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Flashcards in GI Mod 3A Deck (104):

3 regions of SI + lengths

1. duodenum (25-30cm)
2. jejunum (2.5m)
3. ileum (3.5m)


where does the duodenum begin and end

begins - duodenal bulb
ends - ligament of Treitz


what is the hepatopancreatic ampula in SI

aka Sphincter of Oddi
-allow bile and pancreatic enzyme secretions


what are Brunner's glands in SI

submucosal glands
-located in proximal duodenum
-secrete bicarbonate rich mucus to protect against acidic chyme entering the duodenum and lubricate intestinal wall


function of duodenum

digestion and gastric feedback


how does the duodenum perform enzymatic digestion/breakdown of food

stimulates release of digestive enzymes from pancreas and gall bladder


the SI provides feedback to do what?

regulate the rate of gastric emptying


how does the SI provide feedback for gastric emptying

acidic chyme (fats, partially digested protein, hyper/hypotonic fluids) entering duodenum stimulate:
1. long loop reflexes
2. short loop reflexes
3. release hormone messengers


what are long loop reflexes of SI feedback

mechanoreceptors/chemoreceptors stimulate CNS to increase sympathetic and decrease parasympathetic to stomach


what are short loop reflexes of the SI

mechanoreceptors/chemoreceptors in duodenum stimulate enteric neurons in stomach to decrease stomach motility


the SI releases hormone messengers that do what for feedback
-what hormones are involved

inhibit stomach motility/acid production
-secretin, VIP, CCK released from duodenum play role in inhibiting gastric motility and secretion


hormones of the duodenum: secretin function

regulate pH in duodenum, inhibitory to gastric activity and facilitates digestion


hormones of the duodenum: secretin stimulus

acidic (pH


hormones of the duodenum:secretin target organ/action

stomach - inhibits gastric secretions (inhibits gastrin) and inhibits motility
pancreas- stimulate pancreas to secrete watery bicarb solution
liver - stimulates bile output (promote fat digestion)
brunner's glands of duodenum - stimulate secretion of alkaline rich mucus


hormones of the duodenum: CCK function

promotes bile/pancreatic enzyme release and inhibitory to gastric activity


hormones of the duodenum: stimulus of CCK

fatty chyme (fats, partially digested protein) entering duodenum


hormones of the duodenum: target tissue/action

stomach - inhibitory to gastric motility/secretions
pancreas - stimulate release of pancreatic enzymes
liver - stimulates bile output (promote fat digestion)
gallbladder - stimulates contraction to release stored bile


hormones of the duodenum: GIP function

gastric inhibitory peptide
-relative of secretin


hormones of the duodenum: stimulus of GIP

chyme entering duodenum


hormones of the duodenum: target tissue/action of GIP

stomach - inhibitory to gastric motility/secretions (some resources question this role and propose secretin is stimulus)
pancreas - stimulate insulin release


hormones of the duodenum: VIP

vasoactive intestinal peptide


hormones of the duodenum: VIP stimulus

chyme entering duodenum


hormones of the duodenum: VIP target tissue/action

stomach - inhibit gastric acid secretion
intestine - vasodilate BV, promote intestinal motility


hormones of the duodenum: intestinal gastrin role

similar role as gastrin released in the antrum of stomach


hormones of the duodenum: stimulus of intestinal gastrin

chyme entering duodenum


hormones of the duodenum: target tissue/action of intestinal gastrin

stomach - stimulate gastric motility and secretions
intestine - stimulate motility


hormones of the duodenum: motilin role

housekeeper of intestinal tract


hormones of the duodenum: stimulus of motilin

fasting or periodic release (every few hours)


hormones of the duodenum: target tissue/action of motilin

intestine - initiates MMC (migrating motor complex)


list all the hormones of the duodenum

1. secretin
2. CCK
3. GIP
4. VIP
5. intestinal gastrin
6. motilin


how long is the SI



where does the jejunum begin and the ileum end?

begins at ligament of Treitz and ends at ileocecal valve


where does the SI begin and end

pylori sphincter and ends at ileocecal valve


general function of both the jejunum and ileum

continued digestion, absorption and secretion of brush borders enzymes to assist in digestion/absorption


function of jejunum

major site of digested fat, carb, protein, water, and electrolyte absorption


function of ileum

absorb vitB12, bile salts, and remaining digested nutrients and water not absorbed in jejunum


function of mucosal folds of jejunum and ileum

aka plica
physically slow the passage of food


function of villi in jejunum and ileum

cover mucosal folds
considered functional unit of SI: secretion and absorption


composition of villi in jejunum and ileum

1. goblet cells - mucus secreting cells
2. absorptive columnar cells: site of absorption


what are microvilli in jejunum and ileum

located on end of each columnar cell
form the brush border of the mucosal surface
a thin layer of fluid is found along surface of brush border
function: facilitates absorption of all substances except water/electrolytes


