Physiology Flashcards
Define Osmolarity
Concentration of osmotically active particles present in a solution, units = osmol/l or in body fluids mosmol/l
What 2 things do you need to know to calculate osmolarity?
the number of osmotically active particles and the molar concentration
Explain how a 150mM solution of NaCl has the same osmolarity as 100mM of MgCl2?
A 150mM solution of NaCl will have a osmolarity of 300mosm/l as there are 2 osmotically active particles present (1 sodium and 1 chloride ion) and 150 mols of it. 2x150=300.
100mM of MgCl2 would have a osmolarity of 300mosmol/l as there are 3 osmotically active particles present (1 magnesium and 2 chlorides) 3x100= 300mM.
Describe the difference between osmolarity and osmolality?
Osmolality and Osmolarity when talking about body fluid solutions can be used interchangeably. Osmolality has units of osmol/kg of water whereas osmolarity is osmol/l.
What is the approximate osmolarity of body fluids?
300 mosmol/l
Define tonicity?
The effect a solution has on cell volume. Solutions are hypo, hyper or isotonic.
Explain an isotonic solution?
Observe no change in cell volume if you were to add a cell to this solution
Explain a hypotonic solution
Hypo means less so the solution has less solute and therefore more water than the cell. Solution causes the cell to swell, cell increases in volume. As the solution has a greater concentration of water than the cell water moves into the cell by osmosis and the cell swells and due to lack of cell wall it bursts.
Explain a hypertonic solution?
Hypertonic solution has more solute than the cell but less water. Solution causes a decrease in cell volume, cell shrinks. As there is more water in the cell than outside water moves outside the cell by osmosis hence the cell shrinks.
Tonicity takes into account the permeability of membranes… what does this mean?
If there is a solute that can be actively transported this will change the tonicity of the solution but if it can’t be then you are just considering osmosis (passive diffusion of water from high to low concentration areas).
For example because a cell has transport systems for urea it will actively transport it across the cell and water will follow so solutions you would expect to be isotonic may actually cause lysis and bursting of the cell.
Total body water is about ___1__ in males and __2__ in females. This difference is because ____3____
1) 60%
2) 50%
3) females have a higher percentage of fat and fat cells don’t contain much water
Total body water consists as two major fluid compartments ______ (give percentages)
intracellular (67%) and extracellular (33%)
Describe the divisions of extracellular fluid?
Extracellular fluid can be divided into Plasma (aqueous component of blood) and Interstitial Fluid (immediate aqueous environment around cells). Negligible amounts of lymph and transcellular fluid e.g. CSF and Pleural fluid.
Describe how body fluid compartments can be measured?
Tracers
Useful tracers include tritiated water for total body weight, Inulin for ECF and labelled albumin for plasma
So if you can measure TBW and ECF you can therefore also calculate ICF by subtraction
How do tracers allow measuring of body fluid compartments?
By adding a known amount of tracer to unknown volume and allowing it to equilibrate with the water you can then measure the concentration of the tracer in the solution and use equation volume= dose/ concentration.
Describe the 3 inputs of water into the body?
Food intake
Fluid Intake
Metabolism
Describe 5 outputs of water from the body?
Faeces Urine Sweat Breathing/ Lungs Skin
Describe the insensible losses of water from the body?
Insensible losses are losses of water from body in which there are no physiological control mechanism and include skin (simple diffusion DIFFERENT from sweat) and lungs (lose water on exhalation)
Describe the sensible losses of water from the body?
Sensible losses have physiological mechanisms in place. For example sweat loss is determined by activity and temperature.
Largest loss of water from the body is?
production and excretion of urine (typically produce about 1500ml of urine a day)
Explain how in environmental changes water balance must be maintained?
Water balance in environmental changes is maintained by increased water ingestion, decreased excretion by the kidneys alone is insufficient to maintain water balance. We can never fully turn off urinary output as we need to get rid of some of the waste products by solution.
The ionic composition of plasma and interstitial fluid is different or near identical?
Near identical
Interstitial fluid is separated from intracellular fluid by a _____1______
Plasma fluid is separated from the interstitial fluid by the ___2_____
1) plasma membrane
2) capillary wall
What ions are the main ions of the ECF, what does this mean?
Sodium, chloride and bicarbonate ions
They are the major determinants of plasma osmolarity