Human Physiology From Cells to Systems by Lauralee Sherwood free pdf bookHuman Physiology From Cells to Systems by Lauralee Sherwood free pdf book


1.1 Introduction to Physiology 2

Physiology focuses on mechanisms of action. 2

Structure and function are inseparable. 2

1.2 Levels of Organization in the Body 2

The chemical level: Various atoms and molecules make up

the body. 2

The cellular level: Cells are the basic units of life. 2

The tissue level: Tissues are groups of cells of similar

specialization. 5

The organ level: An organ is a unit made up of several

tissue types. 7

The body system level: A body system is a collection of

related organs. 7

The organism level: The body systems are packaged into a

functional whole body. 7

1.3 Concept of Homeostasis 7

Body cells are in contact with a privately maintained

internal environment. 8

Body systems maintain homeostasis, a dynamic steady

state in the internal environment. 8

Concepts, Challengess, and Controversies: Stem Cell Science

and Regenerative Medicine: Making Defective Body Parts Like

New Again 10

A Closer Look at Exercise Physiology: What Is Exercise

Physiology? 13

1.4 Homeostatic Control Systems 16

Homeostatic control systems may operate locally or

bodywide. 16

Negative feedback opposes an initial change and is widely

used to maintain homeostasis. 16

Positive feedback amplifies an initial change. 18

Feedforward mechanisms initiate responses in anticipation

of a change. 18

Disruptions in homeostasis can lead to illness and

death. 18

Homeostasis: Chapter

in Perspective 18

Review Exercises 19

Chapter 2 | Cell Physiology 21

Homeostasis Highlights 21

2.1 Cell Theory and Discovery 22

2.2 An Overview of Cell Structure 22

The plasma membrane bounds the cell. 22

The nucleus contains the DNA. 22

The cytoplasm consists of various organelles, the

cytoskeleton, and the cytosol. 24

2.3 Endoplasmic Reticulum and Segregated

Synthesis 25

The rough ER synthesizes proteins for secretion and

membrane construction. 25

The smooth ER packages new proteins in transport

vesicles. 26

Misfolded proteins are destroyed by the ubiquitin–

proteasome pathway. 27

2.4 Golgi Complex and Exocytosis 28

Transport vesicles carry their cargo to the Golgi complex

for further processing. 28

The Golgi complex packages secretory vesicles for release

by exocytosis. 29

2.5 Lysosomes and Endocytosis 30

Lysosomes digest extracellular material brought into the

cell by phagocytosis. 30

Lysosomes remove worn-out organelles. 31

2.6 Peroxisomes and Detoxification 33

Peroxisomes house oxidative enzymes that detoxify

various wastes. 33

2.7 Mitochondria and ATP Production 33

Mitochondria are enclosed by two membranes. 33

Mitochondria form a mitochondrial reticulum in some cell

types. 34

Mitochondria play a major role in generating ATP. 34

The cell generates more energy in aerobic than in

anaerobic conditions. 39

The energy stored within ATP is used for synthesis,

transport, and mechanical work. 40

Mitochondria play a key role in programmed cell

death. 40

A Closer Look at Exercise Physiology: Aerobic Exercise: What

For and How Much? 41

2.8 Vaults as Cellular Trucks 41

Vaults may serve as cellular transport vehicles. 41

Concepts, Challenges, and Controversies: Apoptosis:

Programmed Cell Suicide 42

2.9 Cytosol: Cell Gel 42

The cytosol is important in intermediary metabolism,

ribosomal protein synthesis, and nutrient storage. 42

2.10 Cytoskeleton: Cell “Bone and Muscle” 44

Microtubules help maintain asymmetric cell shapes and

play a role in complex cell movements. 46

Microfilaments are important to cellular contractile

systems and as mechanical stiffeners. 49

Intermediate filaments are important in cell regions

subject to mechanical stress. 51

The cytoskeleton functions as an integrated whole and

links other parts of the cell. 51

Homeostasis: Chapter

in Perspective 51

Review Exercises 52

Chapter 3 | The Plasma Membrane and

Membrane Potential 55

Homeostasis Highlights 55

3.1 Membrane Structure and Functions 56

The plasma membrane is a fluid lipid bilayer embedded

with proteins. 56

The lipid bilayer forms the basic structural barrier that

encloses the cell. 57

The membrane proteins perform various specific

membrane functions. 58

Concepts, Challenges, and Controversies: Cystic Fibrosis:

A Fatal Defect in Membrane Transport 59

The membrane carbohydrates serve as self-identity

markers. 60

3.2 Cell-to-Cell Adhesions 60

The extracellular matrix serves as biological

“glue.” 60

Some cells are directly linked by specialized cell

junctions. 61

3.3 Overview of Membrane Transport 63

Lipid-soluble substances and small water-soluble

substances can permeate the plasma membrane

unassisted. 63

Active forces use energy to move particles across the

membrane, but passive forces do not. 63

3.4 Unassisted Membrane Transport 63

Particles that can permeate the membrane diffuse passively

down their concentration gradient. 63

Ions that can permeate the membrane also move passively

along their electrical gradient. 66

Osmosis is the net diffusion of water down its own

concentration gradient. 66

Tonicity refers to the effect the concentration of

nonpenetrating solutes in a solution has on cell

volume. 69

3.5 Assisted Membrane Transport 70

Carrier-mediated transport is accomplished by a

membrane carrier changing its shape. 70

A Closer Look at Exercise Physiology: Exercising Muscles

Have a “Sweet Tooth” 72

Facilitated diffusion is passive carrier-mediated

transport. 72

Active transport is carrier mediated and uses energy. 73

With vesicular transport, material is moved into or out of

the cell wrapped in membrane. 75

3.6 Membrane Potential 77

Membrane potential is a separation of opposite charges

across the plasma membrane. 77

Membrane potential results from differences in the

concentration and permeability of key ions. 79

Homeostasis: Chapter

in Perspective 84

Review Exercises 85

Chapter 4 | Principles of Neural

and Hormonal

Communication 87

Homeostasis Highlights 87

4.1 Introduction to Neural Communication 88

Nerve and muscle are excitable tissues. 88

Membrane potential becomes less negative during

depolarization and more negative during

hyperpolarization. 88

Electrical signals are produced by changes in ion

movement across the plasma membrane. 88

4.2 Graded Potentials 89

The stronger a triggering event, the larger the resultant

graded potential. 89

Graded potentials spread by passive current flow. 89

Graded potentials die out over short distances. 90

4.3 Action Potentials 91

During an action potential, the membrane potential

rapidly, transiently reverses. 91

Marked changes in membrane permeability and ion

movement lead to an action potential. 92

The Na1–K1 pump gradually restores the concentration gradients disrupted by action potentials. 94

Action potentials are propagated from the axon hillock to

the axon terminals. 95

Once initiated, action potentials are conducted throughout

a nerve fiber. 96

The refractory period ensures one-way propagation of

action potentials and limits their frequency. 98

Action potentials occur in all-or-none fashion. 99

The strength of a stimulus is coded by the frequency of

action potentials. 100

Myelination increases the speed of conduction of action

potentials. 100

Fiber diameter also influences the velocity of action

potential propagation. 100

4.4 Synapses and Neuronal Integration 102

Synapses are typically junctions between presynaptic and

postsynaptic neurons. 102

Concepts, Challenges, and Controversies: Multiple Sclerosis:

