Large Intestine Flashcards
What are the sacs in the colon called?
Haustra
What re the 3 strips of longitudinal muscle in the large colon called?
Teneai coli
What are the 2 bends in the large colon called and which is higher?
Hepatic flexure and splenic flexure
Splenic flexure is higher
What are the parts of the colon from proximal to distal?
Caecum, Ascending, Transverse, Descending, Sigmoid
Where is McBurnies point and what is it?
1/3rd of the way in from superior anterior ileac spine to umbilicus
Point of maximal tenderness in appendicitis
What does the mesentery on the sigmoid colon put it at risk of?
Twisting around itself and cutting off its blood supply (sigmoid volvulus)
What branches off the aorta from L1-4?1
L1: superior mesenteric artery
L2: renal arteries
L3: inferior mesenteric artery
L4: bifurcation into common ileacs
Which artery supplies the transverse colon and what does it come from?
Middle colic
Superior mesenteric artery
Which artery supplies the ascending colon and which artery does it originate from?
Right colic
Superior mesenteric artery
Which artery supplies the descending colon and which artery does it originate from?
Left colic
Inferior mesenteric artery
What is the only blood supply to the appendix?
Appendicular artery from the superior mesenteric artery
What is the name of the arch of arteries that supplies the ascending, transverse and descending colon?
Marginal artery of Drummond
Anastomoses of right colic, middle colic and left colic
What supplies the sigmoid colon and where does it originate from?
Sigmoid arteries
Inferior mesenteric artery
Does the inferior mesenteric artery supply any of the rectum and anus?
The proximal part of the anal canal (superior rectal artery)
Is there any connection between the hindgut and distal rectal blood supply?
Anastomoses between the superior, middle and inferior rectal arteries (supplied by the IMA and branches of the internal ileac)
What are the 3 anastomoses in the portal venous system?
Skin around umbilicus
distal end of oesophagus
Rectum/anal canal
What causes varicose veins?
Back pressure through the anastomoses between the portal and canal venous systems
What is the gross sign of varicose veins on the abdomen?
Caput medusa
Are polyps benign or malignant and what can they be called?
Can be either
Benign = adenoma
Malignant = adenocarcinoma
What is the progression from normal mucosa to malignancy in the colon?
Normal mucosa --> Adenoma (benign) --> Adenocarcinoma (malignant)
How should adenomas in the colon be dealt with?
Removed as are pre-malignant
What are dukes A, B and C
Staging for colorectal cancer
Dukes A = no metastasis - good prognosis
Dukes B = limited metastasis - poor prognosis
Dukes C = metastases to lymph nodes - very poor prognosis
What is lynch syndrome?
Inherited syndrome that predisposes to lots of polyps which can develop to become malignant - presents in 50s
What is the differences between the internal and external anal sphincter?
At the same place; internal is smooth muscle and external is skeletal muscle
What is the purpose of the appendix?
No purpose in humans
What controls contraction and relaxation of the ileocaecal valve?
Distension of the caecum causes contraction to prevent backflow
Distension of the duodenum causes relaxation to allow passage of food
How is water absorbed from the large intestine?
Absorption of Na and Cl back into the blood which causes water to follow it by osmosis
What is secreted in the large intestine?
Mucous (to form slippery surface gel)
Proteins for host defence
What mixes the contents of the large intestine?
Hautration - very slow process
What is mass movement and how often does it occur?
Contraction of large segments of the large intestine to drive faeces distally - often triggered by a meal
Occurs roughly 3 times per day
What causes the need to defecate?
Faeces in the rectum cause it to stretch, when stretched enough causes relaxation of the internal anal sphincter, the external anal sphincter voluntarily controls until is convenient to defecate
What reduces the resistance to stool achieved by squatting?
Straightening out of the anal-rectal angle
How does intraabdominal pressure affect defecation?
Contraction of abdominal muscles and suspension of breathing increase intraabdominal pressure which assists defecation
Where are the most commensal bacteria in the human body present?
