Regulation of fluid compartments and lymphatic system Flashcards
extracellular
consists of plasma and ISF (outside blood surrounding cells)
osmosis decides
intracellular: extracellular volumes
What decides ISF: plasma volumes
colloid osmotic pressure ( created by proteins) Hydrostatic pressure (created by heart)
Failure to regulate fluid compartments leads to
oedema
Osmosis def
net diffusion of H2O across selectively permeable membrane from high to low water conc
Osmoles
total number of particles (solute) in solution
1 Osm
1 mole (6.02 x 10^23) of solute particles in 1L
ratio of intra to extra particles
intra=extra= 300 mM= 300 mOsm
Osmolarity independent of
molecular weight- dependent on number of molecules not size
More particles =
higher osmotic pressure
osmotic pressure def
pressure required to prevent osmosis
extracellular = 300 mOsm/L
isotonic- no change
extracellular = 200 mOsm/L
hypotonic- cell swells
extracellular = 400 mOsm/L
hypertonic- cell shrinks
why can colloid osmotic pressure occur in the capillaries
capillary mem is semi-permeable
Permits diffusion of ions, water, O2, nutrients, and waste
NOT proteins
hence conc of proteins much higher in plasma than ISF
what is colloid osmotic pressure
pressure exerted by higher levels of protein in the plasma compared with ISF (6x)
Draws water back into plasma by osmosis
hydrostatic pressure
force exerted by blood upon capillary walls
Drives blood from plasma into interstitial space
Pressure drops as blood moves through capillaries
Higher hydrostatic pressure at the beginning than the end
NFP
capillary net filtration pressure
determines overall movement across capillary membrane
NFP =
(Pc + πif)- (Pif + πc)
Pc
capillary hydrostatic pressure
Pif
ISF hydrostatic pressure
πc
osmotic force due to plasma protein conc
πif
osmotic force due to ISF protein conc
P and π
P= hydrostatic pressure π= colloid osmotic pressure
At arterial end of the capillary
High NFP
in mmHg
net outward filtration
hydrostatic pressure dominates
At venous end
low NFP
net inward filtration
colloid pressure dominates
hydrostatic vs colloidal osmotic
filtration vs absorption
How much fluid a day is lost into tissues and what happens to it
8L per day, due to bulk flow
drains into lymphatic system and back into the blood
lymphatics essential for
absorption of ISF
Lymph system 2 main functions
drains fluid from the tissues and returns it to the cardiovascular system
Maintains immune response
Drainage (lymph)
excess fluid passes into lymph capillaries, through lymph nodes (detection of infection) before going back into the bloodstream at the neck (largest is thoracic duct that drains into the subclavian vein)
How is fluid driven in lymph vessels
valves
Action of muscles and breathing
Larger vessels surrounded by smooth muscle that contracts spontaneously and driven by pacemaker cells (heart)
Immunity (lymph)
Lymph fluid has WBCs
Collects antigens
Antigens recognised by B cells in lymph nodes leading to activation of immunity
B cells proliferate to make antibodies
Increased capillary pressure at both ends
leads to oedema and heart failure due to:
- excessive kidney retention of H2O
- Incr arteriolar resistance
- high venous pressure
Decr in colloid osmotic pressure
reduction in plasma proteins
loss of proteins in urine (kidney failure)
loss of protein in denuded skin areas (burns)
malnutrition
blockage of lymph noded
s
water can’t get back into blood- swelling
Intracellular oedema
eg friction blister of the skin
Depression of metabolic systems of the tissues and lack of nutrition to the cells
eg ischaemia: less activity of Na+ pumps leads to accumulation of Na+ in cells, causing osmosis of water into cells, swells
