Anatomy Homeostasis
I. Homeostasis and Disease
A. Homeostasis –
is the maintenance of a relatively constant
internal environment.
• The ability to maintain the balance depends
on two factors
1. The status of the physiological systems
involved.
2. The nature of the stress that’s imposed.
• Homeostasis is a “balancing act” that must
adapt to sudden or gradual changes in our
environment, arrival of pathogens,
injuries…
• Homeostasis is the ability to maintain a
relatively stable internal environment in an
ever-changing outside world
• The internal environment of the body is in a
dynamic state of equilibrium
• Chemical, thermal, and neural factors
interact to maintain homeostasis
What contributes to or effects this
balancing act?
• Age, health, and genetics affect
our ability to maintain
homeostasis. If the physiological values go outside the
normal range it can affect other
systems and can be fatal.
B. Disease is the failure to maintain
homeostatic conditions. It can start in a
specific cell/tissue and continue
throughout the body.
• The body often overcomes some
diseases, for example the flu.
II. Homeostatic Regulation
and
Control Mechanisms
A.
Homeostasis regulation is the
adjustment of physiological systems to
preserve balance/to keep the internal
environment within desired limits
(simply put… it is the communication
within the body to maintain homeostasis)
• Two homeostatic pathways are
involved:
(stop see if students have read pg. 9-11)
1. Afferent pathway- carrying to or toward a
center (receptor carries to the control
center).
2. Efferent pathway –carrying away or away
from (the control center sends a message to
the effector).
B. Control Mechanisms
• Variable produces a change in the body
• Receptor monitors the environments and
responds to changes (stimuli)- sends to the
control center.
• Control center determines the set point at
which the variable is maintained (decides
what message to send to the effector)
• Effector provides the means to respond to
the stimulus. It is a cell or organ that
responds to the command of the control
center. The response then “feeds back” to
influence the stimulus (variable).
• Case study A Spill at Parsenn Bowl: Knee
injury and Recovery
Figure 1.4
Negative Feedback
• In negative
feedback
systems, the
output shuts
off the
original
stimulus
• Example:
Regulation
of blood
glucose
levels
Figure 1.5
Positive Feedback
• In positive feedback
systems, the output
enhances or
exaggerates the
original stimulus
• Example:
Regulation of blood
clotting
Figure 1.6
Review: Feedback mechanisms
regulate biological systems
• Feedback mechanisms allow biological
processes to self-regulate
• Negative feedback means that as more of a
product accumulates, the process that
creates it slows and less of the product is
produced
• Positive feedback means that as more of a
product accumulates, the process that
creates it speeds up and more of the product
is produced
Fig. 1-13
Negative
feedback 
A
Enzyme 1
B
D
Excess D
blocks a step
D
Enzyme 2
D
C
Enzyme 3
D
(a) Negative feedback
W
Enzyme 4
Positive
feedback +
X
Enzyme 5
Excess Z
stimulates a
step
Z
Y
Z
Z
Enzyme 6
Z
(b) Positive feedback
Homeostatic Imbalance:
• is a disturbance of homeostasis or the
body’s normal equilibrium.
• overwhelms the usual negative
feedback mechanisms allowing
destructive positive feedback
mechanisms to take over.