USMLE Step 1 Physiology Review 52 06 Solutions (2 of 2)

USMLE Step 1 Physiology Review 52 06 Solutions (2 of 2)

 

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Begin 52 06 Solutions (2 of 2) Transcription

What is the dispersion of oil in water, where the particles are larger than they are in colloidal solutions? What is this called?

  • An emulsion.

What kinds of substances keep the particles dispersed?

  • Emulsifying agents.

What is it about an emulsifying agent that keeps the particles dispersed?

  • Part of the agent associates with water, while part of it associates with oil.

What is the emulsifying agent for fats in the lumen of the gastrointestinal tract that aids in digestion and transport?

  • Bile acids.

Consider for a moment the components of a solution.  The dilution principle is helpful in finding out about one of these components.  What is the unknown that the dilution principle can be used to determine?

  • The volume of solvent.

What is the first step in applying dilution principle?

  • Add a known amount of solute to an unknown volume of solvent.

What is the next step?

  • Thoroughly mix so there is a true solution.

What is the next step?

  • Take a sample of the solution and determine its concentration. 

Once you know the concentration and the amount of solute, how would you arrange the equation to determine the volume of the solvent?

  • Volume of solvent equals amount of solute divided by the concentration of the solution.

Student Doctor, please pause the tape and summarize the information discussed thus far on emulsions and the dilution principle.

  • An emulsion is the dispersion of oil in water where the particles are larger than they are in colloidal solutions.  Emulsifying agents keep the particles dispersed.  Part of the emulsifying agent associates with water, while part of it associates with oil.  Bile acids are the emulsifying agents for fats in the lumen of the gastrointestinal tract that aid in digestion and transport.  The dilution principle is helpful in determining volume of solvent.   First, add a known amount of solute to an unknown volume of solvent.  Thoroughly mix so there is a true solution.  The next step is to take a sample of the solution and determine its concentration.  Once you know the amount of the concentration and the amount of solute, the equation to determine the volume of the solvent is as follows: Volume of solvent equals amount of solute divided by the concentration of the solution.

How do substances in solution tend to distribute because of diffusion down gradients of chemical activity?

  • Substances in solution tend to distribute uniformly.

Do solutes decrease or increase the chemical activity of water?

  • Decrease.

What is osmotic pressure?

  • It is the hydrostatic pressure required to stop osmosis. 

The diffusion of water from one compartment to another of lower chemical activity through a membrane that is not permeable to solutes; this describes what process?

  • Osmosis.

Student Doctor, please pause the tape and summarize the rest of the information discussed on diffusion and osmosis.

  • Substances in solution tend to distribute uniformly because of diffusion down gradients of chemical activity.  Solutes decrease the chemical activity of water.  Osmotic pressure is the hydrostatic pressure required to stop osmosis.  The diffusion of water from one compartment to another of lower chemical activity through a membrane that is not permeable to solutes is osmosis.

 

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