Introduction to
Human Physiology
Abdul Aleem Khan
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WHAT IT “IS” HOW IT “WORKS”
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A branch of science that deals
with the functioning of Human
body
How does the heart beat ?
How do we breathe ?
How do we see ?
How do we remember ?
How do we move ?
How do we reproduce?
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To answer these global questions it is
essential to understand that the
functional unit of the body is the cell.
How cells (like muscle, nerve) function?
And how similar and dis-similar types of
cells work together at various
organisational levels (integration)  as a
whole organism
All most all life processes are governed
by laws of physics and chemistry
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• Integumentary Physiology (system)
• Cardiovascular Physiology (system)
• Respiratory Physiology (system)
• Gastrointestinal Physiology (system)
• Renal Physiology (system)
• Reproductive Physiology (system)
• Musculo-skeletal Physiology (system)
• Neurophysiology Nervous system
• Endocrine Physiology (system)
• Immune Physiology (system)
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Atoms
Molecules
Organelles
Cells
Tissues
Organs
Systems
Organism
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The cell is the basic structural and
functional unit of living organisms
 The activity of an organism depends on
both the individual and collective activity
of its cells
 The biochemical activities of cells are
dictated by their specific subcellular
structures (principle of complementarity)
 Continuity of life has a cellular basis (cells
come from cells)

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There is really no “typical” cell. Cells have
different shapes, different sizes, different
functions, different life spans.
 Stem cells is pluripotent.
 Examples of Specialized cells:
Many different types of blood cells
Three different types of muscle cells
Fat Storage cells
Nerve cells that transmit electrical
impulses
Cells for reproduction

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“La fixité du milieu
intérieur est la condition
de la vie libre.”
“The fixity of the
internal environment is
the condition for free
life.”
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Claude Bernard in
1829 said: The
proper functioning
of the cells
depends on precise
regulation of
the composition of
their surrounding
fluid.
Surrounding fluid = Internal environment
= Le Milieu interier
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• Water is main solvent in living cells
• Hydrophilic molecules dissolve in water
• Hydrophobic molecules do not dissolve in water
• Amphiphilic - molecule part hydrophilic/part
hydrophobic
Body Water
Intracellular fluid
(inside cells)
Extracellular fluid
(outside cells)
Plasma
(inside
blood vessels)
Interstitial Fluid
(outside
blood vessels)
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Major Elements % body wt
Oxygen
65%
Carbon
18%
Water
Hydrogen
10%
Nitrogen
3.4%
= 60% adult male
Mineral Elements
= 50% adult female
Sodium
0.17%
0.28%
Principal organic constituents Potassium
Chloride
0.16%
Calcium
1.5%
• carbohydrates  sugars
Magnesium
0.05%
• fats  fatty acids
Phosphorus
1.2%
• proteins  amino acids
0.25%
• nucleic acids  nuclotides Sulphur
Trace Elements
Iron
0.007%
Zinc
0.002%
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Nutrients and
oxygen are
distributed by the
blood
Metabolic wastes
are eliminated by
the urinary and
respiratory
systems
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Maintenance of constancy of the
Internal Environment
Walter Cannon
(1929)
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Open Loop Systems
Control center
Effector
Controlled
variable
Closed Loop Systems
(Feedback Systems)
Control center
(Set point)
Effector
Controlled
variable
Sensor
1.
Feedback Systems are of two types:
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Negative feedback 2.
Positive feedback
Maintenance of constancy of the
Internal Environment
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• Process of maintaining the composition of the
internal body compartments within fairly strict
limits (ion concentrations, pH, osmolarity,
temperature etc).
• Require regulatory mechanisms to defend against
changes in external environment and changes due to
activity.
• Cellular homeostasis - intracellular fluid composition
• Organismal homeostasis - extracellular fluid
composition.
• Control system designed to maintain level of given
variable (concentration, temperature, pressure)
within defined range following disturbance.
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Negative feedback loop requires
Sensor (Detector): specific to variable needing to be controlled
Comparator (Control system): reference point for sensor to
compare against
Effector: if sensor  comparator  Error Signal  restore
variable to desired level
Disturbance
Comparator
(reference point)
Error
signal
Effector
Controlled
variable
Sensor
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 Homeostatic range -oscillation around setpoint
 Change in setpoint
1.
Acclimatization
2.
Biorhythms26
The response
reverses
the original stimulus.
Example:Blood
pressure and
blood glucose
regulation
The response
enhances
the original stimulus
Example child birth
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Composed of
1.Detector
2.Control system
3.Effector
The effector
response
Decreases or
increases
the effect of the
original
stimulus
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Stimulus: change
in BP
Receptors:
Baroreceptors
Control Center:
Brain
Effector: Heart
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•Negative feedback control is initiated after variable
is disturbed
•Amount of correction to be applied,
is assessed by
magnitude of error signal  incomplete correction
•Overcorrection  oscillations in controlled variable
•Disadvantages overcome by multiple regulatory
mechanisms.
Regulation of blood [glucose]
Insulin
  [glucose]blood
Glucagon   [glucose]blood
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•Negative feedback - error signal 
reduces deviation from reference point
•Positive feedback - error signal 
increases deviation from reference point
(vicious circle)
Error
signal +
disturbance
+
controlled
variable
effector
sensor
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Stimulus: stretch
of the uterus
Receptors:
stretch receptors
(cervix)
Control Center:
Brain
Effector: Uterus
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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.
Concepts of homeostasis dynamic.
Chemical, thermal, and neural factors
interact to maintain homeostasis.
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