fluid dynamic and edema

majority of water in the body is stored in

intracellular fluid (inside cells)

the rest of the water in the body is stored in

extracellular fluid, in the interstitial fluid (between cells) and plasma

for fluid to pass between intracellular and extracellular

it has to move across the cell membrane

for fluid to move between interstitial fluid and plasma

it has to diffuse through the capillary membrane

capillary is permeable to

water but not proteins

protein is osmotically active

pulls water towards it

we are able to deliver O2, blood, and water to all tissues because

capillaries are surrounded by a single cell layer of endothelial cells

hydrostatic pressure

liquid pressure in every compartment of the body - water always wants to spread out

capillary hydrostatic pressure

always an outward force (pushing against the capillary walls to try and get into the interstitial space)

interstitial hydrostatic pressure

wants to push out of the interstitial space and into the capillary

if Pc = Pif

no movement occurs

if Pc>Pif

fluid leaks out of the capillary, filtration

is Pc

fluid leaks into the capillary, reabsorption

oncotic pressure

effect of proteins on the movement of water

capillary oncotic pressure

accumulated force of each protein trying to hold water towards it, inward pressure

interstitial oncotic pressure

towards interstitial space proteins (small because few proteins in interstitial space)

net filtration pressure (out)

(Pc-Pif)-(πc-πif)

if net filtration pressure is a positive value

filtration is occuring - fluid leaving capillary

if net filtration pressure is a negative value

reabsorption is occuring - fluid is going into capillary

edema

increased fluid in interstitial space

transduate

fluid accumulating in interstitial space has no proteins (purely water)

if net filtration is occuring due to "starling" net filtration, the fluid will be

transduate

exudate

protein rich fluid in interstitial space - proteins have to exit

for exudate edema to occur

capillary must be opened to allow proteins out into the fluid (seen with inflammation)

causes of edema

increased hydrostatic pressure, reduced plasma oncotic pressure, inflammation and lymphatic obstruction

assessment of edema

apply pressure to affected area, measure depth of pit and rebound time

pitting edema

indentation left after pressing skin because fluid went into the capillary from the interstitial space (would return quickly without edema)

pitting edema is an example of

reabsorption

nonpitting edema

swelling that does not indent from pressure due to high interstitial oncotic pressure (lots of proteins in the area)