Things to know for REN Flashcards
What is the relationsip between input and output
INput must generally equal Output
How do we get water into the body
Drinking
Food
Metabolism
How do we lose water
- Lungs: exhaling
- skin: sweatin
- bowels: low volume losses cuz large bowel reabsorbs water
- kidneys can change urinary output in a variety of different ways
What is a fluid
fluid is a substance that deforms under a shear stress.
physiology, the important fluids are those in which water, or a fat/lipid, are the solvent.
What are the body fluid compartments
- Intracellular water (inside cells)
- Interstitial water: filling the space between cells, amongst the extracellular matrix
- Fat
- Plasma (blood)
- Transcellular fluid: separated from the extracellular fluid by a membrane usually lined by epithelial barrier (e.g. CSF, peritoneal fluid, aqueous humor)
- CSF is different compared interstitial fluid
Give examples of transcelluar compartments
- Peritoneal Space: Can greatly expand (used therapeutically during peritoneal dialysis)
- CSF:protected by the Blood-Brain Barrier (endothelial cells joined by tight junctions; with a role for glia)
- Pleural cavity
- Sinovial fluid
How do we measure body fluid
You would inject a substance which is known to distibute in the compartment
and from that work out the volume of distribution
can measure plasma: by using deuterium or tritium to replace the normal hydrogen in water
can label protiens, for example evans blue
can measure extracelluar fluid: thiosulfate, insulin (problem can pass intracellualry)
What are the general concentrations of ions in the body fluids
K+-> high intracelluar, low extracelluar
Cl-: high extracelluar, low intracelluar
Na+: high extracelluar low intracelluar
How much is the usual body osmolality
285mOsm kg-1
How does calcium float around in the body
50% is bound to albumin
the other half is free floating in the plasma
free calcium more biologically active
What would happen to the total calcium conc during liver failure
albuimn conc will fall (liver makes albumin)
then the total calcium concentration would fall
How do we calculate free calcium
Ca corrected= Ca total +0.020 (40-albumin)
What is an osmole
number of molecules that a compound dissociates into when dissolved in solution
100 mmol of NaCl -> 200 mOsm in solution, because it dissociates into Na+ and Cl-.
What is meant my osmolality
number of osmoles per unit mass of the solvent
(Osm.kg-1)
What is meant by osmolarity
number of osmoles per unit volume of the solution (Osm.l-1)
What is meant by osmotic pressure
is a force that drives water movement that is proportional to osmoloaity
high water potential is the same as low osmotic pressure
this means the more salts you have in solution, the more water that moves towards
What is meant by “two solutions are isoosmotic”
they share the same osmolality
What is meant by istonic
when theres no net fluid movement
What is the main osmotic potential in the caps caused by
proteins
force caused by proteins called oncotic pressure as well
What drives water movment in caps
hydrostatic pressure and oncotic pressure
Can you give an example of osmotic pressure chnages
Albumin is a protein is plasma
a fall in albumin can be caused by
liver failure (decreased production)
renal failure (increased protein loss)
What can happen if theres a fall in plasma proteins
- plasma protein can no longer keep water in circulation
- so onoctic pressure falls, so water will move out
- so water will acculamae in intersital spaces
- For example pulmonary, peripheral (Oedema, ascites)
Where is odema a problem
in the brain
How can a brain odemema be corrected
we can use mantitol
- it is a stable sugar alchol
- it is inetced intravasuclarlly so it increases the plasma osmolality
- increases osmotic pressure, so water moves back into circluation
- pulls water from intracellaur and transcualleu aplces
- which helps decreases intracranial haemmoraghe
Modern use: inhaled for cystic fibrosis management
it is also an osmotic diuretic because causes water to move out of the kidneys
