Physiology 3120 Lecture Notes - Cholera Toxin, Symporter, Diarrhea

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indigoweasel955

26 Nov 2011

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Sodium transport (cont"d: primarily in the lower gut. Typified by secondary active transport using a na/cl symporter (1:1 ratio); the transporter is activated by a na concentration gradient across the apical/luminal membrane. Binding of the na (already has high affinity) increases the affinity for the cl site for its substrate (i. e. chloride); when both ions bind, the protein undergoes some conformational change occurs to move the ions to the cytosolic side. Increase in content of prostaglandin e2 associated with cholera toxin. Cholera toxin does 2 things: (1) inhibits apical na/cl symporter, so can"t absorb nacl, and (2) punches holes in apical membrane, causing cl to leak out into the intestinal lumen (and water to follow). Pge2 is specific to the na/cl symporter, so giving electrolyte-rich juice (ginger-ale) can help overcome the net efflux of water. Solvent drag: solvent moves and drags all other substances dissolved in it along for the ride.

Related Questions

Which motion of particles across a membrane requires energy?

A. From high concentration to low concentration

B. From low concentration to high concentration

C. With no concentration gradient

D. Through dynamic equilibrium

cerisesea-lion608

Sucrose is allowed to diffuse along a 12.0-cm length of tubingfilled with water. The tube is 6.0 cm2 in cross-sectional area. Thediffusion coefficient is equal to 5.0 10-10 m2/s, and 8.0 10-14 kgis transported along the tube in 14 s. What is the difference inthe concentration levels of sucrose at the two ends of thetube?

Situations arise in engineering when we want to control the flow rate of a solution. This solution could be pumped into a holding tank, distillation column, heat exchanger, reactor, etc. This means that the flow rate becomes a function of time. When we turn on a pump, the flow rate is (for the most part) constant. The problem is that we may want the flow rate to be very fast at first, and then very slow towards the end of the process. This is especially true in certain chemical reactors where the concentration of reactants is always important. Control systems that could handle this type of situation are very expensive. Pumps (relatively speaking) are cheap. So, having a bank of pumps will usually solve the problem. The pumps are simply turned on or off to regulate the flow. Mathematically, this amounts to taking the volumetric flow rate function and finding a piecewise-linear approximation. Suppose that, because of the application we are running, we need a flow rate given by the function ,where t is in hours and v(t) is in 100 cubic feet per hour (e.g., v(0)=1 which means that at time t=0, we need a flow rate of 1*100=100 cubic feet per hour). Find a linear approximation and a piecewise-linear approximation using first two lines and then three lines. Think about what using more lines would do to the approximation. You will need to find suitable values of t to be able to find your approximation. As a further exercise, try to find values of t for your approximation that keeps the error (i.e., the difference between the approximation and the real function v(t) ) less than 0.1.Hint: to help with this, ask yourself this question: where would more lines be useful - where the function changes a lot or where the function changes a little?]

Physiology 3120 Lecture Notes - Cholera Toxin, Symporter, Diarrhea

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