constipation and diarrhoea Flashcards
peristalsis is the wave like contractions and relaxations of the intestinal tract, how does this allow the movement of food?
the muscle behind the food contracts whilst the muscle in front relaxes hence allowing it to pass smoothly through.
the enteric nervous system controls the motility of the intestinal tract without input from the brain - what are the two main branching networks that the enteric nervous system consists of?
- Meissners /submucosal plexus - this is located in the submucosa and controls the glandular secretions, electrolyte ans water transport and regulates local blood flow.
- Aerbachs /myenteric p-lexus - this innervates the smooth muscle to control contraction and relaxation. sensory neurons in the gi tract detect chemical changes and relay information to the motor neurons which act on smooth muscle causing contraction or relaxation.
how are sensory neurons activated in the local reflex circuit of the gut?
distension of the gut will relay information on afferent sensory neurons causing activation of the sensory neurons so contraction and relaxation occurs.
when the sensory neurons of the gut are activated, what happens?
- sensory neurons trigger excitatory interneurons which trigger motor neurons to release acetylcholine which acts on circular muscle of the intestine to cause an ascending contraction in the proximal end.
- sensory neurons trigger interneurons which cause motor neurons to release VIP nitric oxide or ATP causing descending relaxation at the distal end.
the longitudinal muscle surrounding the food will also contract to squeeze food through.
what happens in the large intestine?
the large intestine is where the faeces is stored and where absorption of water and nutrients occurs
what is haustra?
haustra is segmented pieces of the large intestine thats controlled by pacemaker cells that control the movement of food.
haustra shuttling is a continuous process - there is a gradient of firing from the proximal end to the distal end.
how does defacation occur?
mass movement - occasionally all the haustra contract at once leading to defaecation.
how is the defaecation reflex activated?
by the presence of faeces in the rectum. the faeces in the rectum causes distension that activates stretch receptors so that the internal sphincter relaxes and local peristalsis increases, allowing the faeces to move into the anal canal. the receptors also signal to the brain to relax the external sphincter as this is under voluntary control
what is constipation?
if you have bowel movements less than 3 times a week youre classed as constipated. you may experience infrequent stools, difficult stool pasage, incomplete defaecation and your stools may be dry/hard.
what can constipation cause?
constipation can cause haemorrhoids, rectal prolapse or faecal impaction - this is a sever condition in which faeces rises up the intestine.
whats primary contipation?
the bowel is healthy but not working properly due to lifestyle choices like lack of fibre and excercise, dehydration, toilet position, anxiety stress
whats secondary constipation?
this is asociated with disease like endocrine/systemic diseases, myopathy, lesion of gi tract, or drug use.
opioid are the leading cause for secondary constipation, how does this occur?
the gut naturaly produces endogenous opioids which can act on 3 receptors in the gut but typically mu. this action on the receptor will slow down gi motility however endogenous opiods have little effect due to the low half life. exogenous opioids will have longer effects, inhibiting enteric nerve activity by suppressing enteric nerve excitability, inhibiting motor and secretomotor pathways and inhibiting transmitter release. this therefore leads to inhibition of ion and fluid secretion as well as inhibiting peristalsis and gastric emptying, all of which leads to constipation.
what are bulk forming laxatives?
bulk forming laxaties increase the size and fluid content of the stools, in turn increasing the movement of the gi tract, an example is fibrogel.
what are stool softening laxatives?
stool softening laxatives reduce surface tension and increase the fluid content of stools making them easier to pass e.g. arachis oil
