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Mechanisms of Homeostasis

Chapter 28.2

+Learning Objectives

To be able to: Define the terms negative feedback, positive feedback

and homeostasis Explain the principles of homeostasis in terms of

sensors, targets and negative/positive feedback

Homeostasis, Negative feedback, Positive feedback

Keywords:

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Maintaining the internal environment despite external changes

The following have to be maintained; Body temp Blood glucose conc. Blood salt conc. Water potential of blood Blood pressure Carbon dioxide conc.

Homeostasis is…

+Control systems in the body

SENSORS, also called receptors, gather information about condition inside and outside the body. For example, sensors in your skin detect changes in the temperature.

The body has thousands of internal sensors and other specialized sensors that detect changes in the outside world.

+Control systems in the body

CONTROL CENTER, often the brain, receives information from the sensors. It then compares this information to the ideals at which the body functions best.

When conditions move above or below a set point, the control center responds by sending messages through a communication system.

+Control systems in the body

COMMUNICATION SYSTEMS such as the nervous system and the endocrine system carry messages to all parts of the body. These messages, in the form of nerve impulses of hormones, tell targets in the body how to respond to internal or external changes.

+Control systems in the body

A TARGET is any organ, tissue or cells that changes its level of activity in response to a message.

For example, in a cold environment, a message might cause the muscles to start shivering to generate more body heat.

+Negative feedback

The reversing of a change in the internal environment Change needs to be detected Change must be signalled to other cells Response to reverse the change

The control systems in the body work together in a feedback loop. Most functions in the body are regulated by negative feedback loops.

Change in condition

Receptor

Control center

Communication system

Negative feedback pathway

Target (response)

+Positive feedback Negative feedback loops maintain homeostasis by

counteracting, or reversing, change to return conditions to their set points.

In POSITIVE FEEDBACK, a control center uses information from sensors to increase the rate of change away from the set points. This type of feedback is important whenever change is needed fast. For example, if you cut your finger, positive feedback mechanisms increase the rate of change in clotting factors in the blood until the wound is sealed. Once the injury heals, another positive feedback loop occurs as chemicals are released to dissolve the clot.

Puberty is another example of when positive feedback takes place.