SCCS Anatomy Physiology
Name:
Per:
Date:
Homeostasis
Defined as the maintenance of a stable ____________________ environment.
Out of the 11 major systems of the body, ___________________________ is the only expendable
system. All other systems are necessary for homeostasis!!
Six Factors
There are 6 factors that are constantly homeostatically
regulated by the systems of the human body. These factors must remain within certain
limits at all times, otherwise adverse effects on the body will result.
Concentration of nutrients and oxygen
It is vital that the body has a certain level of nutrients.
What is the main energy source used by the body?
Concentration of salts and electrolytes
The body also needs to have a certain level of ions.
List examples:
Concentration of wastes
Waste products must be monitored to ensure that levels do not exceed a certain amount.
Examples of harmful waste products:
Acid/Base Balance
A very delicate equilibrium must be reached between the levels of acids and bases present
in the fluids of the body. Also, particular areas of the body have their own unique level of
acids or bases that must be maintained.
What is the pH of blood?
What is the pH of stomach acid?
Temperature
The internal temperature of the human body must remain at a fairly constant level.
What is average human body temperature in degrees Fahrenheit?
What is average human body temperature in degrees Celsius?
Pressure and Volume
Pressure of fluids and gases within the body need to be at equilibrium within the body.
Particularly when balancing pressure between the inside and outside of a cell or the inside
of the lungs and the outside air pressure.
Give an example of a situation in which the air pressure is changing outside your body.
What does your body do to maintain homeostasis?
Regulation of Homeostasis: Negative Feedback
In order to maintain homeostasis, the body must be able to detect any changes in the
internal environment AND adjust the internal environment in a manner that returns the
body to normal conditions.
You may better understand how the body regulates homeostasis by comparing the body to
a home heating system. Here is an example:
There are 4 components to
homeostasis:
_________________________The desired level or
concentration of one of the
six factors which are
regulated.
_________________________Cells and areas of the body
that are constantly
monitoring the current
conditions.
_________________________A comparison made by the
nervous system
between the set point and
the sensor’s reading of
current conditions.
_____________________________Parts of the body which
make physical adjustments
to the body, returning
conditions to the desired
level (set point).
Heating System
Human System
Thermostat set at
70 degrees Fahrenheit
Desired level of
blood pressure is 80/120
Metal components within
the
thermostat expand and
contract according to the
__________________temperature.
Current temp.=65 degrees
Sensory cells within the
walls of the blood vessels
detect the pressure of the
__________________ flowing
through the vessels.
Current pressure is
100/160
The heating system detects
the room temp. as too low
when the metal component
contracts and closes a
circuit.
Room temp. is _______________
than the set point.
Messages are sent to the
brain from the sensory cells,
indicating the pressure of
the blood vessels. Brain
makes a decision to
__________________blood
pressure.
Arteries in the body
The heater ________________
______________, so the space in
and begins to blow out warm
which the blood flows is
air. This continues until the
larger. This effectively
sensor and integrator detect lowers the blood pressure,
the desired 70 degree temp.
returning to the set point
level of 80/120.
Quiz yourself:
1. Which of these characteristics of life helps maintain homeostasis when environmental
conditions change?
A) growth and development
B) metabolism
C) organization
D) reproduction
E) responsiveness
2. Given these terms related to negative-feedback:
1. control center 2. effector 3. receptor 4. response 5. stimulus
Arrange them in the correct order as they operate to maintain homeostasis.
A) 1,2,3,4,5
B) 2,3,5,1,4
C) 3,2,1,5,4
D) 4,5,3,2,1
E) 5,3,1,2,4
3. A body temperature of 98.6 degrees F (37 degrees C) is the __________ for body
temperature.
A) constant
B) lower limit
C) normal range
D) set point
E) upper limit
4. Which of these processes illustrates positive-feedback?
A) increase in respiratory rate during exercise
B) increase in heart rate when blood pressure decreases
C) shivering when body temperature decreases
D) increase in uterine contractions when uterine stretching increases during childbirth
E) all of these
5. Failure of negative-feedback mechanisms to maintain homeostasis
A) may produce disease.
B) occurs when blood pressure increases during exercise.
C) can be corrected by stimulating positive-feedback mechanisms.
D) cannot be corrected by medical therapy.
E) all of these
6. According to the concept of negative feedback, a slight increase in blood pressure causes
A) an increase in heart rate.
B) a decrease in heart rate.
C) no change in heart rate.
7. To maintain homeostasis, the normal range of values for a variable
A) is always below the set point.
B) may change in different situations.
C) may not deviate from the set point.
D) occurs because of positive-feedback.