Читать книгу Biochemistry For Dummies - John Moore T., Richard Langley H., John T. Moore - Страница 13
The Fundamentals of H2O
ОглавлениеWater is essential to life; in fact, human beings are essentially big sacks of water. Water accounts for 60 to 95 percent of living human cells, and 55 percent of the water in the human body is in intracellular fluids. The remaining 45 percent (extracellular) is divided among the following:
Plasma (8 percent)
Interstitial (between cells) and lymph (22 percent)
Connective tissue, cartilage, and bone (15 percent)
Water also is necessary as a solvent for the multitude of biochemical reactions that occur in the body:
Water acts as a transport medium across membranes, carrying substances into and out of cells.
Water helps maintain body temperature.
Water acts as a solvent (carrying dissolved chemicals) in the digestive and waste excretion systems.
Healthy humans have an intake/loss of about 2 liters of water per day. The intake is about 45 percent from liquids and 40 percent from food, with the remainder coming from the oxidation of food. The loss is about 50 percent from urine and 5 percent from feces, with the remainder leaving through evaporation from the skin and lungs. A water balance must be maintained within the body. If the water loss significantly exceeds the intake, the body experiences dehydration. If the intake significantly exceeds the water loss, water builds up in the body and causes edema (fluid retention in tissues).
In the following sections, we touch on the basic properties of this must-have liquid, as well as its most important biochemical function.