Chapter 37: Disorders of Gastrointestinal Function

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Welcome to the Deep Dive.

We're here to break down complex subjects into the core knowledge you really need.

Today we're tackling a really important area.

The complex world of gastrointestinal or GI disorders.

It really is vital stuff and maybe not as headline grabbing as heart disease sometimes, but you know, the impact is massive.

GI diseases account for huge healthcare costs, sometimes even more than heart or mental health spending.

Wow.

Yeah, and look at colorectal cancer.

It's actually the third leading cause of cancer deaths.

So understanding this is crucial.

That definitely puts it into perspective.

So we're going to journey through the GI system, focusing on the core pathophysiology, the why behind the diseases.

We'll cover common symptoms, then disorders of the esophagus, stomach, and finally the intestines.

Exactly.

Our goal isn't just to list definitions.

We want you to grasp the mechanisms, understand why these conditions develop, and what the specific risks are.

Those sort of aha moments.

Okay.

Let's start right at the beginning with common manifestations.

First up, anorexia, which is simply loss of appetite.

Now there's a key distinction here we need to make up front.

Absolutely.

The textbook is very clear.

This symptom,

often linked to emotional states like fear or anxiety, is not the same as the eating disorder anorexia nervosa.

It's just the loss of desire to eat.

Right.

And this anorexia often comes before nausea, that really unpleasant, conscious feeling.

And it usually brings friends along those autonomic responses.

You might feel pale, start sweating, heart races, maybe get that watery mouth feeling.

And then, if things progress, comes vomiting or emesis.

We know it's a protective reflex,

but how does the body actually coordinate that forceful expulsion?

It's quite sophisticated, actually.

It's all integrated in the vomiting center, in the medulla, deep in the brain stem.

But this center doesn't act alone.

It's listening to signals from, well, several places.

Like where?

Well, obviously the GI tract itself can send signals.

Then there's input from the higher brain centers, the cerebral cortex, also the vestibular system in your inner ear, that's the motion sickness connection.

Ah, okay.

And the fourth one sounds really critical, the chemoreceptor trigger zone, the CTZ.

Yes, the CTZ is fascinating.

Think of it as the body's chemical surveillance system for the blood.

It sits just outside the blood -brain barrier, so it can directly detect drugs or toxins circulating in your system.

So when certain medications, like chemo drugs, cause vomiting,

it's not necessarily irritating the stomach lining itself.

Often no.

It's the drug hitting the CTZ, which then tells the vomiting center, hey, something's wrong here, expel.

Neurotransmitters like dopamine and serotonin play key roles in relaying these signals.

And the physical act itself, it's pretty violent.

It is.

It involves taking a deep breath, closing off the airway, then this really strong contraction of the diaphragm and abdominal muscles, pushing everything up, while the sphincter at the top of the stomach relaxes to let it out.

Now, that forceful action, especially if it's severe or happens repeatedly, that can cause damage, right?

It can.

That leads us to something called Mallory -Weiss syndrome.

These are longitudinal tears, like little rips, right at the junction where the esophagus meets the stomach.

You see it most often after severe retching or vomiting fits, particularly in people with chronic alcohol issues.

Okay, so damage from force.

Let's transition from that reflex to issues with the structure and function of the esophagus itself.

A common complaint is dysphagia, which is difficulty swallowing.

Right, or odynophagia, if swallowing is actually painful.

The causes can be varied.

Sometimes it's a physical blockage, like a tumor or a narrowing called a stricture.

Or it can be neuromuscular.

Exactly.

Problems with the nerves or muscles involved in swallowing, maybe after a stroke or other CNS damage.

A specific, important example is achalasia.

Achalasia.

What's happening there?

It's a failure of the lower esophageal sphincter, the LES, that muscular ring at the bottom of the esophagus.

It's supposed to relax to let food into the stomach, but in achalasia, due to nerve problems, it just doesn't relax properly.

So food gets stuck.

Precisely.

It backs up, causing the esophagus above the sphincter to dilate, get bigger.

And that creates a real risk of aspirating food or liquid into the lungs, especially when lying down.

Speaking of structural issues at that junction, what about hiatal hernia?

I know there are different types.

That's right.

Imagine the opening in the diaphragm where the esophagus passes through.

That's the hiatus.

The most common type of hiatal hernia is the sliding or axial type.

Here, the very top part of the stomach, along with the LES, just slides up through that opening into the chest.

It often looks like a little bell shape above the diaphragm.

Okay, that's the common one.

