Generality
Irritable bowel syndrome is a set of chronic intestinal disorders, referable to the large intestine tract called colon (as can be guessed from the name of the pathology).
Despite numerous studies on the subject, the causes of irritable bowel syndrome are a question mark. According to the most reliable hypotheses, at the origin of the condition there would be an abnormal communication between encephalon, nerve fibers that innervate the intestine and intestinal muscles.
The typical symptoms of the irritable bowel consist of: pain and cramps in the abdomen, constipation, diarrhea, abdominal bloating, meteorism and mucus in the stool.
Making a diagnosis of irritable bowel syndrome is not at all simple, for at least two reasons: the lack of a specific diagnostic test and the non-specificity of the symptoms (they are symptoms common to many other bowel diseases).
Currently, therapy for irritable bowel syndrome is only symptomatic.
Brief reference to the anatomy of the colon
The intestine is the portion of the digestive system between the pylorus and the anal orifice.
The anatomists divide the intestine into two main sectors: the small intestine, also called small intestine, and the large intestine, also called large intestine .
The small intestine is the first section; it starts at the level of the pyloric valve, which separates it from the stomach, and ends at the level of the ileocecal valve, located on the border of the large intestine. The small intestine consists of three sections (the duodenum, the jejunum and the ileum), is about 7 meters long and has an average diameter of 4 centimeters.
What is irritable bowel syndrome?
Irritable bowel syndrome is a collection of intestinal disorders, specifically coming from the colon.
Irritable bowel syndrome is a chronic condition, which can last for years and require - precisely because of its long duration - a prolonged treatment.
Unlike inflammatory bowel diseases such as, for example, Crohn's disease or ulcerative colitis, irritable bowel syndrome is not responsible for any change in intestinal anatomy and in no way promotes the appearance of colon or tumor cancer of the colorectal .
Curiosity
Researchers have never really demonstrated a correlation between irritable bowel syndrome and colonic motility; therefore, irritable bowel syndrome remains an undefined clinical condition.
Other names
Irritable bowel syndrome is known by several other names, including: irritable bowel syndrome, IBS (from Irritable Bowel Disease ), spastic colitis, nervous colitis, irritable bowel, spastic colon and mucous colitis .
Coined as far back as 1892, the term mucous colitis refers to the high frequency of mucorrhagia (mucus emission mixed with feces) and abdominal colic.
Epidemiology
According to some statistical surveys, the irritable bowel syndrome would affect 15-20% of the population living in so-called "developed countries" (about one in 5) and would have an annual incidence of 1-2% (in essence, every year, the new cases are maximum 2 per 100 people).
According to other research, the areas of the world with the greatest number of patients would be Central America and South America; by contrast, the areas of the world with the fewest sick would coincide with the territories of South-East Asia.
Female sex is much more likely to develop irritable bowel syndrome than men: women with irritable bowel syndrome are at least twice as many as men.
Most individuals suffering from spastic colitis are between 20 and 30 years old.
For reasons still unclear, various problems of a psychic nature, such as major depression, anxiety and personality disorders, accompany the irritable bowel syndrome.
Causes
The precise causes of irritable bowel syndrome are a mystery. However, there is no lack of studies and theories about it.
Most reliable hypothesis
The brain and the intestine are closely connected to each other, through a wide network of nerves.
According to one of the most reliable medical-scientific theories, the irritable bowel syndrome would be due to an abnormal communication between encephalon, nerve fibers that irritate the intestine and intestinal muscles (whose task is to regulate the passage of the digested food inside the intestine).
Physiopathology in short
The layer of muscle cells forming part of the intestinal wall allows, through rhythmic contractions (peristalsis), the transit and progression of food during the digestive process.
According to what the doctors say, the presence of irritable bowel syndrome would be responsible for too strong and too long contractions or, alternatively, for too weak contractions.
Too strong contractions would lead to the onset of symptoms, such as meteorism, a sense of swelling in the abdomen and diarrhea; the too weak contractions, on the other hand, would be at the origin of a slowing of intestinal transit (constipation) and of problems, such as too hard stools or dry stools.
Curiosity
Recently, researchers have observed the presence of inflammatory micro-foci in the thickness of the intestinal mucosa in a group of people with an irritable colon.
This observation would have challenged the bases of irritable bowel syndrome, which has been considered a non-inflammatory pathology for years.
Stimuli of irritable bowel syndrome
Several clinical investigations have shown that the symptoms of irritable bowel syndrome often appear when certain circumstances occur. In the list of such circumstances - that doctors call " triggers " ( triggers, in English) or "stimuli of irritable bowel syndrome" - they fall:
- Taking some special foods . There are people who complain of the typical symptoms of irritable bowel syndrome when they take: chocolate, coffee, tea, spices, fatty foods, fruit, peas, cauliflower, cabbage, broccoli, milk, alcohol, sugary drinks, etc .;
- Excessive stress . Many individuals with spastic colitis tend to experience the worst ailments during times of excessive stress;
- Hormonal alterations . Doctors attribute to the hormones a "trigger" role for the irritable bowel syndrome, due to the fact that women, by their nature subject to cyclical hormonal alterations due to the menstrual cycle, are the most common targets of the disease in question;
- Some infectious diseases of the gastrointestinal tract . According to a considerable number of clinical investigations, there would be a consequential link between severe gastroenteritis of viral or bacterial origin and irritable bowel syndrome ( post-infectious irritable bowel syndrome ).
