The human body is composed primarily of fluids, with water making up about two-thirds of the total body weight. The body's fluids are divided into two main compartments: intracellular fluid (ICF) and extracellular fluid (ECF). ICF makes up about 40% of total body water and is contained within cells, while ECF comprises around 20% and includes interstitial fluid, plasma, and transcellular fluids such as cerebrospinal fluid. ECF volume can be measured using substances that remain in the extracellular space, while total body water and plasma volume are determined through the dilution of markers distributed throughout the body's water compartments. Proper fluid balance is essential for acid-base regulation, electrolyte levels

1. BODY FLUID COMPARTMENTS
Dr Anu Priya J

2. Introduction
• Body is formed of solids & fluids
• The fluid part is more than 2/3 of the
whole body.
• Water forms most of the fluid part

3. 40%
15%
20%
5%
Total Body water
Blood volume 7% of body weight
5L in a 70 kg adult male

6. ECF constitutes of:
A. Interstitial fluid including
lymph
B. Plasma
C. Transcellular fluids
Transcellular fluids:
 CSF
 Intraocular fluid
 Gastrointestinal secretions
 Pleural fluid
 Pericardial fluid
 Peritoneal fluid
 Synovial fluid
 Fluid in urinary tract
More the amount of fat, lesser the ECF volume
Elderly – lesser ECF volume
Infants & children – greater ECF volume

7. Body electrolytes
• 7% of total body weight
• Functions of electrolytes in the human body
− Maintenance of acid-base balance
− Maintenance of normal osmolality and
volume of body fluids
− Ions like Na+,Ca2+,K+,Cl- , etc affects
excitability of cells

10. Distribution of ions across
the cell membrane at rest
Ion ICF (mmol/L of H20) ECF(mmol/L of H20)
Na+ 1.5 150
K+ 150 5.5
Cl- 9 125
Ca2+ 0.0001 1.2
Protein anion 65 <5
Mg2+ 58 3
HCO3- 10 2.8
PO4
3- 75 4

11. Deuterium oxide/heavy water, Tritium oxide, Aminopyrine
Inulin, Mannitol, Sucrose
131I

12. Applied aspect
Infants are prone to dehydration i.e.,
infants are more vulnerable for water loss due to:
• Absolute ECF volume is lesser
• Increased body surface area compared to mass
• Higher metabolic rate
• Physiologic inability of the infant’s kidneys to
concentrate urine
see http://www.ihrdni.org/068b-022.pdf

13. Thank you

14. Measurement of body fluid volumes
• Total body water is measured using dilution
principle.
• A marker is injected that will be evenly distributed in
all the compartments of body fluids.
• Marker that diffuses freely not only in the water
outside the cells, but also crosses the cell membrane
to reach the intracellular fluid.

15. • ECF volume is measured using substances that
cannot enter the cells, but can freely cross the
capillary membrane and thus distribute evenly in the
ECF compartments.
• Plasma volume is measured using substances that
binds specifically to plasma proteins, and will not
diffuse into the interstitium.
Measurement of body fluid volumes

16. http://www.ihrdni.org/068b-022.pdf