Download ? ? ? ? ? ? ? P215 Discussion 15

P215 Discussion 15
Problem 1: Stomach Acid - the Good, the Bad and the Bubbly
Cells in the stomach’s gastric glands produce a pretty potent hydrochloric acid. The acid affects proteins’s shape.
Some of the proteins are in what we eat; some of the proteins are enzymes produced by the stomach itself.
? What are two ways in which the stomach acid affects proteins to help digestion in the stomach?
1) denature proteins in chyme - make the proteins more digestible
2) activate pepsinogen and make the digestive enzyme pepsin more active
ERP!
But stomach acid also contributes to several medical problems.
Compared to the small intestine and the esophagus, the stomach is made out of cast iron. It is built
to handle the acid it produces. The doudenum can’t handle the acid, but it can tell the stomach to
slow down as it squirts chyme into the intestine and it can call on the pancreas to produce bicarbonate
ions to help neutralize the acidity. Like the small intestine, the esophagus is not built to withstand
stomach acid. Closing the opening between the stomach and the esophagus helps prevent reflux of
acid into the esophagus. Reflux of stomach acid into the esophagus can cause discomfort or worse.
? What is happening in the GI tract that produces the less-than-pleasant sensation of heartburn?
acid “burns” sensitive tissue in esophagus; stomach contents pass sphincter at lower end of esophagus
Gastroesophageal reflux disease (GERD) stands for gastroesophageal reflux disease, a common condition
in which stomach acid repeatedly enters the esophagus.
? What dangers does untreated GERD pose for the esophagus?
damage, scarring with blockage, gradual change in cell type, possibly cancer
Problems with heartburn and reflux all involve acid production by cells in the stomach’s gastric glands.
parietal cells
? What kind of cells in gastric glands produce acid by pumping H+ into the lumen of the stomach?
Pumping of H+ is triggered in a number of ways. The drawing below shows how acid production is triggered.
Histamine or ACh bind with their receptors in the plasma membrane of acid-producing cells. This sets in
motion a second messenger system that ultimately turns on active transport of H+ from the cells to the stomach
lumen.
second
histamine
receptor
messenger
+
H+
histamine
second
messenger
+
ACh
acetylcholine
receptor
H+ pump
H+
H+ pump
(high concentrationof H+)
H+
H+
(lower concentration)
cell in gastric gland
lumen of stomach
Eating smaller meals, not lying down after eating and staying away from foods like chocolate, peppermint,
citrus and milk that stimulate acid production, help limit GERD symptoms. In addition, several kinds of helpful
drugs are available to treat heartburn and reflux. All act to lower the acid level of the stomach contents. It
seems that slowing or stopping either one of the histamine or ACh triggers is beneficial. Many drugs are available
by prescription or over-the counter. Treatments for GERD are advertised widely in magazines and on TV.
It’s a multibillion dollar a year business.
Antacid products on the market include Alka-Seltzer, Maalox, Mylanta, Tums, and Rolaids.
Antacids are taken by mouth and contain ingredients such as aluminum hydroxide, calcium carbonate,
? magnesium hydroxide and sodium bicarbonate. In general, how do antacids work?
chemical reactions neutralize some acid fairly rapidly (in 2 minutes to 45 minutes)
for example, bases like BICARBONATE combine with H+
“Histamine blockers” represent another type of drug used to treat GERD. Pepcid, Tagamet, Zantac and Axid
? bind to histamine receptors on acid-producing cells. How do they limit acid production?
prevent histamine from binding to its receptors; don’t stimulate acid production
More recently, a number of effective (and expensive) drugs called “proton pump inhibitors” have come on the
market. They include Prevacid, Prilosec and Nexium (“the little purple pill”).
? How do these drugs limit acid production? slow/stop H+ pumps from working; limit active transport of H+
Finally, as a last resort in severe cases, branches of the vagus nerves (a parasympathetic nerve) to the stomach
? can be surgically cut to reduce acid production. Why would this be an effective treatment?
parasympathetic nerve - promotes digestion, including acid production
ACh is the parasympathetic neurotransmitter
Problem 2: Ulcers of the GI Tract
Approximately one out of every eleven Americans develop peptic ulcers during a lifetime. Going on the
averages, that means that about 17 of us will have to cope with a peptic ulcer at least once in our lives.
A peptic ulcer damages the lining of the gastrointestinal (GI) tract.
