Physiology & Pharmacology of Large intestine Flashcards
Gastro-ileal reflex is stimulated by gastric _. It involves the opening of the _ valve.
Distension
Ileo-cecal
The Ileo-caecal valve acts as as one way valve. Why is this important? (3)
- Allows digested contents of small intestine to enter caecum
- Prevents colonic bacteria proliferating into ileum
- Produces urge to defacate
What are the major functions of the large intestine? (5)
- Absorption of H20 and salt
- Secretion of K, HC03, mucus
- Absorbs short chain fatty acids
- Reservoir
- Periodic elimination of faeces
Large intestine motility can be summarised as mass movements, haustration and defecation reflex. Describe these
Mass movements- Strong peristaltic contractions of circular muscles in large parts of the colon. Triggered by a meal- Gastrocolic reflex.
Haustration- Non propulsive segmentation caused by contraction of circular muscle.
Defecation reflex- Spinal reflex triggered by distension of the rectum.
The Defecation reflex can be triggered by the afferents and the autonomic nervous system. T/F?
True
Summarise the steps involved in the autonomic control of the defecation reflex.
- Mass movement- Rectum fills with faecal matter
- Rectal stretch receptors activated
- Activations of afferents to spinal cords
- Activation of parasympathetic efferents
- Contraction of smooth muscle of rectum and colon- internal anal sphincter relaxes
- Relaxation of external anal sphincter: Defaecation
- Contraction of external anal sphincter: Defaecation delayed.
- Relaxation of external anal sphincter: Defaecation
Summarise the afferent section of the defaecation reflex.
- Mass movement- Rectum fills with faecal matter
- Activation of rectal stretch receptors
- Activation of afferents to brain- urge to defaecate
- Altered firing in efferents to spinal cord
- Relaxation of external anal sphincter: Defaecation assisted by abdominal contraction
- Contraction of external anal sphincter: Defaecation delayed.
- Relaxation of external anal sphincter: Defaecation assisted by abdominal contraction
What are the functions of the colonic flora of bacteria?
- Increase intestinal immunity
- Promote motility and helps maintain mucosal integrity
- Secrete vitamin K2, and free fatty acids
- Activate some drugs- used in IBD
- Role in enterohepatic cycling of compounds.
IBD includes _ and _
Ulcerative colitis and Crohns
Summarise the 4 pharmacological agents used in IBD?
- Aminosalicylates
- Glucocorticoids
- Immunosuppressants
- Biological agents
Effective management also needs
- Drug therapy
- Nutrional help
- Surger- in severe disease
What are the use of Aminosalicylates? What diease is it most useful for.
Long term maintenance of remission
Ulcerative colitis
Give an example of Aminosalicylate.
Sulfasalazine- Azo bond cam link 5-aminosalicylic acid to sulfapyridine.
Action mechanism of Aminosalicylates like Sulfasalazine?
5-Asa (5-aminosalicylic acid) reduces inflammation by inhibiting COX & LOX.
What are some adverse sude effects of aminosalicylates?
Rashes, arthralgias blood dyscrasia (bad mixture)
Mesalazine is newer drug that is better tolerated than Sulfasalazine. T/F?
True
Glucocorticoids are potent in both colitis and Crohn’s. T/F?
True
Examples of steroids?
- Prednisolone
- Budesonide
Two major side effects of Steroids?
- Steroid dependency
- Steroid resistance
When are immunosuppresants used in IBD?
When the IBD is unresponsive to steroids. Also known as steroid sparing drug.
Immunosuppresants has a slow onset of action- 6-12 weeks
What are the 4 most common immunosuppressants in IBD?
- Azathioprine- most common, can be used long term.
- Ciclosporin
- 6-Mercaptopurine
- Methotrexate- once weekly dose.
What are the biological agents used in IBD? (Mab’s)
Mabs- Monoclonal antibodies. V expensive
Given in severe IBD. Hypersensitivity reactions are common
- Infliximab
- Adalimumab
- Vedolizumab
- Golimumab
Main actions of Mabs?
Blocks inflammatory mediator TNFa
Irritable bowel syndrome is a long term condition causing inflammation. T/F?
False
IBS treatment is based on Symptomatic control and improving quality of life
Two main symptoms of IBS?
- Diarrhoea
- Constipation
Main drugs used in IBS?
- Antispasmodic
- Laxative
- Antimotility
Antispasmodic drugs can be of what two types?
- Anti-Muscarininc- propantheline bromide
- Direct smooth musce relaxants- alverine, pepprmint oil
What are the drug types used in Visceral Hypersensitivity?
- Tricyclic anti-depressants- Amitriptyline, low doses used in IBS to reduce pain perception. Not 1st line, used if antispasmodics not working
- Selective Serotonin reuptake inhibitor (SSRI)- Citalopram
