Interstitial fluid
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Interstitial fluid is one of the two components of extracellular fluid, the other being plasma. On average, a person has about 11 liters of interstitial fluid providing the cells of the body with nutrients and a means of waste removal.
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Production and Removal
Plasma and interstitial fluid are essentially identical except for location. Plasma, the major component in blood, communicates freely with interstitial fluid through pores and intercellular clefts in capillary endothelium. Blood pressure causes continuous production of interstitial fluid by pushing plasma through these openings into the interstitium. The pores are too small to allow proteins or cells through, but most other solutes can pass. Additionally, passive diffusion and active cellular transport from the blood also play a role in fluid production.
Eventually, the interstitial fluid is forced back into the capillaries by osmotic pressure. Additionally, the fluid may drain into the lymphatic vessels.
Composition
Interstitial fluid consists of a water solvent containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts, and as well as waste products from the cells.
Physiological Function
Interstitial fluid bathes the cells of the tissues. This provides a means of delivering materials to the cells, intercellular communication, as well as removal of metabolic waste.