Physiology of Large Intestine Flashcards
Large Intestine is made up of?
Caecum Appendix Colon- A,T,D,S Rectum Anal canal Anus
Describe the longitudinal smooth muscle of the large intestine?
3 Strands
Taeniae coli
Which unite around the sigmoid colon & thicken around the internal anal sphincter
Describe the Internal and external sphincters location and muscle?
Same location
2 rings of muscle= smooth and skeletal
What does the caecum recieve?
And what allows this entry?
1-2L of material made up of indigestible residues, unabsorbed biliary components and unabsorbed fluid from terminal ileum a day
Gastroileal reflex
What is the gastro-ileal reflex stimulated by?
Gatric distension
What does the gastro-ileal reflex involve?
- Opening of ileocaecal valve (one-way valve)
- Opens inresponse to gastrin and CCK
What happens to caecum when duodenum is distended?
Relaxes
When does the caecum contract?
In response to distension of ascending colon
Describe the appendix?
Tube with extended lymphoid tissue connected to distal caecum via appendiceal orifice
What occurs when the appendiceal orifice is obstructed? And what obstructs it?
Appendicitis
Faecalith
What happens in the ascending and transverse colon?
Fluid reabsorption
Bacterial fermentation
What happens in the descending and sigmoid colon?
Final drying (dessication) Storage
Functions of large intestine?
- Absorption of H20, Na+ and Cl-
- Secretion of K+. HCO3 and mucus
- Absorption of short cahin fatty acids
- Reservoir for colonic contents
- Periodic elimination of faeces
There is a large amount of villi in colon. True or false?
False
No villi in the colon
There are colonic folds, crypts and microvilli (increased SA)
What do goblet cells do?
Secrete copious amounts of mucus containing glycosaminoglycans- which can form a barrier between bacteria laden faeces and the gut wall
Name for surface epithelial cells in colon?
Colonocytes
What do colonocytes do?
Mediate electrolyte absorption which by osmosis drives absorption of H20
Role of crypt cells?
Mediate ion secretion
What does mass movement in the colon involve?
Drives faeces into distal regions of colon
Triggered by meals
Simultaneous contractions of large sections of circular muscle of A&T colon drive faeces
What is haustration?
Non-propulsive segmentation (Contraction of circular muscle)
allows time for fluid and electrolyte reabsorption
What are haustra?
Sacules caused by alternating contraction of circular muscle
What are peristalic propulsive movements?
Proximal colon drives faeces back towards caecum
What occurs in the defecation reflex?
- Mass movement (rectum fills with faecal matter)
- Activation of rectal stretch receptors
- Activation of pelvic nerve
- Activation of afferents to spinal cord & activation of afferents to brain
- Activates parasympathetuc efferents
- Contraction of smooth muscle of colon and rectum (internal sphincter relaxes)
The rectum is normally empty. True or False?
True
Not designed for storing faeces for prolonged periods
Pudendal Nerve role?
Relaxation and contraction of external sphincter- controls defaecation
What do colonic flora generally?
Increase intestial immunity by competition with pathogenic microbes
Specific roles of colonic flora?
- Promote motility
- Synthesize vitami K2 + free fatty acids
- Activate some drugs
- Role in enterohepatic cycling of compounds
- Beneficial (commensals)
Causes of gas arising?
- Swallowed air
- Bacteria in colon which attack forms of carbs that are indigestible to humans
- Gas that is not absorbed in LI is expelled through anus
What valves separate gas from liquid?
Va,ves of Houston
What is constipation?
Presence of hard dried faeces in colon - because faeces is in colon for too long a time and too much H20 is absorbed
What causes constipation?
- Ignoring urge to defecate
- Decreased colonic motility (bad diet, drugs, netabolic disorders)
- Obstruction of movement
- Paralytic ileus after surgery
- Impairmnet of motility/defecation reflex
What is Hirschprung disease?
Absence of secretion of enteric nervous system
What is IBS?
Irritable bowel syndrome
-Bouts of diarrhoea, constipation or abdominal pain
Treatment fro IBS?
Largely symptomatic
Diet adjustment
Anti-diarrhoeals, Anti-spasmodics and laxatives
Example of an anti-diarrhoeal?
Loperamide
Examples of anti-spasmodics?
Alverine citrate
Mebeverine
Hydrochloride
Peppermint oil
What is linaclotide?
Peptide drug for moderate to severe IBS with constipation in adults
NOT used in IBD
Increases chloride and bicarbonate secretion in intestinal fluid and also increases rate of intestinal transit
Side affect of linaclotide?
Diarrhoea
Drugs used in IBD?
5ASAa (5 aminosalicylic acid)
Glucocorticoids
Immunosippresants
5ASAa?
5 Aminosalicylic acid
-Long term maintenenace of remission (more useful in UC)
-Sulfasalazine
Mesalazine
What is sulfasalazine?
Reduces inflammation by inhibiting COX and LOX
Supplement with folic acid
Side affects of sulfasalazine?
Rashes
Arthralgias
Blood dyscrasias
What is mesalazine used in?
Only in distal disease ]Ulcerative collitis
Mesalazine is better tolerated than sulfasalazine?
True - it is available in enemas
What are glucocorticoids used for?
Acute attacks of IBD
Examples of glucocorticoids?
Prednisolone
Budesonide
What are glucocorticoids effective in?
UC
Crohn’s
Generally discontinued after remission because can cause dependency/resistance
What drug is most frequently used for IBD?
Azothioprine
When are immunosuppressants used to treat IBD?
Severe disease
Steroids don’t work
They inhibit T lymphocyte function & slow onset of action
Examples of immunoseppressants?
Azothioprine
Ciclosporin
6-Mercaptopurine
Methotrexate
