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GI tract layers histology 2006


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copy deck
what are people referring to when they refer to digestive system?
GI tract
glands/accessory organs
examples include:
salivary glands, liver, gall bladder, pancreas
what type of glands are associated with GI tract?
what's the general format for the GI tract?
4 basic layers
1. mucosa
2. submucosa
3. muscularis
4. serosa
what is the mucosa of the GI tract - what does that mean, what does it consist of?
is epithelium
has lamina propria
muscularis mucosa
what is the submucosa of the GI tract? what type of tissue is it and what special kind of structures does it contain?
is loose connective tissue
has Meissner's submucosal plexus
what makes up the muscularis layer of the GI tract?
1. muscularis interna = circular
2. Auerbach's myenteric plexus
3. muscularis externa = longitudinal
what kind of tissue is the serosa of the GI tract and what layers is it associated with? can't think of a better way to phrase that
is loose connective tissue
is epithelium or mesothelium
where does the GI tract start and stop?
starts - oral cavity
stops - anus
what are some important regions of the GI tract?
small intestine - including immune surveillance of GI tract
large intestine
in what order from internal to external from lumen are the four layers of the GI tract?
starts with mucosa
then submucosa
what are the names of the sublayers within the mucosa?
1. epithelium
2. lamina propria
3. muscularis mucosa
describe the epithelium of the mucosa of the GI tract
is a continuous sheet of cells
type and specialization of cells vary regionally adapting to change in function
what is the lamina propria, where is it and what does it do?
is a delicate layer of loose connective tissue
just deep to epithelium
has small blood vessels, lympatic origins, cells of immune system
what's the order of the sublayers of the mucosa of the GI tract?
closest to lumen:
lamina propria
muscularis mucosa
what makes up the muscularis mucosa?
is light layer of smooth muscle
what are the sublayers of the submucosa and in what order are they from lumen external?
connective tissue layer is closest to mucosa
autonomic ganglia is closest to muscularis
what does the connective tissue layer of the submucosa contain?
has larger blood vessels than in lamina propria
is moderately dense layer of connective tissue
what autonomic ganglia are in the submucosa?
layer of autonomic ganglia refer to ganglia and fibers of autonomic nervous system
Meissner's submucosal plexus located here
what does Meissner's submucosal plexus do?
helps control peristalsis
what sublayers are in the muscularis level of GI tract?
2 different layers with a plexus sometimes between
1. muscularis interna is most internal
circularly arranged fibers
2. muscularis externa is outer layer of longitudinal fibers
what can be found between muscularis interna and muscularis externa?
Auerbach's myenteric plexus
what does Auerbach's myenteric plexus?
is second series of ganglia and fibers that i'm assuming also help control peristalsis
what makes up the serosal layer and where is it usually found?
is layer of squamous epithelial cells
has some underlying connective tissue lining peritoneal and pleural cavities
small intestine has serosa on all surfaces
retroperitoneal structures sometimes have no serosa or serosa on only one surface
other areas have only one surface facing peritoneal cavity so they are partly covered with serosa
is the esophagus involved in the process of digestion or absorption?
what does the esophagus do?
is conductive pathway only
conducts bolus of partially-digested food from oral cavity to stomach
what is different about the epithelium in the esophagus opposed to other epithelium as a result of its function?
is resistant to abrasion because epithelium is STRATIFIED SQUAMOUS
is result of coarse, potentially damaging bits from bolus
epithelium also has GLANDS that lubricate bolus to minimize damage
what do the basal layer of cells in epithelium of esophagus look like and how are they attached to the basal lamina?
are cuboidal
linked to underlying basal lamina by hemidesmosomes
what other tissue does the epithelium of the esophagus most closely resemble?
what is a characteristic regarding cellular mitotic activity that esophageal epithelium shares with skin?
cells close to basal lamina are mitotically competent and less differentiated than cells toward free surface which are more differentiated
what keeps cells closer to free surface of epithelium together?
desmosomes, dense intermediate filament networks
what happens once cells in epithelium of esophagus get to free surface?
cells compacted to squamous shape
IF bundles compacted as well
what's a difference between esophageal epithelium and skin?
cells near free surface don't lose nuclei, dont' keratinize, and don't die forming squames
what are the layers of the epithelium of the esophagus?