What's the other type?

The less common, but potentially more problematic one is the parasophageal or non -axial hernia.

In this case, the LES and the very top of the stomach stay put, but a separate pouch of the stomach bulges up next to the esophagus through the hiatus.

I see.

And these issues with the LES and diaphragm function naturally lead us to probably the most well -known GI problem, gastroesophageal reflux disease, or GER'd.

Right.

Simple reflux, or GER, is just stomach contents flowing backward into the esophagus.

GERD is when that reflux becomes chronic, causes noticeable symptoms, or actually starts damaging the esophagus.

And the damage comes from the acid.

Primarily yes.

It's the acidic nature of the stomach contents, usually a pH below 4 .0 combined with how long that assay stays in contact with the esophageal lining, which isn't built to handle it.

The classic symptoms are heartburn, that burning sensation,

and regurgitation.

But you mentioned something important earlier.

Pain doesn't always equal damage.

That's a crucial point.

Someone can have severe heartburn but relatively minor esophageal changes, while someone else might have minimal pain but significant damage, including complications.

And the most serious complication is Barrett's esophagus.

What exactly is that?

Barrett's is a change in the cells lining the lower esophagus.

It's a process called metaplasia.

The normal flat squamous cells are replaced by more column -shaped cells, like those found in the intestine or stomach.

Why is that bad?

Because those abnormal columnar cells are much more prone to becoming cancerous, Barrett esophagus significantly raises the risk of developing esophageal adenocarcinoma, a serious type of cancer.

It's a major warning sign.

Management then focuses on reducing that acid exposure.

Exactly.

Lifestyle changes like avoiding big meals, fatty foods, caffeine, not lying down right And then medications like antacids, H2 blockers, and especially the very effective proton pump inhibitors or PPIs, which drastically reduce acid production.

So we use drugs to fight stomach acid.

But let's back up.

How does the stomach normally protect itself from all that acid it produces?

It has its own defense system, right?

It absolutely does.

It's called the gastric mucosal barrier, or GMB, and it's quite remarkable.

It has several layers of defense.

First, the surface epithelial cells are packed tightly together, making them pretty impermeable to acid.

Then there's a water -repelling hydrophobic lipid layer, and on top of that, a thick layer of mucus containing bicarbonate ions.

This mucus bicarbonate layer creates a sort of neutral pH zone right next to the stomach wall, buffering the acid.

And certain chemicals help maintain this barrier.

Yes.

Prostaglandins are really important.

They help maintain good blood flow to the mucosa, which is needed for repair and bicarbonate production, and they stimulate mucus and bicarbonate secretion.

Okay, so if prostaglandins are key protectors, that immediately tells us why certain drugs are major culprits in damaging the stomach lining.

Exactly.

Aspirin and other N -acides are major offenders because their primary action is to block prostaglandin synthesis, so they directly weaken those protective mechanisms.

Makes sense.

What else can break down the GMB?

Alcohol is a big one.

It's lipid soluble, so it can basically dissolve parts of that barrier.

And bile salts, if they reflux back from the small intestine into the stomach, can also be very damaging.

And when that barrier is breached, we get inflammation gastritis.

There's acute and chronic.

Acute gastritis is usually a temporary inflammation, often caused by direct irritants like N -acides, alcohol or maybe bacterial toxins.

It's typically self -limiting, meaning it resolves on its own, but severe cases can cause bleeding.

And chronic.

Chronic gastritis is different.

It involves long -lasting inflammatory changes that can eventually lead to atrophy,

a thinning and breakdown of the stomach's glandular epithelium, the part that secretes acid and enzymes.

And globally, the number one cause of chronic gastritis is… Let me guess.

That bacteria, Helicobacter pylori.

You got it.

H.

pylori.

It's incredibly adapted to survive in the stomach's harsh acidic environment.

How does it manage that?

It's a spiral -shaped bacterium with flagella that help it move through the mucous layer.

But its real trick is secreting an enzyme called urease.

Urease breaks down urea into ammonia, which is alkaline.

This ammonia effectively neutralizes the stomach acid right around the bacterium, creating a little protective cloud.

Wow.

So it makes its own shield.

Pretty much.

And this chronic infection leads to persistent inflammation,

significantly increasing the risk for not just gastritis, but also peptic ulcers and even stomach cancer down the line.

Okay, that's a perfect segue to peptic ulcer disease, PUD.

Yeah.

So the main causes are H.

pylori infection and… And the use of aspirin or encyides.

