GI Flashcards
lining of endodermal organs
tube from the endoderm
foregut:
- lung
- esophagus
- stomach
- duodenum
- pancreas
- submucosal glands
midgut:
- jejunum
- ileum
hindgut:
- cecum
- colon
- rectum
alimentary canal - mucosa
epi: endoderm derived
LP: loose CT w MALT, glands
alimentary canal - muscularis mucosae
smooth muscle, thin
- inner circular
- outer longitudinal
alimentary canal - submucosa
dense irregular CT
- glands
- submucosal/meissner’s nerve plexus (autonomic)
- induces pancreatic secretions
- controls movement of mucosa and submucosa
alimentary canal - muscularis externa
smooth muscle
- inner circular
- outer longitudinal
- myenteric nerve plexus
alimentary canal - adventitia
loose CT
- if simple sq covering: serosa
- may hang in mesentery
auerbach’s/myenteric nerve plexus
in muscularis externa of alimentary tract
- autonomic
- regulates peristalsis
mesentery
attaches to abdominal wall
- contains BV and nerves to/from alimentary canal
esophagus
pharynx -> stomach
esophagus - mucosa
epi: str sq, non-keratinizing
LP: loose CT
folded when empty, expansion by bolus
esophagus - submucosa
dense irregular CT
- mucous acini, secrete anti-bacterial lysosymes
esophagus - muscularis mucosae
smooth muscle
esophagus - muscularis externae
upper ⅓: skeletal/skeletal
middle ⅓: skeletal/smooth
lower ⅓: smooth/smooth
gastro-esophageal junction
z line
- str. sq. to simple columnar
- slight thickening of m. externa: lower esophageal sphincter
barrett’s syndrome
pre-malig metaplasia of lower esophagus (str sq -> gastric-like simple columnar)
- chronic acid reflux
- leads to esophageal carcinoma
stomach
initiates digestion: enzymes and mechanical breakdown
- diff cell composition in diff sections of stomach
stomach - mucosa
epi: simple columnar
- depressions: gastric glands
- apical secretions: mucous, acid, proteases
- basal secretions: hormones + paracrine factors
stomach - muscularis externa
3 layers of muscle
- thickenings at esophageal and pyloric openings = sphincters
rugae
transient gastric mucosal folds
stomach epithelial cells
surf lining cell
regenerative cell
mucous neck cell
oxyntic/parietal cell
zymogenic/chief cell
enteroendocrine/DNES/APUD cell
surface lining cell
stomach cell, protective mucous
regenerative cell
stem cell
- highly proliferative
- epi turns over each 7 days
mucous neck cell
large amounts of protective mucous
- goblet cell-like
oxyntic/parietal cell
HCl/acid
- tight junctions
zymogenic/chief cell
prod zymogens (activated by acid)
- ex. pepsinogen -> pepsin
- prominent RER
- secretory vesicles
- tight junctions
enteroendocrine/DNES/APUD cell
basal peptide secretion into LP
- paracrine or endocrine
- VIP + gastrin
- present all throughout GI tract
vasoactive intestinal peptide
incr peristalsis of intestines
- endocrine
gastrin
incr parietal cell acid secretion + relaxes pyloric sphincter
- paracrine
pyloric sphincter
stomach -> duodenum
- gastrin causes relaxation + movement into duodenum
small intestine
midgut endoderm
duodenum -> jejunum -> ileum
small intestine - epithelium
simple columnar
- in villi:
- enterocytes
- goblet cells (secrete protective mucous)
- in crypts:
- paneth cells
- stem cells
absorptive mucosa of small intestine
incr surf area w villi and depressions (crypts/glands)
small intestine - LP
loose CT
- vascular + lymph capillaries(=central lacteals) in cores of villi
small intestine - submucosa
brunner’s glands in duodenum
columnar enterocytes
absorptive cells of small intestine
- microvilli
- many channels + transporters in membr
- actin based cytoskeleton merges w terminal web
- microvilli submerged in glycocalyx containing enzymes
terminal web
part of columnar enterocytes
- actin
- associated w terminal bars: adherens and tight junctions
Brunner’s glands
secrete alkaline mucous in duodenum
- protects from stomach acid
- in submucosa
- ducts empty into base of crypts
Paneth cells
deep in crypts of small intestine
