Although this software is designed to work off-campus using a wide range of equipment, for best results we recommend Internet Explorer and a 1024x768 display.
The purpose of these pages is to allow you to check any answers that you are uncertain of. It is NOT intended that you check every answer, or that you use these resources to complete the work session material - both these approaches would be enormously time-consuming, and probably teach you very little. Please use the resources selectively, and return to them for revision later.
To understand the physiological functions of the lower GI tract and their disturbance in some bowel diseases. To appreciate the principal factors influencing lower GI tract motility and gut transit times, the importance of dietary fibre, and the role of the immune system in the pathogenesis of inflammatory bowel disease.
On successful completion of this exercise you will:
Understand the structure, function and histology of the large bowel in healthy people.
Appreciate the longitudinal specialisation of the gut, and the different substances absorbed in the jejunum, terminal ileum and in the large bowel.
Differentiate between the effects of opiates, purgatives, osmotic laxatives and dietary fibre, and understand the development of diverticular disease.
Appreciate the effects of inflammatory bowel disease, and the therapies that can be used to control chronic inflammation.
Understand the role of the immune system in food allergy
This session consists of two parts. Part A is a self directed exercise. The interactive self assessment test below will allow you to check your answers. Part B will be discussed during the tutorial.
PREPARATION FOR THIS SESSION
Before these case studies you should:
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Some useful sources of information | |
| Canadian Society of Intestinal Research |
These leaflets are available via the web and contain accurate but basic information aimed at the general public. You should know most of this material before the exams, but the leaflets on each disease are very similar and you don't need to read them all. |
| Patient leaflets on constipation from NIDDK and CORE | |
| Patient leaflets on diarrhoea from NIDDK and CORE | |
| Tortora and Grabowski "Principles of Anatomy & Physiology" 9th edition (2000) chapters 22 and 24 |
You should study the relevant chapters in your text books as part of this exercise. Sometimes it is helpful to quickly read through the same material explained by several different authors. You will revisit these topics later in the course, so do not try to memorise every last clinical detail. The definitive account in "Immunobiology" (which is our recommended immunology textbook) contains much more information than you need at present. |
| Nelson & Cox "Lehninger Principles of Biochemistry" 4th edition (2005) chapter 5 pages 174 - 182 | |
| Kumar & Clarke "Clinical Medicine"
6th edition (2005) pages 197 - 227: Basic clinical immunology pages 265 - 345: Introduction to gastroenterology pages 309 - 319: Inflammatory bowel disease pages 324 - 325: Diverticular disease pages 326 - 328: Colonic polyps pages 331 - 334: Diarrhoea | |
| Janeway et al "Immunobiology" 4th edn. (1999) | |
| Infliximab patients' home page (drug company site) | It would be a good idea to look at one of these. |
| Lancet editorial on anti-TNFa antibodies in Crohn's | |
| article on TNFa in Crohn's disease | |
| Medscape article on treatment of infectious diarrhoea |
This is supplementary material for clarification and interest. All these reports are available via the Web. Shop around for recent articles that you find interesting and fun to read. |
| Besser et al (1999) E. coli O157:H7 Ann. Rev. Medicine 50, 355-367 | |
| Papadakis & Targan (2000) Cytokines and Inflammatory Bowel Disease Ann. Rev. Medicine 51, 289-298 | |
| Dennis (2006) Australians back bacterial theory for bowel disease Nature Medicine 12(6) 595. | |
We recommend that you read these documents online, and write your answers in the printed work book.
Work through the following self-assessment questions to test your background knowledge of this area. This is a purely formative exercise and your performance is not being recorded. Each question has several correct answers: we don't currently use this style for the Leeds Medical School summative examinations, but you may encounter it elsewhere. The process is important: this isn't a catechism that you are supposed to learn by rote - it is designed to send you to your textbook in such a way that you will properly engage with the material. If you make some mistakes, try to puzzle out what you did wrong, and have another attempt, BEFORE changing the feedback options, otherwise you won't learn very much.
How is the colon adapted to perform these functions?
How does it differ
from the jejunum and the terminal ileum?
Note that the labelling of this image differs slightly from your printed workbook.
Bill W. consulted his GP at his surgery on returning from a business trip abroad: "I've had the terrible runs, doctor. I don't feel that I can move out of sight of the toilet. Do you think I've got cholera?" He explained that his problems had started on the flight home: "We were in the hotel most of the week checking contract drawings, but on the last night we all went out for a meal in down town Beirut..." The interview was interrupted by an urgent visit to the lavatory. His GP handed him a specimen container.
Bill was 38 years old, slightly overweight, temperature 38°C, BP 150/90. His faecal specimen was fluid but otherwise normal appearance, and free from blood or mucus. He said that he had vomited twice on the plane, but not subsequently, and was passing urine normally.
The GP advised him to rest quietly at home, to keep warm and to drink plenty of fluids. He recommended a non-prescription medication containing NaCl, KCl and glucose to be taken in water after every bowel motion. "Take care with your personal hygiene: we don't want you infecting the rest of the family. There is no need to eat unless you feel hungry, but food won't do you any harm. I'll sign a sick note for your employer. Make another appointment if it gets any worse, or if it hasn't cleared up in three or four days."