1. statum germinativum
2. statum spinosum
what happens in stratum germinativum of epithelium of esophagus?
is where most mitotic activity occurs
what happens in the stratum spinosum of epithelium of esophagus?
where IF filaments adn desmosomes proliferate
is blockage of paracellular route achieved with tight junctions between epithelial cells of esophagus?
what blocks paracellular movement in epithelium of esophagus?
deposition of glycoprotein material in extracellular space
occurs about halfway through epithelium
what kinds of cells are present in epithelia of esophagus to act as antigen presenting cells?
langerhans cells
what do langerhans cells in esophageal epithelium do?
act as antigen presenting cells - APCs
what does gastric reflux do to esophageal epithelium?
causes esophageal metaplasia
meta = change
stratified squamous epithelium becomes mucous columnar epithelium
what's an example of how responsive cellular or epithelial phenotype can be to environment?
conversion of stratified squamous to mucous columnar from gastric reflux
what is the lamina propria consist of, and what's in it?
is pretty unremarkable and unspecialized
is loose connective tissue
has collagen and reticular fibers
small blood vessels
white blood cells
some small mucous glands at upper and lower ends of esophagus
where can the muscularis mucosa be found in the esophagus?
not really developed in upper regions, but definite and discreet layer in lower regions
what's in the submucosa of esophagus?
denser connective tissue
larger blood vessels
some mucous secretory glands
what are mucous secretory glands, where are they and where do they drain?
are common to and characteristic of esophageal submucosa
are small lobules drained by single duct to free surface
what's a clinical correlate of the submucosa of esophagus related to cirrhosis of liver?
cause of death among those with cirrhosis is rupture of varices in submucosa of esophagus
what causes varices in submucosa of esophagus?
cirrhosis of liver increases resistance to portal venous flow through liver
this shunts blood to veins of esophageal submucosa creating varices
where are deadly varices of veins in esophagus? what layer of esophagus?
what plexus of ganglia and nerves of autonomic system can be found in submucosa of esophagus?
meissner's submucosal plexus
where could i find meissner's submucosal plexus?
submucosal layer of esophagus
where are meissner's and auerbach's plexuses?
meissner's = submucosa of esophageal epithelium
auerbach's = tween inner and outer layers of muscularis externa IN ESOPHAGUS
what kind of input do meissner's and auerbach's plexuses receive?
both sympathetic and parasympathetic
what kind of stimulation increases and decreases gastric motility - sympathetic or parasympathetic stimulation?
sympathetic inhibits motility
parasympathetic increases motility
what is the enteric nervous system and what does it do?
is local feedback loop with ganglia and fibers that act autonomously from brain to control motility and secretion of intestines
relies on sensory neurons that respond to stretch/distension, pH
what kinds of muscle fiber can be found in muscularis layer of esophagus - skeletal or smooth?
upper 1/3 = skeletal
middle = mix of skeletal and smooth
lower = completely smooth
how does esophageal-gastric sphincter know when to open to allow food in?
when peristaltic wave reaches it, it relaxes and opens
what does chyme mean?
means thick fluid
what happens in empty stomach to mucosa?
mucosa folds up into rugae which are 2-4 mm across
what's the point of the rugae in the stomach?
allows for distension when stomach is filling without increase in lumenal pressure
helps continued dumping of food from esophagus since there's no pressure from stomach up to esophagus until you're full
what the hell are foveolae?
are also called gastric pits
are invaginations of mucosa in stomach
where are gastric glands?
are at bottom of foveolae or gastric pits
what are gastric glands?
are tubular outpocketings of stomach mucosa at bottom of foveolae
how many gastric glands are there usually per foveolae?
what kind of epithelium makes up the stomach and all other parts of GI tract to ano-rectal junction?
simple columnar
can tight junctions account for the barrier to paracellular diffusion of lumenal contents into lamina propria from stomach to remainder of GI tract?
what different kinds of cells are found in the epithelium of the stomach?
