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

The body tries to respond to the NEGATIVE stimulus. o Shiver to keep warm o Sweat to keep cool o Muscles withdraw from painful stimulus o 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 warm  Hypothalamus in brain senses too warm  Blood vessels vasodilate or enlarge to get rid of heat  Sweat 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  CO 2 Regulation  Water Regulation  Sugar Regulation  Hormonal 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 temp  Set Point (what you’re trying to maintain) = 74° F  Control Center (what monitors the variable and compares it to the set point) = thermostat  Effector (target of decision made and what responds to change 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 not being able to maintain or restore homeostasis (known as “homeostatic imbalance”).