Physiology Flashcards
What is the definition of osmolarity?
Concentration of osmotically active particles present in a solution
Why is the unit of osmolarity usually mosmol/l for body fluids?
They are weak salt solutions
How is osmolarity calcluated?
molar concentration of the solution X no. of osmotically active particles present
What is the normal osmolarity of body fluids?
300 mosmol/L
What is the difference between osmolarity and osmolality?
OsmolaLity has units of osmol/kg water
OsmolaRity has units of osmol/l
virtually they are interchangeable
What is tonicity?
the effect a solution has on cell volume
What is meant by an isotonic solution?
Has no effect on cell volume
What effect does a hypotonic solution have on cell volume?
Increases cell volume
What effect does a hypertonic solution have on cell volume?
Decreases cell volume
What can occur in red blood cells if they are placed in a hypotonic solution?
Cell lysis
they burst
How do urea and sucrose have the same osmolarity, yet urea is a hypotonic solution?
red blood cell membrane is more permeable to urea than sucrose
tonicity takes membrane permeability to substances into account
What is the difference in total body water between males and females?
Males ~60% body weight = water
Females ~50% body weight = water (due to increased fat)
More of the total body water is stored in the extracellular fluid compartment. TRUE/FALSE?
FALSE Intracellular fluid (ICF) 67% of TBW Extracellular fluid (ECF) 33% of TBW
What are the different types of extracellular fluid (ECF)?
Plasma 20%
Interstitial fluid 80%
Lymph
Transcellular fluid (pleural/cerebrospinal)
How do we measure the volume of fluid contained in a body fluid compartment?
We use a tracer and measure the distribution volume
What tracers can be used to measure TBW, ECF and Plasma ?
TBW: 3H2O
ECF: Inulin
Plasma: labelled albumin
Body fluid osmolarity changes when there is a water imbalance (AKA input =/ output). TRUE/FALSE?
TRUE
In what situations would you require extra intake of water due to increased output through sweat and other mechanisms?
In hot weather
During exercise
What ions are plentiful in the ECF?
Na+
Cl-
What ion is mainly foind in the ICF and plays a role in setting a membrane potential?
K+
What is the fluid shift?
Movement of water between ICF and ECF in response to an osmotic gradient.
If the fluid osmolarity is changed, both ICF and ECF volumes will change. TRUE/FALSE?
TRUE
whereas if an isotonic solution is added (e.g. 0.9% saline), only ECF volume will change
Why is low salt intake important in maintaining a healthy blood pressure?
NaCl is isotonic and therefore doesnt change fluid osmolarity
=> only changes the ECF volume (e.g. plasma) => more blood to pump round and heart needs to work harder
Why can minor fluctuations in plasma [K+] have detrimental consequences?
If K+ leaks out of cell and changes the membrane potential this can cause issues in excitable cells
=> Muscle weakness/paralysis
=> cardiac irregularities/arrest