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2. Data interpretation Logo

These questions have (and still be) used in examinations. You should be able to answer them in about 10 minutes. You should not have to write more than a few lines for an component of a question.



question 1. Top

The tracings below show contractile activity recorded from the gastric antrum and mid duodenum of a dog. To measure pressure, balloon catheters attached to pressure transducers are placed in the gastric antrum and duodenum. An increase in contraction of the gastric antrum and duodenum has been recorded as an increase in pressure and is shown in the figure below as an upward deflection.
At the 'begin' arrow 100 mM HCl is infused into the duodenum at 6 ml.min-1.



1. Describe the changes that occur during and after the HCl infusion.
2. What is the physiological significance of these effects with respect to:
· the stomach
· the duodenum.
3. Outline the mechanism(s) likely to be responsible these effects.


question 2. Top




NOTE: The question is marked out of 10 in total. Numbers in ( ) give the marks available for that element of the question. A. Describe the graph - Note: Cimetidine is a Histamine type 2 (H2) receptor blocker (1)
B. What does line A show (0.5)
C. What does line B show (0.5)
D. Explain the rise in the concentration of secretin rise in A. (3)
E. Where is the site of action of cimetidine (organ and cell type) (2)
F. Explain the action of cimetidine on plasma [secretin] in B (2)
G. What would be the likely consequences of taking cimetidine on gastric acid secretion. (1)


question 3. Top

You will find this question quite taxing - you will need to think and you may need to consult a text book or two. If you can solve it you're doing well.

Note: The problem makes a big assumption. It assumes that there is only one diffusional barrier between the blood plasma and the gastric lumen. It assumes also that there is only 1 cell (2 membranes) separating the blood and gastric lumen. In reality there are 2 cells - the vascular endothelium, the basement membrane and then the parietal cell.

Our subject is a healthy human being with a blood plasma pH of 7.4. The intracellular [H+] of the parietal cells is 10-10 M and the [H+] is 10-4 M in the gastric juice (a 1 million-fold difference in concentration). The active transport of H+ against a 1 million-fold concentration gradient require 85 kJ.mol-1 of H+.

This concentration of H+ from the blood to the gastric lumen will obviously require energy, and glucose is assumed to deliver that energy. One gram of glucose will produce 15.5 kJ of energy when oxidised (the molecular weight of glucose is 180 g.mol-1). Oxidation needs oxygen!!!

It is assumed that 1 litre of oxygen (standard temperature and pressure, dry; STPD) is equivalent to 20 kJ (for a person burning a mixed diet). During a histmine test (remember histamine will stimulate acid secretion) the total mass of perietal cells secrete 35 mmol H+ h-1.

  1. Define in words the equilibrium (Nernst) potential for H+ over the assumed single membrane.
  2. Calculate the equilibrium potential for movement of H+ between the blood plasma and gastric lumen
  3. Calculate the equilibrium potential for movement of H+ across the apical membrane of the parietal cell into the gastric lumen.
  4. How much glucose must be oxidised in order to transport 1 mol of H+ from the cytosol of the parietal cell into the gastric juice?
  5. Calculate the oxygen uptake necessary to oxidise sufficient glucose for the transport of 35 mmol h-1.
  6. Assume that total oxygen uptake for a person is 300 ml.min-1 (STPD). What proportion of this is used up by the parietal cells?

  1. In case you can't remember the Nernst equation, here it is

equilibrium potential (@ 37 o C) = 60 x log ([H]out/[H]in)


 Do you need a calculator?
Click here if you prefer to use Excel to tackle this question.



question 4. Top

The human gut is about 6.5 m long with about 75% being the small intestine. The surface area available for absorption is increased by throwing the mucosa into folds, having villi (and crypts in the ileum), and by the micovilli brush border on the epithelial cells.

Let’s assume the average diameter of the gut lumen is 3 cm and that the area of the lumen is increased x200 by the folds and villi. Let’s also assume that this area is covered in epithelial cells which for our purposes are 10 microns in diameter and square in cross-section (to pack together neatly). Each epithelial cell is replaced every 72 hours (3 days).

Calculate:
  • the area of the gut that is covered by epithelial cells.
  • the number of epithelial cells replaced per minute.
Do you need a calculator?

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Copyright © 1998 University of Bristol. All rights reserved.
Author: Phil Langton 		Last modified: 11 Jun 1999 07:20
Authored in CALnet