Скачать или смотреть Human Body Fluid Dynamics Quiz base video-2

Summary of Body Fluid Compartments

The body contains several fluid compartments that together maintain internal stability and support normal physiological function. Total body fluid is mainly divided into two major compartments: intracellular fluid (ICF) and extracellular fluid (ECF).

1. Major Fluid Compartments

Intracellular fluid (ICF):
This is the fluid inside the trillions of body cells.
It represents about two-thirds of total body fluid, or 28 liters in a 70-kg adult man.
This equals roughly 40% of total body mass.
Although cell types differ, the internal fluid composition is remarkably similar across different cells and even different species.

Extracellular fluid (ECF):
This includes all fluid outside cells and makes up about one-third of total body fluid, or around 14 liters in a 70-kg man (~20% of body mass).
It has two major subdivisions:

Interstitial fluid: About 11 liters, or more than 75% of the ECF.

Plasma: About 3 liters, nearly 25% of the ECF. Plasma is the fluid portion of blood.

Because capillary pores allow free movement of almost all solutes except proteins, plasma and interstitial fluid have nearly identical compositions except for protein differences.

2. Transcellular Fluid

A smaller specialized group of fluids called transcellular fluids includes:

synovial fluid

cerebrospinal fluid

peritoneal, pericardial, and intraocular fluids

Together, these make up 1–2 liters and are considered specialized ECF because their composition may differ significantly from plasma.

3. Total Body Water Differences

Total body water varies depending on:

Age: Older individuals have less total fluid because of reduced muscle mass and increased fat.

Sex: Females generally have more body fat, so their total body water is lower, around 50% of body mass.

Body composition: Fat contains little water; muscle contains a lot.

Infants: Newborn and premature infants have the highest water content, around 70–75% of body mass.

Modern increases in average body weight also change absolute fluid volumes. For example, adults in the United States often weigh far more than the "standard" 70-kg reference, so their fluid compartment volumes scale upward accordingly.

4. Blood Volume and Hematocrit

Blood is considered a separate compartment because it is contained in the circulatory system.

Total blood volume is about 7% of body mass, roughly 5 liters in adults.

About 60% of blood volume is plasma and 40% is red blood cells.

Hematocrit represents the fraction of blood that is made up of red blood cells.

Typical values: 0.42 in men and 0.38 in women.

Severe anemia can lower it to 0.10, whereas polycythemia may raise it to 0.65.

5. Composition of Fluid Compartments

The ECF and ICF differ in their dominant ions:

ECF: Rich in sodium and chloride.

ICF: Rich in potassium, magnesium, and phosphate.

These differences are essential for electrical activity, cell function, and fluid shifts across membranes.