Volume and Distribution of Body Fluids

Question 1

Body Fluid Compartments

Answer 1

• 60% of body is water
• Intracellular Fluid (ICF) - represents all the fluid inside the cells
• Extracellular Fluid (ECF) - represents all the fluid not inside the cells
• interstitial fluid (ISF)
• plasma - fluid within blood
• transcellular fluid

Question 2

What is Osmosis?

Answer 2

passive movement of water across a semipermeable membrane from a region of low solute concentration (high water conc) to a region of high solute concentration (low water conc)

• if the membrane is permeable to the solute then conditions on either side of the membrane will quickly reach equilibrium by solute driving force, not osmotic forces

Question 3

what is osmolarity?

Answer 3

• the total number of dissolved particles per kg of solvent (water)
• number of osmoles per L of fluid (osmol/L)
• osmole - 1 mole of dissolved particles
• substances which dissolve in H2O increase the number of dissolved particles and increase osmolarity

Question 4

what is osmotic pressure and tonicity?

Answer 4

• osmotic pressure - opposing pressure required to prevent osmotic movement of H2O across a given membrane: kPa or mmHg
• tonicity - osmotic effect of a solution at cell membrane relative to normal extracellular fluid: isotonic, hypotonic or hypertonic

Question 5

fluid exchange between compartments

Answer 5

• continuous movement between: plasma and ISF (capillary wall), ICF and ISF (cell membrane)
• normally ISF is isotonic with ICF - the relative concentrations of solute and water are equal on both sides of the membrane and therefore water does not move in or out of the cell

Question 6

why are isotonic solutions the best choice for infusion directly into bloodstream?

Answer 6

prevents cell swelling (hypotonic) or cell shrinking (hypertonic), allows no change to occur

Question 7

how can the body decrease body water?

Answer 7

• increasing urine output (decreasing ADH)
• sweating in hot climates
• sweating during exercise
• blood loss
• diarrhoea
• vomiting
• burns
• alcoholic beverages
• cholera
• excessive loss can lead to hypovolaemia or dehydration

Question 8

symptoms of decreased ECF volume

Answer 8

• decreased blood pressure
• increased pulse
• dry mucous membranes
• soft/sunken eyeballs
• decreased skin turgor
• decreased consciousness
• decreased urine output