Myelin—Going, Going, Gone 103

Concepts, Challenges, and Controversies: Regeneration: PNS

Axons Can Do It, But CNS Axons Cannot 104

A neurotransmitter carries the signal across a

synapse. 106

Some synapses excite, whereas others inhibit, the

postsynaptic neuron. 106

Each neurotransmitter–receptor combination always

produces the same response. 107

Neurotransmitters are quickly removed from the synaptic

cleft. 108

The grand postsynaptic potential depends on the sum of

the activities of all presynaptic inputs. 108

Some neurons secrete neuromodulators in addition to

neurotransmitters. 110

Presynaptic inhibition or facilitation can selectively alter

the effectiveness of a presynaptic input. 111

Drugs and diseases can modify synaptic

transmission. 112

Neurons are linked through complex converging and

diverging pathways. 112

4.5 Intercellular Communication and Signal

Transduction 113

Communication among cells is largely orchestrated by

extracellular chemical messengers. 113

Extracellular chemical messengers bring about cell

responses by signal transduction. 115

Some water-soluble extracellular messengers open

chemically gated receptor-channels. 116

Some water-soluble extracellular messengers activate

receptor-enzymes. 116

Most water-soluble extracellular chemical messengers

activate second-messenger pathways via G-proteincoupled

receptors. 117

4.6 Introduction to Paracrine Communication 118

Cytokines act locally to regulate immune

responses. 118

Eicosanoids are locally acting chemical messengers derived

from plasma membrane. 118

4.7 Introduction to Hormonal Communication 120

Hormones are classified chemically as hydrophilic or

lipophilic. 120

The mechanisms of synthesis, storage, and secretion of

hormones vary according to their chemical

differences. 121

Hydrophilic hormones dissolve in the plasma; lipophilic

hormones are transported by plasma proteins. 122

Hormones generally produce their effect by altering

intracellular proteins. 122

Hydrophilic hormones alter preexisting proteins via

second-messenger systems. 122

By stimulating genes, lipophilic hormones promote

synthesis of new proteins. 126

4.8 Comparison of the Nervous and Endocrine

Systems 127

The nervous system is “wired,” and the endocrine system is

“wireless.” 128

Neural specificity is a result of anatomic proximity, and

endocrine specificity is a result of receptor

specialization. 128

The nervous and endocrine systems have their own realms

of authority but interact functionally. 129

Homeostasis: Chapter

in Perspective 129

Review Exercises 130

Chapter 5 | The Central Nervous

System 133

Homeostasis Highlights 133

5.1 Organization and Cells of the Nervous

System 134

The nervous system is organized into the central nervous

system and the peripheral nervous system. 135

The three functional classes of neurons are afferent

neurons, efferent neurons, and interneurons. 135

Glial cells support the interneurons physically,

metabolically, and functionally. 136

5.2 Protection and Nourishment of the Brain 139

Three meningeal membranes wrap, protect, and nourish

the central nervous system. 139

The brain floats in its own special cerebrospinal fluid. 139

A highly selective blood–brain barrier regulates exchanges

between the blood and brain. 141

The brain depends on constant delivery of oxygen and

glucose by the blood. 141

Concepts, Challenges, and Controversies: Strokes: A Deadly

Domino Effect 142

5.3 Overview of the Central Nervous System 142

5.4 Cerebral Cortex 144

The cerebral cortex is an outer shell of gray matter covering an inner core of white matter. 144

Neurons in different regions of the cerebral cortex may fire
in rhythmic synchrony. 145
The cerebral cortex is organized into layers and functional
columns. 146
The four pairs of lobes in the cerebral cortex are
specialized for different activities. 146
The parietal lobes accomplish somatosensory
processing. 147
The primary motor cortex located in the frontal lobes
controls the skeletal muscles. 148
Higher motor areas are also important in motor
control. 148
Somatotopic maps vary slightly between individuals and
are dynamic, not static. 150
Because of its plasticity, the brain can be remodeled in
response to varying demands. 150
Different regions of the cortex control different aspects of
language. 151
The association areas of the cortex are involved in many
higher functions. 152
The cerebral hemispheres have some degree of
specialization. 152
The cortex has a default mode network that is most active
when the mind wanders. 152
5.5 Basal Nuclei, Thalamus, and Hypothalamus 153
The basal nuclei play an important inhibitory role in motor
control. 153
The thalamus is a sensory relay station and is important in
motor control. 154
The hypothalamus regulates many homeostatic
functions. 154
5.6 Emotion, Behavior, and Motivation 155
The limbic system plays a key role in emotion. 155
The limbic system and higher cortex participate in
controlling basic behavioral patterns. 155
Motivated behaviors are goal directed. 156
Norepinephrine, dopamine, and serotonin are
neurotransmitters in pathways for emotions and
behavior. 156
5.7 Learning and Memory 157
Learning is the acquisition of knowledge as a result of
experiences. 157
Memory is laid down in stages. 157
Short-term memory and long-term memory involve
different molecular mechanisms. 159
Short-term memory involves transient changes in synaptic
activity. 159
Long-term memory involves formation of new, permanent
synaptic connections. 161
Memory traces are present in multiple regions of the
brain. 162
5.8 Cerebellum 163
The cerebellum is important in balance and in planning
and executing voluntary movement. 163
Concepts, Challenges, and Controversies: Alzheimer’s
Disease: A Tale of Beta Amyloid Plaques, Tau Tangles, and
Dementia 164
5.9 Brain Stem 166
The brain stem is a vital link between the spinal cord and
higher brain regions. 166
Consciousness refers to awareness of one’s own existence,
thoughts, and surroundings. 168
An electroencephalogram is a record of postsynaptic
activity in cortical neurons. 168
Sleep is an active process consisting of alternating periods
of slow-wave and paradoxical sleep. 169
The sleep–wake cycle is controlled by interactions among
three neural systems. 170
The function of sleep is unclear. 171
Impaired states of consciousness are associated with
minimal or no awareness. 172
5.10 Spinal Cord 172
The spinal cord extends through the vertebral canal and is
connected to the spinal nerves. 173
The white matter of the spinal cord is organized into
tracts. 173
Each horn of the spinal cord gray matter houses a different
type of neuronal cell body. 174
Spinal nerves carry both afferent and efferent fibers. 175
The spinal cord is responsible for the integration of many
innate reflexes. 176
A Closer Look at Exercise Physiology: Swan Dive or Belly Flop:
It’s a Matter of CNS Control 178
Homeostasis: Chapter
in Perspective 178
Review Exercises 179
Chapter 6 | The Peripheral Nervous
System: Afferent Division;
Special Senses 181

6.1 Receptor Physiology 182
Receptors have differential sensitivities to various
stimuli. 182
A stimulus alters the receptor’s permeability, leading to a
graded receptor potential. 182
Receptor potentials may initiate action potentials in the
afferent neuron. 183
Receptors may adapt slowly or rapidly to sustained
stimulation. 184
Visceral afferents carry subconscious input; sensory
afferents carry conscious input. 186
Each somatosensory pathway is “labeled” according to
modality and location. 186

