Phsyiology 1 Flashcards
What is osmolarity
Concentration of osmotically active particles present in a solution
What are the units of osmolarity
osmol/L or mosmol/L
What 2 factors need to be known in order to calculate osmolarity
The molar concentration of the solution
The number of osmotically active particles present
What is meant by osmotically active particles. Give 2 examples
NaCl has 2
MgCl2 has 3
Basically the number of elements in a solution
300mM NaCl. Calculate the osmolarity
300x2 = 600mosmol/L
What is the difference between osmolality and osmolarity
Osmolality - osmol/kg water
Osmolarity - osmol/L
They are interchangeable terms for weak salt solutions
What is tonicity
the effect a solution has on cell volume
Describe the movement of particles in an isotonic environment
No overall change in volume and no movement in one particular direction. Particles are still moving all the time
Describe the movement of particles in an hypertonic environment
Water is lost from the cells into the environment and this results in a decrease in cell volume. Cell shrinkage
Describe the movement of particles in an hypotonic environment
Water goes into the cells from the environment and this results in an increase in cell volume. Cell lysis
What determines whether a solution will cause lysis etc.
the ability of the solutes to cross the membrane or not
Why do females have lower total body water than males
Because they have a higher percentage of body fat which don’t contain a lot of water
How much of a) the male body is water and b) the female body
a) 60%
b) 50%
What are the 2 major compartments of total body weight
intracellular fluid (ICF) extracellular fluid (ECF)
What separates the ICF and ECF
cell membrane
What does the extracellular fluid include
Plasma
Interstitial fluid
Lymph and transcellular fluid
Where is plasma found
Circulatory system
What tracer can we use to obtain the distribution volume of TBW
3H2O
What tracer can we use to obtain the distribution volume of ECF
Inulin
What tracer can we use to obtain the distribution volume of Plasma
Labelled albumin
How can we calculate ICF
TBW - ECF = ICF
Describe the dilution principle to measure volume of distribution
Don’t know how much water is held in a container
Add a tracer at a specific dose (D = 42)
Mix them thoroughly and allow it to equilibrate with the water
Take a small sample (5ml) volume from the concentration and measure the concentration (C) of the sample
Use the formula below to calculate the initial volume
C = 0.005mg/5ml = 0.001mg/ml = 1mg/L
V= D/C = 42/1 = 42litres
In what ways do we input water to the body
Fluid intake
Food intake
Metabolism
In what way does water leave the body
Skin Lungs Sweat Faeces Urine
What is meant by insensible loss
we have no regulation over these losses
What is meant by sensible loss
We have some physiological control over these losses
What is water imbalance manifested as
changes in body fluid osmolarity
Why do the kidneys never turn off urinary excretion
They get rid of metabolic waste products which are often only able to be excreted in solution
What ions are in high concentration in ICF
K+
What ions are in high concentrations in ECF
Na, Cl, HCO3
What is the approximate values of ions in ICF
Na+ = 10 K+ = 140 Cl- = 7 HCO3- = 10
What is the approximate values of ions in ECF
Na+ = 140 K+ = 4.5 Cl- = 115 HCO3- = 28
What features allow the cells to maintain internal environments that differ in composition compared to their surroundings
The cell membrane
Membrane transport mechanism
What are the main ions in the ICF
K
Mg
-vely charged proteins
Why are the osmotic concentrations of both ECF and ICF identical
In part due to the kidneys
What is fluid shift
The movement of water between the ICF and ECF in response to an osmotic gradient
What would happen to a) the ECF and b) ICF and c) cell volume d) osmolality if the osmotic concentration of the ECF increased
a) ECF increases
b) ICF decreases and cells become Hypertonic
c) Cell volume decrease
d) osmolality increases
What would happen to a) the ECF and b) ICF and c) cell volume if the osmotic concentration of the ECF decreased
a) ECF decreases
b) ICF increases and cells become Hypotonic
c) Cell volume increases
d) osmolality decreases
If there is a gain of water, what happens to the ICF and ECF
They both increase
If there is a loss of water, what happens to the ICF and ECF
They both decrease
What happens to the ECF and ICF if NaCl increases
ECF increases but ICF decreases
What happens to the ECF and ICF if NaCl decreases
ECF decreases but ICF increases
Why is the regulation of ECF volume so important
For long term regulation of blood pressure
Why is electrolyte balance important
Electrolyte concentrations can directly affect water balance (via changes in osmolarity)
The concentrations of individual electrolytes can affect cell function
Why are Na and K particularly important
They are major contributors to the osmotic concentrations of the ECF and ICF respectively
They directly affect the functioning of all cells
What is the major cation in the ECF
Sodium
What is the major cation found within cells (ICF)
Potassium
What is the major role of K+
establishing membrane potential
What can disruption of K+ concentration result in
Muscle weakness –> paralysis
Cardiac irregularities –> cardiac arrest