5 different kinds
1. surface mucous cells
2. neck mucous cells
3. parietal or oxyntic cells
4. chief or zymogen cells
5. enteroendocrine cells
where are surface mucous cells found in stomach?
mostly on surface and in foveolae
what kind of cells are surface mucous cells in stomach?
are terminally differentiated columnar cells with apically placed mucous secretory granules
what is mucous and what does it do?
is slippery, carbohydrate-rich glycoprotein
major function is to lubricate and protect surface epithelium
what do surface mucous cells of epithelium in stomach do?
secrete two things;
mucous and HCO3-
what's the purpose of HCO3- secretion from surface mucous cells of stomach epithelium?
is to create alkaline mucous blanket to protect cells from harsh environment of lumen
how long do surface mucous cells usually live?
4 days
where are neck mucous cells?
mostly in epithelia of upper regions or neck of gastric glands
what's the purpose of neck mucous cells?
secrete mucous but a different kind of mucous than what's secreted by surface mucous cells - difference is not known
what does autoradiographic labeling suggest about the function of neck mucous cells?
they not only secrete mucous, they are also stem cells for gastric epithelium
where in the stomach are the parietal or oxyntic cells?
in epithlium near lower reaches of gastric gland
what do parietal or oxyntic cells of stomach do?
1. transport hydrogen ions that acidify stomach
2. secrete gastric intrinsic factor
what's gastric intrinsic factor, what does it do, what can it lead to?
is glycoprotein
important for absorption of vitamin B12 from intestines
B12 required for RBC production
problems with parietal cells can lead to pernicious anemia
what's unusual about the apical surface of parietal or oxyntic cells of stomach?
has numerous microvilli
major infoldings that penetrate deep into cell = intracellular canaliculi which also have microvilli
what are intracellular canaliculi?
are characteristic of parietal or oxyntic cells of stomach
are major infoldings that pentrate deep into cell
have microvilli on apical surface
what's the point of the greater surface area of the parietal or oxyntic cells of the stomach?
allows more H+ transporter or H-K ATPase
how is the activity of H-K ATPase regulated in stomach?
parietal or oxyntic cells internalize apical membrane when fasting
when acid required, membrane returned to surface
what is the tubulovesicular system?
refers to appearance of apical membrane when internalized by parietal or oxyntic cells of stomach
do parietal or oxyntic cells have many mitochondria? why or why not?
yes, about 40% of cell is mitochondria
necessary to generate ATP for ion pumps
what do the apical H-K ATPases do?
make H+ and HCO3- from CO2 and H2O
H+ in cytoplasm exchanged for lumenal K+
what does the H-K ATPase do at the basal end of the parietal or oxyntic cell of stomach epithelium?
cytoplasmic HCO3- exchanged for extracellular Cl-
they're trying to say you're gaining a bicarb - doesn't make any sense
what's point of H-K ATPase?
absorption of bircarbonate ion from basal surface sent up gland to protect apical surface of parietal or oxyntic cell in stomach
what stimulates H+ secretion in stomach?
1. activation of receptors for gastrin which is the stomach's principal regulator
2. activation of receptors for histamine H2 and
3. activation of receptors for acetylcholine M3
what drugs treat overproduction of acid in stomach?
how do tagamet and zantac work?
block histamine H2 receptor of parietal or oxyntic cell in stomach epithelium
also block gastric intrinsic factor secretion
what's goal for new heartburn treatment drugs? what should they target to reduce heartburn without side effects?
want to target H-K ATPase of parietal or oxyntic cells or stomach
what's another name for chief cells of epithelium of stomach?
zymogen cells
where are chief or zymogen cells of stomach found?
deepest recesses of gastric glands
what do chief or zymogen cells of stomach do?
secrete pepsinogen which is precursor to pepsin
stores pepsinogen in large granules in apical cytoplasm until release
what stimulates secretion of pepsinogen?
what cells release secretin?
enteroendocrine cells
what converts pepsinogen to pepsin?
cleavage in acidic lumen of stomach
where are the enteroendocrine cells of epithelium of stomach?