A Closer Look at Exercise Physiology: Back Swings and
Prejump Crouches: What Do They Share in Common? 187
Acuity is influenced by receptive field size and lateral
inhibition. 187
Perception is the conscious awareness of surroundings
derived from interpretation of sensory input. 188
6.2 Pain 189
Stimulation of nociceptors elicits the perception of pain
plus motivational and emotional responses. 189
The brain has a built-in analgesic system. 192
6.3 Eye: Vision 192
Protective mechanisms help prevent eye injuries. 192
The eye is a fluid-filled sphere enclosed by three
specialized tissue layers. 193
The amount of light entering the eye is controlled by the
iris. 193
The eye refracts entering light to focus the image on the
retina. 194
Accommodation increases the strength of the lens for near
vision. 196
Light must pass through several retinal layers before
reaching the photoreceptors. 199
Phototransduction by retinal cells converts light stimuli
into neural signals. 200
Rods provide indistinct gray vision at night; cones provide
sharp color vision during the day. 204
Color vision depends on the ratios of stimulation of the
three cone types. 204
The sensitivity of the eyes can vary markedly through dark
and light adaptation. 206
Visual information is modified and separated before
reaching the visual cortex. 206
The thalamus and visual cortex elaborate the visual
message. 208
Visual input goes to other areas of the brain not involved
in vision perception. 209
Concepts, Challenges, and Controversies: “Seeing” with the
Tongue or the Ear 210
Some sensory input may be detected by multiple sensoryprocessing
areas in the brain. 210
6.4 Ear: Hearing and Equilibrium 211
Sound waves consist of alternate regions of compression
and rarefaction of air molecules. 211
The external ear plays a role in sound localization. 212
The tympanic membrane vibrates in unison with sound
waves in the external ear. 213
The middle ear bones convert tympanic membrane
vibrations into fluid movements in the inner ear. 214
The cochlea contains the organ of Corti, the sense organ
for hearing. 214
Hair cells in the organ of Corti transduce fluid movements
into neural signals. 217
Pitch discrimination depends on the region of the basilar
membrane that vibrates. 219
Loudness discrimination depends on the amplitude of
vibration. 220
The auditory cortex is mapped according to tone. 220
Deafness is caused by defects in either conduction or
neural processing of sound waves. 220
The vestibular apparatus is important for equilibrium by
detecting head position and motion. 221
6.5 Chemical Senses: Taste and Smell 224
Taste receptor cells are located primarily within tongue
taste buds. 224
Taste discrimination is coded by patterns of activity in
various taste bud receptors. 226
The gut and airways “taste” too. 227
The olfactory receptors in the nose are specialized endings
of renewable afferent neurons. 227
Various parts of an odor are detected by different olfactory
receptors and sorted into “smell files.” 228
Odor discrimination is coded by patterns of activity in the
olfactory bulb glomeruli. 229
The olfactory system adapts quickly, and odorants are
rapidly cleared. 229
The vomeronasal organ detects pheromones. 229
Homeostasis: Chapter
in Perspective 230
Review Exercises 231
Chapter 7 | The Peripheral Nervous
System: Efferent Division 233
Homeostasis Highlights 233
7.1 Autonomic Nervous System 234
An autonomic nerve pathway consists of a two-neuron
chain. 234
Parasympathetic postganglionic fibers release
acetylcholine; sympathetic ones release
norepinephrine. 235
The sympathetic and parasympathetic nervous systems
dually innervate most visceral organs. 236
The adrenal medulla is a modified part of the sympathetic
nervous system. 239
Several receptor types are available for each autonomic
neurotransmitter. 239
Many regions of the CNS are involved in the control of
autonomic activities. 241
7.2 Somatic Nervous System 242
Motor neurons supply skeletal muscle. 242
Motor neurons are the final common pathway. 242
7.3 Neuromuscular Junction 244
Motor neurons and skeletal muscle fibers are
chemically linked at neuromuscular
junctions. 244

ACh is the neuromuscular junction
neurotransmitter. 244
Acetylcholinesterase ends ACh activity at the
neuromuscular junction. 246
The neuromuscular junction is vulnerable to several
chemical agents and diseases. 246
Concepts, Challenges, and Controversies: Botulinum Toxin’s
Reputation Gets a Facelift 247
Homeostasis: Chapter
in Perspective 248
Review Exercises 248
Chapter 8 | Muscle Physiology 251
Homeostasis Highlights 251
8.1 Structure of Skeletal Muscle 252
Skeletal muscle fibers are striated by a highly organized
internal arrangement. 252
Myosin forms the thick filaments. 254
Actin is the main structural component of the thin
filaments. 255
8.2 Molecular Basis of Skeletal Muscle
Contraction 256
During contraction, cycles of cross-bridge binding and
bending pull the thin filaments inward. 256
Calcium is the link between excitation and
contraction. 258
8.3 Skeletal Muscle Mechanics 262
Whole muscles are groups of muscle fibers bundled
together and attached to bones. 262
Muscle tension is transmitted to bone as the contractile
component tightens the series-elastic component. 262
The three primary types of contraction are isotonic,
isokinetic, and isometric. 263
The velocity of shortening is related to the load. 264
Although muscles can accomplish work, much of the
energy is converted to heat. 264
Interactive units of skeletal muscles, bones, and joints form
lever systems. 264
Contractions of a whole muscle can be of varying
strength. 265
The number of fibers contracting within a muscle depends
on the extent of motor unit recruitment. 266
The frequency of stimulation can influence the tension
developed by each muscle fiber. 266
Twitch summation results primarily from a sustained
elevation in cytosolic Ca21. 267
At the optimal muscle length, maximal tension can be
developed. 268
8.4 Skeletal Muscle Metabolism and Fiber Types 269
Muscle fibers have alternate pathways for forming
ATP. 269
Fatigue may be of muscle or central origin. 272
Increased O2 consumption is necessary to recover from
exercise. 272
The three types of skeletal muscle fibers differ in ATP
hydrolysis and synthesis. 273
Muscle fibers adapt considerably in response to the
demands placed on them. 274
A Closer Look at Exercise Physiology: Are Athletes Who Use
Steroids to Gain Competitive Advantage Really Winners or
Losers? 276
8.5 Control of Motor Movement 276
Motor activity can be classified as reflex, voluntary, or
rhythmic. 276
Concepts, Challenges, and Controversies: Muscular
Dystrophy: When One Small Step is a Big Deal 278
Multiple neural inputs influence motor unit output. 278
Muscle receptors provide afferent information needed to
control skeletal muscle activity. 281
Skeletal muscle reflexes can be triggered by painful
stimulation of the skin. 284
8.6 Smooth and Cardiac Muscle 286
Smooth muscle cells are small and unstriated. 288
Smooth muscle cells are turned on by Ca21- dependent
phosphorylation of myosin. 288
Phasic smooth muscle contracts in bursts; tonic smooth
muscle maintains tone. 289
Multiunit smooth muscle is neurogenic. 290
Single-unit smooth muscle cells form functional
syncytia. 291
Single-unit smooth muscle is myogenic. 291
Gradation of single-unit smooth muscle contraction differs
from that of skeletal muscle. 292
Smooth muscle can still develop tension yet inherently
relaxes when stretched. 293
Smooth muscle is slow and economical. 293
Cardiac muscle blends features of both skeletal and
smooth muscle. 294
Homeostasis: Chapter
in Perspective 294
Review Exercises 295
Chapter 9 | Cardiac Physiology 297
Homeostasis Highlights 297
9.1 Anatomy of the Heart 298
The heart is positioned in the middle of the thoracic
cavity. 298
The heart is a dual pump. 299
Pressure-operated heart valves ensure that blood flows in
the right direction through the heart. 300
The heart walls are composed primarily of spirally
arranged cardiac muscle fibers. 302
Cardiac muscle fibers are interconnected by intercalated
discs and form functional syncytia. 303
The heart is enclosed by the pericardial sac. 303

