CRYDER’S QUIZ #1 MAJOR TOPIC ANSWERS:
#1. Define and describe homeostasis as it relates to the three part control loop we discussed,
including a discussion of negative feedback as it relates to one example covered in class.
Observe the following diagram.
1. Receptors -> 2. Control center -> 3. Effector
Homeostasis and Control Loop
Homeostasis is the body’s ability to use the nervous and endocrine systems to maintain a
stable internal environment regardless of external/internal changes. At the center of this lifesaving process is a three part control loop which includes (1) receptors that monitor the body
and, when conditions change enough to disrupt the body’s dynamic balance, will send the
appropriate sensory impulses into (2) the control center (the CNS). The control center of the
body, which includes the brain and spinal cord, then analyzes this input, interprets its message
and determines the appropriate motor response necessary to stabilize the body and return it to
equilibrium. As the motor impulses round out and complete this loop by targeting and activating
(3) effectors (muscles and glands) which will immediately reverse the specific imbalance and reestablish homeostasis.
Negative Feedback
Homeostasis, which refers to our body’s life-saving ability to maintain its internal balance by
utilizing a wide array of negative feedback mechanisms, requires specific and continuous
nervous and endocrine system detection, analysis, and effector targeting in order to appropriately
respond to potentially life-threatening changes and imbalances and to effectively re-establish
stability before the “equilibrium stimulus” is diminished and subsequently turned off. One
example of this process occurring in the body is seen as the body maintains its desired internal
temperature of 98.6o F. When a human goes from a 700F room to the outdoors where it’s a
scorching 1100 F, a negative feedback loop would be initiated in order to maintain homeostatic
balance and prevent any wide variation in body temperature from occurring. As we heat up
internally; the body’s receptors would recognize the temperature change, send a sensory nerve
impulse to the CNS (control centers within the brain and spinal cord) for analysis and
interpretation, and then it would determine which specific effector (muscles or glandular
secretion) is appropriate and which specific impulse would reverse the imbalance efficiently and
quickly enough to completely stabilize the body’s systems and cool us down. In this case, the
best effectors are in the form of sweat glands (embedded within the dermal layer of the skin and
covering our entire outer surface) which will immediately activate, release sweat onto our
external surface, and quickly cool our core back toward 98.60 F. As balance of temperature is reestablished, the same receptor that initiated the loop will no longer detect imbalance and will
stop sending the sensory signal that started the negative feedback mechanism to begin with; the
stimulus is diminished and shuts off (as quickly as it was initiated).
(Courtesy of Ian Dettman)
#1. Define and describe the three most important organ systems and explain why you’ve
chosen them.
The nervous system and the endocrine system both serve as means of maintaining homeostasis,
which is vital to life. The first, which is composed of the brain, spinal cord, and peripheral
nerves, allows the body to detect changes in the environment and react accordingly. The
endocrine system, on the other hand, consists of a system of glands responsible for hormone
secretion that prolongs the nervous response to the given change in the environment. They each
work together, therefore, to maintain the balance of homeostasis necessary to life. A third
essential body system is the ___________ system, which is made up of the ________________.
It is essential on a minute-by-minute basis to life because its function includes ________________________________________________________________.
#2. Define and describe the structural levels of organization in the body and circle the basic
living unit.
On the minutest level, the basic building blocks of matter, called atoms, come together to form
molecules, which in turn can combine into macromolecules such as DNA. Macromolecules form
organelles, many and varied types of which act in tandem to maintain the cell, the most basic
living unit. Multiple cells form tissues, and a combination of tissues will work together in an
organ to perform a given function that will complement other organs in an organ system.
Finally, an organism survives by maintaining balance between the multiple organ systems that
make it up.
#3. Define and describe homeostasis as it relates to the three part control loop we discussed,
including a discussion of negative feedback as it relates to one example covered in class.
The body is able to detect changes in the environment that threaten dangerous imbalances, such
as high temperature, through sensory receptors. This information is sent to the control center,
i.e., the central nervous system, which interprets and analyzes the data, sensing in this scenario a
rising body temperature. An appropriate motor response is initiated by the CNS to address the
imbalance and the effectors produce corrective action; the sweat glands go off and evaporation
cools the body in an attempt to re-establish/maintain the ideal 98.60 F. Negative feedback in the
form of constant reevaluation of the situation (e.g., body temperature detection) controls the
intensity of the effector response and serves as a shutoff mechanism once equilibrium is reachieved.