Those are the big two.

It's worth noting that ulcers in the duodenum, the first part of the small intestine, are actually about five times more common than ulcers in the stomach itself.

What does PET feel like typically?

The classic symptom is a burning, gnawing, or sort of cramp -like pain, usually in the upper abdomen.

A key feature is the timing.

The pain often occurs when the stomach is empty.

Like between meals.

Exactly.

Or it might wake someone up in the middle of the night, say 1 or 2 a .m.

And characteristically, the pain is often relieved, at least temporarily, by eating food or talking antacids because they buffer the acid, irritating the ulcer base.

What are the major dangers to the complications of PET?

There are three main serious complications.

First is hemorrhage or bleeding from the ulcer.

This might show up as vomiting blood, hematomasis, or passing black terry stools called malena, which is digested blood.

That sounds serious.

It is.

Second, and even more immediately life -threatening, is perforation.

This is where the ulcer erodes completely through the stomach or duodenal wall.

So stomach contents spill out.

Yes.

Highly acidic, enzyme -rich contents spill into the abdominal cavity, causing peritonitis a severe inflammation of the lining of the abdomen.

This causes intense pain, and the abdomen often becomes rigid, sometimes described as board -like.

It's a surgical emergency.

Okay, bleeding, perforation.

Yeah.

What's the third complication?

Gastric outlet obstruction.

This happens if an ulcer near the exit of the stomach causes swelling, muscle spasm, or eventually scar tissue that blocks or narrows the opening, preventing food from leaving the stomach properly.

Are there other rarer causes of ulcers?

Yes.

Briefly, there's Zollinger -Ellison syndrome, caused by a tumor, a gastronoma, that secretes massive amounts of the hormone gastrin, leading to huge acid production and severe ulcers.

And then stress ulcers, like curling ulcers seen after major burns, or cushioning ulcers associated with brain injury or surgery, which seem related to physiological stress, causing reduced blood flow to the stomach lining.

And we mentioned the cancer risk with H.

pylori.

Stomach cancer itself.

Mm -hmm.

Elk isn't great, is it?

Unfortunately, no.

Prognosis is often poor because symptoms usually don't appear until the cancer is quite advanced.

Risk factors include genetics,

certain dietary factors like heavily smoked or salted foods, autoimmune gastritis, and definitely H.

pylori infection.

All right.

Let's move downstream now into the small and large intestines.

First, a very common issue, but one that's different from the others.

Irritable bowel syndrome, or IBS.

Right.

IBS is key because it's classified as a functional disorder.

This means it involves chronic, recurring symptoms like abdominal pain, bloating,

and changes in bowel habits, diarrhea, constipation, or alternating between them.

But crucially, there are no identifiable structural problems like inflammation or ulcers or biochemical abnormalities causing it.

So the structure looks normal, but the function is off.

That's the idea.

The hallmark is often abdominal pain that's typically relieved by having a bowel movement, and it's associated with a change in how often you go or what the stool looks like.

Importantly, the pain from IBS usually doesn't wake people up from sleep at night.

Okay.

So that's functional IBS.

Now, in complete contrast, we have inflammatory bowel disease, IBD.

This isn't functional.

There's real inflammation here.

Absolutely.

IBD refers to two major distinct chronic inflammatory conditions, Crohn's disease and ulcerative colitis, you see.

While they share some underlying factors, likely a mix of genetic susceptibility,

an abnormal immune response to gut microbes,

and environmental triggers, their patterns of inflammation are very different.

Let's break down those differences.

Tell us about ulcerative colitis first.

Okay.

UC is limited only to the colon and rectum.

It almost always starts in the rectum and then spreads upwards, proximally, in a continuous sheet of inflammation.

There are no healthy patches skipped within the diseased area.

And how deep does the inflammation go?

That's another key difference.

In UC, the inflammation is generally superficial, primarily affecting just the mucosa and the layer just beneath it, the sub -mucosa.

You typically see tiny pinpoint hemorrhages, little abscesses in the crypts of the intestinal glands, which can merge together, leading to large, raw areas.

What are the common signs and risks with UC?

Bloody diarrhea is a very common and prominent symptom in UC.

And because of the chronic inflammation in the colon, there's a significant long -term risk of developing colorectal cancer.

That risk increases the longer someone has the disease and the more extensive the colitis is.

Okay, so UC, colon, rectum only, continuous,

superficial inflammation, bloody diarrhea, cancer risk.

Now, contrast that with Crohn's disease.