are infrequent
scattered throughout gastric gland and rest of intestinal epithelium
what do the enteroendocrine cells of stomach epithelium do?
store, release secretory granules with hormones to regulate GI function
what kind of cells are enteroendocrine - are they exocrine or endocrine cells?
answer is in name
they are endocrine cells
secrete only into connective tissue space of lamina propria NOT into lumen
what does it mean to say that the chief or zymogen cells are oriented opposite of enteroendocrine cells?
enteroendocrine products are released at basal side of cell
chief or zymogen cells release pepsinogen on apical side of cell
where are enteroendocrine cells in relation to the stomach lumen and basal lamina?
cell reaches both surfaces - stomach lumen AND basal lamina
what do enteroendocrine cells secrete?
are heterogenous population of cells
secrete dozens of hormones including:
gastrin, serotonin, somatostatin, enteroglucagon
how many enteroendocrine cells are there in our bodies?
about 3 million
where are gastric glands in stomach?
predominate in cardiac region near esophagus
what kind of cells are the cardiac glands, what's their shape, what do they do?
are mostly tubular
are mucous cells so they protect esophagus from acid reflux
where would i find oxyntic glands in the stomach?
mostly in fundus and corpus
as many as 7 glands per foveolus
what do the oxyntic glands in stomach look like and what do they do?
are branched
are main effectors of gastric digestion
where are pyloric glands in the stomach?
mostly in pyloric region
what kinds of cells are in the pyloric glands?
mostly cells like mucous neck cells
also have many enteroendocrine cells
what's the point of the pyloric glands, what do they do?
are designed to protect duodenum
signal to rest of tract what's coming
coordinates digestion and absorption
what layers of the stomach are very similar to the rest of the GI tract and therefore unremarkable?
lamina propria
muscularis mucosa
what is important to know about the muscularis layer of the stomach? how developed is it, how many layers are there?
muscularis is very thick in stomach
has three layers instead of usual two
layers are mixed and tend to merge
how does the volume of the stomach change when empty vs. full?
empty - 200 ml
full - 1.5 liters
how low can pH of stomach go and how is this done?
H-K ATPase pumps H+ out
is there a lot of fluid absorption in stomach?
no - is little to none
what's the volume of gastric secretions put out in a day?
2-3 liters/day
what modulates gastric function?
autonomic innervation
what mediates enteroendocrine cells?
endocrine feedback
what does acid in the duodenum do to levels of secretin and eventually secretion of bicarbonate into duodenum from pancreas?
acid in duodenum causes
duodenal enteroendocrines release secretin
gastric motility inhibited
means acid secretion inhibited
gastric digestion process slowed
pancreatic duct cells stimulated to secrete bicarbonate into duodenum
acid chyme released from stomach neutralized
what's result of presence of fat in duodenum?
fat in duodenum causes
duodenal enteroendocrines to release CCK
CCK causes gall bladder to contract
bile is added to duodenum
bile made in liver, stored in gall bladder, dumped in duodenum to solubilize fats via bile salts
pancreatic acinar cells secrete enzymes to promote fat breakdown
which cell of the stomach epithelium would be most impacted by chemotherapeutic agents?
surface mucous cells
what are the three major parts of the small intestine?
what does the small intestine as a whole do?
1. neutralizes acidic chyme
2. promotes further enzymatic breakdown of chyme with help of pancreatic enzymes
3. absorbs nutrients
4. recovers water and salts
5. immune surveillance
6. self replenishment
7. endocrine control of digestion process
what volume of fluid is absorbed by small intestine every day?
8-9 liters!
2 is absorbed from what's ingested
7 absorbed from what's secreted!
where the hell is the lamina propria?
i think this is the layer just below the villi
where are intestinal glands or crypts of lieberkuhn?
just bottoms of villi in small intestine
what's another name for intestinal glands?
crypts of lieberkuhn
what kind of epithelium lines the crypts of lieberkuhn?
simple columnar
what's the total amplification of surface area achieved by small intestine through anatomical trickery and what's an estimate of the intestinal surface area?
amplification is about 600 fold from villi and shit like that
total intestinal surface area - of small intestine alone? is 200 square meters
what are the tricks the small intestine uses to increase surface area 600 fold?
