BRAIN FUNCTIONS AND THE SENSES
The Regulatory System 90 91Feedback loops
Biological systems operate on a mechanism
of inputs and outputs, each caused by, and
causing, a certain event. Feedback loops
either amplify the output of a system
(positive feedback) or inhibit the output of
the system (negative feedback). Feedback
loops are important because they allow
living organisms to maintain homeostasis.STIMULUS
The body’s
temperature
changes.CONTROL
The hypothalamus
compares to
temperature set
point (98.6°F/ 37°C).RESULT
Normal body
temperature is
achieved.SENSOR
Thermoreceptors
in the skin sense this
temperature
change.EFFECTOR
If too hot, the
brain induces
sweating. If too cold,
the brain initiates
shivering.STIMULUS
The fetus exerts
pressure on
the cervix.CONTROL
The hypothalamus
stimulates the
posterior pituitary
gland, which releases
oxytocin.RESULT
Baby is born.SENSOR
Stretch receptors
are stimulated and
send signals to the
hypothalamus.EFFECTOR
Oxytocin
promotes more
contractions.Positive feedback system
The less common of the two feedback systems, positive
feedback systems are more unstable because they have
the potential to have a knock-on effect on other systems,
creating a “runaway” process. An example of a positive
feedback system is the increase in strength and frequency
of labor contractions, which stop when the baby is born
and the cervix is no longer being stretched.Negative feedback system
Most systems use negative feedback loops,
which are very stable and act to reverse the
direction of change to restore the system to
normal. They include regulation of blood
glucose and body temperature.95 ̊F (35 ̊C)
THE BODY TEMPERATURE AT
WHICH HYPOTHERMIA SETS IN
US_090-091_The_Regulatory_System.indd 91 20/09/2019 12:35