Crohn's is quite different.

First, it can affect any part of the GI tract, from the mouth to the anus, although it most commonly involves the end of the small intestine, the allium, and the beginning of the colon.

And the pattern of inflammation.

Unlike UC's continuous sheet, Crohn's is characterized by skip lesions.

You'll have sharply defined areas of disease, sometimes deep ulcers or thickened wall, separated by segments of bowel that look completely normal.

This patchy involvement gives rise to the term, skip lesions.

Does it go deeper than UC?

Yes.

Crucially, the inflammation in Crohn's is transmural, meaning it penetrates through the entire thickness of the bowel wall, from the mucosa all the way out to the outer cirrhosis layer.

And the type of inflammation is often granulomatous, meaning specific clusters of immune cells

This transmural patchy inflammation often gives the mucosal surface a cobblestone appearance due to the deep ulceration and submucosal thickening.

So transmural inflammation, that probably leads to different complications than UC.

Exactly.

Because the inflammation goes all the way through the wall, Crohn's has a high incidence of complications like fistulas, which are abnormal tunnels connecting the bowel to the other organs, like the bladder, vagina, or skin and strictures, or narrowings of the bowel due to scarring.

Bloody diarrhea can occur, but it's typically less common or less severe than in UC.

That contrast is really clear.

UC is superficial and continuous in the colon, while Crohn's is deep, transmural and patchy.

Skip lesions.

Anywhere in the GI tract.

That's the fundamental difference to grasp for IBD.

Moving on from immune -mediated inflammation, let's talk about infections.

Infectious enterocolitis.

There are viral causes, of course.

Right, like rotavirus, which is a major cause of severe diarrhea in young children, and norovirus, famous for causing outbreaks on cruise ships and in other close quarters, often from contaminated food or water.

But there are some particularly dangerous bacterial forms we should highlight.

Definitely.

First, Clostridium difficile, or C.

diff.

This is strongly associated with antibiotic use.

Antibiotics can wipe out the normal protective gut bacteria, allowing C.

diff, which is often resistant, to overgrow and produce toxins.

What do the toxins do?

They cause severe inflammation and damage to the colon lining, leading potentially to a condition called pseudomembranous colitis, where you get these yellowish plaques forming on the inflamed mucosa.

It can be very serious, even life -threatening.

Okay.

C.

diff.

After antibiotics.

What's the other major bacterial threat mentioned?

E.

coli, 0157 .H, H oven.

This is a specific strain of E.

coli often found in contaminated food, classically undercooked ground beef, but also contaminated produce.

It produces potent toxins similar to those produced by shigella bacteria.

And the big danger with this specific E.

coli is?

The major risk, especially in children, is developing hemolytic uremic syndrome, or HUS.

The toxins damage blood vessels, leading to red blood cell destruction, hemolysis, low platelets, and acute kidney failure.

In fact, HUS is the most common cause of acute kidney failure in young children.

That's terrifying.

Okay, shifting gears slightly to intestinal motility.

Let's talk about diarrhea mechanisms, particularly chronic diarrhea.

The chapter outlines a couple of key types.

Hyperosmotic diarrhea happens when there are poorly absorbed substances in the gut lumen that draw water in by osmosis.

The classic example is lactose intolerance.

Undigested lactose pulls water into the bowel.

A key feature here is that this type of diarrhea usually stops if the person fasts, because they're no longer ingesting the offending substance.

Okay, osmotic pull.

What's the other type?

Secretory diarrhea.

This is caused by increased secretion of water and electrolytes into the bowel, often due to bacterial toxins, like cholera or certain hormones.

The critical difference is that secretory diarrhea typically persists even when the person is fasting, because the underlying secretory process continues.

Got it.

Now what about the opposite problem things not moving through?

Intestinal obstruction.

Right, an impairment of the normal flow of intestinal contents.

We can divide obstructions into two broad categories.

Mechanical obstruction is a physical blockage.

Like what?

Common causes are adhesions, scar tissue, often from previous surgery, hernias, where a loop of bowel gets trapped, interception, where one part of the bowel telescopes into another, or a volvulus, which is a twisting of the bowel on itself.

And the other category.

Paralytic alias or non -mechanical obstruction.

Here the blockage isn't physical, it's due to a loss of peristalsis, the normal muscular contractions of the bowel.

This is often seen temporarily after abdominal surgery or with certain electrolyte imbalances or drugs.

What's the main danger with a mechanical obstruction?

The biggest immediate danger is strangulation.

