In the name of ALLAH, the Compassionate,
the Merciful.
Physiology, a Beauty and a
Philosophy
of
Basic Medical sciences
Cells Are Basic Units Of Life

Obtain food from environment

Perform chemical reactions to provide energy

Eliminate by- products to the environment

Synthesis material for growth and function

Control exchange of materials between cell and
environment

Moving material from one part of the cell to
other to carry out cellular activities.

Being sensitive and responsive to changes in the

environment.
Most cells – reproducing
Modes of intercellular signaling
Major Body Fluid Compartments

Composition of
the body

Organization of
the body fluid compartments

Measurements of
body fluid volume
Components Of Extra Cellular Fluids
Water: largest constituent of body;
55-65% of body weight

Intracellular Fluid

Extracellular Fluid
– 66.6%
– 33%
– Within cells
– Interstitial, space
surrounding cells
– High potassium
– Intravascular; 7-8% of
total body water, 2025% of ECF
– High sodium
Osmotic pressure (concentrations of all solutes in a fluid
compartment) is equivalent between ECF and ICF compartments
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What is Homeostasis?
The maintenance of
a constant
environment in the
body is called
Homeostasis
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Cells – Body system and
Homeostasis
OVERVIEW
• The term HOMEOSTASIS is defined as
constancy of internal environmental & most
often used in biological sense.
• Multicellular organisms requires a homeostatic
internal environment to survive & live.
• Many environmentalists believe that this
principle also applies to the external
environment.
• Many ecological and social systems are
homeostatic.
TYPES OF HOMEOSTASIS
 Strong homeostasis: In it the structure and reserve do
not change in composition. Since the amount of reserve
and structure can vary, still a particular change is allowed
in the composition of the whole body.
 Weak homeostasis: It is the constancy of the ratio in
the amounts of body reserve and structure, as long as
food availability is constant. It is also true when the
organism grows.
 Structural homeostasis: means that the subindividual structures grow in harmony with the whole
individual.
Factors Homeostatically Maintained Are

Concentration of nutrient molecule

Concentration of oxygen and carbon dioxide

Concentration of waste product / toxic substances

Concentration of water, salt and electrolytes

pH maintenance

Temperature regulation

Volume and pressure
How Homeostatic Systems Work?
 These homeostatic system oppose
change to maintain equilibrium.
 If the system does not succeed in reestablishing its balance, it may ultimately
lead the system to stop functioning.

Body cells work best if they have the correct
 Temperature
 Water levels
 Glucose concentration
FLUCTUATIONS
When organisms exhibit equilibrium, their
physiological state is not necessarily static.
Many organisms exhibit endogenous fluctuations
Circadian (period 20 to 28 hours)
Ultra-dian (period < 20 hours) and
Infra-dian (period > 28 hours) rhythms.
Thus even in homeostasis, body temperature,
blood pressure, heart rate and most metabolic
indicators are predictably with time.
Control Systems Of The Body
Homeostasis

Within cell (genetic
control system)

Within organ

Operate through the
body

Regulation of gases

Regulation of
endocrine

Regulation of BP

Regulation of NS
Mechanism of Homeostasis
through Feed Back
• When a change in variable occurs
in a body system, two types of
feedback are used to avert this
change towards normal:
• Negative feed back
• Positive feed back
Characteristic Of Control System
 Negative feed back
Gain of control system is measured
of quality of regulation
Gain =
Correction applied
Residual Change
OR
Correction
error
Higher the gain, higher the accuracy of regulation
 Positive feed back
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Indices of Quality of Regulation
Variabl
Set
Point
Dist.
Change
without
Regul.
Residual
-change
with
Regul.
Correct
Regul.
Regul. Gain
Factor
(R)
B.P
120
mm
Hg
Hge
60 mm Hg
20
mm Hg
40
mm Hg
1/3
2
Body
Temp.
37oC
Cold
17oC
0.5oC
16.5oC
1/34
33
Homeostasis- through Negative Feed Back
Negative feed back is a reaction in which
the system responds to reverse the
direction of change.
 Carbon dioxide concentration in the
human body.
 Thermoregulation.
 Blood Pressure Regulation.
Negative Feedback Control
Operation Of Feedback System
Basic
components

