Physiology of the Renal System I: General renal introduction and water homeostasis Flashcards
what is plasma?
This is the fluid component of the blood, and usually represents about 55% of the blood by volume. The rest of the volume is occupied by cells
What is a haematocrit?
a measure of the proportion of the blood occupied by cells (usually around 45%)
how much protein is in plasma?
About 60g.L-1 of which most of it is albumin.
How can the total calcium concentration change without affecting the free calcium concentration?
Since about 50% of the calcium in the ECF is free, this means the other half is attached to plasma proteins. Therefore changing the concentration of plasma proteins will reduce the total concentration of calcium without reducing the free concentration of calcium.
How do we measure total body water?
Use heavy water (deuterium or tritium) which has neutrons and therefore can be labelled. This means that we can replace the normal water isotope to one that can be detected and therefore measured.
What can be done using hydrogen isotopes to measure total body water?
Inject a known amount of the labelled water, wait for it to mix in the body, then measure the ratio of labelled to non-labelled water.
What marker can be used to measure plasma volumes?
labelled proteins injected intravascularly (evans blue - which binds to plasma proteins)
What marker can be used to measure extracellular fluid?
Thiosulphate
Thiocyanate
Small and charge molecules, therefore the molecules fin it harder to enter into cells due to the polarity and hence will remain in the ECF
What is the volume of distribution?
The volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in the plasma
How do you calculate the volume of distribution?
Vd = Q / Cp
Q = amount of drug Cp = plasma concentration of drug
What is an osmole?
This is a measure of the number of moles that a compound dissociates into when dissolved in solution.
What is osmolality?
number of osmoles per unit mass of the solvent(Osm.kg-1)
Something with a high osmolality has a low water potential
What is osmolarity?
number of osmoles per unit volumeof the solution(Osm.l-1)
Where would you find an osmotic pressure?
At the interface between two solutions, molecules exchange because of diffusion.
What is osmotic pressure?
If the concentration of any species is different on either side of the interface, there will be a net movement of molecules from one side the membrane to the other.
The amount of pressure required to oppose osmosis