what is the lamina propria layer of the jejunum and ileum

extends into each villi
contains lacteal and central arteriole


function of central arteriole in jejunum and ileum

capillary transport substances directly to liver via hepatic portal vein
(carbs, proteins, and some fats to directly to liver)


function of lacteal in jejunum and ileum

transport fat molecules/substances (fats - mnoglycerides & fatty acids) to systemic circulation via thoracic duct


what are the Crypts of Lieburkuhn in jejunum and ileum
-3 types of cells

at the base of villi
3 types of cells:
1. precursor cells
2. paneth cells
3. secretory cells


function of precursor cells in Crypts of Lieburkuhn of jejunum and ileum

in SI epithelium (goblet cells and columnar cells)
turnover of intestinal epithelial cells
-migrate to tip of villi, mature SI epithelial cells slough off into intestine and serve as a source of endogenous protein
-complete turnover of SI is approx 4-7 days


function of paneth cells in the Crypts of Lieburkuhn of jejunum and ileum

immune function - produce/secrete antibiotic peptides


small intestine motility - avg transit time

average transit time in SI - 1-3 hrs (with large variations of 15 min to 5+hrs)


stimulus of SI motility

1. small intestine hormones: secretin, CCK, gastrin, motilin
2. intestinal reflexes


three motility patterns occur in SI

1. segmentation
2. peristalsis
3. migrating motor complex (MMC)


what is segmentation

occurs during feeding
frequent small rhythmic contractions of circular muscle (8-12/min)
occurs more frequently than peristalsis
function: mixes chyme to allow contact with brush border


what is peristalsis

occurs during feeding
coordinated waves of contraction/relaxation of longitudinal muscles (short segments - 10cm)
wave of contraction moves slowly ( 1-2cm/sec) to allow for digestion/absorption
function: moves chyme toward large intestine


what is MMC

aka interdigestive myoelectric complex
occurs during FASTING
slow periodic waves of peristalsis that occurs every 1-2hrs
originate in stomach and pass thru small intestine
motilin plays a role in stimulus


function of MMC

function: "house cleaning" - sweeps out stomach/SI
--pushes along residual chyme, nondigested substances (fiber, bone)
--bacteria homeostasis - transport bacteria to LI, prevent reflux of bacteria from LI


what is the ileogastric reflex

stimulus - ileum distended
action - inhibits gastric motility
result - slows dow adding more chyme to SI to allow terminal ileum to empty contents to LI


what is the intestinointestinal reflex

inhibitory-protective reflex
stimulus - section of SI becomes distended
action - relaxes distal SI
result - allows chyme to be moved toward LI


what is gastroileal reflex

stimulus - increased stomach (gastric motility/secretion)
action - promotes terminal ileum motility/ileocecal valve relaxation
result - empty SI so it can receive more chyme from stomach


ileocecal valve is regulated how and is it usually open or closed

regulated intrinsically
usually closed


regulation of ileocecal valve opening

valve opens similar to LES of esophagus and pyloric valve in stomach
stimulus - approaching peristaltic wave in the ileum
action - relaxation of the ileocecal sphincter


regulation of ileocecal valve closing

stimulus - distension of cecum/ascending LI
action - constriction of ileocecal valve


function of secretory cells of Crypts of Lieburkuhn of jejunum and ileum

secrete brush border digestive enzymes


total length of the large intestine

1.5 m


where does the LI begin and end

begin - ileocecal valve
end - anus


sections of the LI

cecum, appendix, colon, rectum,anus


4 regions of the colon

ascending, transverse, descending, and sigmoid colon


LI is an unique arrangement of what 2 types of muscle

1. circular and longitudinal muscles is unique in LI


what are teniae coli in the LI

3 longitudinal bands if muscle along length of colon


what are haustra in the LI

pouches formed from circular muscle layer of intestine


what is O'Bierne sphincter of LI

controls passage of chyme from sigmoid colon into rectum


LI motility - 2 types

1. segmental
2. peristalsis


what are haustral segment contraction

occurs during fasting
individual haustra segments push contents (fecal mass) back and forth
function - maximize absorption of water and electrolytes in large intestine occurs a majority (90%) of the time


what is multihaustral segmentation

occurs during fasting
several haustral segments contract and relax as a single unit
function - push contents (fecal mass) a short distance forward occurs less often (10% of time)


what is mass movement peristalsis

promote emptying of the intestine into the sigmoid colon and rectum


what are the 2 intestinal reflexes of the colon

1. orthocolic reflex
2. gastrocolic reflex


what is the orthocolic reflex of the colon

stimulus - standing first thing in the morning stimulates peristalsis of LI
action - peristalsis propels fecal mass into sigmoid colon and rectum


what is the gastrocolic reflex of the LI

stim - ingestion of food (occurs during or immediately after eating)
action - peristalsis propels fecal mass into sigmoid colon and rectum
--continuation of gastroileal reflex - increase motility of stomach promotes motility of SI