Colon
Where does intestinal gas occur from?
Swallowing of air (mostly burped up)
Fermentation of certain foods
What is constipation?
Presence of hard dry faeces in the colon that are hard to defecate
What causes constipation?
Delay in defecation causing increased water to be absorbed
What is the difference between a laxative and purgative?
Laxative: assists emptying of the colon
Purgative: clears the whole small and large intestine - used prior to surgery
How does a laxative work?
Softens or lubricates the stool to make it easier to pass
What is a diverticulum?
Outpouching of a mucosal tissue through the muscle wall
What is a false diverticulum?
A diverticulum that does not breach through the muscle coat, these are acquired
How is diverticulosis (the presence of diverticulums) diagnosed?
Colonoscopy
Barium enema
What is diverticulitis?
Inflammation of diverticula
What are the clinical features of diverticulitis?
Left inferior quadrant pain
Sepsis
Altered bowel habit
What is a fistula?
An abnormal connection between 2 epithelial surfaces
What is the treatment for diverticulitis?
Oral antibiotics, can be managed in the community
What are the two types of inflammatory bowel disease and what characterises them?
Crohns disease
Ulcerative colitis
Presence of ulcers in the colon
What are the 4 types of colitis?
Infective colitis,
Ischaemic colti,
Ulcerative coltis,
Crohns colitis
What are the symptoms of colitis?
Diarrhoea (can contain blood)
Abdominal cramps
Dehydration
Sepsis
How is colitis diagnosed?
Sigmoidoscopy (colonoscopy) + biopsy
Stool cultures
Barium enema
How is ulcerative colitis or crohns colitis treated?
IV fluids,
IV steroids,
GI rest
If not better within 3/4 days, surgery
What causes large bowel obstruction?
Tumour,
Stricture,
Volvulus
What are the clinical signs of colonic obstruction?
Vomiting
Absolute constipation
Distended abdomen
Pain
What causes watery diarrhoea?
Collagenous colitis,
Lymphocytic colitis
What are the 4 types of laxatives and how do they work?
Bulk laxatives: increase vol in the GI tract
Osmotic laxatives: increase H2O in the GI tract
Faecal softeners: lubricate stool
Stimulate laxatives: stimulate ENs to increase peristalsis
What are the two types of route that water can be reabsorbed by?
Transcellular or paracellular
Which method of water reabsorption is favoured in the fed state?
Inward movement of Na (and thus water) coupled to glucose or amino acids
What is the use of bicarbonate in water reabsorption?
Mops up excess protons from Na/H exchanger
Movement of what ion is more important in water reabsorption in the fasting state?
Chlorine
Which ion channel is used for secretion of Cl across the apical membrane of enterocytes in the large intestine?
CFTR - means CF also affects water reabsorption
What is the first priority in treatment of diarrhoea?
Maintenance of fluid and electrolyte balance
What is used for treatment of diarrhoea?
Rehydration therapy - specific concentrations of fluid and electrolyte are given to optimise reabsorption of water along the colon
What types of drug (and which is the most common) are used as anti-motility agents in diarrhoea?
Opioids - Loperimide (available over the counter)
What is the key symptom of colorectal cancer?
Rectal bleeding (if painful is less likely to be cancer)
What type of cell change occurs in anal cancers and are they common?
Very uncommon
Squamous cell carcinoma
What diseases increase the risk of colorectal cancer?
IBD (Crohns disease + ulcerative colitis)
What are the symptoms of colorectal cancer?
Rectal bleeding, Colicky abdominal pain, Change in bowel habit, Weight loss, Iron deficiency anaemia, Abdominal mass
What investigations are done to investigate possible colorectal cancer and what is the gold standard?
Barium enema
CT colonography
Colonoscopy/Sigmoidoscopy - gold standard
What screening test is done for colorectal cancer?
FIT test - stool sample
If positive, offered colonoscopy
How is colorectal cancer usually treated and how successful is this?
Surgery - colectomy
Very successful
What is the follow up for colorectal surgery?
CT scans
