Elsevier's Integrated Physiology E-Book

Robert G. Carroll

• Éditeur: Mosby
• Année: 2006
• ISBN:
  9780323082914
• Sujet: Medicine
• Sous-sujet: Physiology

Each title in the new Integrated series focuses on the core knowledge in a specific basic science discipline, while linking that information to related concepts from other disciplines. Case-based questions at the end of each chapter enable you to gauge your mastery of the material, and a color-coded format allows you to quickly find the specific guidance you need. Bonus STUDENT CONSULT access - included with the text - allows you to conveniently access the book's content online · clip content to your handheld device · link to content in other STUDENT CONSULT titles · and more! These concise and user-friendly references provide crucial guidance for the early years of medical training, as well as for exam preparation.

• Includes case-based questions at the end of each chapter
• Features a colour-coded format to facilitate quick reference and promote effective retention
• Offers access to STUDENT CONSULT! At www.studentconsult.com, you'll find the complete text and illustrations of the book online, fully searchable · "Integration Links" to bonus content in other STUDENT CONSULT titles · content clipping for handheld devices · an interactive community center with a wealth of additional resources · and much more!

1

Physiology: The Regulation of Normal Body Function

CONTENTS

PHYSIOLOGY

LEVELS OF ORGANIZATION

COMMON THEMES

Common Theme 1: Movement Across Barriers

Common Theme 2: Indicator Dilution

Common Theme 3: Feedback Control

Common Theme 4: Redundant Control

Common Theme 5: Integration

Common Theme 6: Graphs, Figures, and Equations

Common Theme 7: Autonomic Nervous System

Common Theme 8: Physiologic Research

APPLICATION OF COMMON THEMES: PHYSIOLOGY OF THERMOREGULATION

TOP 5 TAKE-HOME POINTS

PHYSIOLOGY

Body function requires a stable internal environment, described by Claude Bernard as the “milieu intérieur,” in spite of a changing outside world. Homeostasis, a state of balance, is made possible by negative feedback control systems. Complex neural and hormonal regulatory systems provide control and integration of body functions. Physicians describe “normal” values for vital signs—blood pressure of 120/80 mm Hg, pulse of 72 beats/min, respiration rate of 14 breaths/min. These “normal” vital sign values reflect a body in homeostatic balance.

A stable milieu interior also requires a balance between intake and output. Intake and production will increase the amount of a compound in the body. Excretion and consumption will decrease the amount of a compound in the body. Body fluid and electrolyte composition is regulated about a set point, which involves both control of ingestion and control of excretion. Any changes in ingestion must be compensated by changes in excretion, or the body is out of balance.

Life is not always about homeostasis and balance. The body must also adapt to changing requirements, such as during exercise. Now the normal resting values are physiologically inappropriate, since an increase in muscle blood flow, cardiac output, and respiratory rate are necessary to support the increased metabolic demands associated with physical activity. Physiology is the study of adaptive adjustments to new challenges.

Life is a state of constant change. The physiology of the body alters as we age. An infant is not a small adult, and the physiology of an octogenarian is different from that of an adolescent. Chapter 16 provides a concise summary of physiologic changes in each sex across the life span.

Finally, physiology makes sense. As a student, you need to look for the organizing principles in your study of the body. There are more details and variations than can be memorized. However, if you focus on the organizing principles, the details fall into a logical sequence. Look for the big picture first—it is always correct. The details and complex interactions all support the big picture.

LEVELS OF ORGANIZATION

Medical physiology applies basic principles from chemistry, physics, and biology to the study of human life. Atoms are safely in the realm of chemistry. Physiologic study begins with molecules and continues through the interaction of the organism with its environment (Fig. 1-1).

Figure 1-1 Physiology bridges the gap between chemistry and ecology. Physiology incorporates the investigational techniques from cell biology and molecular biology as well as ecology in order to better understand the function of the human body.

Physiology is the study of normal body function. Physiology extends to the molecular level, the study of the regulation of the synthesis of biomolecules, and to the subcellular level, details of the provision of nutrients to support mitochondrial metabolism. Physiology includes cellular function, the study of the role of membrane transport, and describes organ function, including the mechanics of pressure generation by the heart. Integrative physiology is the study of the function of the organism, including the coordinated response to digestion and absorption of the nutrients in a meal.

The components of physiology are best approached as organ systems. This approach allows all aspects of one system, e.g., the circulatory system, to be discussed, emphasizing their commonalities and coordinated function.

COMMON THEMES

Common Theme 1: Movement Across Barriers

Life is characterized as a nonequilibrium steady state. The body achieves homeostatic balance—but only by expending energy derived from metabolism. Although the processes listed below appear different, they share common features. Movement results from a driving force and is opposed by some aspect of resistance (Table 1-1).

TABLE 1-1

Specific Examples of the Movement Theme

Process	Movement	Driving Force	Modulated by
Flow	Flow	Pressure gradient	Resistance (−)
Diffusion	Net flux	Concentration gradient	Permeability (+)
			Surface area (+) Distance (−)
Osmosis	Water	Particle gradient	Barrier particle permeability (−)
			Barrier water permeability (+)
Electrochemical	Current	Ionic gradient	Membrane permeability (+)
Capillary filtration	Flow	Combined pressure and oncotic gradient	Capillary surface area (+)
Transport	Secondary active	Ion gradient	Concentration gradient (−)

+, Modulators enhance the movement; –, modulators impede the movement.

Movement against a gradient requires energy. ATP is ultimately the source of energy used to move compounds against a gradient. This is important, because after the gradients are created, the concentration gradients can serve as a source of energy for other movement (e.g., secondary active transport and osmosis).

Common Theme ...