Unit 4 (Feedback)

topic 5

Set points

• Values for various physiological conditions that the body tries to maintain

• Has a normal range for which it can fluctuate (ex. body temperatures)

Homeostasis

The state of relatively stable internal conditions (balance)

• Organisms detect and respond to a stimulus

• The body maintains homeostasis through feedback loops

Stimulus

A variable that will cause a response

Receptor/sensor

Sensory organs that detect a stimulus.

• This information is sent to the control center (brain)

Effector

Muscle or gland that will respond

Responses

Changes (increases or decreases) that effect the stimulus

Negative Feedback

• Most common feedback mechanism

• Reduces the effect of the stimulus

• Ex. Blood sugar, sweat, breathing rate

Positive Feedback

• Thermogenesis: Endotherms regulate their body temp through activity and shivering.

• Some mammals use non-shivering thermogenesis to generate heat (increase in metabolic activity produces heat instead of ATP)

• Babies and hibernating animals use brown fat to produce heat

• Increases effect of the stimulus

• Ex. Childbirth, blood clotting, fruit ripening

Homeostasis Imbalances CAUSES

• genetic disorders

• drug or alcohol abuse

• intolerable conditions (extreme heat/cold)

Disease

When the body is unable to maintain homeostasis

• Cancer: The body cannot regulate cell growth

• Diabetes: The body cannot regulate blood glucose levels

Cell signaling as a Means of Homeostasis

• In order to maintain homeostasis, the cells in a multicellular organism must be able to communicate

• Communication occurs through signal transduction pathways