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Homeostasis
At the end of presentation,students should be able
to


Describe homeostatic mechanisms of the major
functional systems.
Describe control systems of the body

Examples of control mechanisms

Characteristics of control mechanism
Homeostasis
Homeostasis, from the Greek words for
"same" and "steady," refers to any process
that living things use to actively maintain
fairly stable conditions necessary for
survival.
Homeostasis

Homeostasis mean maintenance of nearly
constant conditions in the internal environment.

60% of adult human body is fluid,1/3 is ECF,
contains ions and nutrients,internal environment
of the body.

Concept by Claude Bernard, French physiologist
of 19th century

Name- American physiologist Walter B. Cannon.
THE INTERNAL ENVIRONMENT
 The
internal environment or milieu
interieur
Extracellular
 Importance
fluid
ECF fluid transport and mixing system:
2 stages:
1.
Movement of blood in the blood vessels
2.
Fluid movement in between blood
capillaries and the intercellular spaces
between the tissue cells.
Blood circulates once each min throughout the
body at rest and six times each min when
active.
Large amount of fluid and dissolved constituents
diffuse back and forth between blood and tissue
spaces.
Origin of nutrients in the ECF
Respiratory system:
Blood picks up O2 in the alveoli
Alveolar membrane 4-2 micrometers thick
GIT:
Carb, fatty acid, amino acids absorbed from
the ingested food into the ECF of the blood.
Liver:
Change chemical composition of many
absorbed substances to more usable forms.
•
Removal of metabolic end products
•
Removal of carbon dioxide by the lungs
•
Removal of urea, uric acid by the kidneys
and also excess of ions and water.
COMPOSITION OF BODY FLUIDS
COMPOSITION OF BODY FLUIDS
CATIONS (mmol/l)
Plasma
Interstitial
Intracellular
Na
142
139
14
K
4.2
4.0
140
Ca
1.3
1.2
0
Mg
0.8
0.7
20
ANIONS
(mmol/l)
O2
Cl
108
108
4.0
HCO3
24.0
28.3
10
Protein
1.2
0.2
4.0
HPO4
2.0
2.0
11
Essentials of homeostasis

Conc of oxygen and carbon dioxide

pH of the internal environment

Concentration of nutrients and waste
products

Conc of salts and electrolytes


volume and pressure of ECF
Temperature regulation
EXAMPLES OF HOMEOSTASIS
Body water regulation by osmoreceptors
and kidneys.
 Excretion of waste products by kidneys and
respiration
 Temperature regulation
 Blood glucose regulation
 Constant supply of nutrients
 Maintenance of pCO2 and pO2
 Maintenance of pH

Homeostasis is

Essential for survival of each cell

Each cell contribute its part in homeostasis

Interdependent relationship of all cells, body
systems and homeostasis
Regulation of body functions
by the major systems
The major systems
Cardiovascular system
 Transportation
 O2, CO2, nutrients, waste products, hormones etc
 Digestive system
 Digestion, Absorption of nutrients, excretion of wastes
 Transfer of materials from external environment to
internal environment
 Respiratory System :
 Supply O2 of & elimination of CO2
 Acid base balance

The major systems
Urinary System
 Elimination of waste products
 Water & electrolytes balance
 Acid base balance
 Blood pressure regulation
 Skeletal system
 Support & protection
 Movement
 Reservoir for calcium

The major systems

Muscular system
 Movements
 Most

towards or away from different elements
of the voluntary movements by skeletal muscles
Integumentary system
 Protection
 Temperature

regulation
Immune System
 Defense
against foreign invaders
 Defense
against Cancer
The major systems
Nervous System
 Control system of the body
 Coordination of body activities
 Quick response to stimuli
 Consciousness, memory and intellectual functions
 Endocrine System
 Another major control system
 Control of metabolism
 Control of nutrients supply, storage and utilization
 Reproductive system
 Reproduction – continuation of life

Regulatory Mechanism
Most physiological systems in
the body use feedback to
maintain the body's internal
environment exactly balanced
EXAMPLES of control mechanism

Oxygen buffering function of hemoglobin

Baroreceptor system as rapidly acting
mechanism to decrease high blood pressure

Regulation of Carbon dioxide conc in ECF
Normal ranges and physical characteristics
of important ECF constituents:

Increase in body temperature by 11
degrees F (7 degrees C)___Increase in
cellular metabolism----cell destroys.

pH

K+

Ca

Gl
Control of homeostasis
Feedback Systems in
Homeostasis
1.
Negative feed back
system
2.
Positive feed back system
Regulatory Mechanism
Negative feed back control
System reacts in such a way as to arrest the
change or reverse the change.
 Positive feed back control
System reacts in such a way as to enhance
or amplify the change in the same direction.

Feedback Systems in Homeostasis

Negative feedback
 Used
by most of the body's systems
 The
response caused by the feedback is
opposite to the change (stimulus).
↑
Thyroxin → → → → ↓ TSH → ↓ Thyroxin
↓
Thyroxin → → → → ↑ TSH → ↑ Thyroxin
Negative feed back control of
thyroxin
Examples of negative feed back control:

High conc. of carbon dioxide initiates events
that decrease the concentration towards
normal.

High AP causes a series of reactions that
lead to lowered pressure. This effect is
negative with respect to the initiating
stimulus.
Feedback Systems in Homeostasis
Positive feedback
 Control is used in some cases.
 The response caused by the feedback is in the
direction of the change (stimulus).
 Input increases or accelerates the response.
Positive feed back
Labor Oxytocin →↑ uterine contraction
→↑Oxytocin

Clotting

Generation of nerve impulses

Useful positive feedback itself is part of an
overall negative feedback process.
Feed forward control
Sensory nerve signals from the moving parts
apprise the brain whether movement is
performed correctly. If not , the brain corrects the
feed forward signals that it sends to the muscles
the next time the movement is performed. This is
called adaptive control and is a delayed
negative feedback.
Pathophysiology
Disruption of Homeostasis
Failure of homeostasis
Disease
Death