Change in Arteries at

Different Distances from the Heart 147

Blood Pressure Is Measured by a

Sphygmomanometer in Human

Patients 148

Summary 150

Case 7-1 150

C H A P T E R 8

THE MICROCIRCULATION

AND LYMPHATICS. 153

Functional Anatomy 153

Arterioles Are the Stopcocks of the

Circulation 153

Capillaries Permit the Exchange of Water,

Solutes, and Gases 154

The Law of Laplace Explains How

Capillaries Can Withstand High

Intravascular Pressures 155

The Endothelium Plays an Active Role in

Regulating the Microcirculation 156

The Endothelium is at the Center of Flow-

Initiated Mechanotransduction 157

The Endothelium Plays a Passive Role in

Transcapillary Exchange 158

Diffusion Is the Most Important Means of

Water and Solute Transfer Across the

Endothelium 159

Diffusion of Lipid-Insoluble Molecules Is

Restricted to the Pores 159

Lipid-Soluble Molecules Pass Directly

Through the Lipid Membranes of the

Endothelium and the Pores 162

Capillary Filtration Is Regulated by the

Hydrostatic and Osmotic Forces Across

the Endothelium 163

Balance of Hydrostatic and Osmotic

Forces 165

The Capillary Filtration Coefficient

Provides a Method to Estimate the Rate

of Fluid Movement Across the

Endothelium 165

Pinocytosis Enables Large Molecules to

Cross the Endothelium 167

The Lymphatics Return the Fluid and Solutes

That Escape Through the Endothelium to

the Circulating Blood 167

Summary 168

Case 8-1 169

Case 8-2 169

C H A P T E R 9

THE PERIPHERAL CIRCULATION

AND ITS CONTROL 171

The Functions of the Heart and Large Blood

Vessels 171

Contraction and Relaxation of Arteriolar

Vascular Smooth Muscle Regulate

Peripheral Blood Flow 172

Cytoplasmic Ca++ Is Regulated to Control

Contraction, via MLCK 175

Contraction Is Controlled by Excitation-

Contraction Coupling and/or

Pharmacomechanical Coupling 176

Control of Vascular Tone by

Catecholamines 178

Control of Vascular Contraction by Other

Hormones, Other Neurotransmitters,

and Autocoids 178

Intrinsic Control of Peripheral Blood

Flow 179

Autoregulation and the Myogenic

Mechanism Tend to Keep Blood Flow

Constant 179

The Endothelium Actively Regulates Blood

Flow 180

Tissue Metabolic Activity Is the Main

Factor in the Local Regulation of Blood

Flow 181

Extrinsic Control of Peripheral Blood Flow Is

Mediated Mainly by the Sympathetic

Nervous System 183

Impulses That Arise in the Medulla

Descend in the Sympathetic Nerves

to Increase Vascular Resistance 183

Sympathetic Nerves Regulate the

Contractile State of the Resistance and

Capacitance Vessels 184

The Parasympathetic Nervous System

Innervates Blood Vessels Only in the

Cranial and Sacral Regions of the

Body 185

Epinephrine and Norepinephrine Are the

Main Humoral Factors That Affect

Vascular Resistance 185

The Vascular Reflexes Are Responsible for

Rapid Adjustments of Blood

Pressure 185

The Peripheral Chemoreceptors Are

Stimulated by Decreases in Blood

Oxygen Tension and pH and by

Increases in Carbon Dioxide

Tension 189

The Central Chemoreceptors Are Sensitive

to Changes in Paco2 189

Other Vascular Reflexes 190

Balance Between Extrinsic and Intrinsic

Factors in Regulation of Peripheral Blood

Flow 191

Summary 192

Case 9-1 194

C H A P T E R 10

CONTROL OF CARDIAC OUTPUT:

