Water Balance Flashcards
If a patient had sunken eyes, was refusing fluids, had a rapid pulse, dry mouth, weight loss, concentrated urine, low blood pressure and lack of skin turgor: what is likely to be wrong with them?
DEHYDRATION
Vomiting, diarrhoea, excessive sweating, low water intake, drainage from burns and damage to the hypothalamus can contribute to a deficit in what?
Body Fluids…. WATER
Chemical reactions that are important for acid balance occur in what?
Water
What is a major component of plasma and cells?
Water
What lubricates joints and organs?
Water
What has a high ability to absorb and retain heat, and stays in a liquid state over a broad range of temperature (0-100degrees)?
Water
What needs a large amount of heat to increase its temperature, and therefore is used to stabilise body temperature and can carry heat away from the body by sweating?
Water
How does sweating cool you down?
It absorbs heat away from the body and then evaporates on the surface of the skin
How many litres should our total body water be at any given time?
31-40 litres
Name 3 ways we take in water and how many mls:
Drinks - 1500mls
Food - 750 mls
Water of Metabolism - 250 mls
What 4 ways do we excrete water? (and give mls)
Urine - 1500 ml
Stools - 100 ml
Sweat - 200ml
Respiratory Loss - 700ml
Do men or women need more water in the body?
Men
What % of the male body is made up of water?
60%
Every cell in the body contains water. Where is 2/3 or 66% of it?
25 L is found in Intracellular Fluid (cells)
Every cell in the body contains water. Where is 1/3 or 30% of it?
Extracellular fluid 15 L
Interstitial = 12 L (between cells and not in blood vessels) Plasma = 3L (in blood)
Where is 3% of our water found?
0.7L is in our joints and CSF etc
Is there more water in the plasma or interstitial fluid?
There is more water in the interstitial fluid.
12L is found in between the cells whilst 3L is in blood.
There is even more in intracellular fluid = 25L.
What process allows substances to move in and out of cells?
Diffusion
Define simple diffusion
Movement from an area of high concentration to an area of low concentration: DOWN the gradient
What kind of membrane does diffusion cross?
Semi-permeable membrane
Name 5 factors that affect the rate of diffusion:
Temperature (higher = faster) Molecular Weight (larger = slower) Steepness of Gradient (steeper = faster) Membrane Surface Area (larger = faster) Membrane Permeability (more doors = faster)
Where will water always move to?
An area where it is less concentrated
What is a homogenous mixture of one or more dissimilar substances?
A solution
What is a solution usually made up of?
A liquid (solvent) and a solute (electrolyte/dissolved particle)
In what type of solution do small molecules dissolve and ionic compounds dissociate?
Aqueous Solutions
(the electrolytes dissolve and become ions with a charge so can conduct electricity - this is how we have nerve impulses)
What type of solution has proteins or other large molecules as a solute?
Colloids
e.g. blood - plasma proteins
What type of solution has even larger molecules than colloid solutions, where particles will settle if undisturbed?
Suspensions
blood also a suspension as red cell settle at bottom
pH is the concentration of what ions?
What type of pH does the body try and maintain?
Hydrogen
Neutral
Define osmotic pressure
The force (thrust) of water movement into the higher concentration solution
Name the 3 ways that the concentration of solutions can be measured as
g/L - Weight per volume
%
Moles - the number of molecules present in a sample, equal to the molecular weight in grams
What is the best way to measure a solution?
In moles
Define osmolarity
The number of osmoles per litre of solution
Osmotic concentration of body fluids has a great effect on cell function. It is dependent on number of particles dissolved.
So if urine has high osmolarity = more concentrate
More molecules dissolved = less water
Does water move faster if there is a high osmolarity?
Yes. The area will be more concentrated (less water) so water moves in faster
What does ISO-OSMOTIC mean?
Where two solutions have the same osmolarity
So plasma contains 300 mosmol of salt and glucose
Define tonicity
The ability of a solution to affect the cell (it depends on the concentration and the permeability of the membrane to the solute)
What is ISOtonic?
Same tonicity
What is HYPOtonic?
Low tonicity
What is HYPERtonic?
High tonicity
Can solutes cause water to move?
Yes if hypotonic or hypertonic
Does water move if the electrolytes outside the cell are equal to inside the cell?
No. It is isotonic and nothing will happen
What happens to the cell shape if it is isotonic
Nothing. The water will not move.
What happens to the cell shape if it is in a hypotonic solution?
It will swell and possibly burst.
This is because there is more water in the solution than in the cell.
(The solution has a low concentration of solutes that do not cross the membrane and a high water content).
The water therefore moves to where there is less water and into the cell.
What happens to the shape of a cell in a hypertonic solution?
It shrinks.
This is because there is not much water outside of the cell as there is lots of solutes. (Low water concentration and high concentration of solutes that do not cross membrane).
The water moves out of the cell to try and balance the concentration.
What mechanism tells the body we need more or less water?
Thirst
The amount of water in the body is detected by baroreceptors (that respond to pressure changes) and osmoreceptors (that detect changes in concentration if not enough fluid).
Where do these signals get picked up by?
Thirst centre in hypothalamus
If the hypothalamus picks up you need water, what 2 things does it do?
Releases ADH from PPG so less water in urine
Makes thirsty and gives dry mouth so want to drink
Name 4 treatments for dehydration
Fluid Therapy
Gelofusine (emergency as expands plasma and shrivels cells - hypertonic)
5% glucose solution - isotonic
0.9% saline - isotonic (don’t give to someone with high sodium levels)
What is hyponatraemia?
Overhydration/water intoxication
Where can’t excrete water
What will always result in a change in osmotic pressure (electrolytes on one side of membrane) therefore changing the cell in size?
Fluid movement
What does water always follow?
Salts
What is a universal solvent?
Water
What are the 3 fluid compartments in the body?
Extracellular - (interstitial and plasma)
Intracellular
What % of us is water?
60%
What do we call substances that are dissolved in solutions?
Solutes
Which of the following is the most concentrated solution?
0.9% saline
100g/l saline
9mg/100mls saline
100g/l
What is water balance interdependent on?
Electrolyte balance
When solutes move, what follows?
Water