1. elongation of GI tract itself
2. plica circularis or valves of kerkring
3. villi
4. microvilli
how long is the normal GI tract, what kind of amplification of surface area is achieved by elongation of GI?
for normal people, GI usually less than a meter
expanding length of GI tract to 5 meters increases surface area by 1 "level of amplification" whatever the hell that means
what are the plica circularis or valves of kerkring?
are crescent-like folds of mucosa and submucosa
10 mm high and 4 mm thick
extend only halfway around the lumen
do the plica circularis or valves of kerkring disappear with distension like the rugae of the stomach?
what's the point of the plica circularis or valves of kerkring?
add surface area
disrupts flow of bolus, promotes mixing
what's another name for the plica circularis?
valves of kerkring
what's another name for the valves of kerkring?
plica circularis
what layer of the gut is villi a projection of?
mucosa - NOT submucosa
how long are villi?
1 mm
what strategy for increasing surface area is the single most effective?
microvilli - they increase surface area by 30 times
what kind of cell is most predominant throughout the gut epthelium?
what shape and stratification of cell characterizes the epithelium of the mucosa of the small intestine?
simple columnar
how many and what are the names of the major epithelial cell types in the small intestine?
are 6
1. absorptive cells
2. Goblet cells
3. enteroendocrine cells
4. stem cells
5. paneth cells
6. M cells
what are the major functions of the most predominant cell type in the epithelium of the mucosa of the small intestine?
1. sodium and water recovery
2. enzymatic digestion
3. lipid absorption
what's another name for the brush border?
striated border
what cells and in what part of the lining of the small intestine can the brush border be found?
on absorptive cells in epithelium of mucosa
what is the brush border or striated borrder?
just microvilli
how big are microvilli compared to villi?
villi are 1 mm long, microvilli are 1.4 microns long!
how many microvilli are there per absorptive cell?
about 3,000
what structure stabilizes the microvilli and how does it do that?
actin filaments
insert into web of actin at base of microvilli
can show up in H&E staining
are microvilli motile?
what's the terminal web? where can it be found?
terminal web is web of actin filaments just deep to microvilli
in absorptive cells of mucosa epithelium
what structures project from the microvilli?
glycocalyx = projections of integral membrane proteins which are glycosylated
what is the glycocalyx?
are projections of glycosylated integral membrane proteins
what does the glycocalyx do?
binds water and creates a slick surface to protect epithelium
binds pancreatic enzymes to create high concentration of digestion products like carbs or amino acids near the surface of the cell for better absorption
what kinds of organelles are predominant in the absorptive cells of the mucosal epithelium of the small intestine?
mitochondria, ER, SER
what's the total fluid input to the small intestine per day?
about 8-9 liters
break down where the fluid that's entering the small intestine comes from
ingestion = 2 liters/day
saliva = 1.5 liters/day
gastric secretions = 2 liters/day
bile = 0.5 liters/day
pancreatic secretions = 1.5 liters/day
duodenal secretions = 1.5 liters/day
how much of fluids hitting small intestine is absorbed in small and large intestines?
about how many mg of sodium are ingested daily and how many are secreted by intestinal mucosa?
ingested = 6,000 mg
secreted = 20-30,000 mg
how much sodium do we excrete in our feces and why?
not much sodium leaves body; most of it is reabsorbed actively via Na-K ATPase on basolateral surface of absorptive cells
how is sodium absorbed from absorptive cell?
Na-K ATPase on basolateral surface pump sodium ions to lamina propria
what kind of activities are the plasma membrane (apically), microvilli and integral membrane proteins capable of?
proteolytic and disaccharidase activities
enzymes from what organ get help from proteolytic and disaccharidase activities of apical plasma membrane and microvilli and glycocalyx?
what kinds of transporters are in apical membrane of absorptive cells?
amino acids and sugar transporters
what simpler units are dietary fats broken down into in small intestine?
monoglycerides, free fatty acids
how are monoglycerides and free fatty acids kept soluble in intestinal lumen?
they complex into micells with bile salts from liver
how do monoglycerides and free fatty acids get into absorptive cells?
after forming micelles, they diffuse into cell and accumulate in apical cytoplasm
what happens once micelles of free fatty acids and monoglycerides (with bile salts) diffuse into absorptive cells?