COUPLING OF HEART AND

BLOOD VESSELS . 195

Factors Controlling Cardiac Output 195

The Cardiac Function Curve Relates Central

Venous Pressure (Preload) to Cardiac

Output 196

Preload or Filling Pressure of the

Heart 196

Cardiac Function Curve 196

Factors That Change the Cardiac

Function Curve 197

The Vascular Function Curve Relates Central

Venous Pressure to Cardiac Output 200

Mathematical Analysis of the Vascular

Function Curve 203

Venous Pressure Depends on Cardiac

Output 205

Blood Volume 205

Venomotor Tone 206

Blood Reservoirs 206

Peripheral Resistance 206

Cardiac Output and Venous Return Are

Closely Associated 207

The Heart and Vasculature Are Coupled

Functionally 207

Myocardial Contractility 209

Blood Volume 209

Peripheral Resistance 210

The Right Ventricle Regulates Not Only

Pulmonary Blood Flow but Also Central

Venous Pressure 211

Heart Rate Has Ambivalent Effects on Cardiac

Output 214

Ancillary Factors Affect the Venous System

and Cardiac Output 216

Gravity 216

Muscular Activity and Venous

Valves 218

Respiratory Activity 219

Artificial Respiration 220

Summary 221

Case 10-1 221

C H A P T E R 11

CORONARY CIRCULATION . 223

Functional Anatomy of the Coronary

Vessels 223

Coronary Blood Flow Is Regulated by

Physical, Neural, and Metabolic

Factors 225

Physical Factors 225

Neural and Neurohumoral Factors 227

Metabolic Factors 228

Diminished Coronary Blood Flow Impairs

Cardiac Function 230

Energy Substrate Metabolism During

Ischemia 231

Coronary Collateral Vessels Develop in

Response to Impairment of Coronary

Blood Flow 233

Summary 235

Case 11-1 236

C H A P T E R 12

SPECIAL CIRCULATIONS 237

Cutaneous Circulation 237

Skin Blood Flow Is Regulated Mainly by

the Sympathetic Nervous System 237

Ambient Temperature and Body

Temperature Play Important Roles in

the Regulation of Skin Blood

Flow 239

Skin Color Depends on the Volume and

Flow of Blood in the Skin and on the

Amount of O2 Bound to

Hemoglobin 240

Skeletal Muscle Circulation 240

Regulation of Skeletal Muscle

Circulation 240

Cerebral Circulation 243

Local Factors Predominate in the

Regulation of Cerebral Blood

Flow 243

The Pulmonary and Systemic Circulations

Are in Series with Each Other 245

Functional Anatomy 245

Pulmonary Hemodynamics 247

Regulation of the Pulmonary

Circulation 249

The Renal Circulation Affects the Cardiac

Output 250

Anatomy 250

Renal Hemodynamics 252

The Renal Circulation Is Regulated by

Intrinsic Mechanisms 252

The Splanchnic Circulation Provides Blood

Flow to the Gastrointestinal Tract, Liver,

Spleen, and Pancreas 254

Intestinal Circulation 254

Hepatic Circulation 256

Fetal Circulation 257

Changes in the Circulatory System at

Birth 259

Summary 260

Case 12-1 262

Case 12-2 262

Case 12-3 262

C H A P T E R 13

INTERPLAY OF CENTRAL AND

PERIPHERAL FACTORS THAT

CONTROL THE CIRCULATION 263

Exercise 264

Mild to Moderate Exercise 264

Severe Exercise 268

Postexercise Recovery 268

Limits of Exercise Performance 269

Physical Training and Conditioning 269

Hemorrhage 269

Hemorrhage Evokes Compensatory and

Decompensatory Effects on the Arterial

Blood Pressure 270

The Compensatory Mechanisms Are

Neural and Humoral 270

The Decompensatory Mechanisms Are

Mainly Humoral, Cardiac, and

Hematologic 273

The Positive and Negative Feedback

Mechanisms Interact 275

Summary 276

Case 13-1 277

Case 13-2 277

APPENDIX: CASE STUDY

ANSWERS . 279