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Chapter 1

Chapter Notes for Chapter 1 of Human Physiology 5e

Biological Sciences
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Human Physiology (Fifth Edition)
Silverthorn, D. U.
Chapter 1 Introduction to Physiology
To treat disease and injury appropriately, we have to understand the human
body in its healthy state
Physiology: the study of normal functioning of a living organism and its
component parts, including all its chemical and physical properties; literal
meaning: knowledge of nature
Physiological Systems
Levels of organization: atoms -> molecules -> cells -> tissues -> organs -> organ
systems -> organisms -> populations of one species -> ecosystem of different
species -> biosphere
oPhysiology is concerned with the molecular level up to the populations of a
Cells are collections of molecules separated from the external environment by a
cell membrane
Tissues are collections of cells that carry out related functions
Physiological organ systems in the human body
oIntegumentary system: composed of the skin, forms protective boundary
between the body’s internal and external environments
oMusculoskeletal system: provides support and body movement
oRespiratory system: exchanges gases between internal and external
oDigestive system: takes up nutrients and water and eliminates wastes
oUrinary system: removes excess water and waste material
oReproductive system: produces eggs or sperm
oCirculatory system: distributes materials throughout the body by
pumping blood through vessels
oNervous and endocrine systems: coordinate body functions
oImmune system: made up of cells that are programmed to protect the
internal environment from foreign invaders
Function and Process
Function/event of a physiological system = why
Process/mechanism of a physiological system = how
Homeostasis: the ability of the body to maintain a relatively constant/stable
internal environment; key principle in physiology
Humans = large, mobile, terrestrial animals whose bodies maintain relatively
constant water content despite their dry, highly variable external environment
Most cells in our bodies are not tolerant of changes in their surroundings
Organisms that are able to survive in highly variable external environments are
doing so by keeping their internal environment relatively stable
Extracellular fluid: watery internal environment of multicellular animals that
surrounds the cells; the transition, or buffer zone, between an organisms
external environment and the intracellular fluid
When the extracellular fluid composition varies outside of its normal ranges,
mechanisms activate and the return the fluid to its normal state
Many cells depend on the constancy of the extracellular fluid to maintain normal
Our body monitors its internal state and takes action to correct disruptions that
threaten its normal function
Walter Cannon described internal secretions, which are the hormones and
other chemicals that our cells use to communicate
If the body fails to maintain homeostasis of osmolarity, temperature, pH, sodium,
etc., normal function is disrupted, and a pathological condition may result if the
body is unable to compensate
Physiology: Moving Beyond the Genome
Genome: collective term for all the genetic information contained in the DNA of a
A single genome was thought to be coded for one protein, but later researchers
found that a genome may code for many proteins
Themes In Physiology
Homeostasis and Control Systems: regulated variables (i.e. blood pressure,
blood-glucose conc., etc.) are monitored and adjusted by control systems
oControl systems have 3 parts: an input signal, a controller, and an output
Biological Energy Use: processes that occur in organisms require continuous
energy input
Structure-Function Relationships
oMolecular interactions: essential for biological function, related to
molecule structure
oCompartmentation of the body and cells: compartmentation (presence of
separate compartments) allows cells/tissues/organs to specialize and
isolate functions
oMechanical properties of cells, tissues, and organs: properties such as
compliance, elastance, strength, fluidity
Communication: cells need to communicate rapidly and efficiently, information
flow takes the form of chemical or electrical signals, mass flow the movement
of substances within and between compartments of the body made possible by a
driving force, i.e. concentration gradient