9.2 Electrical Activity of the Heart 303
Cardiac autorhythmic cells display pacemaker
activity. 303
The sinoatrial node is the normal pacemaker of the
heart. 305
The spread of cardiac excitation is coordinated to ensure
efficient pumping. 307
The action potential of cardiac contractile cells shows a
characteristic plateau. 308
A long refractory period prevents tetanus of cardiac
muscle. 309
The ECG is a record of the overall spread of electrical
activity through the heart. 310
Different parts of the ECG record can be correlated to
specific cardiac events. 311
The ECG can detect abnormal heart rates and rhythms and
heart muscle damage. 312
A Closer Look at Exercise Physiology: The What, Who, and
When of Stress Testing 314
9.3 Mechanical Events of the Cardiac Cycle 314
The heart alternately contracts to empty and relaxes to
fill. 314
Two normal heart sounds are associated with valve
closures. 317
Turbulent blood flow produces heart murmurs. 318
9.4 Cardiac Output and Its Control 319
Cardiac output depends on heart rate and stroke
volume. 319
Heart rate is determined primarily by autonomic
influences on the SA node. 319
Stroke volume is determined by the extent of venous
return and by sympathetic activity. 321
Increased end-diastolic volume results in increased stroke
volume. 321
Sympathetic stimulation increases the contractility of the
heart. 322
High blood pressure increases the workload of the
heart. 323
A failing heart cannot pump out enough blood. 324
9.5 Nourishing the Heart Muscle 326
The heart receives most of its blood supply through the
coronary circulation during diastole. 326
Atherosclerotic coronary artery disease can deprive the
heart of essential O2. 327
Concepts, Challenges, and Controversies: Atherosclerosis:
Cholesterol and Beyond 328
Homeostasis: Chapter
in Perspective 331
Review Exercises 332
Chapter 10 | The Blood Vessels and
Blood Pressure 335
Homeostasis Highlights 335
10.1 Patterns and Physics of Blood Flow 336
To maintain homeostasis, reconditioning organs receive
blood flow in excess of their own needs. 336
Blood flow through a vessel depends on the pressure
gradient and vascular resistance. 337
The vascular tree consists of arteries, arterioles, capillaries,
venules, and veins. 338
10.2 Arteries 339
Arteries serve as rapid-transit passageways to the organs
and as a pressure reservoir. 340
Arterial pressure fluctuates in relation to ventricular
systole and diastole. 340
Blood pressure can be measured indirectly by using a
sphygmomanometer. 341
Mean arterial pressure is the main driving force for blood
flow. 341
10.3 Arterioles 343
Arterioles are the major resistance vessels. 343
Local control of arteriolar radius is important in
determining the distribution of cardiac output. 344
Local metabolic influences on arteriolar radius help match
blood flow with the organs’ needs. 345
Local histamine release pathologically dilates
arterioles. 347
The myogenic response of arterioles to stretch helps tissues
autoregulate their blood flow. 348
Arterioles release vasodilating NO in response to an
increase in shear stress. 348
Local heat application dilates arterioles and cold
application constricts them. 349
Extrinsic control of arteriolar radius is important in
regulating blood pressure. 349
The cardiovascular control center and several hormones
regulate blood pressure. 350
10.4 Capillaries 350
Capillaries are ideally suited to serve as sites of
exchange. 351
Water-filled capillary pores permit passage of small, watersoluble
substances. 353
Many capillaries are not open under resting
conditions. 354
Interstitial fluid is a passive intermediary between blood
and cells. 355
Diffusion across capillary walls is important in solute
exchange. 355
Bulk flow across the capillary walls is important in
extracellular fluid distribution. 356

The lymphatic system is an accessory route for return of
interstitial fluid to the blood. 358
Edema occurs when too much interstitial fluid
accumulates. 359
10.5 Veins 360
Venules communicate chemically with nearby
arterioles. 360
Veins serve as a blood reservoir and as passageways back
to the heart. 360
Venous return is enhanced by several extrinsic
factors. 361
10.6 Blood Pressure 365
Blood pressure is regulated by controlling cardiac output,
total peripheral resistance, and blood volume. 365
The baroreceptor reflex is a short-term mechanism for
regulating blood pressure. 367
Other reflexes and responses influence blood
pressure. 369
Hypertension is a national public-health problem, but its
causes are largely unknown. 369
A Closer Look at Exercise Physiology: The Body Gets a Jump
on Jogging: Cardiovascular Changes during Exercise 370
Concepts, Challenges, and Controversies: The Ups (Causes)
and Downs (Treatments) of Hypertension 372
Orthostatic hypotension results from transient inadequate
sympathetic activity. 374
Circulatory shock can become irreversible. 374
Homeostasis: Chapter
in Perspective 377
Review Exercises 377
Chapter 11 | The Blood 380
Homeostasis Highlights 380
11.1 Plasma 381
The hematocrit is the packed cell volume of blood; the rest
of the volume is plasma. 381
Plasma water is a transport medium for many inorganic
and organic substances. 381
Many of the functions of plasma are carried out by plasma
proteins. 381
11.2 Erythrocytes 383
Erythrocytes are well designed for their main function of
O2 transport in the blood. 383
The bone marrow continuously replaces worn-out
erythrocytes. 384
Erythropoiesis is controlled by erythropoietin from the
kidneys. 385
A Closer Look at Exercise Physiology: Blood Doping: Is More
of a Good Thing Better? 386
Anemia can be caused by a variety of disorders. 386
Polycythemia is an excess of circulating erythrocytes. 388
Blood types depend on surface antigens on
erythrocytes. 388
Concepts, Challenges, and Controversies: In Search of a
Blood Substitute 390
11.3 Leukocytes 392
Leukocytes primarily function as defense agents outside
the blood. 392
There are five types of leukocytes. 392
Leukocytes are produced at varying rates depending on
the body’s changing needs. 393
11.4 Platelets and Hemostasis 395
Platelets are cell fragments shed from
megakaryocytes. 395
Hemostasis prevents blood loss from damaged small
vessels. 395
Vascular spasm reduces blood flow through an injured
vessel. 395
Platelets aggregate to form a plug at a vessel injury. 395
Clot formation results from a triggered chain reaction
involving plasma clotting factors. 397
Fibrinolytic plasmin dissolves clots. 399
Inappropriate clotting produces thromboembolism. 399
Hemophilia is the primary condition that produces
excessive bleeding. 400
Homeostasis: Chapter
in Perspective 400
Review Exercises 401
Chapter 12 | Body Defenses 404
Homeostasis Highlights 404
12.1 Immune System: Targets, Effectors,
Components 405
Pathogenic bacteria and viruses are the major targets of
the immune system. 405
Leukocytes are the effector cells of the immune
system. 405
Immune responses may be either innate and nonspecific or
adaptive and specific. 406
12.2 Innate Immunity 408
Inflammation is a nonspecific response to foreign invasion
or tissue damage. 408
Inflammation is an underlying culprit in many common,
chronic illnesses. 412
Nonsteroidal anti-inflammatory drugs and glucocorticoids
suppress inflammation. 412
Interferon transiently inhibits multiplication of viruses in
most cells. 412
Natural killer cells destroy virus-infected cells and cancer
cells on first exposure to them. 413
The complement system punches holes in
microorganisms. 413
Newly discovered immune cells straddle innate and
adaptive defenses. 415

