Gastrointestinal tract
Understand what’s special about each region of GI tract
Mucous is secreted by two cell types of stomach
Relative abundance of tehse cell types changes in different regions of stomach
Q: Which layer is unusual in the esophagus?
Answer:
A:
Submucosa
B:
Muscuarlis mucosae
C:
Glands
D:
Muscularis externa
E:
Lamina propia
F:
A,B,and D are correct
Only two places in GI tract where you have glands in the submucosa
Muscvle layer is continiuous
Muscularis externa is different becayse you have skeletetal muscle, mixed skeletal muscle, and
smooth muscle
Gastric glands
Carida has NO Chief cells, but many surface lining cells
Fundus regions has the largest number of parietal cells of all of the layers
Glands are simple or brachned glands. IN cardia they are coiled but pits are quite shallow. IN
the fundus or in the body, althouch the pits are challow, the glands are really long but they’re
strait
In the pylorus there are very deap pids but branched lgands
Remember: these regions have differences in cell type distn and design of glands
Parietal cellshave two specializiations, with prominent nucleus
Tubulovesicales…?
Canalliculi – invagentations in PM. When parietal cells get activated, vesicles turn into
microvilli
HCL releas
Picture is in fundus region. Cells look like fried eggs
Gastrin, histamine , Ach cause PC cells to release HCL
Vagus nerve releases Ach on onto this cell.
Duodenum is short, but is main part of small intestine where you get enzymatic digestion.
There are no longer pits in small intestine. Mucosa forms out finger-like projections called villi.
INbetween villi arge glands in cryps of lieberkuhn. Glands are in lamina propa. Openin
up between villi.mucosa is extruded throuch finger-like projecytions.
Surface cells on villi are absorptive cells. They do not synthesize or secrete mucuous. Goblet
cells are nto the only mucous secreteing cells in the remainder of the GI tract.
Regenerative cells are now in the base of the crypt of lieberkuhn
Paneth cell – secrete lysozyme
Also have enteroendcrine cells here
Overall morphology of mucosa has changed from a pit to a villus
There are no parasympathetic cell bodies within the gut
Enteric nervous system is the intrinsic nervous system of the gut, and it functions independently
Small insteine
Ways to increase surface area for digestion and absorption
Plica circularis – very large folds, similar to ruggae of stomach
Villi – finger like projections of mucosa
Microvilli – on surface epithelium
Epithelium
Chylomicrons leave GI tract throuch villi
Regional differences
Villous structure throuchout small instines change
Need big surface area to absorb what’s coming through the stomach
Illium – vlli are smaller apart so that crypts of liberhum have larger surface area to open out
Cells of intestinal glands
Glands open between villi not within (different than stomach)
Regenerative cells move up to top of villi and then get slouched off
Enteroendocrine cells mainly in crypt of liberhum
Goblet cells are scarred throuchout villus and crypt
Faster mitosis in small intestine than stomach
Patienst undergoing chemotherapy have a problem with gut function
Paneth cells – large, at base of crypt, and filled with secratory granules
Crypts of lieberkuhn – have same types of cells with exception of panneth cells
Are simple branched tubular glands
Lacteal – where cylomicrons are reabsorbed and returned into circulation – important
specialization
Submucosa of duodenum
Thin lamina propia
Muscularis mucosa very thin
Submucosa is villed with tubularalveolar glands calle dbrunner glands, secrete alkaline flud to
neutralize chime. Is the only other place of Gi tract where there are glands in submucosa
(also in esophagus)
Pyers patches in ilium one side opposite to mesentery
Use lamina propia
Can displace villi if quite large
In ilium, villi are shorter and farther apart. Crypts are more prominent
Q: The duodenum and esophagus have what feature in common?
A:
They both have two layers in the muscularis mucosae
B:
They both have glands in the lamina propia
C:
They both have glands in the submucosa
D:
they both have skeletal muscle
In duodenum, glands are in submucosa.
Understand the differences between parts of GI tract
What portion of the gut is characterized by villi, microvilli, and submucosal glands
A:
small intestine
B:
Duodenum
C:
Illeum
D:
Jejunum
E:
non of the above
Small intestine would be correct if a more specific choice weren’t there
Large intestine
Funciton is to absorb water. There is no longer digestion.
Large intestine no lonver have villi. It’s composed 100% by crypts of liberhum
Overtaken by goblet cells on surface – to lubricate so that it’s not damaged
Regenerative cells are found at base
There are no panneth cells, (diagnostic not of large intestine)
Features
Goblet cells are extermemly dense.
Longitudinal muscle of muscularis externa forms three bands around outside called tenia coli.
The muscile is in a constant state of contraction, which pulls the large intestine int bulges called
haustra coli aka saculation. Perminanet structre because constant tone, which is there to help
support the feces.
Lobules of fat in large intestine.
Rectum and anal canal. Crypts less dense and depper than colon. In the anus, epithelium is
stratified squamous for protection.There are s series of branched glands that put out
seroumucuous out onto surface
Anus
Longitudinal muscle thinds out and disappears and turns into fibrelastic band. Circular muscle
comes down and thickens out to make the internal anal sphincter SM, involuntary. Skeletal
muscle comes in from floor of pelvic region which forms external sphincter. Two sets of
hemmheroidal plexi. Can get hemmoroids in either plexus. In normal state are large vascular
structure that can get swollen in abnormal state
Muscosa throuwn into folds called anal valves or columns of organnae. Folds are there to
provide structure and support for feces. Specilizations are here to prevent gamage and control
defication
Pectinate line  point where there is a change between columnar and stratified epithelium.
Becomes caritinized upon reaching external. Sebacous gland
Columns at junction that secrete a watery mucus
Columns of morgagni
Q: A patient comes to the ER and a blood test shows high lvels of antibodies against parietal cell
proteins. The patient complains of poor apitite and fatige. What would their hematocrit likely
show?
A:
A normal hematocrit
B:
An increased hematocrit
C:
A decreased hematocrit
In pernicious anemia you don’t have a change in hematocrit.
Q: The sympathetic ganglie of the enteric nervous system regulate peristalsis:
A: False – The peristaltic reflex is modulated my myenteric ganglia