Lower GI Tract Flashcards
(41 cards)
What does the lower GI tract consist of anatomically?
Specifically the large bowel
Cecum (and appendix) –> ascending colon –> transverse colon –> descending colon –> sigmoid colon –> rectum –> anus
What is the blood supply to the ileum and colon?
Ileum - supplied by branches of the superior mesenteric artery (SMA)
Colon - supplied by branches of the SMA and inferior mesenteric artery (IMA) covers left side of colon
Venous uptake from bowel is through the superior mesenteric vein (SMV) and inferior mesenteric vein (IMV) that join the portal vein which then join the inferior vena cava (IVC)
What are the 4 layers of the colon, starting from innermost to outermost?
Innermost
Mucosa - continuous with the epithelium; contains many glands to produce mucin = important in lubricating bowel = easier to pass stool
Submucosa - between the mucosa and muscularis layer; contains the submucosal plexus = enteric nerve supply (e.g. regulating GI blood flow, epithelial function etc.)
Muscularis - made up of the inner circular and outer longitudinal muscles; contains the myenteric plexus = nerve supply for controlling GI motility
Serosa - like a duvet over the other layers containing the blood vessels and nerves
Outermost
What is the sympathetic and parasympathetic nerve supply to the colon?
Parasympathetic:
Vagus = ascending colon and most of transverse colon
Pelvic nerves = more distal colon
Sympathetic:
Lower thoracic and upper lumbar spinal cord
Somatic motor fibres of pedunal nerves = external anal sphincter
What is the enteric NS composed of?
Why is the ENS important (especially in the rectum)?
Afferent sensory neurons detect pressure
Myenteric plexus in the muscularis layer
Important because:
Pressure detectors send signals to brain - important for emptying process of rectum (i.e. when to poop)
Important in Hirschsprung’s disease (no enteric intramural ganglia) - causes problems passing stool
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What are the 6 types of Lower GI disorders and what are some examples of each?
- Inflammatory
- Inflammatory Bowel Disease (IBD)
- Microscopic colitis
- Infective
- C Diff
- E Coli .. etc
- Structural
- Diverticular disease
- Haemorrhoids
- Fissures
- Functional
- Irritable bowel syndrome
- Neoplastic
- Colonic polyps & colon cancer
- Other
- Neurological, metabolic & vascular
What is inflammatory bowel disease (IBD)?
Comprised of Crohn’s disease and Ulcerative colitis
Lifelong chronic disease characterised by inflammation in the bowel, often affecting young people
What is the peidemiology of IBD?
Affects 1.5 million people in America and 2.2 million in Europe
New Zealand and Australia have particularly high rates of IBD
Several hundred thousand more worldwide
Why is IBD increasing worldwide?
Increasing number of IBD worldwide
Mixing of genetic pool, migration and movement of people
What is the health burden of IBD?
Due to chronicness of disease, patients require lifelong treatment
This is a huge health burden = Burden of therapy for patients Hospitalisation Surgery Health-related quality of life Economic productivity Social functioning
What are the 2 types of IBD?
What are their characteristics?
Ulcerative colitis (UC):
Inflammatory disorder limited to the colonic mucosa
Superficial
Continuous
Always involves the rectum
Affects males and females equally
No granulomas
Crohn’s disease (CD):
Can affect any part of the GI tract - anywhere from the mouth to the anus
Deep ulcerations and deep involvement of the mucosa
Patchy chronic transmural granulomatous inflammation (patchy = different segments of the colon)
Tendency to form fistula or strictures - strictures = fibrous, stiff tissue due to exposure to severe inflammation
Females more affected than males (1.5:1)
What are the main differences of UC vs CD?
UC vs CD
Continuous vs patchy
Superficial vs deep inflammation / penetration
Always involves rectum vs any part of digestive tract but often segments of the small and large intestine
Can type of IBD change?
Yes, patients can present with UC, then CD, and they can switch between them
What are the different types of UC?
Always involves the rectum
Proctitis = only rectum
Protosigmoiditis = rectum and sigmoid
Distal colitis = rectum, sigmoid and descending colon
Extensive colitis = rectum, sigmoid, descending and transverse colon
Pancolitis = rectum, sigmoid, descending, transverse, ascending, caecum, and appendix
What are the different types of CD?
Patchy = combination of different segments of the colon
What are the symptoms of IBD?
They depend on the side of inflammation:
Collitis = bleeding, mucus, urgency to pass stool, diarrhoea
Perianal (CD only) = anal pain, leakage, difficulty passing stool
Small bowel disease (CD only) = symptoms relate to lack of absorption of nutrients = abdominal pain, weight loss, tiredness / lethargy, diarrhoea, abdominal mass
Why does IBD present at sites outside of the colon / GI tract?
As it is an autoimmune condition - can affect other sites
What are some extra-intestinal manifestations of IBD?
Arthritis =
Axial – Ankylosing Spondylitis
Peripheral
Skin =
Erythema nodosum
Pyoderma gangrenosum
Eyes =
Anterior uveitis
Episcleritis/Iritis
Liver =
Primary Sclerosing Cholangitis (PSC)
Autoimmune hepatitis
What causes IBD?
Still unknown
A final common pathway that reflects a combination of an impaired mucosal immune response to the gut microbiota in a genetically susceptible host = in certain patients, the immune system responds inappropriately to the gut microbiota
What factors contribute the development of IBD?
Genetic susceptibility = NOD2, HLA, ATG, Il23R
Immune response = anti-saccaromyces cervisiae (ASCA) - Crohn’s; pANCA - UC
Environmental factors = diet, mycobacterium paratuberculosi, MMR?
Why does diet affect the development of IBD?
Diet affects gut microbiota
Results in dysbiosis i.e. unhealthy gut microbiota
Why factors can be protective to developing IBD?
Why do patients with appendectomy not develop UC but can develop CD?
Physically active
Those who have and appendectomies do not get UC
Oddly, smoking - patients who stop smoking can develop IBD, although smoking worsens IBD once it develops
Apprendix = holds many of the gut microbiota
What are the risk factors for developing a poor, unbalanced microbiota?
How does a poor, unbalanced gut microbiota affect IBD development?
Lack of vitamin D exposure Overly hygienic Stress Genetic susceptibility Gut microbiome Medications - e.g. antibiotics Poor diet Appendectomy - develop CD, never UC
All can contribute to development of poor and unbalanced gut microbiota, which then triggers immune response leading to autoimmunity, allergy and metabolic disorders