Chapter 1
Homeostasis
• Recall the concept and components of
homeostatic systems, describing how
cells, tissues, organs and organ systems
maintain important physiological set
points. This will be measured by quiz and
exam scores.
Outline
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Physiology
Levels of organization
Basic Cell function
Tissues
Body systems
Homeostasis
Physiology
• Study of body functions
• Two processes explain body functions
– Teleological
• Explanations are in terms of meeting a bodily need
– Mechanistic
• Explanations are in terms of cause and effect
sequences
– Body is viewed as a machine
Physiology is the study of body functions
• Physiologists explain body function in terms of cause-and-effect
sequences
Two approaches are used to explain events that occur in the body:
– The purpose of a body process
– The underlying mechanism
• Anatomy is the study of structure
• Physiology and anatomy are interrelated because functions depend
on structure
Structure-Function relationships of the body Examples:
• Heart receiving and pumping blood
• Teeth tearing and grinding food
Levels of Organization-Cells
Basic Cell Functions
• Obtain nutrients and oxygen from surrounding
environment
• Perform chemical reactions that provide energy for the
cell
• Eliminate carbon dioxide and other wastes to
surrounding environment
• Synthesize needed cellular components
• Control exchange of materials between cell and its
surrounding environment
• Sensing and responding to changes in surrounding
environment
• Reproduction
– Exception
• Nerve cells and muscle cells lose their ability to
reproduce during their early development
Why Study Cells?
• Stem Cell Research (pg 10)
• 5 minutes
Tissues
• Groups of cells with similar structure and
specialized function
• Four primary types of tissues
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Muscle tissue
Nervous tissue
Epithelial tissue
Connective tissue
Tissues
• Muscle tissue
– Specialized for contracting and generating force
– Three types of muscle tissue
• Skeletal muscle
– Moves the skeleton
• Cardiac muscle
– Pumps blood out of the heart
• Smooth muscle
– Encloses and controls movement of contents through
hollow tubes and organs
• Connective tissue
– Cells dispersed in a matrix
– Connects, supports, anchors tissue
Tissues
• Nervous tissue
– Consists of cells specialized for initiating and
transmitting electrical impulses
– Found in brain, spinal cord, and nerves
• Epithelial tissue
– Consists of cells specialized for exchanging
materials between the cell and its environment
– Organized into two general types of structures
• Epithelial sheets
• Secretory glands
Fig. 1-4a, p. 7
Credit: © Carolina Biological/Visuals Unlimited
Sweat gland duct in the skin. LM X5.
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Credit: © Carolina Biological/Visuals Unlimited
Simple Squamous Epithelium. LM X75.
Credit: © David Phillips/Visuals Unlimited
Microscopic technique series - Cheek cells. Phase view. LM X75.
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301193
Credit: © G.W. Willis, MD/Visuals Unlimited
Stratified squamous epithelium from mouth mucosa. H&E stain. LM X100.
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Credit: © Carolina Biological/Visuals Unlimited
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Credit: © G.W. Willis, MD/Visuals Unlimited
Human pseudostratified columnar epithelium lining the bronchus of the lung. H&E stain.
X180.
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Credit: © Carolina Biological/Visuals Unlimited
Areolar (loose) connective tissue. LM X60.
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Credit: © Dr. Fred Hossler/Visuals Unlimited
Hyaline cartilage. X64.
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Credit: © Dr. David Phillips/Visuals Unlimited
Collagen or dense connective tissue. X155.
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Credit: © Dr. Richard Kessel/Visuals Unlimited
Reticular fibers, silver preparation. X100.
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Credit: © G.W. Willis, MD/Visuals Unlimited
Human unilocular (white) fat and adipose (adult fat). H&E stain. LM X100.
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Credit: © Carolina Biological/Visuals Unlimited
Bone section showing osteocytes in lacunae arranged in concentric circles surrounding
Haversian canals. LM X75.
