W3006    Fall 2003     Mini-exam #5         Physiology              Last 5 digits of CU ID #__________________________ 

1.  Gastric ulcers occur when acid and pepsin are able to destroy the epithelial lining of the stomach.  One treatment for this is a class of drugs called proton pump inhibitors.  Describe the exact location of proton (H+) pumps in the stomach, what they are doing there, and why inhibiting them would help.  (30)

Proton pumps are found in the luminal membrane (5) of parietal cells (5) (in the gastric pits) of the stomach.   

H+ is produced in these cells by the reaction of CO2 +H2O, catalyzed by carbonic anhydrase to produce H2CO3, which dissociates to H+ and HCO3-.  (5) The proton pump actively transports this H+ into the lumen of the stomach, where it helps attract Cl-, which enters the parietal cell in exchange for the HCO3-, leading to a high concentration of HCl in the lumen. (5) This acid is needed to activate pepsinogen conversion to pepsin, and to provide the proper low pH for pepsin function. (5) Luminal acid also is beneficial in that it denatures protein, kills bacteria, and breaks down connective tissue in our food.  (5)  Any 3 of these 4 statements for 15 points. 

Inhibiting the proton pumps means less HCl is present in the stomach, less pepsinogen is activated to produce pepsin, and therefore less chance of destruction of the epithelium.  (5)

  2.  In 1906, scientists had an idea for a new treatment of diabetes.  This was before the discovery of insulin, and they just knew that diabetes was a condition in which blood glucose was high.  Their idea was to grind up part of the duodenum and inject it into diabetics.  They tried this on dogs.  The dogs were injected with an extract of the duodenum and it did cause a sudden fall in their blood glucose levels.  But this idea lost favor, and only recently did we learn what was going on in those earlier studies, which was _____?  Your answer should include a definition of the duodenum, what it secretes that would lead to a fall in blood glucose, what the usual function of this secretion is, and the mechanisms by which it caused blood glucose levels to fall.  (40)

The duodenum is ____the first part of the small intestine___________________________________.   The relevant secretion is

____GIP (Glucose-dependent Insulinotropic Peptide__, which functions to ___stimulate insulin secretion from the pancreas____. 

It causes blood glucose to fall by:  increasing uptake of glucose into cells of the body.  Specifically:

In liver cell (5) , insulin stimulates activation of glucokinase, which converts glucose to glucose-6-P(5).  It also stimulates glycogen synthesis.  This means less free glucose within the cell, so the concentration gradient is maintained, maximizing diffusion of glucose out of blood and into the liver.  (5)

In muscle and adipose cells,(5) insulin stimulates insertion of GLUT 4 carriers into membranes,(5) so more glucose can be transported out of the blood and into these cells. 

3.   Lipase alone is actually unable to digest the fats that are in an emulsion, and digests fats only in the presence of a second enzyme, colipse, which, like lipase, is produced by the ____pancreas______.    Colipase moves aside the (bile salts) (prostaglandins)  (chyme)  which surrounds the particles of the emulsion, and thereby allows lipase to contact and digest the fat molecules there.   (10)

4. True or False.  If false, correct to make it true.  There may be more than one way of making the sentence correct, but your correction should be a significant change, not simply inserting the word “not”.    Both A and B are false.

A.  There are many lipoproteins on the surface of a chylomicron. (10)

Any of these were acceptable corrections:
There are many phospholipids on the surface of a chylomicron.
There is one apoprotein on the surface of a chylomicron.
A chylomicron is a type of lipoprotein.

B. In the enteric nervous system, cell bodies of neurons are found within the spinal cord.  (10)

Any of these were acceptable corrections:

In the enteric nervous system, cell bodies of neurons are found in the periphery or outside the spinal cord or near the digestive tract.