preview:• The endocrine function is producing hormones but exocrine is producing digestive enzymes.
• In the second portion will be looking at conditions associated with malabsorption of nutrients and there's quite a few of these.
• In comparison to previous lectures where we've looked at...
The endocrine function is producing hormones but exocrine is producing digestive enzymes.
In the second portion will be looking at conditions associated with malabsorption of
nutrients and there's quite a few of these.
In comparison to previous lectures where we've looked at the heart or the kidney for
instance they are confined organs which are relatively small and if you look at the overall
picture not that complex but when we talk about the GI tract it consists of numerous organs
and structures such as the pancreas, the stomach, the large and small intestine, the
oesophagus etc so it's a complex group of organs which have various structures and
morphology so investigating disorders of the GI tract can be a little tricky just based on
anatomical reasons.
Although we will be looking at biochemical tests with regards to the GI tract the non-
biochemical tests are as important if not sometimes provide more diagnostic value so things
like taking a biopsy, CAT scans (computer aided tomography scans) or endoscopy (a
procedure that allows a doctors to view the inside of a person's body and originally
endoscope is only used in the oesophagus, stomach and colon now as technology is
advanced you can fit an endoscopic in any organ section of the GI tract).
An endoscope is a pretty decent piece of kit, during an endoscopy the clinician inserts an
endoscope into a person's body.
They are thin tubes with a powerful light source, or you can see what's going on and it has a
tiny camera attached to it as well. There are several types of endoscopes and their length
and flexibility depend on the area that the clinician wishes to investigate for example an
endoscope that helps a doctor examine the joints is often rigid however one used to view
the inside of the colon for example would be rather flexible.
There are these little ports which can take a biopsy or a suction channel so this is particularly
useful as the endoscope could take small samples and it kind of vacuums them up into a
little tube which the clinician can then retrieve and send off to cytopathology or histology for
further assessment.
The endoscope will be a key non-biochemical diagnostic tool which will help identify
problems of the GI tract.
When we speak of the GI tract most commonly, we’ll be thinking of issues which concern the
stomach and one of the most common issues people have in the GI tract is a peptic ulcer. It
is caused by helicobacter pylori; these germs can enter into your body and live in your
digestive tract for a while.
Even after many years they cause sores called ulcers in the lining of your stomach or the
upper part of your small intestine and infections with h. pylori are rather common, about
2/3 of the world's population has had it in their body at some point.
After h. pylori enters your body it attacks the lining of his stomach which usually protects
you from the acid your body uses to digest your food, your stomach acids have a very low pH
they are very acidic and the stomach has a nice lining on the inside which prevents that acid
from damaging the stomach tissue itself but here the bacteria breakdown that lining so once
the bacteria have done enough damage the acid that your body produces can get through
the lining which damages the tissues on the inside and leads to ulcers and in advanced cases
can even cause bleeding and therefore infections.
, 5. Gastrointestinal Tests
Histology will provide a visual result, or you could simply take a bit of the tissue and send it
to histology and of course would require an invasive procedure so this will be a biopsy, you
would take a small chunk of the stomach tissue out.
Another procedure that can be done from a biopsy which is quantitative will test for urease
which is an enzyme only present in h. pylori. Urease breaks down urea to produce an
alkaline ammonia which causes a colour change so there is a scope for a colorimetric assay
there as well.
Another thing which can be done which is non-invasive is serological testing, you can do an
ELISA on the stool antigens for h. pylori because if there are large amounts of this bacteria in
your stomach eventually it's going to funnel through the large intestine and be excreted in
the waste.
A rather unique test is the breath test, it requires you to inhale radioactive urea and then
you can track its clearance, this is more specific because when you check for antibodies
because the body is capable of producing memory cells and therefore you have antibodies
persist even for a while after the infection may have gone. The point there is because your
immune system forms these plasma and memory cells if you just quantified antibodies to h.
pylori you might get a positive result even though the bacteria has been cleared (because
you have memory cells which produce antibodies).
You give someone radioactive urea, the h. pylori contains the enzyme urease and urease will
break that down into ammonia and carbon dioxide, that radioactive element will be joined
to the carbon dioxide and it eventually travels to your alveoli and when you exhale it out you
can measure it and that would be an indication of the h. pylori infection.
It's a unique test it works quite well but there are reservations about it because of course it's
radioactive urea that you're taking in so there's dangers associated with taking that level of
ionisation.
Another type of test which can be done for stomach disorders is plasma gastrin.
Gastrin is a peptide hormone that stimulates secretion of gastric acid by the parietal cells of
the stomach and aids in gastric motility, gastrin is key as causes the extracellular cells to
release histamine and the parietal cells to therefore release hydrochloric acid and this is very
useful in digesting your stomach components. For instance, hydrochloric acid breaks down
proteins in your stomach to prepare them for digestion and it also kills certain bacteria in the
stomach, it also helps convert the inactive enzyme pepsinogen into the active enzyme
pepsin which is responsible for further digesting proteins.
Gastrin is released from the g cell, it binds an ecl cell which releases histamine and then via
the g coupled receptors eventually leads to hydrochloric acid secretion from the parietal
cells so you can kind of use this as a diagnostic tool that gastrin is a quantitative biomarker
to pick up defects in the GI tract.
You can measure by immunoassay which is straight forward one of your ELISAs would be
good at this particular a sandwich ELISA, but sometimes elevated levels of gastrin can be
indicative of a gastrinoma, this is a tumour within the stomach which is over secretin gastric
so if you found large amounts of it in the blood plasma then you know it's something
serious.
Speaking of carcinomas like gastrinoma, acute pancreatitis is also a severe condition.
The pancreas has both endocrine and exocrine function and both of them are involved in the
digestion process.
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