By Dr Barakat Shahin - جامعة الشام الخاصة

By

Dr Barakat Shahin

GID2 By Dr Barakat Shahin1

DefinitionAn ulcer is a local defect or excavation of the surface of an organ or tissue

which is produced by the sloughing of inflammatory necrotic tissue.

Ulcers which arise at any site of the GIT exposed to acid pepsin digestion

are called peptic ulcers.

Sites of Peptic Ulcer

Common sites1. Ulcer at duodenum principally the first part — Duodenal ulcer

2. Stomach mainly at the antrum — Gastric ulcer

3. At the lower end of the esophagus — Esophageal ulcer

4. At the jejunum — After gastrojejunal anastomosis ulcer is called

anastomotic ulcer

5. Meckel’s diverticulum — When it contains ulcers in its mucosa then it

is called diverticular ulcer.

Immune siteSecond part of duodenum is almost immune to ulcer, because of arrival of

pancreatic and biliary secretion, the HCl of gastric chyme is neutralized,

pH is raised, and pepsin becomes inactive.


PhysiologyParietal and peptic cells are normally present in the gastric mucosa, HCl is

secreted by the parietal cells whereas pepsin (in the form of pepsinogen)

is secreted by the peptic cells. Pepsin can digest protein only when the

pH is sufficiently low, between 2 to 3. At higher pH (>5) pepsin becomes

inactive and cannot digest protein. Therefore, presence of a strong acid

(like HCl) is necessary to convert pepsinogen to pepsin. Now a question

is, if acid pepsin mixture can digest the food protein, then why it does not

digest the gastric mucosa itself ?

The answer is, in the gastric mucosa, as well as in the first part of the

duodenum there is a defense mechanism. In normal persons the defense

mechanism is adequate and no ulcer develop. Where the defense

mechanism is weakened or the aggressive mechanism is strengthened,

the peptic ulcer should be developed.


Components of the gastric defense mechanism1. Gastric mucus

2. HCO–3

secreted by the gastric mucosal cells

3. Vasculature

4. Presence of tight junctions between the epithelial cells.

• Gastric mucus forms a layer over the epithelium of the mucosa. Some

mucosal cells secrete HCO3

– which remain in between epithelial cells

and the mucus and the pH at this spot is higher (6 or 7 ). Therefore, in

the luminal surface of the mucus the pH is low, about 1.5 to 3. The peptic

activity is high, digestion is possible.

Mechanical barrier offered by the mucus, present on the surface of

gastric epithelium is very important component of the defense. If this

mucus is thick and sticky, the acid-pepsin-mixture fails to penetrate

it. Acid-pepsin-mixture cannot reach close to the epithelial cells, so no

digestion of the epithelial cells.


Sequences1. Big pepsin molecules require good deal of spaces through which they

can traverse.

2. Normally mucopolysaccharide molecules are polymerized in the

mucosa.

3. Depolymerization of mucopolysaccharide cause loss of stickiness

and increases the permeability of pepsin.

• Tight junction: Nothing passes through them normally, but Aspirin

like drugs can damages tight junction and inhibits the PGs synthesis

within the gastric epithelial cells. These are two effects which weaken the

defense mechanism.












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By Dr Barakat Shahin - جامعة الشام الخاصة