S1: Body Fluids Flashcards
What percentage of our body weight is water?
60%
What are the 2 reasons water is important?
Acts as a medium for nutrients and waste products
For diffusion of nutrients and water products
Stable volume and composition of the body fluids is essential for metabolism (homeostasis)
How does water content vary?
Decreases with elderly
Increases with increased body fat
State some ways how we gain and lose water
- we intake water through ingested fluids
- we intake water through metabolism
- we loose water primarily by urine (main regulator of fluid loss)
- water loss from skin/lungs
- loss of water through faeces and sweat
Intake of fluids should match output
What is the 60 40 20 rule?
60% of body is water
40% is in the intracellular fluid
20% is in the extracellular fluid
What is the barrier between blood vessel and interstitium?
Capillary wall
What is the barrier between intracellular fluid and interstitium?
Plasma membrane
Explain the different in permeability of the cell membrane and capillary wall?
CELL MEMBRANE
semi-permeable
-allows water only
It is impermeable to most ions and proteins but has pumps to AT molecules. Water can move freely usually through channels.
💧Osmotic pressure drives this movement of water
CAPILLARY WALL
More permeable
- allows water, electrolytes but not proteins
It is made of endothelial cells, only large molecules (e.g. proteins) can exert an osmotic pressure across it.
💧Hydrostatic pressure drives movement of water.
What two factors affect the movement of between compartments?
Pressure
- ionic pressure
- osmotic pressure
The nature of the barrier
- cell membrane
- capillary wall
Does the ECF or ICF have more protein?
ICF: Rich in protein
ECF: Poor in protein
Compare the ionic compositions of ICF and ECF
ECF——
High in sodium (150mM)
High in chloride (120mM)
Some bicarbonate (26mM)
ICF—— Low in sodium (15mM) Minute chloride (<1mM) High in K+ (140mM) High in phosphate
Define diffusion
Movement of molecules down a concentration gradient due to random motion
Define osmosis
Net diffusion of water across a selectively permeable membrane, from region of high water concentration to a region of lower concentration
What is an osmole?
This is a unit of measurement to describe the concentration of solute particles
1 osmole= 1 mole= 6.02x10^23 osmotically active particles
Examples:
1 mol of glucose= 1 osmole (doesn’t dissociate in solution)
1 mol of NaCl= 2 osmole (Na+ and Cl-)
1 mol of sodium sulphate (2Na+ and SO4 2-)
What’s the difference between osmolality and osmolarity?
Osmolality: osmole/kg of water
Osmolarity: osmole/L of solution