12.3 Adaptive Immunity: General Concepts 415
Adaptive immune responses include antibody-mediated
immunity and cell-mediated immunity. 415
An antigen induces an immune response against
itself. 416
12.4 B Lymphocytes: Antibody-Mediated
Immunity 416
The antigens to which B cells respond can be
T-independent or T-dependent. 417
Antigens stimulate B cells to convert into plasma cells that
produce antibodies. 417
Antibodies are Y shaped and classified according to
properties of their tail portion. 417
Antibodies largely amplify innate immune responses to
promote antigen destruction. 418
Clonal selection accounts for the specificity of antibody
production. 420
Selected clones differentiate into active plasma cells and
dormant memory cells. 420
Active immunity is self-generated; passive immunity is
“borrowed.” 421
The huge repertoire of B cells is built by reshuffling a small
set of gene fragments. 421
Concepts, Challenges, and Controversies: Vaccination: A
Victory Over Many Dreaded Diseases 422
12.5 T Lymphocytes: Cell-Mediated Immunity 422
T cells bind directly with their targets. 423
The three types of T cells are cytotoxic, helper, and
regulatory T cells. 423
Cytotoxic T cells secrete chemicals that destroy target
cells. 423
Helper T cells secrete chemicals that amplify the activity of
other immune cells. 425
Regulatory T cells suppress immune responses. 427
T cells respond only to antigens presented to them by
antigen-presenting cells. 427
The major histocompatibility complex is the code for selfantigens.
The immune system is normally tolerant of selfantigens.
Autoimmune diseases arise from loss of tolerance to
specific self-antigens. 432
An interplay among immune cells and interferon defends
against cancer. 432
A regulatory loop links the immune system with the
nervous and endocrine systems. 434
A Closer Look at Exercise Physiology: Exercise: A Help or
Hindrance to Immune Defense? 435
12.6 Immune Diseases 435
Immunodeficiency diseases result from insufficient
immune responses. 435
Allergies are inappropriate immune attacks against
harmless environmental substances. 436
12.7 External Defenses 438
The skin consists of an outer protective epidermis and an
inner, connective tissue dermis. 439
Specialized cells in the epidermis produce melanin,
keratin, and vitamin D and participate in immune
defense. 440
Protective measures within body cavities discourage
pathogen invasion into the body. 441
Homeostasis: Chapter
in Perspective 442
Review Exercises 442
Chapter 13 | The Respiratory System 445
Homeostasis Highlights 445
13.1 Respiratory Anatomy 446
The respiratory system does not participate in all steps of
respiration. 446
The respiratory airways conduct air between the
atmosphere and alveoli. 447
The gas-exchanging alveoli are thin-walled air sacs
encircled by pulmonary capillaries. 447
The lungs occupy much of the thoracic cavity. 448
A pleural sac separates each lung from the thoracic
wall. 449
13.2 Respiratory Mechanics 450
Interrelationships among pressures inside and outside the
lungs are important in ventilation. 450
The transmural pressure gradient stretches the lungs to fill
the larger thoracic cavity. 450
Airway resistance influences airflow rates. 456
Airway resistance is abnormally increased with chronic
obstructive pulmonary disease. 457
The lungs’ elastic behavior results from elastin fibers and
alveolar surface tension. 458
Pulmonary surfactant decreases surface tension and
contributes to lung stability. 458
The work of breathing normally requires only about 3% of
total energy expenditure. 460
The lungs normally operate about “half full.” 460
Alveolar ventilation is less than pulmonary ventilation
because of dead space. 462
Local controls act on bronchiolar and arteriolar smooth
muscle to match airflow to blood flow. 465
13.3 Gas Exchange 466
Gases move down partial pressure gradients. 466
O2 enters and CO2 leaves the blood in the lungs down
partial pressure gradients. 468
Factors other than the partial pressure gradient influence
the rate of gas transfer. 468
Gas exchange across the systemic capillaries also occurs
down partial pressure gradients. 471

13.4 Gas Transport 471
Most O2 in the blood is transported bound to
hemoglobin. 471
The PO2 is the primary factor determining the percent
hemoglobin saturation. 472
Hemoglobin promotes the net transfer of O2 at both the
alveolar and the tissue levels. 473
Factors at the tissue level promote unloading of O2 from
hemoglobin. 474
Hemoglobin has a much higher affinity for carbon
monoxide than for O2. 475
Most CO2 is transported in the blood as bicarbonate. 476
Various respiratory states are characterized by abnormal
blood-gas levels. 477
13.5 Control of Respiration 479
Respiratory centers in the brain stem establish a rhythmic
breathing pattern. 479
Concepts, Challenges, and Controversies: Effects of Heights
and Depths on the Body 480
Ventilation magnitude is adjusted in response to three
chemical factors: PO2, PCO2, and H1. 481
Decreased arterial PO2 increases ventilation only as an
emergency mechanism. 482
CO2-generated H1 in the brain is normally the main
regulator of ventilation. 483
Adjustments in ventilation in response to changes in
arterial H1 are important in acid–base balance. 484
Exercise profoundly increases ventilation by unclear
mechanisms. 485
Ventilation can be influenced by factors unrelated to the
need for gas exchange. 486
During apnea, a person “forgets to breathe”; during
dyspnea, a person feels “short of breath.” 486
A Closer Look at Exercise Physiology: How to Find Out How
Much Work You’re Capable of Doing 487
Homeostasis: Chapter
in Perspective 448
Review Exercises 448
Chapter 14 | The Urinary System 491
Homeostasis Highlights 491
14.1 Kidneys: Functions, Anatomy, and Basic
Processes 492
The kidneys perform a variety of functions aimed at
maintaining homeostasis. 492
The kidneys form urine; the rest of the urinary system
carries it to the outside. 492
The nephron is the functional unit of the kidney. 493
The three basic renal processes are glomerular filtration,
tubular reabsorption, and tubular secretion. 496
14.2 Glomerular Filtration 498
The glomerular membrane is considerably more permeable
than capillaries elsewhere. 498
A Closer Look at Exercise Physiology: When Protein in the
Urine Does Not Mean Kidney Disease 499
Glomerular capillary blood pressure is the major force that
causes glomerular filtration. 499
Changes in GFR result mainly from changes in glomerular
capillary blood pressure. 500
The GFR can be influenced by changes in the filtration
coefficient. 504
The kidneys normally receive 20% to 25% of the cardiac
output. 504
14.3 Tubular Reabsorption 505
Tubular reabsorption is tremendous, highly selective, and
variable. 505
Tubular reabsorption involves transepithelial
transport. 505
Na1 reabsorption depends on the Na1–K1 ATPase pump
in the basolateral membrane. 506
Aldosterone stimulates Na1 reabsorption in the distal and
collecting tubules. 507
The natriuretic peptides inhibit Na1 reabsorption. 509
Glucose and amino acids are reabsorbed by
Na1-dependent secondary active transport. 510
In general, actively reabsorbed substances exhibit a tubular
maximum. 510
Glucose is an actively reabsorbed substance not regulated
by the kidneys. 511
Phosphate is an actively reabsorbed substance regulated by
the kidneys. 512
Active Na1 reabsorption is responsible for passive
reabsorption of Cl2, H2O, and urea. 512
In general, unwanted waste products are not
reabsorbed. 514
14.4 Tubular Secretion 514
Hydrogen ion secretion is important in acid–base
balance. 514
Potassium ion secretion is controlled by aldosterone. 514
Organic anion and cation secretion hastens elimination of
foreign compounds. 516
14.5 Urine Excretion and Plasma Clearance 517
Plasma clearance is the volume of plasma cleared of a
particular substance per minute. 517
Clearance rates for inulin and PAH can be used to
determine the filtration fraction. 520
The kidneys can excrete urine of varying concentrations
depending on body needs. 520
Long Henle’s loops establish the vertical osmotic gradient
by countercurrent multiplication. 521
Vasopressin controls variable H2O reabsorption in the final
tubular segments. 523
The vasa recta preserve the vertical osmotic gradient by
countercurrent exchange. 526
Water reabsorption is only partially linked to solute
reabsorption. 527
Renal failure has wide-ranging consequences. 527
Urine is temporarily stored in the bladder, from which it is
emptied by micturition. 528

