Fluid Compartments

Extracellular fluid (ECF)

Makes up 1/3 of total body water, divided into blood plasma and interstitial fluid, maintaining appropriate composition and volume of ecf = essential for proper functioning of cells and tissues

Interstitial fluid

Allows for exchange of nutrients, gases and waste products between cells and blood vessels

Intracellular fluid (ICF)

Makes up 2/3 of total body water, fluid within cells of body, consists mainly of water with dissolved solutes (ions, proteins, nutrients), composition of icf carefully regulated to support cellular processes

ICF and ECF

Movement of substances between ecf and icf occurs via osmosis, diffusion, active transport and filtration, have same osmotic pressure = solute concentrations inside and outside cells are relatively balanced

Water movement

Via osmosis when there is a difference in solute concentration between two sides of semipermeable membrane

Osmosis 

Process by which water molecules move from an area of lower solute concentration to a higher solute concentration through a membrane that allows only water to pass and not the solutes

Hypertonic solution

If a cell is placed in a solution with higher solute concentration than solute concentration inside the cell, water will move out of the cell to dilute the higher concentration outside = cell will shrink or undergo crenation

Hypotonic solution

If a cell is placed in a solution with lower solute concentration than solute concentration inside the cell, water will move into the cell = cell will swell and potential bust = cell lysis

Isotonic solution

if a cell is placed in a solution with the same solute concentration as solute concentration inside the cell, there will be no net movement of water = cell size remains relatively stable

Electrolytes

Electrically charged particles or ions, primarily dissolved in bodily fluids including blood, plasma, interstitial fluid and icf, released when inorganic ions dissociate, critical role in maintaining proper fluid balance

Sodium concentration

Determines ecf volume, as plasma sodium increases plasma volume will need to increase to maintain constant concentration - can cause water to move out of cells into blood plasma

Kidneys and sodium concentration

Kidneys work to maintain proper balance of sodium and water to prevent imbalances from becoming severe, kidneys will increase water reabsorption when acted on by ADH