FLUID COMPARTMENTS
EXTRA CELLUAR
FLUID
PLASMA
INTRA CELLULAR
FLUID
INTERSTITIAL
FLUID
CSF
Intra ocular
Pleural
Peritoneal
Synovial
Digestive Secretions
TRANSCELLULAR
FLUID
Transcellular fluid:
is a small compartment that represents all those
body fluids which are formed from the transport
activities of cells. It is contained within epithelial
lined spaces. It includes CSF, GIT fluids, bladder
urine, aqueous humour and joint fluid.
Composition Of Body Fluids
The solutes in ICF and ECF body fluids
are organic and inorganic .
 Organic :compounds of small molecular
sizes such as glucose , urea, uric acid .
 Inorganic electrolytes such as Na+ , K+
 Cl- ……. .

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
Cl
108
108
4.0
HCO3
24.0
28.3
10
Protein
1.2
0.2
4.0
HPO4
2.0
2.0
11
ANIONS (mmol/l)
Interstitial Fluid:
Interstitial fluid consists of a water solvent containing
amino acids, sugars, fatty acids, coenzymes, hormones,
neurotransmitters, salts, as well as waste products from
the cells.
The composition of tissue fluid depends upon the
exchanges between the cells in the biological tissue and
the blood. This means that tissue fluid has a different
composition in different tissues and in different areas of
the body.
Physiological Function Of The ISF:
Interstitial fluid bathes the cells of the tissues. Thus
providing a media through which materials and metabolic
waste are exchanged between the cells and blood ,and
acting as a media for intercellular communication.
Interstitial Fluid:
Interstitial fluid consists of a water solvent containing
amino acids, sugars, fatty acids, coenzymes, hormones,
neurotransmitters, salts, as well as waste products from
the cells.
It is similar in composition to blood plasma, except for a
relatively low protein content (due to the low permeability
of capillaries to plasma proteins) .
Physiological Function Of The ISF:
Interstitial fluid bathes the cells of the tissues. Thus
providing a media through which materials and metabolic
waste are exchanged between the cells and blood ,and
acting as a media for intercellular communication.
Intracellular Fluid:

The cytosol or intracellular fluid is the liquid
found inside the cells .

Physiological Function :

The cytosol has no single function and is instead
the site of multiple cell processes including
metabolic processes (such as
glycolysis,gluconeogenesis, PPP) . It is also
involved in signal transduction from the cell
membrane to sites within the cell .
Homeostasis:
Refers to the variety of mechanisms that have evolved for
regulation of the volume and composition of the body fluids within
fairly narrow limits
.
Osmosis: Refers to
the movement of water across membranes
in response to differences in osmotic pressure between the two
sides of the membrane .Water generally migrates from the side
of the membrane with the more dilute solute to that containing
the concentrated solute.
Since water passes freely across cell membranes ,the volumes of
the various fluid compartments are determined by unique
solutes that are confined to each space . Which is the plasma
proteins in the intravascular volume ,sodium in the ECF
compartment and Potassium in the ICF compartment .
Homeostasis:
The osmolarity of ICF is determined mainly by its K+
concentration while that of the ECF by Na+ concentration
The volume of both compartments is maintained at
constant levels through mechanisms that provide
adjustments in the excretion of water , Na+ , and K+ in
response to variations in the enviroment.
 These adjustments are accomplished mainly by the
kidneys .

Homeostatic Regulatorty
Mechanisms:




The regulatory
mechanism involves
- a sensor .
- a controller .
- an affector .
Regulatory Mechanisms;
1-Existance of receptors sensitive to variations in
osmolar concentration of the ECF comopartment
2- The alterations in production and release of key
hormones such as ADH antidiuretic hormone and
aldosterone which regulate the excretion of water
Na+ and K+ .
3-The Intrarenal mechanisms concerned with
excretion of water and solutes .
How does it work ?
Blood diluted
sensed by
osmoreceptors in the brain
will
inhibit ADH secretion
which lead to
excretion of water from the renal tubules
resulting in the excretion of a large volume of
diluted urine .
 Blood concentrated (dehydration)
sensed by osmoreceptors
stimulate
ADH secretion
promoting water
reabsorption from the kidney tubules
more water is returned to blood thus
decreasing blood osmolarity .

Control Of Body Fluid
Volume(Homeostasis):

In health the volume and composition of
various body fluid compartments are
maintained within physiological limits
even in face of wide variations in intake
of water and solutes .
Antidiuretic hormone is produced by the
hypothalamus ,stored in the pituitary gland
and causes the reabsorption of water from
the distal tubules ,collecting tubules and
parts of loops of henle .
 Aldosterone produced by the adrenal
cortex and is responsible for 95% of all Na+
tubular reabsorption from the distal tubules
 ,collecting tubules and part of loop henle.