Concepts, Challenges, and Controversies: Dialysis: Cellophane
Tubing or Abdominal Lining as an Artificial Kidney 530
Homeostasis: Chapter
in Perspective 532
Review Exercises 533
Chapter 15 | Fluid and Acid–Base
Balance 535
Homeostasis Highlights 535
15.1 Balance Concept 536
The internal pool of a substance is the amount of that
substance in the ECF. 536
To maintain stable balance of an ECF constituent, its input
must equal its output. 536
15.2 Fluid Balance 537
Body water is distributed between the ICF and the ECF
compartments. 537
Plasma and interstitial fluid are similar in composition, but
ECF and ICF differ markedly. 538
Fluid balance is maintained by regulating ECF volume and
osmolarity. 538
Control of ECF volume is important in the long-term
regulation of blood pressure. 539
Control of salt balance is primarily important in regulating
ECF volume. 539
Controlling ECF osmolarity prevents changes in ICF
volume. 540
During ECF hypertonicity, cells shrink as H2O leaves
them. 541
A Closer Look at Exercise Physiology: A Potentially Fatal
Clash: When Exercising Muscles and Cooling Mechanisms
Compete for an Inadequate Plasma Volume 542
During ECF hypotonicity, the cells swell as H2O enters
them. 543
No water moves into or out of cells during an ECF isotonic
fluid gain or loss. 543
Vasopressin control of free H2O balance is important in
regulating ECF osmolarity. 543
Vasopressin secretion and thirst are largely triggered
simultaneously. 545
15.3 Acid–Base Balance 547
Acids liberate free hydrogen ions, whereas bases accept
them. 547
The pH designation is used to express [H1]. 548
Fluctuations in [H1] alter nerve, enzyme, and K1
activity. 549
Hydrogen ions are continually added to the body fluids as
a result of metabolic activities. 549
Chemical buffer systems minimize changes in pH by
binding with or yielding free H1. 550
The H2CO3:HCO3
2 buffer pair is the primary ECF buffer
for noncarbonic acids. 551
The protein buffer system is primarily important
intracellularly. 552
The hemoglobin buffer system buffers H1 generated from
CO2. 552
The phosphate buffer system is an important urinary
buffer. 552
Chemical buffer systems act as the first line of defense
against changes in [H1]. 553
The respiratory system regulates [H1] by controlling the
rate of CO2 removal. 553
The respiratory system serves as the second line of defense
against changes in [H1]. 553
The kidneys adjust their rate of H1 excretion by varying
the extent of H1 secretion. 554
The kidneys conserve or excrete HCO3
2 depending on the
plasma [H1]. 555
The kidneys secrete ammonia during acidosis to buffer
secreted H1. 558
The kidneys are a powerful third line of defense against
changes in [H1]. 558
Acid–base imbalances can arise from either respiratory or
metabolic disturbances. 558
Respiratory acidosis arises from an increase in
[CO2]. 559
Respiratory alkalosis arises from a decrease in [CO2]. 559
Metabolic acidosis is associated with a fall in
2]. 561
Metabolic alkalosis is associated with an elevation in
2]. 561
Homeostasis: Chapter
in Perspective 563
Review Exercises 563
Chapter 16 | The Digestive System 565
Homeostasis Highlights 565
16.1 General Aspects of Digestion 566
The digestive system performs four basic digestive
processes. 566
The digestive tract and accessory digestive organs make up
the digestive system. 569
The digestive tract wall has four layers. 570
Regulation of digestive function is complex and
synergistic. 571
Receptor activation alters digestive activity through neural
and hormonal pathways. 572
16.2 Mouth 573
The oral cavity is the entrance to the digestive tract. 573
The teeth mechanically break down food. 574
Saliva begins carbohydrate digestion and helps swallowing,
speech, taste, and oral health. 574
Salivary secretion is continuous and can be reflexly
increased. 575
Digestion in the mouth is minimal; no absorption of
nutrients occurs. 575

16.3 Pharynx and Esophagus 575
Swallowing is a sequentially programmed all-or-none
reflex. 576
During swallowing, food is prevented from entering the
wrong passageways. 576
The pharyngoesophageal sphincter prevents air from
entering the digestive tract. 576
Peristaltic waves push food through the esophagus. 576
The gastroesophageal sphincter prevents reflux of gastric
contents. 578
Esophageal secretion is entirely protective. 578
16.4 Stomach 578
The stomach stores food and begins protein
digestion. 578
Gastric filling involves receptive relaxation. 579
Gastric storage takes place in the body of the
stomach. 579
Gastric mixing takes place in the antrum of the
stomach. 579
Gastric emptying is largely controlled by factors in the
duodenum. 579
A Closer Look at Exercise Physiology: Pregame Meal: What’s
In and What’s Out? 581
Emotions can influence gastric motility. 582
The stomach does not actively participate in
vomiting. 582
Gastric digestive juice is secreted by glands located at the
base of gastric pits. 582
Hydrochloric acid is secreted by parietal cells and activates
pepsinogen. 584
Pepsinogen is activated to pepsin, which begins protein
digestion. 585
Mucus is protective. 585
Intrinsic factor is essential for absorption of
vitamin B12. 585
Multiple regulatory pathways influence the parietal and
chief cells. 585
Control of gastric secretion involves three phases. 586
Gastric secretion gradually decreases as food empties from
the stomach into the intestine. 587
The gastric mucosal barrier protects the stomach lining
from gastric secretions. 587
Carbohydrate digestion continues in the body of the
stomach; protein digestion begins in the antrum. 588
The stomach absorbs alcohol and aspirin but no
food. 588
16.5 Pancreatic and Biliary Secretions 588
Concepts, Challenges, and Controversies: Ulcers: When Bugs
Break the Barrier 589
The pancreas is a mixture of exocrine and endocrine
tissue. 590
The exocrine pancreas secretes digestive enzymes and an
alkaline fluid. 590
Pancreatic exocrine secretion is regulated by secretin and
CCK. 592
The liver performs various important functions, including
bile production. 593
Bile is continuously secreted by the liver and is diverted to
the gallbladder between meals. 595
Bile salts are recycled through the enterohepatic
circulation. 595
Bile salts aid fat digestion and absorption. 595
Bile salts stimulate bile secretion; CCK promotes
gallbladder emptying. 597
Bilirubin is a waste product excreted in the bile. 597
Hepatitis and cirrhosis are the most common liver
disorders. 597
16.6 Small Intestine 598
Segmentation contractions mix and slowly propel the
chyme. 598
The migrating motility complex sweeps the intestine clean
between meals. 599
The ileocecal juncture prevents contamination of the small
intestine by colonic bacteria. 599
Small-intestine secretions do not contain any digestive
enzymes. 599
The small-intestine enzymes complete digestion within the
brush-border membrane. 599
The small intestine is remarkably well adapted for its
primary role in absorption. 600
The mucosal lining experiences rapid turnover. 602
Energy-dependent Na1 absorption drives passive H2O
absorption. 603
Digested carbohydrates and proteins are both absorbed by
secondary active transport and enter the blood. 603
Digested fat is absorbed passively and enters the
lymph. 605
Vitamin absorption is largely passive. 605
Iron and calcium absorption is regulated. 605
Most absorbed nutrients immediately pass through the
liver for processing. 609
Extensive absorption by the small intestine keeps pace
with secretion. 609
Biochemical balance among the stomach, pancreas, and
small intestine is normally maintained. 609
Diarrhea results in loss of fluid and electrolytes. 610
16.7 Large Intestine 610
The large intestine is primarily a drying and storage
organ. 610
Concepts, Challenges, and Controversies: Oral Rehydration
Therapy: Sipping a Simple Solution Saves Lives 611
Haustral contractions slowly shuffle the colonic contents
back and forth. 611
Mass movements propel feces long distances. 612
Feces are eliminated by the defecation reflex. 612
Constipation occurs when the feces become too dry. 612
Intestinal gases are absorbed or expelled. 612
Large-intestine secretion is entirely protective. 613
The colon contains myriad beneficial bacteria. 613
The large intestine absorbs salt and water, converting the
luminal contents into feces. 614

