Large Intestine Flashcards
Give 2 functions of mucus in large intestine
Provide adherent medium for faecal matter
Protection against acid abrasion and bacteria
Give 4 functions of gut microbes
Form secondary bile acids Synthesise vitamin K Digest mucus Degrade digested enzymes Conversion of bilirubin to urobiligens Metabolise undigested polysaccharides
What drives H2O movement in large intestine from lumen into blood?
Na movement, water follows by osmosis
Which proteins are involved in the movement of Na from lumen into blood in large intestine?
Electrogenic channels from lumen into cell
Na/K ATPase from cell into lateral space and then blood
What route does water take from lumen to blood in large intestine?
Transcellular due to tight junctions
What are the 2 types of motility in the large intestine?
Haustral contractions - mixing in ascending
Mass movements - propulsive in transverse and descending
What is the gastrocolic reflex?
When food is taken into mouth
Strength of mass movements increased
Response to gastrin and extrinsic autonomic nerves
Pushes the colonic contents into the rectum, triggering the defaecation reflex
What is the ileocaecal valve?
Valve between ileum and caecum
One way sphincter
Controls rate of chyme entry into large intestine
What is constipation?
Infrequent bowel movement <3 times per week
Incomplete evacuation of faces
Hard stools
Difficulty during defaecation - straining during 25% bowel movements
Type 1/2 Bristol stool chart
Name the 5 causes of constipation
Dietary Hormonal Anatomical Medication Illness
Which people are most prone to constipation?
Elderly
Children
Women>men
What are the 4 types of purgatives used to treat constipation?
Bulk laxatives
Osmotic laxatives
Stimulant purgatives
Faecal softeners
What are methylcellulose and isphaghula husk?
Bulk laxatives
Name 3 osmotic laxatives
Lactulose
Magnesium sulphide
Magnesium hydroxide
Which purgative would you use before a procedure requiring a clean bowel?
Saline purgatives - magnesium sulphide or magnesium hydroxide
How does lactulose work?
Semi-synthetic disaccharide not broken down in SI
Colonic bacteria convert it to monosaccharides which are poorly absorbed in this region, they are fermented and then draw water into the lumen by osmosis
Act: within 1-3 days, Usage: useful against constipating effects of opioids, Side effects: abdominal cramping, gas, borborygmus and flatulence. Less common side effects, nausea and vomiting.
Excessively high dosage can cause explosive and uncontrollable diarrhoea. Tolerance can develop
Name 2 stimulant purgatives
Senna
Bisacodyl
Abuse of stimulant purgatives can cause…
Melanomas coli - dark pigment in colon, increased risk of colon cancer
Cathartic colon - weak and floppy colon
Anorexia
What are 5 causes of diarrhoea?
Infectious agents Toxins Anxiety Illness Drugs
What are the 4 types of diarrhoea?
Secretory
Osmotic
Inflammatory
Motility related
What is Loperamide and what is it used to treat?
It is an opioid drug, m-opioid receptors
Relatively selective to GI tract
Doesn’t cross BBB
Used to treat diarrhoea by reducing motility. Increases tone and rhythmic contractions of colon, but diminishes propulsive activity
Pyloric, ileocaecal and anal sphincters are contracted
What are the constituents of oral rehydration therapy?
NaCl
Glucose
Isotonic or hypotonic solution
Describe the blood supply to the hindgut segment of large intestine
From IMA which branches into Left colic Sigmoid Superior rectal Marginal artery provides anastamoses
Describe lymph drainage from GI tract
Lymph follows arteries Drains to cisterna chyli Drains to thoracic duct Drains to subclavian artery Into SVC
Which segment of large intestine is easiest to palpate and why?
Descending colon because faeces are compacted and solid at this point
What can surgeon use as reference point to help find appendix?
Follow taeniae coli down caecum
Appendix is at point where 3 bands join
Near ileocaecal junction
What is the classic pain pattern for appendicitis?