If the obstruction, like a twist or a trapped hernia, also cuts off the blood supply to that segment of bowel, the tissue can die very quickly, necrosis leading to perforation and peritonitis.

It's a surgical emergency.

And you mentioned peritonitis, inflammation of the abdominal lining.

What causes that?

It can be caused by chemical irritation, like spilled bile or pancreatic enzymes.

But more commonly, it's due to bacterial invasion.

This usually happens when an organ perforates like a ruptured appendix, a perforated ulcer, or a gangrenous bowel segment spilling bacteria into the normally sterile peritoneal cavity.

It causes severe pain, abdominal rigidity, fever, and fluid shifts that can lead to shock.

Okay, let's touch on problems with absorbing nutrients.

Malabsorption syndrome.

Malabsorption is essentially the failure to transport dietary components, fats, carbs, proteins, vitamins, minerals from the gut lumen into the bloodstream.

This leads to characteristic GI symptoms like diarrhea, bloating, gas, abdominal pain.

And systemic effects too.

Yes, because you're not absorbing essential nutrients.

A classic sign is stidaria, bulky, foul -smelling, fatty stools, because fat isn't being absorbed.

You can also see weight loss, muscle wasting, and specific deficiencies, like easy bruising due to lack of vitamin K, or anemia from poor B12 or folate absorption.

And a prime example of a disease causing malabsorption is celiac disease.

Exactly.

Celiac disease, also called gluten -sensitive enteropathy, is an immune -mediated disorder.

It occurs in genetically susceptible people when they ingest gluten, specifically a component called alpha -gliadin, found in wheat, barley, and rye.

What does the immune system do?

It mounts a T -cell -mediated attack against the lining of the small intestine.

This immune response causes inflammation and, characteristically, damages or destroys the villi, those tiny finger -like projections that are essential for absorbing nutrients.

This loss of villi dramatically reduces the surface area for absorption.

So the treatment is?

Complete and lifelong avoidance of gluten in the diet.

That's the only emergative treatment to allow the intestinal lining to heal and prevent symptoms and long -term complications.

Finally, let's talk about growths in the intestine neoplasms, starting with polyps.

Right.

Adenomatous polyps are the most common type of neoplasm in the intestine.

They are technically benign growths, but they are important because most colorectal cancers actually arise from these pre -existing adenomas.

Are all adenomatous polyps the same?

No, they're broadly classified based on their structure.

Tubular adenomas are more common and generally have a lower risk of becoming cancerous.

Villous adenomas are less common but have a much higher potential to harbor or develop into cancer, especially if they are large.

Which leads us to colorectal cancer itself.

We mentioned it's a leading cause of cancer death.

It is, and that underscores the importance of screening, like colonoscopy, which can detect and remove those pre -cancerous polyps before they turn into invasive cancer.

If cancer is diagnosed, what's the most important factor for prognosis?

The single most critical factor determining the patient's outcome is the stage of the cancer at the time of diagnosis, basically, how far it has spread.

This is often described using the TNM system, tumor size invasion, node involvement, metastasis.

Early stage cancers confined to the bowel wall have a much better prognosis than those that have spread to lymph nodes or distant organs.

Wow.

We've really covered a lot of ground from the brain's control over vomiting through the stomach's defenses and vulnerabilities, the complexities of IBD, infections, obstructions, and finally the progression to cancer.

It really highlights how interconnected everything is and how GI health depends on this delicate balance of motility, secretion, absorption, immune function, and barrier integrity.

And we saw repeatedly how disruptions like H.

pylori infection or the immune dysregulation in IBD can cause chronic inflammation that fundamentally changes the tissue itself.

Yeah, that chronic inflammation thing kept coming up, leading to metaplasia in the esophagus, atrophy in the stomach, and driving cancer risk in both UC and from H.

pylori.

Exactly.

Which leads to a final thought for you to consider.

We've seen how chronic inflammation, whether from microbes or faulty immune responses, can be a powerful engine for serious disease, especially cancer, within the GI tract.

Thinking more broadly, how might tackling chronic inflammation early, understanding its triggers and mediators, be a crucial frontier, not just for digestive health, but for preventing a whole range of chronic diseases throughout the body?

That's a really powerful point to ponder.

The gut truly is central to so much of our overall health.

Absolutely.

Well, thank you for joining us on this deep dive into GI pathophysiology.

We hope it provided some clarity on these complex conditions.

Thanks for listening.

We'll catch you next time on The Deep Dive.