16.8 Overview of the GI Hormones 614
Homeostasis: Chapter
in Perspective 615
Review Exercises 616
Chapter 17 | Energy Balance
and Temperature
Regulation 618
Homeostasis Highlights 618
17.1 Energy Balance 619
Most food energy is ultimately converted into heat in the
body. 619
The metabolic rate is the rate of energy use. 619
Energy input must equal energy output to maintain a
neutral energy balance. 621
Food intake is controlled primarily by the
hypothalamus. 621
Obesity occurs when more kilocalories are consumed than
are burned. 624
A Closer Look at Exercise Physiology: What the Scales Don’t
Tell You 625
People suffering from anorexia nervosa have a pathological
fear of gaining weight. 627
17.2 Temperature Regulation 627
Internal core temperature is homeostatically maintained at
100°F (37.8°C). 627
Heat input must balance heat output to maintain a stable
core temperature. 628
Heat exchange takes place by radiation, conduction,
convection, and evaporation. 628
Sweating is a regulated evaporative heat-loss
process. 630
The hypothalamus integrates a multitude of thermosensory
inputs. 630
Shivering is the primary involuntary means of increasing
heat production. 630
The magnitude of heat loss can be adjusted by varying the
flow of blood through the skin. 632
The hypothalamus simultaneously coordinates heatproduction
and heat-loss mechanisms. 632
During a fever, the hypothalamic thermostat is “reset” at
an elevated temperature. 633
Concepts, Challenges, and Controversies: The Extremes of
Heat and Cold Can Be Fatal 634
Hyperthermia can occur unrelated to infection. 634
Homeostasis: Chapter
in Perspective 635
Review Exercises 636
Chapter 18 | Principles of Endocrinology;
The Central Endocrine
Glands 638
Homeostasis Highlights 638
18.1 General Principles of Endocrinology 639
Hormones exert a variety of regulatory effects throughout
the body. 640
The effective plasma concentration of a hormone is
influenced by the hormone’s secretion, peripheral
conversion, transport, inactivation, and excretion. 640
The effective plasma concentration of a hormone is
normally regulated by changes in the rate of its
secretion. 641
Endocrine disorders result from hormone excess or
deficiency or decreased target-cell responsiveness. 642
The responsiveness of a target cell can be varied by
regulating the number of hormone-specific
receptors. 643
18.2 Hypothalamus and Pituitary 646
The pituitary gland consists of anterior and posterior
lobes. 646
The hypothalamus and posterior pituitary act as a unit to
secrete vasopressin and oxytocin. 646
Most anterior pituitary hormones are tropic. 647
A Closer Look at Exercise Physiology: The Endocrine
Response to the Challenge of Combined Heat and Marching
Feet 648
Hypothalamic releasing and inhibiting hormones help
regulate anterior pituitary hormone secretion. 648
Target-gland hormones inhibit hypothalamic and anterior
pituitary hormone secretion via negative feedback. 651
18.3 Endocrine Control of Growth 652
Growth depends on GH but is influenced by other
factors. 652
GH is essential for growth, but it also directly exerts
metabolic effects not related to growth. 653
GH mostly exerts its growth-promoting effects indirectly
by stimulating insulin-like growth factors. 653
GH, through IGF-I, promotes growth of soft tissues by
stimulating hypertrophy and hyperplasia. 654
Bone grows in thickness and in length by different
mechanisms, both stimulated by GH. 654
GH secretion is regulated by two hypophysiotropic
hormones. 656
Abnormal GH secretion results in aberrant growth
patterns. 657
Concepts, Challenges, and Controversies: Growth and Youth
in a Bottle? 658
Other hormones besides growth hormone are essential for
normal growth. 658