Organs
• Consist of two or more types of primary
tissues that function together to perform a
particular function or functions
• Example
– Stomach
• Inside of stomach lined with epithelial tissue
• Wall of stomach contains smooth muscle
• Nervous tissue in stomach controls muscle contraction
and gland secretion
• Connective tissue binds all the above tissues together
Levels of Organization-Organs
• Organs are combinations of two or more types of tissues
that function together
An example is the stomach:
– Lined with epithelial tissue
– Wall contains smooth
muscle and nervous tissues
– Connective tissue
binds various tissues together
Body Systems
• Groups of organs that perform related
functions and interact to accomplish a
common activity essential to survival of the
whole body
• Do not act in isolation from one another
• Human body has 11 systems
Body Systems
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Circulatory System
Digestive System
Respiratory System
Urinary System
Skeletal System
Muscular System
• Integumentary
System
• Immune System
• Nervous System
• Endocrine System
• Reproductive System
BODY SYSTEMS
Information from
the external
environment relayed
through the
nervous system
NERVOUS
SYSTEM
Regulate
RESPIRATORY
SYSTEM
O2
CO2
Urine containing
wastes and
excess water and
electrolytes
ENDOCRINE
SYSTEM
INTEGUMENTARY
SYSTEM
Sperm leave male
Sperm enter
female
EXTERNAL
ENVIRONMENT
Keeps internal
fluids in
HOMEOSTASIS
Keeps foreign
materials out
URINARY
SYSTEM
IMMUNE SYSTEM
Nutrients, water,
electrolytes
Feces containing
undigested food
residue
Body systems
maintain
homeostasis
DIGESTIVE
SYSTEM
REPRODUCTIVE
SYSTEM
MUSCULAR AND
SKELETAL
SYSTEM
Exchanges with
all other systems
Exchanges with
all other systems
Protects
against
foreign
invaders
Homeostasis
essential for
cell survival
Enables the
body to
interact
with the
external
environment
CELLS
CIRCULATORY SYSTEM
Cells make
up body
system
What contribution does each system make to whole body homeostasis?
Homeostasis vs. Allostasis
• Homeostasis
– ideal set point through local regulatory mechanism
• Claude Bernard 1865 and Walter Cannon 1926
– ex. Kidneys figure this out and decrease fluid output
• Allostasis:
– The brain coordinating body-wide changes often including
changes in behavior.
– “remaining stable by being variable”
– Sterling and Eyer 1988.
Sterling, P.; Eyer, J. (1988). "Allostasis: A new paradigm to explain arousal pathology". In Fisher, S.; Reason, J. T. Handbook of
life stress, cognition, and health. Chicester, NY: Wiley.
Concept of Homeostasis
• Homeostasis defined as maintenance of a relatively stable internal
environment
– Does not mean that composition, temperature, and
other characteristics are absolutely unchanging
• Homeostasis is essential for the
survival of each cell
• Each cell helps maintain the internal
• environment shared by all cells
• Factors maintained homeostatically:
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concentration of nutrients
concentration of O2 and CO2
concentration of waste products
pH
concentrations of water, salt, and other electrolytes
volume and pressure
temperature
Fluid Compartments
• The fluid inside the cell is
intracellular fluid (ICF)
• The fluid outside the cells is
extracellular fluid (ECF)
– ECF is the body’s internal
environment
• Consists of the plasma and
interstitial fluid Most body cells
are not in direct contact with the
external environment
• Cell survival depends on
maintaining a relatively stable
internal fluid environment
Homeostatic Control Systems
• In order to maintain homeostasis, control
system must be able to
– Detect deviations from normal in the internal
environment that need to be held within narrow
limits
– Integrate this information with other relevant
information
– Make appropriate adjustments in order to restore
factor to its desired value
Homeostatic Control Systems
• Control systems are grouped into two
classes
– Intrinsic controls
• Local controls that are inherent in an organ
– Extrinsic controls
• Regulatory mechanisms initiated outside an organ
• Accomplished by nervous and endocrine systems
Homeostatic Control Systems
• Feedforward
– Term used for responses made in anticipation of
a change
• Feedback
– Refers to responses made after change has been
detected
– Types of feedback systems
• Negative
• Positive
Homeostatic Control Systems
• Negative feedback system
– Primary type of homeostatic control
– Opposes initial change
– Components
• Sensor
– Monitors magnitude of a controlled variable
• Control center
– Compares sensor’s input with a set point
• Effector
– Makes a response to produce a desired effect
Homeostatic Control Systems
• Positive feedback system
– Amplifies an initial change
– Do not occur as often as negative feedback
system
– Example
• Uterine contractions become increasingly stronger until
the birth of the baby
• Pathophysiology
refers to abnormal functioning of the body
associated with disease
When a homeostatic disruption becomes so severe
that it is no longer compatible with survival, death results