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
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 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.