Starts in umbilical region, poorly localised. Referred pain
Moves to right iliac fossa and becomes sharp and extremely painful as peritoneum has become irritated
Which part of the stomach will you likely be able to see on a radiograph when patient is standing?
Fundus because it is often full of air
What is McBurney’s point?
2/3rd distance from umbilicus to anterior superior iliac spine (ASIS). Point that used to be used for appendectomy surgery
What effect can diarrhoea have on acid base balance?
Large loss of NaHCO3 so can cause metabolic acidosis
What position does the appendix normally sit in?
Retrocaecally
What are paracolic gutters?
Spaces formed because ascending and descending colon are secondarily retroperitoneal
Routes for fluid movement/infection spread from rectum to diaphragm
What are the branches of the IMA?
Left colic
Sigmoid
Superior rectal
Where can GI Cancer spread to?
Para-aortic lymph nodes Cisterna chyli Left subclavian nodes (via thoracic duct) Liver via portal venous system Sacral nodes Peritoneal cavity
What are the functions of the large intestine?
Extract Na+ and water from the luminal contents
Make and store faeces
Move faeces towards the rectum
Which cells secrete mucus?
Goblet cells
What is the ileocaecal valve and what does it do?
Separates the terminal end of the ileum from the caecum
Is a one-way valve guarded by a sphincter prevents back-flow of faecal contents from the colon
Controls the rate at which ileal chyme enters the colon
Regulated by neural and hormonal mechanisms
What does the motility of the large intestine allow?
Facilitates the efficient absorption of water and salts
Permits the orderly evacuation of faeces
What are haustral contractions?
Longitudinal muscle of the colon in 3 bands called taeniae coli
Combined contractions of the taeniae coli and the circular muscle layer causes the colon to bulge into ovoid segments called haustrae
Haustral contractions (segmented) mix the contents of the proximal
colon which facilitates water absorption
What are mass movements?
Propel the luminal contents from the beginning of the transverse
colon to the sigmoid colon
Are a series of modified peristaltic events
Occur 1-3 times a day
What is cathartic colon?
Anatomical and physiological changes in the colon that occurs with chronic use of stimulant laxatives (> 3 times/week for 1 year)
laxative dependency, tachyphylaxis (requires higher doses)
Medical consequences such as fluid and electrolyte imbalance, steatorrhoea, vitamin and mineral deficiencies
Signs and symptoms include bloating, a feeling of fullness, abdominal pain, and incomplete faecal evacuation
How can constipation be prevented?
The relief of constipation with osmotic agents, i.e. lactulose or magnesium salts, should immediately be followed with prevention using increased fibre and a nightly decreasing dose of osmotic laxative In various conditions (such as chronic use of opioids), combinations of hydrating (e.g. lactulose), bulk-forming and stimulant agents may be necessary to prevent constipation
What is diarrhoea?
Frequent watery loose bowel movements
What are 4 types of diarrhoea?
Secretory
Osmotic
Motility related
Inflammatory
What is secretory diarrhoea?
Increased active secretion, or an inhibition of absorption. No structural damage, e.g. cholera
What is osmotic diarrhoea?
Loss of water due to a heavy osmotic load, e.g.in maldigestion (e.g. Coeliac disease), where the nutrients remain in lumen, in turn pulling
water into the lumen
What is motility related diarrhoea?
Abnormally high GI motility, decreasing time available for absorption of nutrients and water. Can occur in diabetic neuropathy
What is inflammatory diarrhoea?
Damage to the mucosal lining or brush border leads to a passive loss of protein-rich fluids, and a decreased ability to absorb these lost fluids. Caused by bacterial infections,viral infections, parasitic infections or autoimmune problems e.g. inflammatory bowel disease
What can be used to treat Severe Campylobacter infections?
erythromycin or ciprofloxacin
What can chronic anti motility agent use lead to?
Chronic use leads to constipation, abdominal cramps, dizziness. Paralytic ileus can also occur. Do not use in young children
