Homeostasis
Chapter 1
Learner Outcome:
• To discover and describe homeostatic
regulation in the human body and predict
the consequences of the failure to
maintain homeostasis.
Question:
• Are a cough and sneeze examples of
positive or negative feedback?
• A: Cough is caused as the body’s
mechanism of removing harmful particles
(bacteria, etc.) from lungs & throat. Sneeze
is involuntary reaction that expels same
reactants from sinus passages. Generally
accepted answer is NEGATIVE* b/c in
response to a perturbation, a negative
feedback system will tend to re-establish
equilibrium.
Defined
• Homeostasis is the relative constancy of
the body’s internal environment.
• External (environmental) conditions may
change drastically.
• Dynamic Equilibrium
• If internal conditions change to a large
degree – the result is illness.
Terminology
• Normal Range – a range of values for a variable that
allow for normal function of the body and its tissues.
• Set Point – the ideal value of a variable.
• Sensor – the part of the body that detects an internal
environmental change and signals the regulatory center.
• Effector – the part of the body that receives the
information from the regulatory center and reverses or
amplifies the change.
• Regulatory Center – part of the body that recognizes
values outside of the normal range and activates the
effector.
Negative Feedback
• Homeostatic mechanism that keeps a
variable close to a particular value or set
point.
Fig. 1.7a
Negative Feedback
Fig. 1.7b
Mechanical Example
Fig. 1.8
Positive Feedback
• Homeostatic mechanism that brings about
an even greater deviation from the set
point.
• EX: Birth process
Baby  Cervix  stimulates secretion of
oxytocin from pituitary  causes uterine
contractions  etc.
Disease
• The result of homeostatic failure and the
malfunctioning of the structure due to that
failure.
• Local diseases are located in a specific
area of the body whereas systemic
diseases affect the entire body.
• Acute diseases occur suddenly and
usually last a short time whereas chronic
disease tend to be severe and long term.
Homeostasis Lab
• Research Question:
Are breathing rate, pulse rate and blood
pressure positive or negative feedback
mechanisms as a reaction to aerobic
activity?
Blood Pressure Background…
• BP is pressure exerted by blood flowing
against walls of blood vessels throughout
body.
• Heart provides force for blood to flow.
When heart beats, blood is forced through
the vessels increasing the pressure. This
is highest pressure in the cycle, referred to
as SYSTOLIC BLOOD PRESSURE.
• In between beats, heart relaxes and BP
decreases. This is DIASTOLIC BP.
• Complete series of events occurring in
single heartbeat is called CARDIAC
CYCLE.
• Measured in millimeters (mm) of Mercury
(Hg). Systolic/Diastolic
• Normal range is 120-129/80-84 mmHg;
Optimal is <120; <80
Tips for using BP cuff
• Place on left wrist; place elbow on table
and raise hand until cuff is level with the
heart.
• Don’t do anything while taking reading
(talk, move, etc) body should be in
relaxed state.
• Rest 15 min. prior to taking reading.
Remove constrictive clothing or jewelry
from wrist.
Lab Tips
• Plan for a minimum of 4 trials. Each trial
needs to be the same exercise run for the
same length of time.
• Plan to have 4-5 minutes in between each
trial.
• Each trial should last 2-3 minutes.
• 40-45 minutes total for the exercises.
Data Table
Variable
BR
(set pt.)
PR
(set pt.)
BP
(set pt.)
Trial 1
Ex.
Trial 2
R Ex.
Trial 3
R. Ex.
R.