physiology of large intestine Flashcards
what happens in mechanical digestion in the large intestine
- chyme enters through the ileocaecal valve
- haustral churning
- peristalsis occurs slowly (mass movement)
what happens in chemical digestion in the large intestine
- only bacterial enzymes are present
- carbohydrates are fermented to produce flatus
- break down remaining amino acids
what is the predominant mixing in the large intestine
segmental contractions
how do mass movements work
intense and prolonged peristaltic contraction which can clear sections of the colon of all contents
are mass movements seen anywhere else in the digestive tract
no
what stimulates colonic motility
morning wakening
what does gastrocolic reflex cause
increased motility in colon in response to stretch in stomach and byproducts of digestion in the small intestine
what influences transit
diet - eg fibre increases faecal weight and reduces transit time
stress can increase motility
what does immobility lead to
constipation
how does age affect colonic motility
can prolong transit time
do women have slower or faster colonic transit time
women have slower transit time
how much water enters large intestine per day and how much is reabsorbed
0.5-1L and all except 100ml is reabsorbed
what does faeces consist of
- undigested food
- inorganic salts
- sloughed off epithelial cells
- bacterial products
- bacteria
what is in the ascending (right) colon
it is relatively fluid
has the consistency of muesli with large aggregates beginning to form
what is in the transverse colon
less water and some gas
what is there a risk of in the descending colon
risk of impaction in faeces
what initiates defecation reflex
distension of rectum
(parasympathetic input to open internal anal sphincter)
it is involuntary
what does increased pressure in rectum cause
the longitudinal muscle to shorten
are contractions of diaphragm and abdomen during defaecation voluntary or involuntary
voluntary
last part of defaecation process
external anal sphincter opens
what are the disorders of the large intestine
- disorders of motility (constipation and diarrhoea)
- ibs
- haemorrhoids
what causes constipation
- idiopathic
- gender (women more likely)
- psychiatric (depression etc)
- disease
- iatrogenic (morphine etc)
what causes diarrhoea
(that isn’t severe enough for treatment)
- diet
- mild food poisoning
what causes diarrhoea
(that is severe enough for treatment)
- disease (neoplasia, UC etc)
- drug induced
- travel
what causes IBS
- abnormal GI motility
- psychological factors (anxious patients who worry excessively)
- luminal compounds which may irritate the bowel (allergens etc)
- altered serotonin levels
what happens to veins when you have haemorrhoids
overdistended veins in submucosa of the lower rectum
what causes haemorrhoids
excessive straining in constipation
what complications can haemorrhoids cause
thrombosis of local blood vessels
what can ease defaecation
bulk/lubricant laxatives
what can relieve symptoms of haemorrhoids
topical preparations
such as
- preparation H
- anusoyl
- anaesthetics
- anti inflammatories
what are the two regions of the colon
proximal and distal
how can the distal part of the colon be reached
rectally (useful when treating haemorrhoids)
how can the proximal section of the colon be reached
via the oral route
which part of the colon is sufficiently fluid for drug absorption
the ascending colon
treatment for constipation
- diet changes
- laxatives
- motility enhancers
treatment for diarrhoea
- oral rehydration
- antimotility agents
- adsorbents
- antimicrobial therapy
how to treat IBS
- patient support (reassure them to stop anxiety)
- diet changes
- antispasmodic
- antidepressants/hypnotherapy
how to change diet to treat IBS
for constipation
- high fibre diet
- laxatives
for diarrhoea
- avoid fresh fruits/salds
- loperamide
how do antidepressants/hypnotherapy treat IBS
strong brain/gut link
new 5-HT receptor targeted drugs may prove beneficial
what are some functions of the gut bacteria
- metabolism of indigestible material
- vitamin synthesis
- neurochemical synthesis
- anti-inflammatory effects
- promotion of bone growth
- positive effects on brain and cardiovascular health
what factors affect the gut microbiome
- diet
- age
- host genetics
- exercise
- antibiotics
- smoking
- geographical impact
what are intervention strategies for the gut bacteria
- probiotics
- faecal microbiota transplant
- phage therapy to selectively target bacteria
