Physiology 1 Flashcards
What is osmolality?
osmol/ kg water
= 1 l in weak body fluids
What is the unit of osmolarity?
osmol//
What is tonicity?
the effect a solution has on cell volume
solution can either be hypo, hyper or iso
What is an isotonic solution?
No net movement of water
Hypotonic solution
Increase in cell volume
more water outside the cell and water moves inside the cell
Hypertonic solution
the cell shrinks as the water is more inside the cell and water moves out
What is lysis of the RBC?
If the RBC has been put in a hypotonic solution it will be filled with water and cause lysis
What happens when a cell is put in a hypertonic solution?
it shrinks
Osmolarity of body fluids
300 mosmol/l
Osmolarity of cells
300 mosmol/l
What happens if the cell is introduced to a fluid with osmolarity >300mosmol/l?
hypertonic solution and the cell shrinks
What is a hypotonic solution?
osmolarity <300 mosmol/l
Comment on the osmolarity of the 300 mmol sucrose and 300mmol urea wrt
isotonic - sucrose
hypotonic - urea solution
depends on the solute in the solution - permeabiltiy
the RBC are very permeable to urea (as it has transporters) and it moves the urea molecules from the outside to inside the cell. It leaves behind water in outer environment -> hypotonic solution -> filling up of the cell
What other factors does tonicity and osmolarity depend on?
depends on the permeability of the solute in the solution
What is the RBC more permeable to, urea or sucrose?
Urea
What percentage of the body composition of females is made of water?
females - 50% of body weight
males - 60% of body weight
Which component is more common in females body composition?
fat
2/3rds of water in the body where is it found?
Intracellular fluid (67% of TBW)
What does the ECF include?
Plasma (20%)
Intersitial fluid(80%)
Lymph + transcellular
How is the volume of a fluid compartment measured?
Tracers
ECF
inulin
Plasma
labelled albumin
TBW
3H20
What is the formula for TBW?
ECF + ICF
How to measure the tracer fluid compartment?
dose/sample concentration
How to measure distribution voume of a tracer?
Add a known quantity of tracer X (QX; mol or mg) to the body
Measure the equilibration volume of X in the body ([X])
“Distribution volume “(“litres”) = (Q_X (“mol” ))/([X] (“mol/litre” ))
Where does most of the input for water come from?
fluid intake, food intake, metabolism
Where does the output of water come from?
Insensible loss - skin and lungs
sensible loss - sweat, faeces, urine
How is water imbalance manifested in the body?
changes in the body fluid osmolarity
Where is the most amount of water lost from the body?
urine - 1 ml/ min
but also depends on the hydration status of the body
How does change in water balance affect osmolarity of the fluid compartments?
water will move y osmosis across the fluid compartments to maintain the osmolarity
How is the water balance maintained due to changes by environmental temperature and water?
increased water ingestion
decreased secretion of water by the kidney –> but it is only the only thing that is necessary, can’t cope by itself
What is the importance of kidney?
maintaing the ionic composition of the major fluid compartments (salt that is being absorbed or excreted in the body)
Maintains water balance
alters composition and volume of ECF
Ionic concentration of various minerals btw ECF and ICF
Na and Cl -> more in the ECF
K - more inside the cell
Compare ECF and ICF
Similar ionic concentration btw the plasma and interstitial fluid
What seperates the ECF and ICF?
intracellular fluid and interstitial fluid - plasma membrane
Interstital fluid and capillaries - capillary wall
How is the concentration of the ECF and ICF related in value?
identical osmolarity
What is the fluid shift?
movement of water btw the ICF and ECF in response to an osmotic gradient
lose water but not salt -> ECF could become hypertonic
volume of the ICF wil decrease and ECF volume will icnrease
What happens if the osmoic concentration of the ECF decreases (add more water)?
Hypotonic solution
the cells become large and swell up with water
What ahppens if the ECF is to retain salt?
ECF hypertonic, and the ICF loses water and the ECF swells up with water
How does the gain or loss of isotonic fluid change homeostasis?
no change in fluid osmolarity but change in the ECF fluid volume only
What is the importance of regulation of ECF?
long term regulation of blood-pressure
when does an electrolyte balance occur?
When rates of gain of the electrolyte = rate of loss
What is the cause of the osmolaity/ fluid of the ECF?
Na
What is the major determination of the ECF volume?
Na - water follows the salt
WHat is the major ion that is important in setting up the resting membrane potential in excitable cells?
K
Why should the plasma concentration of K be highly monitored?
small leakages or ↑ cellular uptake may severely affect [K+]plasma leading to:
(i) muscle weakness → paralysis
(ii) cardiac irregularities → cardiac arrest
Where is most of the salt excreted from the body?
urine
How does sodium imbalance affect fluid compartments?
changes the ECF fluid volume
