HomeostasisHomeostasisBalancing the internal environmentBalancing the internal environment

External vs. Internal External vs. Internal EnvironmentEnvironment

What is the difference?What is the difference?

External environment:

Your surroundings.

The factors that cause your body to change in order to stay in homeostasis. (Cold outside, working out, bacteria)

Internal EnvironmentInternal Environment

Conditions within the fluid surrounding Conditions within the fluid surrounding its body cellsits body cells

Comprised of self-regulating control Comprised of self-regulating control systems – systems – homeostatic homeostatic mechanismsmechanisms

Feeling Feverish?Feeling Feverish?

Homeostatic MechanismsHomeostatic MechanismsHave three common components:Have three common components:

Receptors – Receptors –

Set point –Set point –

Effectors -Effectors -

provides information about provides information about specific conditionsspecific conditions

tells what a particular value tells what a particular value should beshould be

Cause the response that alter conditions in the internal environment.

Response – Change Corrected

Receptor

Set Point

Control Center

Effectors

Stimulus – change in external environment

Homeostatic Mechanism

Negative vs. Positive Negative vs. Positive feedback mechanismsfeedback mechanisms

Negative Feedback SystemsNegative Feedback Systems

There is a change from the set point and There is a change from the set point and negative feedback corrects this change or negative feedback corrects this change or brings it back to normal. brings it back to normal.

This correction reduces the action of the This correction reduces the action of the effectors until the body is back in effectors until the body is back in homeostasis. homeostasis.

Hyperthermia Heat receptors in the skin

Hypothalamus

StressSensors Control Center

Increased activity of

sweat glands

Increased blood flow to the skin

Effectors

Perspiration evaporates

cooling the skin

Effect

Stress is reduced shutting down mechanism

Homeostatic Regulation of Body Temperature through Negative Feedback

Homeostasis Using a Neural Pathway

Control center

Many homeostatic mechanisms use a nerve pathway in which to produce their effects. These pathways involve an afferent path which brings sensory messages into the brain and an efferent path which carries outgoing nerve messages to effectors.

Positive Feedback SystemsPositive Feedback Systems

Change that occurs is in the same direction Change that occurs is in the same direction as the initial disturbance. as the initial disturbance.

Deviation from the set point is acceleratedDeviation from the set point is accelerated

No correction to the action of the effectorsNo correction to the action of the effectors

Body will shut down, however some Body will shut down, however some positive feedback systems work in favor of positive feedback systems work in favor of the body – ie. Childbirth.the body – ie. Childbirth.

Positive Feedback Mechanisms

Typical Positive Feedback Process

EffectorIntensifies

Control CenterSensor

Stress

Homeostatic Regulation of Child Birth through Positive Feedback

Pressure of Fetus on the Uterine Wall

Nerve endings in the uterine wall carry afferent messages

to the Hypothalamus

Production and Release of Oxytocin into the

BloodIncreasing strength of uterine contractions

Intensifies

The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

Harmful Effects of Positive FeedbackPositive feedback can be harmful. A specific example of these harmful outcomes would be:

Positive feedback is frequently a normal way of producing rapid change. However, positive feedback can be harmful to the body. For example, if the body temperature rises above 108o F a dangerous positive feedback loop may be created. This high temperature will increase the metabolic rate, thus producing heat faster than the body can get rid of it. Thus, temperature rises still further, increasing metabolic rate and heat production still more. This becomes fatal at approximately 113o F.

Some examples of what your Some examples of what your body can regulate: body can regulate:

Body temperatureBody temperature

Blood pressureBlood pressure

Oxygen needed or RespirationOxygen needed or Respiration

Heart Rate (or blood delivered to heart)Heart Rate (or blood delivered to heart)

Glucose level or blood sugar level. Glucose level or blood sugar level.