1. go to SMOOTH ER
are resynthesized into TRIGLYCERIDES
that collect to make lipid droplets
2. lipid droplets transported to GOLGI
lipid droplets glycosylated to make CHYLOMICRA, also called glycolipoprotein droplets
3. chylomicra or glycolipoprotein droplets move to BASOLATERAL membrane where they're pushed out into LAMINA PROPRIA
4. chylomicrons then mve into LYMPHATICS aka the central lacteal and then to
5. BLOOD stream so they can form plaques that can kill you
what's another name for chylomicrons?
glycolipoprotein droplets
what are chylomicrons or glycolipoprotein droplets made of and where are they made?
made of triglyceride lipid droplets that were glycosylated
are made in GOLGI
what are the two organelles that help move fat through absorptive cells?
1. smooth ER which basically resynthesize fat from building blocks that came in
2. golgi which basically make fat transportable across basolateral membrane so it can get to lamina propria and then lymph and then blood
what's the path in general of fat through absorptive cells and out?
1. in absorptive cell via diffusion
2. to smooth ER - become bigger fats
3. to golgi - become sugary fats (chylomicrons)
4. to basolateral membrane where they're pushed out
5. lamina propria
6. lymphatics - central lacteal
7. blood
what do goblet cells in mucosal epithelium of small intestine do?
secrete mucous
provide viscous lubricating film to surface of intestine
this protects intestine from abrasion
where in the mucosal epithelium of the small intestine are goblet cells?
they're randomly scattered among absorptive cells
what does being randomly scattered among absorptive cells mean for goblet cells, what's another name for that, given their function?
they're single cell glands
what do goblet cells look like in histologic section, why are they called goblet cells?
called that because apical end of cell huge due to large mucous secretory granules while basal end is small
this is only artifact of swelling of mucous granules during fixation though
cells don't really look like that in practice
why don't goblet cells actually look like goblets when functioning in the intestinal mucosal epithelium?
because the secretory granules swell when exposed to water, that's their whole purpose, once they leave goblet cell, they swell when exposed to water, creating protective layer
shouldn't happen in the cell however because it's kept dehydrated in there
what's the protein/carb breakdown of goblet cell secretory product?
mucous is about 20% protein and 80% carb
what do enteroendocrine cells of intestinal mucosal epithelium do?
same thing they do in the stomach - better review that
important thing to remember is that they are
1. secretory cells
2. secrete towards LAMINA PROPRIA not towards lumen
the mucosa in what part of the GI tract has the fastest turnover rate of any cell in the entire body?
mucosa of jejunum
how long does it take to replace the entire epithelium of the jejunum?
3-4 days
where are stem cells in mucosal epithelium of small intestine?
are in lower end of crypts of VILLI
what effect do stem cells have for mucosal epithelium of small intestine?
they create new cells at crypts of villi
older cells are pushed forward by younger ones until they fall to their deaths off the tip of the villi into the intestinal lumen
what's a downside to the rapid turnover of the small intestine?
can lead to malignancy
90-95% of malignant tumors of GI come from intestinal epithelial cells, usually in colon
what's a clinical manifestation of the rapid turnover rate of intestinal epithelium in regards to chemotherapy?
are more susceptible to cytotoxins given in chemotherapy because these drugs target rapidly dividing cells
what are some problems resulting from chemotherapy's effects on intestinal epithelium?
malabsorption, diarrhea
where are paneth cells?
are also at base of mucosal epithelium crypts of intestine, like stem cells
found only in small intestine
how can paneth cells be distinguished in histologic section?
have large eosinophilic secretory granules
what does eosinophilic mean?
means that proteins are being stained
eosin is acidic, so it stains basic structures
what's the difference between paneth and enteroendocrine cells?
paneth are polarized toward lumen
what do paneth cells do?
their function is unclear
might regulate intestinal flora via secretory products
what do paneth cells secrete?
secrete lysozyme and defensins
what are M cells and where are they found?
are in mucosal epithelium of small intestine
are immune surveillance
what kind of tissue is the lamina propria?
is loose, delicate, connective tissue
what cells are in the lamina propria?
