0307 Osmosis, osmotic pressure and maintenance of equlibrium Flashcards
• Osmosis occurs as particles diffuse down their concerntration gradients • H2O permeability is via aquaporins • Osmolality is an absolute measure, tonicity is a relative measure • Protein causes large osmotic flux • Osmolality determines the cell volume • Active cell processes regulate cell volume (eg Na+/K+‐ATPase) by altering intracellular ionic composition • Isotonic fluid replacement is essential to minimise cell volume changes
What is a concentration (or chemical gradient)
A concentration gradient is defined as a difference in concentration of solutes between two regions separated
Describe the affect of increasing, membrane permeability, surface area of membrane, molecular weight of substance and thickness of membrane of diffusion rate between 2 regions with a concentration gradient
Membrane permeability = increased diffusion. Surface area of membrane = increased diff. Molecular weight of substance = decreased diff. Thickness if membrane = decreased diff.
What is osmotic pressure?
Osmotic pressure (hydrostatic pressure difference) is the difference in concentration of water between 2 regions
What is the name of the protein responsible for H2O permerability
Aquaporins
What is the formula for measuring the osmolarity of a solution
Osmolarity = osmotic coefficient x no. of molecules that make up the soluate x [solute]
What is the difference between osmolarity and tonicity? What is the prefix given to a solution that is; equal to a another solution, higher [solute] and lower [solute]
Osmolarity describes a particular solution relative to normal physiological conditions. Tonicity is relative to a reference solution. The prefixes (in order) iso, hyper, hypo
Why does a measurement of tonicity ignore [urea] while osmolality does not?
Because tonicity can move freely across cell membranes and therefore does not contribute any difference between the no. of particles between 2 compartments
What would initially happen to a red blood cell in a hypertonic and hypotonic environment (in terms of shape)
Hypertonic = cell shrinking. Hypotonic = cell expanding
What is the Gibbs-Donnan equilibria and what is it’s relevant to oncotic pressure (pressure due to proteins in a cell)
The equlibria describes the uneven distribution of charged particles across a membrane. Because proteins are negatively charged, more cations will naturally enter the cell (and therefore will need to be pumped out to stop cell from exploding)
Describe the process of regulatory volume decrease and increase (in terms of solutes and pumps)
In volume decrease: Cell swells as extracellular osmolality decreases (water rushes in). Over time, the membrane transporters pump solutes out of the cell, decreases intracellular osmolarity (water goes out of cell). Vice versa for decrease
Why is isotonic fluid replacement the best form of fluid replacement
Isotonic fluid is isotonic with the intracellular environment. Therefore, there is no movement of fluid between intracelular and extracellular compartments. The volume of fluid you administer/ingest is the volume that gets added to the extracellular compartments