Risk factors
According to medical research conducted so far, the risk factors for irritable bowel syndrome would be:
- Suffer from abnormal bowel movements (eg: intestinal transit too fast, intestinal transit too slow, etc.);
- The presence of visceral hyperalgesia. For visceral hyperalgesia, we mean a pathological increase in pain sensitivity from abdominal viscera, particularly bowel;
- A previous gastroenteritis of viral or bacterial origin. According to some studies, the development of post-infectious irritable bowel syndrome would depend on: the duration of the infection, the type of infectious germ, the female sex, the young age and the absence of vomiting during infection;
- The presence of the so-called intestinal bacterial proliferation syndrome, a condition also known by the acronym SIBO;
- The presence of hormonal imbalances or neurotransmitters.
Deepening on the pathophysiology of irritable bowel syndrome
To better understand the complex physiological activity, and consequently the pathophysiology, it is good to know more in depth the dynamics underlying the function of the colon.
The intestinal contents reach the colon, from the small intestine, in liquid form; the primary function of this organ - the colon - is to reabsorb the liquid fraction and mineral salts; at the end of the path along the colon, therefore, there is the final expulsion of the digestion products.
The colon has its own semi- autonomic nervous system, called Enteric Nervous System ( SNE ); the SNE covers various functions, including:
- The production of the neurotransmitter serotonin . A task of serotonin is to increase intestinal motility, thus favoring the transit of food inside the intestine.
The production of serotonin by the SNE also depends on the particular relationship that links the latter to the brain (central nervous system - CNS). This means, in other words, that the SNE produces or blocks the production of serotonin even under the influence of the brain (it is the so-called "two-brain theory" or " Brain-Gut Axis ").
If the stimulus to the production of serotonin is excessive, the intestinal transit of the products of digestion undergoes a sharp acceleration, which involves the development of diarrhea; on the contrary, if there is an excessive limitation to the production of serotonin, the intestinal progression of the digestive products is slowed down and the phenomenon of constipation appears.
- The regulation of the permeability of blood and lymphatic vessels, typical of the colon, located immediately below the mucosa (the inner surface, or lining, of the colon). This network of blood and lymphatic vessels is responsible for the reabsorption of the liquid part of what passes into the colon.
- Immune regulation, through the ability to recognize harmful substances, which humans introduce with food (eg traces of pesticides, viruses, parasites etc.), and the ability to activate all the organic protection and rapid expulsion functions, of these substances, from the human organism.
Curiosity on post-infectious irritable bowel syndrome
Patients with post-infectious irritable bowel syndrome show an increase in the number of lymphocyte colonies and enteroendocrine cells in the mucosa (cells responsible for the production of substances, such as serotonin, which affect motility, vascularization and colon's own immune response).
In the irritable colon, enteroendocrine cells show secreting high levels of serotonin, therefore they seem to be the original responsible for the episodes of diarrhea.
Traditional theories concerning physiopathology can be divided into 3 complex chapters:
- Gastrointestinal motility;
- Hyperalgesia;
- Psychopathology.
1) The alteration of gastrointestinal motility includes specific modifications of the motor function of the small and large intestine:
- a) the myoelectric activity of the colon (the ability to make the feces proceed to the evacuation) is composed of a succession of slow waves of muscular contraction, over which spikes of action potentials overlap (ability of the muscle cell to contract in an energetic way). In irritable bowel syndrome, the dysmotility (altered motility) of the colon is manifested by a variation in the frequency of the slow muscle contraction waves, interrupted, especially as a post-prandial response, by spikes of action potentials. Patients subjected to diarrhea demonstrate this disparity to a greater extent than patients predominantly subject to constipation.
- b) The dysmotility of the small intestine is manifested by a slow transit of food, in subjects with a prevalence of constipation, and with an accelerated transit of food, in subjects with prevalence of diarrhea; the latter also show shorter intervals between successive propulsion waves (so-called predominant interdigestive waves of the small intestine).
- c) According to current theories, people with irritable bowel syndrome would be subject to a general increase in smooth muscle activity; therefore, the affected organs would not only be small and large intestines, but also the organs of the urinary tract, which also have a considerable smooth musculature.
These theories would explain why patients with irritable bowel sometimes have urinary symptoms, such as increased frequency and urgency to urinate, nocturia (increase in night-time urination), etc.
2) Visceral hyperalgesia, ie the pathological increase in sensitivity (hypersensitivity) to pain coming from abdominal viscera:
- The abnormal perception of physiological intestinal motility and the marked visceral sensitivity to pain are two characteristic elements of irritable bowel syndrome.
During tests for the evaluation of visceral sensitivity to pain, the distension of the balloon probe, in the rectum-sigma and in the small intestine, produces pain at much lower volumes in patients with irritable bowel syndrome, compared to what happens in patients control (healthy people).
Moreover, from the tests of this typology another curious and surely to be noted aspect emerges: patients with irritable bowel syndrome feel pain not only where the balloon probe resides, but also in cutaneous areas of the abdomen anatomically distant from the rectum-sigma etc. The explanation of this phenomenon is simple: the nerve endings that transmit pain from the colon and the rectum-sigma pass through the posterior horns of the spinal cord, where also the nerve endings deputed to the perception of pain on the abdominal skin arrive; therefore, due to this overlap, the activation of the first nerve endings (those of the colon and the rectum-sigma) tends to activate also the second ones (the cutaneous ones) and this involves the perception of a widespread pain.
3) Psychopathology:
- The association between psychiatric disorders and irritable bowel syndrome has never really been clarified or demonstrated. However, it is a fact that:
- Patients suffering from psychological disorders are faced with debilitating diseases much more frequently than the healthy population, representing the so-called control sample;
- Patients in continuous search of medical therapies for chronic diseases, have a high incidence of panic crisis, depressive states, anxiety and hypochondria, compared to the healthy control population;
- An alteration of the Brain-Gut Axis coincides with the onset of digestive disorders in approximately 77% of individuals.
A mystery remains, whether psychopathological disorders induce irritable bowel syndrome or vice versa.
