Gastrointestinal Pathophysiology IV

Second last post on GI pathophysiology!

Obstruction

A main focus of this lecture (or what I think is one of the main foci of this lecture) is how the gut can become obstructed, and what the consequences are of obstruction. Most obstructions cause colicky (recurrent) pain due to the rhythmic contractions of the gut.

First, let's zero in on the blood vessels. If there is some obstruction causing lack of inflow of blood, that area of the gut will become hypoxic and ischaemic, and after a while may even become necrotic. If there is some obstruction causing lack of outflow of blood, that area of the gut will have oedema (swelling).

Mechanical Obstruction

Mechanical obstruction is basically where the gut moves in such a way that food simply can't get through.

In intussusception, the mucosa is loose, or there is some kind of tumour, allowing one region of the intestines to slide up into another. This can squish the blood vessels, resulting in further consequences (see above). Most cases of this are in young children below 2 years of age. Symptoms include pain, vomiting, diarrhoea and something called "currant jelly stool." Currant jelly stool is, well, stool that looks like currant jelly. (Google it and you'll see what I mean. Alternatively, don't.)

Another type of obstruction is called a volvulus. In this, the mesentery fails to keep the intestines all nice and organised, so loops and twists can form. Some people appear to have congenital predispositions to this.

Adhesions are inappropriate connections that can form between parts of the gut. They can be caused by inflammation, and may even form after the inflammation has been resolved. They can cause restriction in movement.

Hernias, where intestines poke through some weakness in the abdominal wall, can cause entrapment and strangulation of the intestine. Naturally, this also causes obstruction.

Congenital Obstruction

Congenital obstruction encompasses forms of obstruction that develop congenitally (i.e. in utero).

Atresia, which is thankfully pretty rare, is a disorder where parts of the intestine may not be connected together.

Congenital aganglionosis (Hirschprung's disease) is a disorder where some areas of the gut lack intramural ganglia, meaning that that part has no motility. Regions preceding the non-motile area may become distended due to a "backlog" of food, which can in turn lead to toxicity. This can be treated by excising out the non-motile part.

Ileus

Ileus is a somewhat different condition in which the gut is functionally paralysed and, as such, no bowel sounds can be heard. There is also no colicky pain associated with ileus, because as alluded to earlier, colicky pain is resulted to the rhythmic contractions of the gut. Ileus always follows some kind of intestinal manipulation (*cough*surgery*cough*) but other offenders include trauma and disease. This can lead to other issues, such as peritonitis.

Peritonitis

Peritonitis, as I think I've mentioned at some point, is inflammation of the peritoneal cavity. This usually happens following some kind of perforation of the gut wall, and can spread rapidly. Symptoms include ileus, fluid accumulation in the peritoneal cavity and guarding, which is a reflex contraction of abdominal muscles designed to protect the peritoneum.

Oral Cavity and Pharynx

There isn't too much you need to know about this area, unless you want to study dentistry in the future. Many problems that occur here are opportunistic infections, occurring only when you have some kind of vulnerability like immune suppression, use of some antibiotics, or chronic conditions such as diabetes. Poor oral hygiene might also lead you at risk to infections of the periodontium (tissues that surround and support the teeth), or gingivitis (gum disease). Remember to brush twice a day!

Oesophagus

To get food into the oesophagus, you have to swallow. Swallowing requires a mix of both voluntary and involuntary actions: voluntary being chewing (mastication) and tongue movements, and involuntary being a complex sequence initiated by the trigeminal and pharyngeal nerves. Difficulty in swallowing is called dysphagia.

After that happens, food has to be propelled down the oesophagus and through a relaxed lower oesophageal sphincter into the stomach. If there is a failure in propulsion or in sphincter relaxation, this is called achalasia. This is usually caused by a defect in inhibitory innervation from the enteric nervous system.

Just like in the intestines, atresia (discontinuous gut tube) may occur in the oesophagus, but this is pretty rare.

Going down a bit further, let's have a look at GERD, short for gastro-esophageal reflux disease (hopefully you realise that oesophageal and esophageal are just British/American spellings). Sometimes acid from the stomach can enter the lower oesophagus, resulting in inflammation. This may be due to a lax sphincter, too much acid or a hiatal hernia. A hiatal hernia is essentially when the stomach is pushed through the diaphragm, so now diaphragmatic muscle is surrounding and squeezing some other random part of the stomach. This often causes pain, and if prolonged, can lead to Barrett's oesophagus, which is a kind of pre-cancerous syndrome, which in turn can lead to oesophageal cancer. Thankfully, GERD can be treated with surgery, or with drugs such as proton pump inhibitors, which serve to reduce acid production.

Only one more lecture to go!