Stimulus

Receptors

Control center

Effectors
Feed Back of Home Heating
System
Controlling body temperature
Volume : Surface
area ratio = 1:6
Volume : Surface
area ratio = 1:5
The bigger the
Volume : Surface Area ratio
is, the faster heat will be lost.
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Two Kinds of Thirst
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Volume homeostasis
Thirst is triggered by increased plasma osmolality
Thirst is
inhibited by
decreased
plasma
osmolality
(OVLT
receptors) and
by increased
blood pressure
(hypervolemia)
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Volume homeostasis
Hypovolemia triggers not
only thirst, but also salt
appetite
Blood volume is corrected
only by replacing both
water and salt
Drinking water alleviates
thirst (by reducing plasma
osmolality), but triggers salt
appetite, whereas
consuming salt triggers
subsequent thirst (by
increasing plasma
osmolality)
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Volume homeostasis
A loss of blood volume (hypovolemia) leads to compensatory
mechanisms, which include thirst and increased salt consumption
Baroreceptors sense
hypovolemia and cause
kidney to secret renin
Renin interacts with
angiotensinogen to
produce angiotensin I,
which is converted to
angiotensin II (AII)
AII is a vasoconstrictor
and promotes aldosterone
secretion from adrenal
cortex and AVP secretion)
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Controlling Glucose levels
Your cells also need an exact level of
glucose in the blood.
 Excess glucose gets turned into glycogen
in the liver
 This is regulated by 2 hormones
(chemicals) from the pancreas called:

Insulin
Glucagon
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Glycogen
If there is too
much glucose in
the blood,
Insulin converts
some of it to
glycogen
Glucose in the blood
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Glycogen
If there is not
enough glucose
in the blood,
Glucagon
converts some
glycogen into
glucose.
Glucose in the blood
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Negative Feed Back
Feed Back Control Of B.P.
Blood volume and blood pressure are partially regulated
by hydrostatic and osmotic pressure gradients
Starling equilibrium:
Distribution of fluid
between intravascular
and interstitial space
is determined by
balance between
hydrostatic pressure
of the blood and
osmotic pressure
from plasma proteins
Also compliance and
glomerular filtration
rate help regulate
fluid balance
Interstitial
Intravascular
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Homeostatic Regulation of BP
Disturbance:90

Increase/decrease
B.P.
80
70
60
50

Receptors (BR)
East
West
North
40
30
20

Control center (VMC)
10
0

Effectors (Heart/BV)
1st 2nd 3rd 4th
Qtr Qtr Qtr Qtr
Positive Feed Back
In positive feedback mechanism the change
occurred is further amplified as its response.
• This has destabilizing effect, so does not result in
homeostasis.
• It is less common in naturally occurring systems
then negative feedback.
• e.g. Blood clotting , childbirth ,nerve
action potential are other types of positive
feedback.
Positive feedback control of labor contractions
Disturbance:Increase-contraction
of wall of uterus
Receptors- Stretch-
sensitive nerve cell
Control centerBrain interprets and
releases oxytocin
Effectors- Muscle of
uterus contract
Positive Feed Back
Compliment System
Intrinsic Pathway For Clotting
Application to human body
 Complex systems, such as human
body, must have homeostasis to
maintain stability and to survive.
 These systems not only give
tolerance to body for survival; but
they also adapt themselves and
evolve to modifications of the
environment.
Characteristics of best Homeostasis
 Sustainable systems require combinations
of both kinds of feedback.
 Generally with the recognition of
divergence from the homeostatic condition
positive feedbacks are called into play,
whereas:
 Once the homeostatic condition is
approached, negative feedback is used for
“fine tuning” responses.
Homeostatic Centre
• Most of these organs are controlled
by hormones secreted from the
pituitary gland, one of the
important homeostatic centre,
which in turn is directed by the
hypothalamus.
Role of body System in homeostasis
1) Nervous System: Act control of rapid of responses of body
2) Respiratory system: Regulate o,co2 &Ph
3) Circulatory system: Transport material and nutrient
4) Unary system: Regulate fluid volume, electrolytes and pH
5) Digestive system: Obtain nutrients water and electrolytes
6) Immune system: Defends against foreign invaders
7) Endocrine system: Release of hormones to blood
8) Reproduction system: Perpetuation of species
9) Muscular Skelton system: Protect body parts and allows
movement of the body
10) Integumentary system: protective barrier between external
environment