T lymphocyte
what role do macrophages play in immune system?
they ingest bacteria
phagocytose antigens
present antigens to local T cells, then to B cells
this keeps immune system's weapons up to date with local conditions
what kinds of structures are in the lamina propria?
1. immune cells
2. central lacteal or lymphatics
3. capillaries
4. smooth muscle
what's a central lacteal? where can it be found?
is the beginning of the lymphatic system
is in intestinal villus
what does the central lacteal do?
conducts many of lipid products absorbed from intestine to blood stream
where does the central lacteal drain? what helps it drain?
drains into submucosa, joining plexus of other lymph vessels
smooth muscle cells in lamina propria push contents into submucosa via periodic contractions
where does the capillary bed in the mucosal epithelium of the small intestine go? what does it do?
it drains into liver portal vein, which then breaks up into a second capillary bed
it absorbs stuff that small intestine absorbed
what does it mean to say that there are a few smooth muscle cells in lamina propria - where does that mean there is smooth muscle, how do they milk lacteals?
smooth muscle cells must run up into villus from muscularis mucosa
when these cells contract, they shorten and compress villus which milk the lacteals
what layer of the GI tract is the musularis mucosa considered?
still part of mucosa! name says it all
need to have some muscle right by surface to get things moving
what is the muscularis mucosa? where is it - in what structures can it be found?
this is a relatively discreet and continuous layer of muscle in small and large intestine
is in plicae, but not in villi
remember plicae are crescenteric folds visible to naked eye and villi are too small
the submucosa of the duodenum is an exception from other submucosa why?
because has glands of brunner
these go through muscularis mucosa into submucosa
these are only in duodenum because they secrete alkaline mucous to balance acid of stomach chyme
meissner's plexus is not just in the submucosa of the esophagus! what other submucosa can meissner's plexus be found in?
submucosa of small intestine
auerbach's plexus is prsent in muscularis layer of what other part of GI tract other than esophagus?
small intestine! just like meissner's plexus in submucosa
what does auerbach's plexus of muscularis do in small intestine?
because is between muscle layers, again seves to control muscle activity here
helps muscle mix lumenal contents, propelling it along
are there gap juntions in the small intestine - what layer would they be in and what function might they have for the small intestine?
yes; are in muscularis level of small intestine so that APs can spread from cell to cell, creating peristaltic wave
what's the body's response to immunity - would you say it's mostly proactive or reactive based on histology of small intestine?
would say it's proactive, because it's continuously sampling organisms from its environment, updating immune system
what's MALT?
stands for Mucosa Associated Lymphoid Tissue
refers to subepithelial lymphoid tissue in small intestine
what are the cells of the diffuse immune system? what is constantly patrolling our bodies?
macrophages, WBCs, antigen presenting cells
where are cells of diffuse immune system? where can they be found?
in ALL connective tissue, usually deep to epithelia = everything but mucosal epithelia
what's the immune system's presence in the small intestine - where does it reside and in what forms?
usually in lamina propria
can exist as
1. diffuse tissue = isolated cells
2. frequent nodules with germinal centers
where in small intestine are regions of aggregations of immune system cells large and consistently present?
1. Peyer's Patches = many germinal centers
2. appendix
what are Peyer's Patches?
are many germinal centers collected together
are macroscopically visible
why is the appendix considered mostly a lymphoid organ?
its lamina propria is so packed with immune cells and nodules that you can't really see a distinction between lamina propria and submucosa
how does the immune system sample the contents of the intestinal lumen?
