Homeostasis

1
Homeostasis
Homeo similar, stasis condition

• Defined as the ability to maintain a relatively
  stable internal environment

• The human body maintains hundreds of
  physiologically controlled parameters (variables)
  close to a setpoint

body temperature, blood glucose levels, blood
pressure, body CO2 levels, body pH
these parameters are constantly changing due to
external and internal changes
The body uses control systems to maintain these
parameters at or close to their respective
setpoint
2
Maintenance of Homeostasis
Local Control

• relatively isolated change occurs in the vicinity
  of a cell to evoke a localized response through
  the secretion of chemicals from the affected cells

• the secreted chemicals diffuse a short distance
  and affect neighboring cells

• the response is restricted to the region of cells
  that received the secreted chemical

Reflex Control
-response to more widespread or systemic changes
3
-control of the response to a change occurs
outside the organ that carries out the response
-uses the nervous and or endocrine system through
feedback loops to receive input about a change,
integrate the information and react appropriately
4
Local Control
5
Reflex Control
6
Feedback Loops for Reflex Control

• Reflex control of homeostasis uses feedback loops
  to maintain homeostasis

The beginning of a reflex pathway is a
disturbance in a controlled parameter called a
stimulus

• The stimulus is sensed by a sensor (receptor)

• continuously monitoring the environment
• when a change is detected, it sends out a signal

The signal travels from the receptor by way of an
afferent pathway to the control (integrating)
center
The control center evaluates the incoming signal,
compares it to the homeostatic setpoint of the
parameter and decides on the appropriate response
7

• The control center sends out a signal that
  travels by way of an efferent pathway to the
  effector

• The effector is a cell or tissue that carries out
  the appropriate response to bring the parameter
  back to within normal limits (setpoint)

8
Feedback Loops for Reflex Control
9
Feedback Loops for Reflex Control
10
Feedback Loops

• Most (over 99) feedback loops are referred to as
  negative feedback loops where the response of the
  effector opposes or removes the cause of the
  parameters imbalance

• can restore the normal state of the parameter,
  but cannot prevent the initial disturbance out of
  the normal range

• The minority (less than 1) of the feedback loops
  are referred to as positive feedback loops where
  the response of the effector reinforces the a
  stimulus rather than opposing or removing it

• the response destabilizes the parameter
  triggering a viscous cycle of ever increasing
  response and sending the system temporarily out
  of control

11
(No Transcript)