![]() The volume of body fluid, blood glucose, oxygen, and carbon dioxide levels are also tightly homeostatically maintained. Homeostasis regulates, among others, the pH, sodium, potassium, and calcium concentrations in the ECF. ![]() The ECF composition is therefore crucial for their normal functions, and is maintained by a number of homeostatic mechanisms involving negative feedback. The extracellular fluid, in particular the interstitial fluid, constitutes the body's internal environment that bathes all of the cells in the body. The ECF can also be seen as having two components – plasma and lymph as a delivery system, and interstitial fluid for water and solute exchange with the cells. The remaining small portion of the ECF includes the transcellular fluid (about 2.5%). Lymph makes up a small percentage of the interstitial fluid. Plasma and interstitial fluid are the two components that make up at least 97% of the ECF. The main component of the extracellular fluid is the interstitial fluid that surrounds cells.Įxtracellular fluid is the internal environment of all multicellular animals, and in those animals with a blood circulatory system, a proportion of this fluid is blood plasma. Extracellular fluid makes up about one-third of body fluid, the remaining two-thirds is intracellular fluid within cells. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight women and the obese typically have a lower percentage than lean men. In cell biology, extracellular fluid ( ECF) denotes all body fluid outside the cells of any multicellular organism. The physical barrier between the intracellular fluid and interstitial fluid is the cell plasma membrane, and the physical barrier between the interstitial fluid and plasma is the capillary endothelium.The distribution of the total body water in mammals between the intracellular compartment and the extracellular compartment, which is, in turn, subdivided into interstitial fluid and smaller components, such as the blood plasma, the cerebrospinal fluid and lymph These fluid compartments are emphasized by the gray background color. If we examine this figure carefully, and if we consider the functional interconnections of the fluid compartments, it becomes clear that there are three major fluid compartments: (1) intracellular fluid, (2) interstitial fluid, and (3) plasma. Transcellular fluid generally comprises up to about 2.5% of the total body water (or up to ~1 L). Cerebrospinal fluid (the fluid bathing the brain and the spinal cord), intraocular fluids (aqueous and vitreous humors), inner ear fluids (endolymph and perilymph), pericardial fluid, peritoneal fluid, synovial fluids (in joints), as well as some other fluids are components of the transcellular fluid in the body. This fluid is generally separated from the plasma by an additional epithelial layer in addition to the capillary endothelium. Transcellular fluid is found in small amounts in different body regions and, in total, comprises a very small portion (though not unimportant) of the total body water. It is generally about 75% of the volume of ECF (or ~10.5 L). Interstitial fluid is the fluid that directly bathes the cells and tissues in the body. The extravascular compartment is further subdivided into two compartments: interstitial fluid and transcellular fluid. The volume of plasma is about 3 L and is generally about 25% of the volume of ECF. Plasma is the fluid portion of blood (i.e., whole blood minus the so-called formed elements red cells, white cells, and platelets). The fluid in the intravascular compartment is the fluid that is present in all of body blood vessels. These two compartments are separated by the capillary endothelium (lining of the walls of the capillaries). The extracellular fluid (ECF) compartment is further subdivided into the intravascular compartment and the extravascular compartment. Approximately 33% of the total body fluid (or ~20% of total body weight) is in the extracellular fluid (ECF) compartment. The intracellular fluid is separated from the extracellular fluid by the cell plasma membrane. Therefore, the total volume of ICF is ~28 L (cytoplasmic volume of all cells combined). ![]() Approximately 67% of total body water (or ~40% of total body weight) is in the intracellular fluid (ICF) compartment, which is the fluid that is present in the cytoplasm of all cells of the body. If we use 70 kg (155 lb) to represent the average adult male, the total volume of water in the body can be calculated to be about 42 L. In a typical adult male human, approximately 60% of the total body weight is composed of water. ![]()
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