2 ways:
1. T lymphocytes leave basal lamina to epithelia - stay there for a while then return to lamina propria
2. M cells - endocytize lumenal contents periodicallly, send it to basal surface where macrophages and lymphocytes wait to process
how do M cells function? what do they do?
they sample intestinal contents to keep the immune system aware of environment - is proactive, preventive position
apical surface of M cell faces lumen directly
clathrin coated pits take up samples
vesicles go straight to basal surface instead of being digested by lysosomes
macrophages and lymphocytes process
how does HIV gain access to CT in intestine?
via M cell-mediated uptake
would it be possible to get HIV from ingestion?
no because stomach acids would kill it - although if HIV enters intestine say from semen, would be able to cross to CT via M cells
what is the major antibody of the blood and lymph?
what is IgA and what does it do?
is an antibody
transported from CT
through epithelijm
to lumen
where can IgA be found?
saliva, tracheal secretions, intestine
where does IgA come from, what makes it?
plasma cells in lamina propria of intestine
where do plasma cells of lamina propria of intestine come from?
are B lymphocytes that were exposed to antigens via T lymphocytes that were stimulated by a macrophage that ingested that antigen
the B cell becomes a plasma cell after migrating to mesenteric lymph nodes
plasma cells then enter vasculature, go to lamina propria and then make IgA
once antigen enters system, what's process of recognition, stimulation until an antibody is made?
antigen enters
macrophage recognizes, digests and presents it
this stimulates T cell
T cell stimulates B cell
B cell go to lymph nodes and become plasma cells
plasma cells enter blood, go to lamina propria and start to make IgA
where does IgA go once its made?
1. some binds to BASAL membrane of intestinal epithelium
transported through cell to apical surface where its pooped out
then reabsorbed by surface of epithelial cell?
2. most enters circulation
picked up by liver hepatocytes
actively secreted into bile
then dumped into intestine
so basically its wasted eventually
what part of the GI tract the most impacted by the serosa?
small intestine outer wall covered with serosa
serosa also on surface of mesentery
what's a clinical correlate of the serosa in the intestine?
when serosa ruptures, bacteria dumped into peritoneal cavity which leads to peritonitis which kills quickly
what's the difference between peritoneal dialysis and regular dialysis?
in peritoneal dialysis, fluids are infused into peritoneal cavity where serosa equilibrates it with intestinal CT
difference with regular dialysis is you're using body's own tissues as filter as opposed to synthetic material
what's a common clinical correlate of the ileo-cecal junction besides colon cancer?
crohn's disease of small intestine frequently stops at transition from small to large intestine
what are the parts of the large intestine?
cecum, appendix
ascending, transverse, descending, sigmoid colons,
rectum, anus
what's the main function of the large intestine?
how much of volume that enters large intestine is absorbed?
is there more or less need for lubrication in large intestine vs. small and why?
more need because bolus is becoming harder, thicker
what changes of the epithelium take place in the large intestine when compared to the small intestine?
large intestine still dominated by absorptive cells, but now has more goblet cells because of greater need for lubrication
plicae circularis and villi disappear
what's a result of the disappearance of plicae circularis and villi in the large intestine?
less resistance to movement of bolus
what makes up the bulk of poop?
dead bacteria
undigestible vegetable matter
what contributions do dead bacteria in poop make to body?
bacteria make vitamin B12 - needed for hemopoiesis
made vitamin K - needed for blood clotting
where do diverticulae come from?
originate from pathological dilations of crypts in large intestine
even though there are no villi, there are crypts
what kind of tissue make up the epithelium of the large intestine?
are siple columnar epithelium as in small intestine
what cells in the large intestine are responsible for mitotic division?
enteroendocrine cells
are there paneth cells in the large intestine?
what are the differences between the epithelial cells of small and large intestine?
still have absorptive cells
have more goblet cells
still have enteroendocrine cells, but they're taking over work of stem cells
no stem cells
no paneth cells
what's the second most common form of cancer?
what makes up the lamina propria in the large intestine?
loose CT, lymphoid cells, occasional lymphoid nodules, small blood vessels and lymphatics
what are the differences between the lamina propria in the small intestine vs. the lamina propria in the large intestine?
no difference
what are the changes between the muscularis mucosa and submucosa between the small and large intestine?
there are no differences

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