CHAPTER 40 – PHYSIOLOGY, HOMEOSTASIS, AND TEMPERATURE
40.1 Why Must Animals Regulate Their Internal Environments?
-All animals need nutrients and oxygen and must eliminate carbon dioxide and other waste
products of metabolism.
Single-celled organisms meet all these needs by direct exchange with the external
An internal environment makes complex multi-cellular animals possible
Internal Environment – the physical and chemical characteristics of the extracellular fluids of
Individual cells get their nutrients from this extracellular fluid and dump their waste into
A stable internal environment makes it possible for an animal to occupy habitats that
would kill its cells if they were exposed to it directly.
-As multi-cellular organisms evolved, cells became specialized for maintaining specific
aspects of the internal environment.
-The evolution of physiological systems to maintain different aspects of the internal
environment made it possible for multi-cellular animals to become larger, thicker, more
complex, and more adaptable to external environments that are very different from the
Homeostasis – the maintenance of a steady state, such as a constant temperature or a stable
social structure, by means of physiological or behavioral feedback responses.
Essential feature of complex animals.
If a physiological system fails to function properly, homeostasis is compromised, and as a
result cells are damaged and can die.
-To avoid loss of homeostasis, physiological systems must be controlled and regulated
in response to changes in both the external and internal environments.
Homeostasis requires physiological regulation
- The activities of all physiological processes are controlled – speeded up or slowed down – by
actions of the nervous and endocrine systems.
- To regulate the internal environment, information is required.
Set point – in a regulatory system, the threshold sensitivity to the feedback stimulus.
Feedback information – information relevant to the rate of a process that can be used by a
control system to regulate that process at a particular level.
Error signal – any difference between the set point and the feedback information when they are
Suggests corrective actions.
Effectors – some components of physiological systems; they effect the changes n the internal
They are controlled systems because their activities are controlled by commands from
Regulatory Systems – a system that uses feedback information to maintain a physiological
function or parameter at an optimal level.
They obtain, process, and integrate information, then issue commands to controlled
A sensor is an important component of any regulatory system.
-It provides feedback information that is compared to the internal set point.
Negative Feedback – Information relevant to the rate of a process that can be used by a control
system to return the outcome of that process to an optimal level.
Most common use of sensory information in regulatory systems.
It is a stabilizing influence in physiological systems.
It tends to return a variable of the internal environment to the set point from which it
Positive Feedback – amplifies a response (i.e., increases the deviation from the set point).
Not as common as negative feedback.
Examples include the responses that empty body cavities, such as, urination, defecation,
sneezing, and vomiting.
Another example is sexual behavior.
Feedforward Information – information that can be used to alter the set point of a regulatory
Anticipates changes in the internal environment before that change occurs.
Physiological systems are made up of cells, tissues, and organs
-Each physiological system is composed of discrete organs, such as the liver, heart, and
kidneys that serve specific functions in the body.
These organs are made up of tissues.
Tissue – a group of similar cells organized into a functional unit; usually integrated with other
tissues to form part of an organ.
There are only four types of tissues:
They are sheets of densely packed, tightly connected epithelial cells that cover inner and
outer body surfaces.
They act as barriers and provide transport across those barriers.
They form the skin and line the hollow organs of the body, such as the gut.
Epithelial cells have many roles in the body:
-Secreting hormones, milk, mucus, digestive enzymes, or sweat.
-Some have cilia that move substances over surfaces or through tubes.
-They can provide information to the nervous system. (e.g., smell and taste receptors
are epithelial cells that detect specific chemicals.)
-They create boundaries between the inside and the outside of the body and between
-They line the blood vessels and make up various ducts and tubules.
-Important functions of epithelial cells are filtration and transportation.
-They control what molecules and ions can leave the blood to enter the internal
environment or the urine.
-They can selectively transport ions and molecules from one side of an epithelial
membrane to the other. (e.g., the absorption of nutrient molecules from the gut and
the secretion of acid into the stomach.)
The skin and the lining of the gut are examples of epithelial tissues that receive much
wear and tear.
Consist of elongated cells that can contract to generate forces and cause movement.
The most abundant tissues in the body, and when animals are active, muscles use most of
the energy produced in the body.
There are 3 types of muscle tissues:
1.Skeletal Muscle Tissue
-They mostly attach to bones.
-Responsible for locomotion and other body movements such as facial
expressions, shivering, and breathing.
-They are under both conscious and unconscious control.
2.Cardiac Muscle Tissue
-Makes up the heart.
-Responsible for the heart beat and the pumping of blood.
-They are not under conscious control, but are controlled by physiologically
All animals need nutrients and oxygen and must eliminate carbon dioxide and other waste products of metabolism. single-celled organisms meet all these needs by direct exchange with the external environment. An internal environment makes complex multi-cellular animals possible. Internal environment the physical and chemical characteristics of the extracellular fluids of the body. individual cells get their nutrients from this extracellular fluid and dump their waste into it. a stable internal environment makes it possible for an animal to occupy habitats that would kill its cells if they were exposed to it directly. As multi-cellular organisms evolved, cells became specialized for maintaining specific aspects of the internal environment. Homeostasis the maintenance of a steady state, such as a constant temperature or a stable social structure, by means of physiological or behavioral feedback responses. if a physiological system fails to function properly, homeostasis is compromised, and as a result cells are damaged and can die.