what is the rectal reflex of a bowel movement

aka defecation
stim - stretch of rectum wall
action - relaxation of internal anal sphincter and the urge to have BM
inhibited - voluntary control; cerebral cortex input/motor pathways in spinal cord: contract the external anal sphincter


clinical of rectal reflex - cauda equina syndrome

damage to nerve roots of lower spine
loss of bowel control


digestion of carbs in the mouth

enzyme - salivary amylas
action - starches broken into smaller molecules (dextrin and oligosaccharides)


digestion of carbs in SI

1. pancreatic role
enzyme - pancreatic amylase secreted from pancreas
action - further breakdown starches into major oligosaccharides (lactose, maltose, sucrose)
2. brush border
enzyme - brush border enzymes (lactase,maltase,sucrase) secreted from secretory cells of base of villi (Crypts of Lieburkuhn)
action - breakdown oligosaccharides (lactose, maltose, sucrose) into monosaccharides (galactose, glucose, and fructose)


absorption of carbs

location - brush border of villi
action - monosaccharides (galactose, glucose, and fructose) are absorbed by villi capillaries and transport directly to liver via hepatic portal vein
NOTE: insulin not required for intestinal uptake of glucose


digestion of proteins begins where?



digestion of protein in stomach

enzyme: pepsin
NOTE: pepsinogen released from chief cells is converted into pepsin when combined with gastric acids (HCl)
action: break down protein into smaller protein molecules (proteoses, peptones)
NOTE: this site of protein digestion is not essential...SI is primary site


digestion of protein in SI

1. pancreatic role:
enzyme: pancreatic enzymes (trypsin, chymotrypsin, carboxpeptidase) secreted by pancreas into duodenum
action: breakdown protein molecules into smaller peptides (polypeptides and dipeptides)
2. brush border role
enzyme: brush border enzymes (aminopeptidases/dipeptidase) are secreted from secretory cells of base of villi (Crypts of Lieburkuhn)
action: breakdown smaller peptides (polypeptides and dipeptides) into amino acids


absorption of proteins

location - villi in SI
action - amino acids are absorbed by villia capillaries and transported directly to liver (via hepatic portal vein)


digestion of fats requires what



emulsifying agents in GI

fatty acids, monoglycerides, lecithin, cholesterol, protein, bile salts


what do emulsifying agents do

surround small fat articles and prevent them from reforming into larger fat droplets
emulsification reduces the surface tension and separates the molecules


digestion of fats starts where



digestion of fats in stomach

enzyme: gastric lipase
action: initiate breakdown of fats


digestion of fat in SI

1. emulsification of fat droplets
action - smaller fat droplets are formed in the presence of emulsifying agents
2. lypolysis
enzymes: lipase, phospholipase, hydrolipase secreted from pancreas
action - emulsified fat molecules are broken down into diglycerides, monoglycerides, FFAs, glycerol


absorption of fats

fast molecule must be made water soluble to reach intestinal epithelium
--accomplished by formation of micelles (water soluble molecule)


steps in fat absorption

1. Micelles formation
2. Transport of fats into columnar epithelial cell of SI
3. transport of fats into lacteals


what happens in Micelles formation

bile salts, fat molecules, cholesterol, fat soluble vitamins (A,D,E,K) combine to form a micelle


what happens in the transport of fats into the columnar epithelial cell of SI

-micelle can pass thru aqueous brush border fluid and contact epithelial cell
-fat contents of micelle then diffuse into epithelial cell
-left over bile salts from micelle remain in intestine and are reabsorbed in the distal ileum


what happens during transport of fats into lacteals

-inside the epithelial cells the fat molecules are resynthesized into triglycerides and phosphoplipids
-these new fat particles are called chylomicrons
-the chylomicrons exit the intestinal wall (epithelial cell) into lacteals of villi and are transported to heart and systemic circulation
-NOTE: most fats are absorbed via lacteals however some fat(glycerol and fatty acids) are absorbed directly into capillary system


chylomicrons exit the cell via what process in the transport of fats into lacteals

CHYLOMICRONS EXIT the cell via exocytosis


fluid is ingested or secreted into GI tract thruout which regions of GI

all regions


total ingested/secreted fluid into GI tract



which part of GI will absorb most fluid back into blood stream

SI - approx 85-90% reabsorbed in SI


what will secrete and absorb the final fluid balance

LI - driven by electrolyte balance
--fine tunes fluid and electrolyte homeostasis


how much fluid is excreted in stool in normal BM

100ml (1/10L)


normal renal excretion of fluid

renal excretion = 1-2L/day


vit b12 absorption

occurs in terminal ileum
absorption requries B12 to bind with IF - which is secreted by gastric parietal cells


lack of B12 causes

pernicious anemia (macrocytic anemia) - poor RBC formation
liver and kidneys store enough B12 to last for years