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Introduction to Physiology
Homeostasis
Def. ? maintenance of the constancy of the
internal environment of the body.
Internal environment ? milieu interieur
extracellular fluid which includes
interstitial fluid.
Simple diffusion -
Movement of molecules from higher
concentration to lower concentration till
equilibrium is reached
Diffusion can takes place through:
a) Lipid bilayer
i) Lipid soluble substances-
O2,Co2,alcohol, steriods etc
ii) Lipid insoluble ? water (through
spaces bet lipid mol) urea, sugar
(less or no permeability)
iii) Electrolytes ? impermeable
? charge on fatty acid chain
- Hydrated forms are larger
Factors affecting rate of diffusion
? Lipid solubility
? Molecular size & wt.
Molecular
? Temperature
? Thickness of membrane
Membrane related
? Surface area
? Concentration gradient
? Pressure gradient
Gradients
? Electrical gradient
p. Fick's law of diffusion ?
Im
Q
CPA
MW X
Q = net rate of diffusion
C = conc. gradient of a substance
P = permeability of membrane to the sub.
A = surface area of a membrane
MW = molecular wt. of sub.
X = thickness or distance
Two big jump in the tree of LIFE
? Movement
? Multicellularity
Volume and composition of this fluid
should be maintained constant (within
narrow limits) in spite of changes in
external environment for the normal
function of cell.
Failure of homeostasis leads to disease
Some regulating systems and their
functions ?
Resp. system - CO2 content
Liver and pancreas ? glucose
Kidney ? conc. of ions
CVS ? blood flow and temp regulation
Nervous and endocrine systems
regulate the function of other systems
Composition of ECF is same all over
the body because of constant mixing
of interstitial fluid and blood and
circulation of blood
Foundation steps for the movement
? Mass and Newton law of motion
? Self generated movement (Intention and will )
? Role of dual nature of Charge
The role of permeability and RMP
? Cell membrane
? Lipid bilayer
? Lipid soluble substance can freely pass though the cell
membrane
Thought question???
? Does lipid soluble substance pass through the gap between
two lipid molecule or it pass through the lipid itself?
Transport of charge ions across cell membrane
? Need for special carrier or channel or transporter
? Sodium channel
Thought question
? Size of sodium channel
? Approximate number of sodium channel in typical cell
? Carrying capacity of sodium channel
? Number of transported molecule in unit time
? Duty cycle duration
Body fluid compartments-
60% of body wt.(70kg.) ? 42 lits.
ICF-2/3 -28lits
ECF ? 1/3 ? 14 lits
2 lits in RBC
Transcellular -
Plasma -3lits -
Interstitial fluid 1-2 lits
5% 1/5
-11 lits. 3/4
7% of fluid in intravascular compartment
Body fluids
?62% of body wt in males and 52 % in
females
?72% of lean body mass (adipose free)
body wt is 70kg in man
body water is 42 lits.
28 lits ( 2/3) ICF ? 2 lits - intravascular
14 lits. (1/3) ECF ? 3 lits - intravascular
Body fluids
Measurement of body fluid compartments-
?indicator dilution technique ?
?Criteria for ideal dye ?
?Dye should get uniformly diluted only in
the compartment whose whose volume
is to be measured
Body fluids
?Dye should be nontoxic,
?should not change fluid volume,
? should not be metabolized, altered
?or excreted in significant amount
? should be able to estimate easily
Body fluids
Two spaces are calculated indirectly ?
- Intracellular fluid compartment
( TBW ? ECF)
- Extravascular fluid compartment
(ECF - plasma vol.)
Body fluids
Example
Inulin for ECF ? 100 mg inulin injected
After 30 min. inulin conc in blood ?
0.75 mg /dl
25 mg excreted in urine during 30
mins.
ECF vol = 100 ? 25 / 0.75 = 10000 ml
= 10 lits.
Body fluids
Substances used ?
TBW ? D2O, tritiated H2O, aminopyrine
ECF ? Na thiosulphate, sucrose, mannitol,
Intravascular fluid ?
Plasma vol. - Evan's blue, T
131
1824 ,
I2
Hematocrit
Osmolarity of ECF = 290 mOsm / lit
? Control system
? OR
? Regulating system
Limitations ?
- age
Undamped oscillations due to long dead
time and more gain of system ?
overcorrection
e.g. Chyene Stoke's breathing, clonus
during deep reflexes
Body fluid compartments-
60% of body wt.(70kg.) ? 42 lits.
ICF-2/3 -28lits
ECF ? 1/3 ? 14 lits
2 lits in RBC
Transcellular -
Plasma -3lits -
Interstitial fluid 1-2 lits
5% 1/5
-11 lits. 3/4
7% of fluid in intravascular compartment
This post was last modified on 08 April 2022