Homeostasis

Topics: Feedback, Negative feedback, Homeostasis Pages: 12 (803 words) Published: May 20, 2015
Homeostasis
A condition in which the internal
environment of the body remains
relatively constant despite changes in
the external environment. Examples
would be the maintenance of body
temperature and levels of glucose in
the blood

Homeostatic mechanisms are designed to reestablish
homeostasis when there is an imbalance.
The Home Heating System
1. When the temperature of a room decreases below a set point, the thermostat electrically starts the furnace.
2. As the temperature of the room rises to the set point, the thermostat shuts down the furnace.
3. As the room cools, step one is repeated.

There are three components to this system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor and sends a message to the Effector.
3. The Effector which receives the message from the control center and produces the response which reestablishes homeostasis.

There are three components to a homeostatic system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor and sends a message to adjust the stress.
3. The Effector which receives the message from the control
center and produces the response which reestablishes
homeostasis

It should be noticed that
1. the heat produced by the furnace shuts the furnace down
through the thermostat.
2. the original stress is reduced, i.e., the room warms up.

Homeostatic mechanisms that show these two
characteristics are operating by negative feedback

Homeostatic Regulation of Body Temperature through
Negative Feedback
Hyperthermia
Stress

Heat receptors
in the skin

Stress is reduced
shutting down
mechanism
Perspiration
evaporates
cooling the skin
Effect

Hypothalamus
Control Center

Sensors

Increased
activity of
sweat glands
Increased blood
flow to the skin
Effectors

Homeostasis Using a Neural
Pathway

Control center

Many homeostatic
mechanisms use a
nerve pathway in which
to produce their effects.
These pathways
involve an afferent path
which brings sensory
messages into the
brain and an efferent
path which carries
outgoing nerve
messages to effectors.

Homeostatic Regulation of Blood Sugar through
Negative Feedback
Hyperglycemia
Stress

Pancreas-beta cells
Sensor and Control center

Stress is reduced
shutting down
mechanism

Blood glucose
is reduced

Liver and Muscle cells
take up glucose from
the blood
Effectors

Insulin is released
into blood

Negative Feedback Via a Hormonal Pathway
Regulation of Blood Sugar
Hormones play an important role in many homeostatic pathways. Hormones are produced by endocrine glands. They enter the
blood after being produced and travel throughout the body.
However, hormones have their effect on specific target tissues.

Positive Feedback Mechanisms
Homeostatic systems utilizing positive feedback exhibit two primary characteristics:
1. Time limitation – Processes in the body that must be completed within a constrained time frame are usually modified by positive feedback. 2. Intensification of stress – During a positive feedback process, the initial imbalance or stress is intensified rather than reduced as it is in negative feedback.

Typical Positive Feedback Process

Stress

Intensifies

Sensor

Control Center

Effector

Homeostatic Regulation of Child Birth through
Positive Feedback
Pressure of Fetus on
the Uterine Wall

Nerve endings in the uterine
wall carry afferent messages
to the Hypothalamus

Intensifies

Increasing strength of
uterine contractions

Production and Release
of Oxytocin into the
Blood

The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk
letdown and blood clotting.

Feedback in Coagulation

Positive feedback “mini-loops” are built into pathway to speed up production of chemicals needed to form the clot. Entire...
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