26 6-16 Flashcards
- List the factors that determine body water content and describe the effect of each factor.
Age - starts at 73% in infancy - declines to about 45% in elderly,
Body mass - skeletal muscle is 75% h2o so more muscle = more water,
Body fat - Adipose is least hydrated tissue 10%.
- Indicate the relative fluid volume of the fluid compartments of the body.
ICF - 40% of weight/25L,
ECF 20% of weight/15L (IF = 80%, Plasma = 20%)
Also, major anion in ICF is phosphate, chloride in ECF.
Water is ? % of body weight?
60%
- Indicate the relative solute composition of the fluid compartments of the body.
Na+ - 90% ECF (split between IF/plasma),
K+ - 98% ICF,
Ca2+ - 99% bone
- Contrast the overall osmotic effects of electrolytes and nonelectrolytes.
Electrolytes - dissociate in water to ions, can carry a charge. Inorganic salts, acids, bases, some proteins.
Non-electrolytes - Do not dissociate in water, do not carry a charge. Most organic molecules, (glucose, urea.)
Electrolytes have much greater osmotic power than nonelectrolytes because each electrolyte dissociates into 2 or more ions.
Because water moves from an area of lesser osmolity to greater, electrolytes have the greatest ability to shift water.
Electrolyte concentrations are expressed in?
mEq/L
- Describe factors that determine fluid shifts in the body.
Anything that changes solute concentration in any compartment leads to net water flows.
Substances must pass through both the plasma and IF to reach ICF (exchanges occur continuously.)
Protein free plasma is forces out of the blood by hydrostatic pressure and almost completely reabsorbed due to colloid osmotic pressure of plasma proteins.
Movement of water between IF and ICF involses osmotic flow that is equal in both directions.
Ion fluxes between IF and ICF are restricted, but movement of gases, nutrients and wastes typically occur in one direction.
How does water enter the body?
Ingested foods 30% and liquid 60%, cellular metabolism 10% (“metabolic water”.)
How does water leave the body?
Sensible: Feces 4%, Sweat 8%, Urine 60%
Insensible: losses via skin and lungs 28%
How much water to remain properly hydrated?
2500ml in, 2500 out. Input must equal output.
Obligatory water loss
Occurs regardless of the state of hydration because of insensible water loss and 500ml of urine needed to get rid of nitrogenous waste.
Faculative water loss
Controlled water loss that is dependent on state of hydration and is hormonally regulated in DCT/CD
Which five hormones that are involved in regulating fluid output.
ADH - secretion is promoted/inhibited by hypothalamus in response to changes in the solute concentration of ECF/large BV or BP changes/vascular baroreceptors.
Angio II - stimulates hypothalamus and post pit/ADH.
Aldosterone - save salt and water will follow.
ANP/BNP - increases urine output to ↓ BV and BP
(ADH is most important of these)
Fluid imbalance with constant osmolarity:
Hemorrhage, sever burns, chronic vomit, decreased fluid loss thru kidneys.
Fluid imbalance with changes in osmolarity:
(fluid loss/gain that is not isotonic/isosmotic) Dehydration - due to profuse sweating, ect, water output exceeds input.
Water intoxication/hypotonic hydration - result of renal insufficiency or excessive H2O quickly. Leads to cerebral edema/lysis of neurons.
Edema - accumulation of fluid in IF from ↑ HP/permeability.
Hypoproteinemia - Tissue edema because of protein deficient plasma.
