Physiological outline of water and electrolytes in the body

2021-06-17 04:11 PM

Water is the body's largest single component. Children have the highest percentage of water to body weight, 75%.


The chemical reactions that occur in body fluids are essential to life. Many reactions are catalysed by enzymes that are only active under certain conditions. Small changes in total water content, pH, or electrolyte concentrations will alter these chemical reactions. The kidneys, respiratory system, skin system, and digestive system participate in the regulation of these parameters to stabilize homeostasis. The nervous and endocrine systems are also involved in regulation together with the above organ systems.

Body fluid compartments

Body fluids are divided into two categories:

Intracellular fluid: makes up two-thirds of body fluid, which is the fluid that resides within cells.

Extracellular fluid: accounts for 1/3, consisting of plasma and interstitial fluid found in the intercellular spaces. Some extracellular fluid is still localized in special compartments such as lymphatic fluid; cerebrospinal fluid; synovial fluid; vitreous humour; external and internal fluid in the ear; pleural, pericardial and peritoneal fluid; glomerular filtrate.

Components of body fluids

Components of body fluids:

Water is the body's largest single component. Children have the highest percentage of water to body weight, at 75%. This percentage decreases with age. In adult males, water accounts for 60%; for women, this rate is 55%.

Soluble substances:

Body fluids contain many different dissolved chemicals.

Electrolytes: Substances that dissociate into ions when dissolved in water. Mostly inorganic substances such as acids, bases, and salts. A few organic substances such as citric acid, oxaloacetic acid, lactic acid and many amino acids in proteins are also ionized.

Non-electrolytes: Substances that do not form ions when dissolved in water. Consists of mostly organic matter, such as glucose, urea and creatine. Only a small percentage of chemicals in body fluids are non-electrolyte.

Electrolytes in body fluids

Comparison of plasma and interstitial fluid:

Plasma contains many protein anions, while interstitial fluid contains almost no, because normal capillary membranes are not permeable to proteins. Plasma also contains slightly more Na+ than interstitial fluid, but less Cl-. The other components of the two translations are almost equivalent.

Compare intracellular and extracellular fluids :

The electrolyte composition of the intracellular fluid is significantly different from that of the extracellular fluid. In extracellular fluid, the most abundant cation is Na+ and the most anion is Cl-. In intracellular fluid, the most cations are K+ and the most anions are proteins and HPO42-.