Body water

• Adult person contains ~60% of water, i.e. 70

kg weighting person 42 l

• 2/3 (~28 l) of body water is intracellular fluid
• , 1/3 (~14 l) extracellular fluid
• 4/5 of extracellular fluid (~11 l) is interstitial

fluid and 1/5 (~3 l) the blood plasma

• Extracellular fluid also contains transcellular

fluids: cerebrospinal fluid (CSF), secretions of
exocrine glands, etc

Body fluids

• Glandular secretions, filtrates or

composites of several
simultaneously running processes

• Body fluids usually contain many

components

• Body fluids have several functions

based on their component
properties.

Transfer of substances

between different fluid

compartments

• Inside of the compartment:

concentration or pressure gradient

• Between compartments:

Extracellular space – cells: ordinary

and osmotic diffusion
Blood plasma – interstitial space:

diffusion - filtration (see the Starling

equation by microcirculation or

ultrafiltration in kidneys)

Estimation of the fluid

compartment volume

•

The most popular way to estimate those

volumes is the dilution method, which takes into

account a decrease of indicator substantce

content in a new common volume.

•

D

2

O as an indicator is good to measure total

body water

•

Inulin is good to measure volume of extracellular

fluid compartmet, because it can penetrate

capillaries but not cell membranes.

•

Evans blue or radioactive

131

I are good to

measure blood plasma volume, because they

well in circulation.

Ionic composition of

extracellular and intracellular

fluids (mmol/liter)

ECF

ICF

Na

+

145

12

K

+

4,5

150

Ca

++

2,5

10

-4

pH

7,4

7,0-7,2

Cl

-

103

4

HCO

3

-

27

12

Daily water balance

Intake

Loss

Drinking 1,5 l

Urine 1,5 l

Food 1,0 l

Sweating and

evaporation from

skin 0,7 l

Metabolism 0,3 l

Evaporation from
airways 0,5 l
Faeces 0,1 l

In sum: 2,8 l

In sum: 2,8 l

Blood, general features

• Fluid connective tissue, amount 7-8%

of body weight, ~5 L

• ~55% of blood volume is plasma and

~45% cells

• Blood is a temporary home for its

constituents, they have different
ways and mechanisms to appear and
leave blood.

Main functions of blood

1. A giant transportation system
2. Milieu or homeostatic funtion. Organism tries to

keep blood composition stable and it help to
hold interstitial environment stability

3. Defense

3.1. Defense against blood loss or bleeding –

hemostasis, blood coagulation.

3.2. Defense against foreign biological material

or immunological defense

To realise those functions blood has to be

permanently circulating !!!!

Physical and chemical

properties of blood

Total blood density 1050-1060 g/l
Plasma density 1024-1030 g/l
Density of blood cells 1089-1097 g/l
Osmotic pressure 7,4-7,6 atm
Colloidosmotic or oncotic pressure 25-30

mmHg 0,002 atm

Freezing temperature -0,55° C
Surface tension 67-77 mN/m
Total relative viscosity 4,0-5,0
Plasma relative viscosity ~1,8

Blood plasma

• 90-92% water
• 6-8% plasma proteins
• 1-2% heterogenic group of low

molecular weight substances

Plasma proteins

• Albumins (60%), globuliins &

fibrinogen (40%)

• Electrophoresis is classical method to

separate proteins

Albumins

• A homogeneous group of proteins

produced by hepatocytes

• Molecular weight: ~70 000 D
• Functions: nonspecific transport

vehicle (also endogenous regulatory
substances and drugs), main part of
the colloidosmotic or oncotic pressure
(~25 mmHg), nutritional function

Globulins

• A heterogeneous group of proteins,

produced by hepatocytes and plasma
cells (antibodies)

• α-, β- , γ-globulins
• Functions: transport (e.g. metals,

lipids etc), clotting factors, antibodies
against antigenes.

The synthesis of plasma

proteins

• 17 g albumins and 5 g globulins per

day.

• The half life time of albumins is 10-

15 days and globulins 5 days

The heterogeneous group of low

molecular weight substances (I)

Members of this group have different

structure, metabolisam and funtions,

but their blood contents are relatively

• The initial, intermediate and final

products of cell metabolism.

Initial products: glucose, amino acids,

lipids, O

2

Intermediate products: lactate
Final products: CO

2

, urea, uric acid, H

2

O

The heterogeneous group of low

molecular weight substances (II)

• Ions
Cations: Na

+

, K

+

, Ca

2+ etc

Anions: Cl

-

, HCO

3-

• Protons (H

+

)

, pH=7,35-7,45

Their contents have held very constant

which is important for body homeostasis

• Bioregulators: hormones, transmitters etc
• Vitamines