In pharmacokinetics

Pharmacokinetics

Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism...

, a compartment is a defined volume of body fluids. It is distinguished from anatomic compartments, which are bounded by fasciae. It is used in multi-compartment model

Multi-compartment model

A multi-compartment model is a type of mathematical model used for describing the way materials or energies are transmitted among the compartments of a system. Each compartment is assumed to be a homogenous entity within which the entities being modelled are equivalent...

s.

Examples

There are five major body compartments:

• blood plasma
  Blood plasma
  Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
  
  
• interstitial fluid
  Interstitial fluid
  Interstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
  
  
• fat tissue
• intracellular fluid
• transcellular fluid
  Transcellular fluid
  Transcellular fluid is the portion of total body water contained within epithelial lined spaces. It is the smallest component of extracellular fluid, which also includes interstitial fluid and plasma. It is often not calculated as a fraction of the extracellular fluid, but it is about 2.5% of the...
  
  

The transcellular compartment includes fluids in the pleural cavity

Pleural cavity

In human anatomy, the pleural cavity is the potential space between the two pleura of the lungs. The pleura is a serous membrane which folds back onto itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural cavity; it normally...

 or peritoneal cavity

Peritoneal cavity

The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...

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Comparison table

Compartment	estimated % of body mass
blood plasma	5
interstitial fluid	16
fat tissue	20 (see also body fat percentage Body fat percentage A person's body mass percentage is the total weight of the person's fat divided by the person's weight and consists of essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than... )
intracellular fluid	35
transcellular fluid	2

Mnemonic: 60-40-20-15-5: % of TBW, Intracellular fluid, Extracellular fluid, interstitial fluid, plasma