Small and Large Intestine Flashcards
parts of small intestine
duodenum, jejunum, ilieum
function of SI
helps to further digest food coming from the stomach.
It absorbs nutrients and water
move food along
what increases surface area in the small intestine?
cylindrical, circular folds (plicae), villi, microvilli
what is the function of villus and crypt cells in SI
villus - absorbs, crypt - secretes Cl and water
what is the importance of H2O secretion in digestion
- maintain lumenal contents in liquid state
- promotes mixing of nutrients w digestive enzymes
- aids nutrient presentation to absorbing surface
- dilutes and washes away toxins
what transporter does Cl go through at the apical membrane in SI
CFTR
what regulates the transportation of Cl through the membrane in SI
Adenylate cyclase
what are the 2 types of movement in s intestine
segmentation and peristalsis
what is segmentation
- contraction ↔ relaxation of short segments
- contraction moves chymes (up&down) into areas of relaxation
- relaxed areas then contract and push chyme back
- thorough mixing of contents w digestive enzymes
what generates segmentation contractions
depolarisation generated by pacemaker cells in longitudinal muscle
basic electrical rhythm produces oscillations in membrane potential → threshold → AP → contraction
what is the frequency of segmentation determined by
BER (basic electrical rhythm), decreases as move down tract
what determines strength of contraction in segmentation
AP frequency
what effect does parasym and symp have on contraction in segmentation
para - inc contraction,
symp - dec
when does peristalsis start
following absorption of nutrients, segmentation stops and p starts
what is the migrating motility complex
patterns of peristaltic activity travelling down small intestine,
starts in gastric antrum
ends in terminal ileum
what does the MMC migrating motility complex do
move undigested material into large int
limit bacterial colonisation of small int
what hormone is involved in initiation migrating motility complex
Motilin
what is the law of the intestine
bolus always moves down to colon, mediated by myenteric plexus
what is the gastroileal reflex
- opening of ileocaeceal valve
- chyme enter large int
- distention of colon
- reflex contraction of ileocaecal valve ( prevents backflux into small int)
structure of large int, parts and epithelium
ascending, transverse, descending, sigmoid
muscularis externa - circular muscle layer complete but longitudinal not
what are the 3 bands around the colon
teniae coli
what does the colon do
- no important nutrient absorption
- transports Na from lumen into blood, absorption of water, dehydrates chyme, solid faecal pellets
what is the importance of long residence time in colon
what is the importance of long residence time in colon
what does bacteria do in colon
breakdown cellulose Bacterial fermentation of undigested carbohydrate - short chain FA - Vitamin K - gas
what is the anus closed by
- internal anal sphincter (smooth muscle under automatic control)
- external anal sphincter (skeletal muscle under voluntary control)
what reflex gives you the urge to defaecate and why
defaecation reflex
distention of rectal wall produced by mass movement of faecal material into rectum → mechanoreceptors
what is the defaecation reflex
- under parasymp control via pelvic splanchnic nerves
- contraction of rectum
- relaxation of internal and contraction of external anal spinchter
- inc peristaltic activity in colon, inc pressure on spinchter → relax under voluntary control → faeces come out
what causes constipation
distention of rectum
what causes diarrhoea
too frequent passage of faeces which are too liquid, causes dehydration
enterotoxigenic bacteria
enterotoxigenic bacteria
Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells
inc H2O secretion
elevate intracellular second messengers
H2O secretions swamps absorptive capacity of villus cells
how do you treat Secretory Diarrhoea
Give sodium/glucose solution
rehydration
oral rehydration therapy
