Homeostatic control mechanisms or systems. In order to maintain homeostasis cells must be in an environment
that allows them to function properly with
changing external conditions. Almost all of the organs and systems in the
body must work to maintain homeostasis. If the body needs to change the
internal environment it does so through what is called
homeostatic control mechanisms. For instance, when you go for a
run, your body needs more oxygen, and your body produces more carbon dioxide. So, the internal environment must
adapt to the changing needs. During your run, your breathing
will increase, bringing more oxygen in and eliminating the increased
production of carbon dioxide, your heart beat and stroke volume
will increase, thus increasing the amount of nutrient rich blood
being sent throughout your body. This process of the body
adjusting to a change is called a feedback control loop or
feedback control system. These control loops transmit
information in mainly 2 ways, through nervous impulses or by
chemical messengers called hormones. Whether the nervous impulses or hormones
are transmitting the information, the feedback control loops work in the same
way and have the same basic components. The feedback control loops
consist of 4 main components. A sensor mechanism, an
integrator or control center, an effector mechanism and feedback. Hormone producing glands and sensory nerve
cells can act as homeostatic sensors. If something changes outside of the
normal set point range for homeostasis, a sensor transmits a
signal to the next component of the feedback
loop, the integrator. The integrator is the control
center of the feedback loop and many times it is
in an area of the brain. It gets this signal or variable and
analyzes it and checks it with other signals or variables it has
received from other sensors. It checks the value of the
variables it has received against the normal set point
range for those variables. If the integrator
determines these variables are outside of the
normal set point range, then some type of action is needed. If action is necessary, the integrator
sends a signal to the third component of the feedback control
loop, the effector mechanism. Effectors are organs, like
glands or muscles, which provide the response that the integrator,
or control center desires. The goal of the effectors is to influence
or change the values of the variables. This can be positive or negative
changes to the variables, such as increasing or decreasing
heart rate, or altering the concentration of glucose
in the blood stream. Glucose being the main
source of fuel for cells. As these effectors make changes,
the variables attain new values, and this is sent back through
the feedback control loop. For instance, if you are walking, then
you start jogging, effectors will increase your heart rate, based on the
mechanisms of the feedback control loop. Many sources use a diagram
of a furnace controlled by a thermostat to explain
this process more clearly. Here (on screen) we have a house, and
here we have a person (on screen). Let’s say that in both
situations a stimulus happens, that being a cold front blows in,
causing a decrease in temperature. The house has a thermometer,
which is its sensor, and the person has
temperature receptors in the skin, which are the sensor
mechanism for the body. The thermometer sends the information
that the temperature or variable has decreased, through wires to
its integrator, the thermostat. The temperature receptors in the skin
send the variable change through nerve fibers to the brain, or the integrator
for the body in this situation. The integrators, or control centers
for both the body and house, check the value of the newly received
variables against the set point range that each of them has allowed
for this type of variable. Since this temperature variable change
does not lie in the set point range, the integrators send a signal
to effectors to do something to get these variables
within this set point range. In the case of the house the
thermostat sends a message through wires to the furnace
to crank the heat up. In the body, the brain sends a
message through nerve fibers to the muscles to start shivering
to generate some heat. In both the house and the body
of the person, the heat that is generated brings them both
to a state of homeostasis. Once homeostasis is reached,
both sensor mechanisms, the thermometer and temperature
receptors in the skin are sending new variable
values, or feedback to their integrators that lie within
the set point ranges. One note worth repeating, homeostatic control systems can be based
on positive or negative feedback. And that, be the homeostatic
control mechanisms or systems.