18.4 Pineal Gland and Circadian Rhythms 660
The suprachiasmatic nucleus is the master biological
clock. 660
Concepts, Challenges, and Controversies: Tinkering with Our
Biological Clocks 661
Melatonin helps keep the body’s circadian rhythms in time
with the light–dark cycle. 661
Homeostasis: Chapter
in Perspective 663
Review Exercises 663
Chapter 19 | The Peripheral Endocrine
Glands 665
Homeostasis Highlights 665
19.1 Thyroid Gland 666
The major cells that secrete thyroid hormone are organized
into colloid-filled follicles. 666
Thyroid hormone is synthesized and stored on the
thyroglobulin molecule. 666
To secrete thyroid hormone, the follicular cells phagocytize
thyroglobulin-laden colloid. 668
Thyroid hormone increases the basal metabolic rate and
exerts other effects. 668
Thyroid hormone is regulated by the hypothalamus–
pituitary–thyroid axis. 669
Abnormalities of thyroid function include both
hypothyroidism and hyperthyroidism. 669
A goiter develops when the thyroid gland is
overstimulated. 671
19.2 Adrenal Glands 672
Each adrenal gland consists of a steroid-secreting cortex
and a catecholamine-secreting medulla. 672
The adrenal cortex secretes mineralocorticoids,
glucocorticoids, and sex hormones. 672
The major effects of mineralocorticoids are on Na1 and K1
balance and blood pressure homeostasis. 674
Glucocorticoids exert metabolic effects and play a key role
in adaptation to stress. 674
Cortisol secretion is regulated by the hypothalamus–
pituitary–adrenal cortex axis. 675
The adrenal cortex secretes both male and female sex
hormones in both sexes. 676
The adrenal cortex may secrete too much or too little of
any of its hormones. 676
Concepts, Challenges and Controversies: Still a Big Question:
Why Do We Age? 678
The adrenal medulla consists of modified sympathetic
postganglionic neurons. 681
Epinephrine and norepinephrine vary in their affinities for
different receptor types. 681
Epinephrine reinforces the sympathetic nervous system
and exerts metabolic effects. 681
Epinephrine is released only on sympathetic stimulation of
the adrenal medulla. 682
19.3 Integrated Stress Response 682
The stress response is a generalized pattern of reactions to
any situation that threatens homeostasis. 683
The multifaceted stress response is coordinated by the
hypothalamus. 683
Activation of the stress response by chronic psychosocial
stressors may be harmful. 684
19.4 Endocrine Pancreas and Control of Fuel
Metabolism 685
Fuel metabolism includes anabolism, catabolism, and
interconversions among energy-rich organic
molecules. 685
Because food intake is intermittent, nutrients must be
stored for use between meals. 687
The brain must be continuously supplied with
glucose. 687
Metabolic fuels are stored during the absorptive state and
mobilized during the postabsorptive state. 688
Lesser energy sources are tapped as needed. 689
The pancreatic hormones, insulin and glucagon, are most
important in regulating fuel metabolism. 689
Insulin lowers blood glucose, fatty acid, and amino acid
levels and promotes their storage. 690
The primary stimulus for increased insulin secretion is an
increase in blood glucose. 692
The symptoms of diabetes mellitus are characteristic of an
exaggerated postabsorptive state. 693
Concepts, Challenges, and Controversies: Diabetics and
Insulin: Some Have It and Some Don’t 696
Insulin excess causes brain-starving hypoglycemia. 698
Glucagon in general opposes the actions of insulin. 698
Glucagon secretion is increased during the postabsorptive
state. 698
Insulin and glucagon work as a team to maintain blood
glucose and fatty acid levels. 699
Glucagon excess can aggravate the hyperglycemia of
diabetes mellitus. 699
Epinephrine, cortisol, and growth hormone also exert
direct metabolic effects. 699
The hypothalamus plays a role in controlling glucose
homeostasis. 701
19.5 Parathyroid Glands and Control of Calcium
Metabolism 701
Plasma Ca21 must be closely regulated to prevent changes
in neuromuscular excitability. 701
Control of Ca21 metabolism includes regulation of both
Ca21 homeostasis and Ca21 balance. 702
Parathyroid hormone raises free plasma Ca21, a life-saving
effect. 702
Bone continuously undergoes remodeling. 703
Mechanical stress favors bone deposition. 704
PTH raises plasma Ca21 by withdrawing Ca21 from the
bone bank. 704
PTH’s immediate effect is to promote transfer of Ca21
from bone fluid into plasma. 704

PTH’s chronic effect is to promote localized dissolution of
bone to release Ca21 into plasma. 705
A Closer Look at Exercise Physiology: Osteoporosis: The Bane
of Brittle Bones 706
PTH acts on the kidneys to conserve Ca21 and eliminate

  1. 706
    PTH indirectly promotes absorption of Ca21 and PO4
    32 by
    the intestine. 708
    The primary regulator of PTH secretion is plasma
    concentration of free Ca21. 708
    Calcitonin lowers plasma Ca21 concentration but is not
    important in the normal control of Ca21
    metabolism. 708
    Vitamin D is actually a hormone that increases Ca21
    absorption in the intestine. 709
    Phosphate metabolism is controlled by the same
    mechanisms that regulate Ca21 metabolism. 710
    Disorders in Ca21 metabolism may arise from abnormal
    levels of PTH or vitamin D. 712
    Homeostasis: Chapter
    in Perspective 712
    Review Exercises 713
    Chapter 20 | The Reproductive
    System 715
    Homeostasis Highlights 715
    20.1 Uniqueness of the Reproductive System 716
    Unique among body systems, the reproductive system
    does not contribute to homeostasis but plays other
    roles. 716
    The reproductive system includes the gonads, reproductive
    tract, and accessory sex glands, all of which differ in males
    and females. 716
    Reproductive cells each contain a half set of
    chromosomes. 718
    Gametogenesis is accomplished by meiosis, resulting in
    genetically unique sperm and ova. 718
    The sex of an individual is determined by the combination
    of sex chromosomes. 718
    Sexual differentiation along male or female lines depends
    on the presence or absence of masculinizing
    determinants. 721
    20.2 Male Reproductive Physiology 723
    The scrotal location of the testes provides a cooler
    environment for spermatogenesis. 723
    The testicular Leydig cells secrete masculinizing
    testosterone. 725
    Spermatogenesis yields an abundance of highly specialized,
    mobile sperm. 726
    Throughout their development, sperm remain intimately
    associated with Sertoli cells. 728
    LH and FSH from the anterior pituitary control
    testosterone secretion and spermatogenesis. 729
    GnRH activity increases at puberty. 730
    The reproductive tract stores and concentrates sperm and
    increases their fertility. 730
    The accessory sex glands contribute the bulk of the
    semen. 731
    20.3 Sexual Intercourse between Males and
    Females 732
    The male sex act is characterized by erection and
    ejaculation. 732
    Erection is accomplished by penis vasocongestion. 732
    Ejaculation includes emission and expulsion. 734
    Orgasm and resolution complete the sexual response
    cycle. 734
    Volume and sperm content of the ejaculate vary. 735
    The female sexual cycle is similar to the male cycle. 735
    Concepts, Challenges, and Controversies: Environmental
    “Estrogens”: Bad News for the Reproductive System 736
    20.4 Female Reproductive Physiology 736
    Complex cycling characterizes female reproductive
    physiology. 736
    The steps of gametogenesis are the same in both sexes, but
    the timing and outcome differ sharply. 738
    The ovarian cycle consists of alternating follicular and
    luteal phases. 741
    The follicular phase is characterized by development of
    maturing follicles. 741
    The luteal phase is characterized by the presence of a
    corpus luteum. 744
    The ovarian cycle is regulated by complex hormonal
    interactions. 744
    Cyclic uterine changes are caused by hormonal changes
    during the ovarian cycle. 749
    A Closer Look at Exercise Physiology: Menstrual Irregularities:
    When Cyclists and Other Female Athletes Do Not Cycle 751
    Fluctuating estrogen and progesterone levels produce
    cyclical changes in cervical mucus. 751
    Pubertal changes in females are similar to those in
    males. 752
    Menopause is unique to females. 752
    The oviduct is the site of fertilization. 752
    The blastocyst implants in the endometrium by means of
    its trophoblastic enzymes. 755
    The placenta is the organ of exchange between maternal
    and fetal blood. 757
    Concepts, Challenges, and Controversies: The Ways and
    Means of Contraception 758
    Hormones secreted by the placenta play a critical role in
    maintaining pregnancy. 761
    Maternal body systems respond to the increased demands
    of gestation. 763
    Changes during late gestation prepare for
    parturition. 763
    Scientists are closing in on the factors that trigger the
    onset of parturition. 764
    Parturition is accomplished by a positive-feedback
    cycle. 766

Lactation requires multiple hormonal inputs. 767
Breast-feeding is advantageous to both the infant and the
mother. 770
The end is a new beginning. 770
Homeostasis: Chapter
in Perspective 771
Review Exercises 771
Appendix A
A Review of Chemical Principles A-1
Appendix B
Text References to Exercise Physiology A-16
Appendix C
Answers A-19
Glossary G-1
Index I-1

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