This document summarizes key concepts from Chapter 1 of the Textbook of Medical Physiology. It defines physiology and pathophysiology. It describes the human body as having different levels of organization from cells to organ systems. It explains how homeostasis is maintained through regulation and integration at all levels via negative feedback, feed-forward, and positive feedback control. Specific examples are given of negative feedback control of blood pressure and positive feedback in hemorrhagic shock and action potentials.

1. UNIT I
Textbook of Medical Physiology, 11th Edition
Chapter 1:
Functional Organization of the Human Body
and Control of the “Internal Environment”
Slides by John E. Hall, Ph.D.
GUYTON & HALL
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2. 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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3. Pathophysiology
• The study of disordered body
function (i.e. disease)
• The basis for clinical medicine
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4. 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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5. 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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6. Homeostasis
The maintenance of a stable
“ milieu interieur”
Claude Bernard (1813 - 1878)
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7. General Organization
of the Circulatory
System
Figure 1-1;
Guyton & Hall
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8. Exchange Between the Capillaries
and Interstitial Fluid
Figure 1-2; Guyton & Hall
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9. Feedback Control
• Negative feedback: promotes stability
• Feed-forward: anticipates change
• Positive feedback: promotes a change
in one direction, instability, disease
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10. Negative Feedback Control of Arterial
Pressure Promotes Stability
Art. Pressure Sympathetic
Activity
Heart Rate
Vasoconstriction
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11. Baroreceptor Reflex :
Negative Feedback System - Promotes Stability
Set-point
Error signal Effectors
+
Vasomotor Sympathetic Blood vessels,
Centers System Heart
Controlled
Sensor Variable
Blood
Baroreceptors
Pressure
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12. Cardiopulmonary Reflexes:
Feed-Forward Control of Blood Pressure –
Anticipates a Change
Cardiopulmonary Cardiopulmonary
Receptors Pressures
Set-point
+ Error signal Effectors
Vasomotor Sympathetic Blood vessels,
Centers System Heart
Controlled
Sensor Variable
Blood
Baroreceptors
Pressure
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13. Feedback Gain
A measure of the effectiveness of a feedback system
Correction
Gain =
Error
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14. What is the feedback gain in this example ?
Hemorrhage 1.5 liters
100
Arterial Pressure
“ error ”= + 25
75
feedback = - 25
50 “correction”
Correction - 25
Gain = = = - 1.0
Error 25
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15. 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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16. Positive Feedback of Hemorrhagic Shock
Figure 1-3;
Guyton & Hall
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17. Hemorrhagic Shock:
Positive Feedback
Severe Hemorrhage
Venous Return
+
Cardiac Output
Blood Pressure
Coronary Blood Flow
Cardiac Contractility
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18. Action Potential:
Positive Feedback
Cell Depolarization
+
Cell Na Permeability
Na Influx
Cell Membrane Potential
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