1. Objectives
Define homeostasis with examples.
Describe how homeostasis is maintained by
different organ system.
Discuss negative and positive feedback
mechanisms with examples.
2.
3. Definition
The term coined by American physiologist
Walter B. Cannon.
He described homeostasis as "the
maintenance of the steady states in the body
by coordinated physiological mechanisms".
4. French physiologist Claude Bernard described it as
“It is the fixity of the internal environment that is the
condition of free and independent life…All vital
mechanisms, however varied they may be, have only
one object, that of preserving constant the conditions
of life in the internal environment”.
5. Internal environment
Life originated in the sea.
Multicellular organisms carry their own sea
within their body which makes up the internal
environment of the body.
The extracellular fluid (ECF) of the body makes
the internal environment .
Maintenance of this internal environment is
known as homeostasis.
6. Different organ system
Lung
Heart and circulatory system
Gastointestinal tract
Kidney
Endocrine system
Reproductive system
Muscles and Integumentary system
Brain
7. Conditions e.g, oxygen tension, pH,
temperature, concentration of waste products,
hormones are all closely regulated.
Changes in the internal environment of the
body do occur but the magnitude of these
changes are small and are kept in narrow limits
through multiple coordinated homeostatic
processes.
8.
9. Cells, the fundamental units of life, exchange nutrients
and wastes with their surroundings:
The intracellular fluid is “conditioned by”…
the interstitial fluid, which is “conditioned by” …
the plasma, which is “conditioned by” …
the organ systems it passes through.
Balancing the Internal and External Environment
ICF ISF plasma organs
external
environment
internal environment
10. Why do we need stable environment
A stable environment allows an organism
to be independent of changes in the
external environment.
17. Negative feedback
Most of the feedback system of the body is
negative feedback.
Negative feedback mechanism decreases the
cause that initiated it.
Ex-
18.
19. Requirements for Maintaining Homeostasis
Communication within the body: accomplished by
endocrine & nervous systems.
The factor being regulated is the variable
(temperature, blood sugar levels, blood pressure
etc.).
All homeostatic control mechanisms have at 3
interdependent components:
sensor, integrating center and effector.
20.
21. Input from sensory receptors: sensory
receptors respond to stimuli (detect changes) to
the body, an awareness of what is happening
internally & externally.
22. Control / Integrating center: brain,
spinal cord, or endocrine glands.
They receive sensory information and bring
about a response (efferent signal) via nerve
impulses or hormones, intended to change
conditions back to normal.
23. The control center determines a set point
(the range) at which a variable is to be
maintained; it analyzes afferent signals &
responds with an efferent signal.
24. Effectors bring about the change specified
by the integrating center (e.g., skeletal muscle,
glands & organs).
25. Positive feedback
It increases the disturbance that causes it to
increase further.
Ex- blood clotting mechanism and labor.
26. Homeostatic Regulation of Child Birth through
Positive Feedback
Pressure of Fetus on
the Uterine Wall
Nerve endings in the uterine
wall carry afferent messages
to the Hypothalamus
Production and Release
of Oxytocin into the
Blood
Increasing strength of
uterine contractions
Intensifies
The birth of the child will bring this process to a close. Other examples of positive
feedback regulation occur during blood clotting.
27. Positive feedback “mini-loops” are built into pathway to
speed up production of chemicals needed to form the clot.
Entire sequence of clotting is a negative feedback pathway.
Positive Feedback in Coagulation
