small intestine structure and function Flashcards
what is the function of the duodenum?
gastric acid neutralisation
digestion
iron absorption
what is the function of the jejunum?
nutrient absorption
what is the function of the ileum?
NaCl and water absorption for chyme dehydration
how many fluid do we lose in our GI tract?
200ml
how does the ileum restore some of the water lost from the GI tract?
it absorbs Na/Cl which causes water to follow
how is the absorptive surface area of the small intestine enhanced?
the intestine has lots of folds, villi and microvilli which increase the surface area for absorption
what are the secretory cells and where are they found?
goblet cells found in the intestinal crypt
how is water secreted from the crypts?
crypt cells actively secrete Cl into the intestinal lumen which builds an osmotic gradient for water to follow
what is the main function of the villi?
absorption
why is water secreted in the small intestine?
maintains luminal contents in a liquid state
promotes mixing of nutrients with digestive enzymes
helps in absorption of nutrients
dilutes and washes away any potentially harmful substances
crypt cells secrete Cl to drive water out of the cell into the lumen, but how does villi absorb water?
villi absorb NaCl which builds the osmotic gradient for H20 to follow and enter the cell
how do patients with cystic fibrosis suffer from malabsorption?
there is a gene defect in CFTR chanel protein which allows Cl to exit the cell.
the defect prevents Cl from leaving the cell thus an osmotic gradient isn’t build up so water cannot be secreted.
water secretion is required to aid in absorption of nutrients
what are the 2 types of intestinal motility?
peristalsis
segmentation
what is responsible for the production of segmentation?
depolarisation from pacemaker cells in the longitudinal muscle layer produces the BER
however these signals don’t reach the membrane potential
if Ach is released from the parasympathetic system it reaches threshold firing an action potential = contraction
what is the nerve supply for segmentation and what are their effects?
sympathetic - splanchnic nerves - decrease strength of contraction
parasympathetic - vagus - increases strength of contraction
what effect does the autonomic nervous system have on the basic electrical rhythm?
no effect
they may increase or decrease the strength of contraction but it doesn’t affect the BER which determines the speed of contractions
migrating motility complex is used to describe what process?
peristalsis
what does the migrating motility complex aim to do?
moves undigested material into the large intestine
limits bacterial colonisation of small intestine
what hormone is involved in the initiation of the MMC?
motilin hormone
what nerve supply is responsible for the movement of material through the intestine?
the myenteric plexus (aucherbach plexus)
what prevents the back flow of material from the caecum into the ileum?
reflex contraction of the ileocaecal sphincter
what is the length of the duodenum?
25cm
what is the length of the jejunum?
2.5m
what is the length of the ileum?
3.5m
what part of the small intestine absorbed nutrients?
jejunum
what part of the small intestine does the final chymal dehydration occur and how does this happen?
ileum
absorption of Na, Cl and H20
whats the function of the crypt cells?
secretion of 1500ml of H20 per day
driven by the active secretion of Cl into the lumen
what is the gastroileal reflex?
as faecal material moves from the small intestine into large intestine, the ileocaecal valve relaxes and the caecum dilates.
when material is in the large intestine the ileocaecal valve contracts to prevent backflow of material.
