This document is from Chapter 1 of the Textbook of Medical Physiology, 11th Edition. It provides an overview of physiology and homeostasis. Key points covered include: - Physiology is the study of body function and processes at the cellular, tissue, organ, and organ system levels. - The human body is made up of cells organized into tissues, organs, and organ systems that work together through regulation and integration. - Homeostasis refers to maintaining stable internal conditions and involves feedback control systems at multiple levels. - Examples of feedback control discussed include the baroreceptor reflex maintaining blood pressure and the potential for positive feedback in hemorrhagic shock.

1. U N I T I
Textbook of Medical Physiology, 11th Edition
GUYTON & HALL
Copyright © 2006 by Elsevier, Inc.
Chapter 1:
Functional Organization of the Human Body
and Control of the “Internal Environment”
Slides by John E. Hall, Ph.D.

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Physiology
The science that is concerned with the function
of the living organism and its parts, and of
the physical and chemical processes involved.
• Human Physiology

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• The study of disordered body
function (i.e. disease)
• The basis for clinical medicine
Pathophysiology

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The Human Body - A Complex
Society of Differentiated Cells
• Cells: the basic structural and functional unit
(~ 100 trillion)
• Tissues: (e.g. muscles, epithelial, nervous )
• Organs: (e.g. kidney, heart, liver, pancreas)
• Organ systems: (e.g. cardiovascular, urinary)

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Regulation and Integration
• Exists at all levels of organization
• Cells: e.g., genes, operons, repressor proteins,
transcription factors, membrane
transport
• Tissues: e.g., autacoids, paracrines
• Organ systems: e.g., nervous and endocrine
systems

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Homeostasis
The maintenance of a stable
“ milieu interieur”
Claude Bernard (1813 - 1878)

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Figure 1-1;
Guyton & Hall
General Organization
of the Circulatory
System

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Figure 1-2; Guyton & Hall
Exchange Between the Capillaries
and Interstitial Fluid

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Feedback Control
• Negative feedback: promotes stability
• Feed-forward: anticipates change
• Positive feedback: promotes a change
in one direction, instability, disease

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Negative Feedback Control of Arterial
Pressure Promotes Stability
Art. Pressure Sympathetic
Activity
Heart Rate
Vasoconstriction

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Baroreceptor Reflex :
Negative Feedback System - Promotes Stability
Blood vessels,
Heart
Baroreceptors
Set-point
Error signal
Vasomotor
Centers
Sympathetic
System
Effectors
Blood
Pressure
Sensor
Controlled
Variable
+

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Cardiopulmonary Reflexes:
Feed-Forward Control of Blood Pressure –
Anticipates a Change
Blood vessels,
Heart
Baroreceptors
Error signal
Vasomotor
Centers
Sympathetic
System
Effectors
Blood
Pressure
Sensor
Controlled
Variable
Set-point
Cardiopulmonary
Receptors
Cardiopulmonary
Pressures
+

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Feedback Gain
A measure of the effectiveness of a feedback system
Gain =
Correction
Error

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What is the feedback gain in this example ?
Hemorrhage 1.5 liters
100
50
75
Arterial Pressure
feedback
“correction”
= - 25
“ error ”= + 25
Gain =
Correction
Error
=
- 25
25
= - 1.0

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Feedback and Feed-Forward Control
• Negative feedback: promotes stability
• Feed-forward: anticipates change
• Positive feedback: promotes a change
in one direction, instability, disease

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Positive Feedback of Hemorrhagic Shock
Figure 1-3;
Guyton & Hall

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Hemorrhagic Shock:
Positive Feedback
Severe Hemorrhage
Venous Return
Cardiac Output
Blood Pressure
Coronary Blood Flow
Cardiac Contractility
+

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Action Potential:
Positive Feedback
Cell Depolarization
Cell Na Permeability
Na Influx
Cell Membrane Potential
+