Lecture 2: Body fluid compartments Flashcards
1
Q
What is the water distribution within humans?
A
2
Q
Osmolarity vs osmolality
A
- Osmolarity is number of osmotically active particles per litre of total solution
- Osmolality is number of osmotically acitve particles per weight of solvent
- Osmolarity replaced osmolality
3
Q
What is tonicity?
A
- It describes the osmotic pressure a solute exerts across a cell membrane
- Hypotonic solution makes a cells swell
- Hypertonic makes a cell shrink
4
Q
What happens if there is a charged ion that cant diffuse across the membrane on one side?
A
- Will cause the ions of the opposite charge to diffuse towards it and will cause that side to be hypertonic which generate an oncotic pressure towards that side
- This is called the gibs-donnnan equilibrium
5
Q
How do cells balance the oncotic pressures across their membranes?
A
- Pump out osmotically active ions (Na+) against their ocncentration gradient with Na/K pump
- This results in K+ and proteins inside cells being isotonic with Na+ outside the cell
6
Q
What charges to proteins tend to have and what effect does this have?
A
- They are negatively charged
- effects gibs-donnan equilibrium (reason for Na/K pump)
7
Q
Why is ECF osmolarity very important?
Hence what happens if it begins to change?
A
- Variation by only 1-2% will cause it to either make brain shrink or expand which is bad
- If ECF osmolarity begins to change ECF volume must change accordingly to return osmolarity back to normal. It can be regulated within a range of 15%
8
Q
What happens if you eat a lot of salt?
A
- trasient increase in plasma osmolarity –> Increased renal salt excretion (with a few days lag) hence:
- increase in water retention
- increased thirst
9
Q
Why is water cleared much more quickly than saline?
A
- Water decreases osmolarity which causes increased excretion by the kidneys and is hence rapily excreted
- Saline does not alter osmolarity hence is retained
