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David Sadava, David M. Hillis,
H. Craig Heller, May R. Berenbaum
La nuova
biologia.blu
Anatomia e fisiologia dei viventi S
Physiology, Homeostasis, and
Temperature Regulation
What Are the Relationships between Cells, Tissues, and Organs?
Physiological systems are made up of organs that
serve specific functions, e.g., heart, lungs, kidneys.
Organs are made up of tissues—assemblages of
similar cells.
Organs consist of more than one type of tissue.
Four types of tissue:
•Epithelial
•Muscle
•Connective
•Nervous
What Are the Relationships between Cells, Tissues, and Organs?
Epithelial tissues: sheets of tightly connected cells
that create boundaries between the inside and the
outside of the body.
Skin, blood vessel linings, ducts and tubules, gut lining.
Controls movement of molecules between body
compartments by selective transport.
What Are the Relationships between Cells, Tissues, and Organs?
Epithelial cells have many specialized roles:
• Secretion of hormones, milk, mucus, digestive
enzymes, and sweat
• Some have cilia that move substances over surfaces
or through tubes
• Some provide information to the nervous system
(e.g., smell and taste receptors)
What Are the Relationships between Cells, Tissues, and Organs?
Muscle tissues consist of elongated cells with protein
filaments called actin and myosin that work together to
generate force and cause movement.
There are three types of muscle tissues:
•Skeletal muscle—attached to bones; responsible for
locomotion and movement
•Cardiac muscle makes up the heart; responsible for
heartbeat and blood flow
•Smooth muscle makes up the walls of many organs
(e.g., gut, bladder, blood vessels)
Muscle Cells Contain Protein Filaments
What Are the Relationships between Cells, Tissues, and Organs?
Connective tissues: cells are dispersed in an
extracellular matrix secreted by the cells.
The matrix varies, but protein fibers are always
present:
• Collagen is dominant— fibers are strong and
resistant to stretch, strengthens skin and connections
between muscles and bones;
• Elastin stretches and recoils— abundant in tissues
that are regularly stretched (e.g., lungs, arteries).
Connective Tissues
• Cartilage and bone provide firm structural support
• Blood consists of cells dispersed in a liquid
extracellular matrix, the blood plasma
• Adipose tissue stores lipids, cushions organs, and
reduces heat loss
What Are the Relationships between Cells, Tissues, and Organs?
Nervous tissues contain two basic cell types:
• Neurons encode and conduct information as
electrical signals to other cells.
Chemical signals from a neuron are received by target cells, which can be
other neurons, muscle cells, or cells secreting hormones.
• Glial cells, or glia, provide a variety of support
functions for neurons.
One type creates a barrier between blood vessels and neural tissue that
protects the nervous system from potentially harmful chemicals in the
blood.
Tissues Form Organs
Organs consist of more than one
tissue type; most contain all four
types.
The wall of the gut is an example.
Individual organs are part
of an organ system, a
group of organs that work
together (e.g., the digestive
system).
Organizational hierarchy:
Cells → Tissues → Organs
→ Organ systems→
Individual organism
How Do Multicellular Animals Supply the Needs of Their Cells?
Homeostasis is the maintenance of stable physical
and biochemical conditions in the internal
environment.
If homeostasis is compromised, cells can be damaged
and can die.
Maintenance of homeostasis is a central theme of
physiology.
How Do Multicellular Animals Supply the Needs of Their Cells?
Physiological systems are controlled by actions of the
nervous and endocrine systems.
To regulate these systems
and maintain homeostasis,
information are required.
A thermostat is an analogy
for this.
How Do Multicellular Animals Supply the Needs of Their Cells?
Components of physiological systems:
Effectors effect changes in the internal environment,
(e.g., muscles).
Effectors are controlled systems because they are
controlled by neural or hormonal signals from
regulatory systems.
How Do Multicellular Animals Supply the Needs of Their Cells?
Regulatory systems:
• Obtain, integrate, and process information
• Issue commands to controlled systems
• Have sensors to provide feedback information to
compare to set points
How Do Multicellular Animals Supply the Needs of Their Cells?
Types of information necessary for physiological
systems:
• Set point—a reference point
• Feedback information—information that is
compared to the set point
• Error signal—any difference between the set point
and feedback information
How Do Multicellular Animals Supply the Needs of Their Cells?
Negative feedback is information that corrects an
error signal.
Whatever force is pushing the system away from its set
point must be “negated”.
Positive feedback amplifies a response and increases
deviation from a set point.
Responses tend to reach a limit and terminate rapidly.
Examples: sexual behavior and the birth process.
How Do Animals Alter Their Heat Exchange with the Environment?
Both ectotherms and endotherms can influence body
temperature by altering four avenues of heat
exchange:
• Radiation—heat transfer via infrared radiation
• Convection—heat transfer through a surrounding
medium
• Conduction—heat transfer by direct contact
• Evaporation—heat transfer through evaporation of
water from a surface (e.g., sweating)
Animals Exchange Heat with the Environment
How Do Animals Alter Their Heat Exchange with the Environment?
Controlling blood flow to the skin helps maintain body
temperature.
Increased blood flow to the skin increases heat loss
and lowers body temperature.
Constriction of blood vessels to the skin results in less
heat loss.
In mammals the hypothalamus in the brain is the
major control center for temperature.
Experiments show that cooling of the hypothalamus
causes restriction of skin blood vessels and increases
metabolic heat production.
How Do Endotherms Regulate Their Body Temperatures?
Fever is an adaptive response that helps the body fight
pathogens.
Fever is a rise in body temperature caused by
pyrogens.
Pyrogens can be exogenous—foreign proteins (e.g.,
bacteria and viruses) or endogenous—produced by
immune cells in response to infection.
How Do Endotherms Regulate Their Body Temperatures?
Pyrogens cause a rise in the hypothalamic set point.
Shivering and getting under blankets results in
increase of body temperature to match the new set
point.
Moderate fevers help the body fight infections, but
extreme fevers can be dangerous.
Adapted from
Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014
Inc. All rights reserved