? What are the parts of the GI tract where peptic ulcers occur most often? stomach and small intestine (doudenum)
Normally, the lining of the GI tract has several protective features:
i) a layer of mucus
ii) tight junctions between cells in the stomach wall
iii) continuous replacement with new mucus and cells
acid, pepsin and chyme
mucus layer
tight junctions
cells in wall of stomach
? How does the mucus help protect the wall of the stomach from digestive processes?
it’s alkaline, helps to neutralize acidity near stomach
? How do the tight junctions help protect the wall of the stomach from digestive processes?
limits passage of acidic contents between cells; cells form a first barrier
? How does the replacement of new cells help protect the wall of the stomach from digestive processes?
helps maintain the integrity of the stomach wall as older cells are damaged
But, these defenses can be overcome. Below are ten statements regarding peptic ulcers.
Some are facts; some are myths. Just for the heck of it, find the true statements.
Answers are on the next page. But, take a shot at answering the questions before looking at the answers.
*(NSAID) = Non-Steroidal Anti-Inflammatory Drugs
Ten Statements About Peptic Ulcers
1) Myth. But it may make some kind of contribution. How?
2) Myth.
3) Fact. A fairly small fraction of peptic ulcers.
4) Myth. The lining of the duodenum, the first section of the small intestine.
5) Fact.
6) Fact. The duodenum is vulnerable to acid
7) Fact.
8) Myth. They will help, but should be used with antibiotic in most peptic ulcers.
9) Myth. Peptic ulcer patients who smoke are advised to stop.
10) Fact. The majority of peptic ulcers are associated with an infection of a bacterium, Heliobacter pylori.
Another reason Mom was right when she said to wash hands before eating.
Helicobacter pylori
Many people around the world are infected with this bacterium, including about
35% of Americans. In many people, this bug seems to cause no immediate problem,
but the great majority of peptic ulcers, in the stomach and in the duodenum, are
associated with infections of H. pylori. These bacteria survive the acidity of the
stomach by secreting chemicals that help neutralize acidity in their location. They
move by whipping their tail-like flagella and escape the sloughing of old mucus
or find a more congenial spot. They can attach to cells in the walls of the stomach
or duodenum, secrete substances that damage the cells and move on and let the
immune system attack the damaged cells. Pepsin and stomach acid then work on
the weakened spot.
pathophysiology of peptic ulcers due to H. pylori
acid, pepsin and chyme
mucus layer
damaged
cell
cell at risk
cells in wall of GI tract
dead
cell
white
blood
cell
Treating ulcers with mediations that reduce acid production can help reduce ulcer symptoms, but the
symptoms often return when the drugs are no longer used.
? What sort of medications should be used along with acid-reducers if tests reveal that H. pylori is present
in someone suffering from a gastrointestinal ulcer?
antibiotics
taken for the entire course of treatment
Problem 3: Bariatric Surgery
A growing number of Americans are relying on stomach reduction surgery to help them lose quite a bit
of weight. There are a couple of major types of surgeries used to in bariatric procedures.
One kind of surgery - stomach restriction - relies on staples and/or bands to limit the volume of the stomach.
A second kind of surgery - malabsorption - can reduce the stomach volume, but also reduces the length
of the small intestine, by sending chyme from the stomach into the lower part of the small intestine and
bypassing the upper part of the small intestine, including the duodenum.
malabsorption
stomach restriction
esophagus
esophagus
remove
part of stomach
staples
band
duodenum
and jejunum
stomach
ileum
stomach
duodenum
jejunum
ileum
large intestine
large intestine
The reasons that these kinds of surgeries can be effective depend on the digestive functions of the stomach
and the small intestine.
Here are several questions concerning the strategy of surgical treatments for weight loss.
? What sort of changes in eating habits have you heard must be made after surgery that bands, staples or
resects (removes part) of the stomach? eat smaller portions; chew thoroughly
? How does banding, stapling and resecting the stomach help someone lose weight?
(Think about the major digestive functions of the stomach.) storage during digestion, mixing of chyme
not able to put as much into stomach
some digestion (proteins), little absorption
feel fuller after eating less
The stomach produces intrinsic factor. Those who lose a portion of their stomach may not have enough
intrinsic factor and absorption of vitamin B12 in the small intestine is insufficient. This, in turn, can result
in a form of anemia - pernicious anemia.
? What is anemia? diminished oxygen delivery by blood
? How does absence of intrinsic factor lead to anemia?
less absorption of Vit B12 in small intestine
Vit B12 is needed for normal RBC production fewer, larger RBCs in this condition
? What is a simple way to prevent pernicious anemia in those who’ve lost a part of the stomach?
give Vit B12 (intramuscular injections)
? How does bypassing a significant part of the small intestine help someone lose weight
(Think about the major digestive functions of the small intestine.)
small intestine - site of most digestion and most absorption
lesser length of small intestine = less digestion and less absorption