Homeostasis What is homeostasis? What do we call the body when it is not in homeostasis? What is a model for homeostasis? What is a stimulus? What is the afferent and efferent pathway? What is a positive feedback loop? What is a negative feedback loop? What are examples of positive and negative feedback loops in the body?

Necessary Life Functions Maintain boundaries Movement Locomotion Movement of substances Responsiveness Ability to sense changes and react Digestion Break-down and absorption of nutrients

Necessary Life Functions Metabolism—chemical reactions within the body Produces energy Makes body structures Excretion Eliminates waste from metabolic reactions Reproduction Produces future generation Growth Increases cell size and number of cells

Homeostasis is a coordinated effort to maintain balance! Figure 1.3

Homeostasis Homeostasis—maintenance of a stable internal environment A dynamic state of equilibrium Homeostasis is necessary for normal body functioning and to sustain life Homeostatic imbalance A disturbance in homeostasis resulting in disease

Variable (in homeostasis) Input: Information sent along afferent pathway to Control center Output: Information sent along efferent pathway to activate Receptor (sensor) Effector Change detected by receptor Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4

Variable (in homeostasis) Figure 1.4, step 1a

Variable (in homeostasis) Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4, step 1b

Variable (in homeostasis) Receptor (sensor) Change detected by receptor Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4, step 2

Variable (in homeostasis) Input: Information sent along afferent pathway to Control center Receptor (sensor) Change detected by receptor Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4, step 3

Variable (in homeostasis) Input: Information sent along afferent pathway to Control center Output: Information sent along efferent pathway to activate Receptor (sensor) Effector Change detected by receptor Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4, step 4

Variable (in homeostasis) Input: Information sent along afferent pathway to Control center Output: Information sent along efferent pathway to activate Receptor (sensor) Effector Change detected by receptor Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis Stimulus: Produces change in variable Imbalance Variable (in homeostasis) Imbalance Figure 1.4, step 5

Maintaining Homeostasis The body communicates through neural and hormonal control systems Receptor Responds to changes in the environment (stimuli) Sends information to control center

Maintaining Homeostasis Control center Determines set point Analyzes information Determines appropriate response Effector Provides a means for response to the stimulus

Feedback Mechanisms Negative feedback Includes most homeostatic control mechanisms Shuts off the original stimulus, or reduces its intensity Works like a household thermostat

Feedback Mechanisms Positive feedback Increases the original stimulus to push the variable farther In the body this only occurs in blood clotting and during the birth of a baby