Physiology Flashcards
What is osmolarity? The unit of osmolarity is ____
The concentration of osmotically active particles present in a solution. Osmol/L
What is the osmolarity of 150mmol/L NaCl? Explain why
Concentration = 150mmol/L number of osmotically active particles = 2 (1xNa & 1xCl) 150 x 2 = 300mosmol/L
What is the osmolarity of 100mmol/L MgCl2? explain why.
Concentration = 100mmol/L number of osmotically active particles = 3 (1xMg & 2xCl) 100 x 3 = 300mosmol/L
The osmolarity of the human body is approximately ______
300mosmol/L
Define tonicity
Tonicity is the effect that a solution has on cell volume if a cell is placed in that solution.
Explain hypo/iso/hypertonic
isotonic - no change in cell volume, no net movement of water Hypotonic - increase in cell volume, water moves from outside to inside cell. Hypertonic - decrease in cell volume, water moves from inside cell to outside.
Using urea and sucrose with RBCs as examples, explain why membrane permeability must be taken into account when thinking about tonicity?
- Osmolarity of both is approximately 300mosmol/L. - Urea is much more permeable than sucrose so moves in RBCs immediately and change osmolarity - therefore water follows - Cell will lyse - Sucrose is isotonic - does not move into cells - no net changes in water volumes/cell volume as osmolarity inside and out is the same.
70% of male and female body weight is water - true/false?
false - 60% of males/50% of females
Females have a lower total body water percentage than males - true/false. If true, explain.
True Women have a higher body fat percentage (22-25% F/15-18%M) and fat cells contain very little water.
The two main fluid compartments in the body are ____ & _____, which are separated by _______.
Intracellular and extracellular, separated by the plasma membrane.
What proportion of the total body water is in each fluid compartment?
2/3rds (67%) intracellular 1/3rds (33%) extracellular
The extracellular fluid compartment can be split into what constituents? What percentage of fluid lies in each compartment?
Interstitial fluid - 80% Plasma - 20% Transcellular fluid (e.g. CSF and intrapleural fluid) - negligible Lymph - negligible
Which tracers are used to calculate each fluid compartment’s volume?
Total Body Water = 3H2O
Plasma = Albumin
inulin = ECF
If there is no direct way to measure intracellular fluid volume, how might we calculate it indirectly?
We can detect the volume of TBW and the volume of the ECF directly using the tracers (3H2O for TBW, Inulin for ECF) and then realise that TBW = ECF + ICF
therefore ICF = TBW - ECF.
Explain the dilution principle for measuring the fluid volumes of distribution in the body.
If you add a known amount of a tracer to an unknown volume, you can work out the volume by taking off a small, known volume and calculating the concentration of your tracer in that volume. Scale up for 1L and then use:
Volume = Dose/Concentration
where dose is the total amount of tracer used.
Approximately how much of our fluid intake comes from each of the following sources:
- Food
- Fluids
- Metabolism
What percentage of daily intake does that equate to?
- Food = 1200ml/day = 48%
- Fluid = 1000ml/day = 40%
- Metabolism = 300ml/day = 12%
total = 2500ml
What are insensible fluid losses?
What are sensible fluid losses?
Skin & lungs are insensible
Sweat, faeces and urine are sensible losses
How much fluid on average is lost each day from the following sources:
- Urine =
- Faeces =
- Sweat =
- Lungs =
- Skin =
What percentage of daily loss does each equate to?
- Urine = 1500ml/day = 60%
- Faeces = 200ml/day = 8%
- Sweat = 100ml/day = 4%
- Skin = 350ml/day = 14%
- Lungs = 350ml/day = 14%
Total = 2500ml/day
Sodium concentration is greater outside the cell than inside - true/false
True - think of it as we all evolved from sea creatures so our cells like to be surrounded in salt (sodium and chloride ions much higher concentration in ECF than ICF)
ICF is lower in potassium than ECF -true or false
False
Chloride and bicarb are of higher concentrations in the ICF than the ECF - true/false
False - higher in the ECF than the ICF
if the concentrations of solutes are different in the ICF and ECF, how does the cell regulate the concentrations in each?
the membrane is a selectively permeable membrane with transporter molecules specific for each ion - e.g. the sodium/potassium-ATPase pump which pumps sodium out of and potassium into cells.
There is a difference in osmolarity in the ECF and ICF due to the difference of sodium and potassium concentrations - true/false
False - the ECF and ICF have identical osmolarity as any changes in osmotic gradient cause a movement of water to change the osmolarity back to equilibrium.
Gain of loss of water from one fluid compartment will cause a compensatory shift in the other compartment - e.g. if water is lost from ECF, water will move from the ICF to the ECF to restore equilibrium - true/false
True