Introduction to Human Physiology

Abdul Aleem Khan

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Le Milieu Intérieur And

Homeostasis I and II

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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 bodyHow does the heart beat ?

How do we breathe ? How do we see ?

How do we remember ? How do we move ?

How do we reproduce?

What is human Physiology

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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 5

• 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)

Divisions of Physiology

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Atoms

Molecules

Organelles

Cells

Tissues

Organs

SystemsOrganism

Various levels of structural organization

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A Cell

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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)

Cell theory

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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 cellsThree different types of muscle cellsFat Storage cellsNerve cells that transmit electrical impulsesCells for reproduction

Cell Diversity

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Cells internal Environoment

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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.”

Claude Bernard

(1813-1878)

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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

Internal

Environment

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Internal

Environment

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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

Intracellular fluid(inside cells)

Body Water

Plasma(inside

blood vessels)

Interstitial Fluid(outside

blood vessels)

Extracellular fluid(outside cells)

Body water

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Major Elements % body wtOxygen 65%Carbon 18%Hydrogen 10%Nitrogen 3.4%Mineral ElementsSodium 0.17%Potassium 0.28%Chloride 0.16%Calcium 1.5%Magnesium 0.05%Phosphorus 1.2%Sulphur 0.25%Trace ElementsIron 0.007%Zinc 0.002%

Principal organic constituents

• carbohydrates sugars• fats fatty acids• proteins amino acids• nucleic acids nuclotides

Water = 60% adult male= 50% adult female

Chemical composition of body

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Nutrients and oxygen are distributed by the blood

Metabolic wastes are eliminated by the urinary and respiratory systems

Organ system

Interrelationship

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Co-ordination of Organ System

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Walter Cannon(1929)

Homeostasis

Maintenance of constancy of the Internal Environment

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Control Systems

Open Loop Systems

Closed Loop Systems (Feedback Systems)

Control center(Set point) Effector Controlled

variable

Sensor

Control center Effector Controlledvariable

Feedback Systems are of two types: 1. Negative feedback 2. Positive

feedback 21

Maintenance of constancy of the Internal Environment

Homeostasis

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Physiological variables

maintained by controlled systems

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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.

Homeostasis

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Negative feedback loop requiresSensor (Detector): specific to variable needing to be controlledComparator (Control system): reference point for sensor to compare againstEffector: if sensor comparator Error Signal restore variable to desired level

Comparator(reference point) Effector Controlled

variable

Sensor

DisturbanceErrorsignal

Feedback loop

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Homeostatic range -oscillation around setpoint

Change in setpoint1. Acclimatization 2. Biorhythms

Homeostasic

Setpoint

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The response reverses

the original stimulus.

Example:Blood pressure and blood glucose

regulation

The response enhances

the original stimulus

Example child birth

Negative

feedback System

Negative feedback System

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Maintenance of body

temperatureComposed of 1.Detector2.Control system3.Effector

The effector response Decreases or increases the effect of the original stimulus

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Stimulus: change in BPReceptors:

BaroreceptorsControl

Center: BrainEffector: Heart

Negative feedback System

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Negative feedback System

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Negative feedback System

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Negative feedback System

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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

Limitation of negative

feedback

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•Negative feedback - error signal reduces deviation from reference point

•Positive feedback - error signal increases deviation from reference point (vicious circle)

controlledvariable

disturbance

effector

sensor

++Errorsignal

Positive

feedback

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Stimulus: stretch of the

uterusReceptors:

stretch receptors (cervix)

Control Center: Brain

Effector: Uterus

Positive feedback System

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Positive feedback

System

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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.

Homeostasis

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