The body receives a stimulus via a receptor o Cold-extrinsico Heat-extrinsico Pain-extrinsic or intrinsico An odor-intrinsico Fatigue-intrinsico Can you name any other stimuli?

The body tries to respond to the NEGATIVE stimulus. o Shiver to keep warmo Sweat to keep coolo Muscles withdraw from painful stimuluso You go to sleep

If we get too cold we will____

If we get too hot our proteins will______

Our body is at work all the time to maintain internal homeostasis

Example 1: Temperature regulation

Skin sensory organs sense too warmHypothalamus in brain senses too warmBlood vessels vasodilate or enlarge to get rid of heatSweat glands produce sweat which evaporates to cool the body

Temperature Regulation-too cold

Skin sensors and hypothalamus sense body temperature too low

Hypothalamus sense message to vessels to vasoconstrict so skin might turn blue

Goose bumps raise hair to trap air which is a good insulator

Muscles shiver to generate heat

Other examples of homeostasis regulation

CO2 RegulationWater RegulationSugar RegulationHormonal Regulation

What do they all have in common?

INPUT

Receptor(sensory cells;

i.e. skin, eyes, etc)

Integrator(or Control Center)

(brain & nerves & glands in brain)

Effector(muscles & glands;i.e. sweat glands)

OUTPUT

Analogy: Maintaining a comfortable room tempSet Point (what you’re trying to maintain) = 74° F

Control Center (what monitors the variable and comparesit to the set point) = thermostat

Effector (target of decision made and what responds tochange the variable) = air conditioner

Two Kinds of Feedback Systems:1) Negative feedback

1) Positive feedback

1) Negative Feedback System:

Where the body works to reverse the direction of the change/disturbance. The body generates responses to “fix” the disturbance and bring the body back to “normal”.

Like how a thermostat monitors room temp.

Examples of Negative Feedback in the body:

Maintaining body temperature

Maintaining proper amounts of salt in bloodstream

Maintaining proper amounts of hormones in bloodstream

2) Positive Feedback Systems (Loops):The body’s response to a change is to continue the direction of the change. The initial conditions/ stimulus triggers a chain of events that intensify until something stops the process.

This type of system has a de-stabilizing effect so it does not initially result in homeostasis (when process is complete, then homeostasis occurs).

Examples of Positive Feedback Systems in the body:

Childbirth

Blood clotting

Defecating

(Positive feedback systems are rare in body;Most systems work using negative feedback)

Animations of homeostasis

Positive feedback

Positive vs. Negative Feedback

Lastly, most diseases are the result of the body notbeing able to maintain or restore homeostasis (known as “homeostatic imbalance”).