LEWIS STRUCTURE OF A WATER MOLECULE • • • O H • H H • • + + H Covalent bond A covalent bond is a chemical bond formed by the sharing of a pair of electrons between two atoms. • O O • • • • • • • • • • • • • H H The approximate shape and charge distribution of water.
BODY WATER CONTENT Its about 75% in the newborn. Total water content declines throughout life. Healthy males are about 60% water; healthy females are around 50% This difference reflects females’: Higher body fat Smaller amount of skeletal muscle Less than 50% in older individual. Water content is greatest in brain tissue (about 90%) and least in adipose tissue (10%).
DAILY WATER BALANCE Daily Balance of Water Intake and Production in Sedentary Healthy Adults In a Temperate Climate At least 500 ml of urine per day is required just to excrete urea, creatinine, and other Solutes. Insensible losses from the skin and from the lungs can occur even when resting at normal room temperature.
FLUIDS COMPARTMENTS Fluid between the cells (intercellular or interstitial) Cell membrane Nucleus ICF Blood vessel
FLUIDS COMPARTMENTS Water occupies two main fluid compartments. Intracellular fluid (ICF) – about two thirds by volume, contained in cells Extracellular fluid (ECF) – consists of two major subdivisions Plasma – the fluid portion of the blood Interstitial fluid (IF) – fluid in spaces between cells Other ECF – lymph, cerebrospinal fluid, eye humors, synovial fluid, serous fluid, and gastrointestinal secretions.
COMPOSITION OF BODY FLUIDS Solutes are broadly classified into: Electrolytes – inorganic salts, all acids and bases, and some proteins Nonelectrolytes – examples include glucose, lipids, creatinine, and urea Electrolytes have greater osmotic power than nonelectrolytes Water moves according to osmotic gradients
ELECTROLYTES Nucleus The major components of plasma, intestitial fluid, and intracellular fluid. Crosshatching refers to other or minor components. Pr- , anionic proteins.
WATER DISORDERS Dehydration (loss of water) Edema(accumulation of water) Atypical accumulation of fluid in the interstitial space, leading to tissue swelling.
DEHYDRATION Cells lose H2O to ECF by osmosis; cells shrink 3 ECF osmotic pressure rises 2 Excessive loss of H2O from ECF 1 Mechanism of dehydration
BODY FLUID AND ELECTROLYTES Electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity. Sodium. Potassium Chloride Bicarbonate Help keep fluids in proper compartments. -Intracellular water -Extracellular water
Is the movement of water across a semipermeable membrane
Is affected by the concentration gradient of dissolved substances
OSMOSIS Water can flow both ways across the divider, but has a greater tendency to move from side A to side B, where there is a greater concentration of solute. The volume of water becomes greater on side B, and the concentrations on side A and B become equal. With equal numbers of solute particles on both sides, the concentrations are equal, and the tendency of water to move in either direction is about the same. 3 2 1 Now additional solute is added to side B. Solute cannot flow across the divider (in the case of a cell, its membrane).23
OSMOSIS When immersed in water, raisins get plump because water moves toward the higher concentration of sugar inside the raisins.
When sprinkled with salt, vegetables “sweat” because water moves toward the higher concentration of salt outside the eggplant.
The concentration of solutes is less than it is inside the cell, and the cell will gain water
Hypertonic solution Hypotonic solution Isotonic solution Animal cell. An animal cell fares best in an isotonic environ- ment unless it has special adaptations to offset the osmotic uptake or loss of water. (a) H2O H2O H2O H2O Normal Shriveled Lysed H2O H2O H2O Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environ- ment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. (b) H2O Turgid (normal) Flaccid Plasmolyzed THE WATER BALANCE OF LIVING CELLS