The glucose in the life-saving recipe below could advantageously be replaced by boiled rice flour in countries where this is more readily available, and the bicarbonate by any organic anion (such as acetate, lactate or citrate) that is metabolised to yield bicarbonate / CO2 in the body.
"I can't possibly do that, doctor. We're about to sign the contract. I absolutely must be London tomorrow to meet this Lebanese group and clinch the deal. My job depends on it."
"In that case, you could try Imodium. Don't take it for any longer than is strictly necessary, and give the practice a ring if your symptoms get any worse."
Lorna D. was a medical social worker who consulted her GP about
chronic diarrhoea. "It's all day, every day, doctor. It's such a problem
visiting clients. I just don't know how I am going to cope." She said she tried
to eat a balanced diet, and couldn't think of any foods that seemed to upset
her. A stool culture showed nothing unusual. Her motions were negative for
occult blood.
Lorna was admitted to hospital for further tests. She passed 950ml of faeces over a 24-hour period. While conducting a colonoscopy examination the consultant noted the situation shown in image 2.
She questioned Lorna very closely about her eating habits before referring her to a psychiatric colleague for further advice.
Michael E. was a 59 year-old Glaswegian bricklayer who developed a
sudden pain in his left iliac fossa. On examination his temperature was 38°C, BP 160/95. He was overweight, but had previously been in
good health apart from chronic constipation. "I feel like I need a crap right
now, doctor, but I can't do anything."
His rectum was empty, but tender mass could be felt in the affected region. When asked about his diet, he described himself as "a real steak and eggs man" who didn't like vegetables...
His immediate problem resolved spontaneously, but the consultant
decided to perform a more detailed colonoscopic examination because Michael's
motions contained some visible blood. He noted, and removed, the structure shown
in image 3 (above). Further colonoscopic examination revealed the situation
shown in image 4 (left).
This condition can also be diagnosed from X-ray pictures taken after a barium enema:
Image 5
Development of several bowel diseases has been associated with diets low in resistant polysaccharides or "dietary fibre". The differences between these polysaccharides may be tiny: starch (easily digested) and cellulose (completely resistant) differ only in the orientation of one chemical bond.
Some resistant polysaccharides are not digested at all, but some can be slowly fermented by bacteria in the lower gut. What are the major products of such fermentation? What are the obvious physiological effects?
Angela F. had suffered for many years from cramping, lower abdominal pain, associated with bloody diarrhoea. She was underweight, slightly anaemic, and sometimes also suffered from arthritis in her spine, hips and knees. Colonoscopy revealed the situation shown below but other areas of her colon were apparently normal. A biopsy showed that the disease involved the full thickness of her intestinal wall.
 diseased |
 normal |
The severity of her condition varied over time, and on this occasion forced her to seek a hospital appointment.
"Its getting bad again, doctor, and as usual I have these painful mouth ulcers as well."
Her consultant prescribed prednisone for 14 days, gradually tapering the dose to zero over several weeks. Angela had previously been treated with mesalazine, but in view of her relapse on this agent, her consultant decided to continue treatment with 6-mercaptopurine.
Why was the consultant reluctant to use prednisone indefinitely? [Look up the side effects.]
This disease follows a highly variable course, but in severe cases may involve strictures, fistulae, peri-anal fissures and abscess formation. Eventually Angela may require surgery, but the smallest possible length of bowel would be removed because the recurrence rate is high.
What would be the physiological consequences of removing her terminal ileum? Or her colon?
Colonic disease is sometimes treated by creating an ileostomy. What are likely to be the four principal disadvantages, from the patient's point of view?
INTRODUCTION TO PART B
This section will allow you to consolidate some of the information given in Professor Carding's lecture. The first section follows on from Part A, in which you considered the diagnosis and treatment of inflammatory bowel disease, and considers autoimmune disease in a broader context. The second section considers the molecular mechanisms underlying allergic responses. These are two of the most common types of disorder involving the immune system.
Section 1 Autoimmune disease
Some additional reading for interest - a New Scientist article describes a recently proposed theory to explain why women are more prone to auto-immune disease than men
Infliximab is new biological therapy recently licensed for the treatment of Crohn's disease. It is a chimeric mouse-human monoclonal antibody against TNFa.
Section 2: Allergic reaction
Clinical Case
Samantha, aged 22, was brought unconscious into the casualty department. her partner told the doctor that they had been having a meal in a local restaurant when Samantha complained of feeling ill; she said that her lips were tingling and she felt hot and nauseous. Within two minutes she had collapsed, and an ambulance had been called. Ambulance staff had given her oxygen.The doctor found that Samantha was very flushed; her lips and tongue were swollen and her breathing noisy, with a pronounced wheeze. Her pulse was 120bpm and her blood pressure very low. The doctor immediately gave her a subcutaneous injection. Two other drugs were administered through an intravenous line.
After 5 minutes, Samantha had regained consciousness, her breathing was easier, and her blood pressure had risen to 90/50. Her partner later recalled that she had suffered from swelling of the lips on several previous occasions in the last year, once after eating some mixed nuts at a party.