- secrete antibacterial lysosymes
- can become phagocytic + APCs
B and T cell aggregates (small intestine)
no CT capsule
- activated by paneth/M cells
- pale germinal centers = B cell activation
- incr towards end of small intestine (ileum)
- fill entire LP in appendix
- peyer’s patches
large intestine - mucosa
absorption, especially water
- crypts and glands, but no villi
large intestine - epi
simple columnar
- enterocytes
- high number of goblet cells
large intestine - submucosa
no brunner’s glands
large intestine - m. externa
smooth muscle, inner circular, outer taeniae coli
- terminal thickening: anal sphincter
taeniae coli
outer 3 longitudinal layers of large intestine’s m. externa
- varies in thickness
anal/rectal canal - m. externa
smooth muscle internally, skeletal muscle externally
rectum-anus junction
simple columnar -> str. sq, keratinized at outer surface
- a bit lower is pectinate line: endoderm -> ectoderm
- right below pectinate line is internal then external sphincter
anus
Superior and interior hemorrhoidal veins in submucosa
- hilton’s white line: lack of veins
digestive glands
develop from endoderm near start of small intestine
- connected to small intestine through ducts
pancreas
dual structure:
i. endocrine islets, insulin + glucagon (blood)
ii. exocrine acini, digestive enzymes + bicarbonate ions (ducts)
- posterior abdominal wall behind stomach and duodenum
- tubuloacinar gland
liver
multiple functions all occurring in hepatocytes
- endocrine (plasma proteins)
- exocrine (bile)
- detox
- storage (glycogen)
gallbladder
stores and concentrates exocrine product of liver (bile)
- when no food, sphincter of oddi is closed: bile accumulates and goes into gall bladder
sphincter of oddi
exocrine ducts of pancreas, liver, and gallbladder empty into small intestine
- pancreatic tissue
endocrine islets
chromophobic, secrete insulin + glucagon into blood
exocrine acini
chromophilic, secrete digestive enzymes and bicarbonate ions into intralobular duct
duct organization, exocrine pancreas
centroacinar cell -> intercalated duct -> intralobular duct -> small interlobular duct -> main interlobular duct
acinar cells
secrete digestive zymogens
- stimulated by cholecystokinin (CCK) prod by DNES cells from small intestine
- CCK also relaxes smooth muscle in sphincter of oddi
- merocrine secretions
centroacinar cells
secrete bicarbonate ion
- stimulated by intestinal hormone secretin
merocrine glands
exocytosis
apocrine glands
small portion of cytoplasm buds off
holocrine glands
disintegration of cell and release of product
pancreatic injury
digestive enzymes build up -> inflammation
- leads to metaplasia of acinar lobules into ductal lobules
- could be reversible
chronic pancreatitis
fibrotic changes: cystic fibrosis
- collagen/fibrosis + metaplasia
- lobes still organized properly
pancreatic ductal adenocarcinoma
unorganized neoplastic ductules
- abnormal growth of new cells
- collagen/fibrosis
alpha cells
secrete glucagon, incr blood glucose
beta cell
secrete insulin. decr blood glucose
- dominate islets
diabetic islet
beta cells greatly reduced
Type I diabetes
immune system attacks beta cells
Type II diabetes
may have hypersecretion of insulin, as body cells become insulin-resistant
- still have beta cells
- resistance caused by:
- decr in cell surf receptors
- downstream signalling defects
hepatocytes
prominent:
- Euchromatin (transcribing)
- RER (plasma proteins)
- SER (detox)
- mitochondria
- glycogen granules
hepatic portal triad
hepatic portal vein + hepatic artery + bile duct
- HPV + HA go into liver
- bile duct goes out of liver
hepatic portal vein
drains GI and spleen, enters liver
- high in nutrients and bilirubin
bilirubin
heme pigment breakdown, produced by spleen
hepatic artery
abdominal aorta, entering liver
- High in O2
bile ducts
drain exocrine prod (bile) from liver
- helps w lipid emulsification in small intestine
venous sinusoids
in lobules, where hepatic portal vein and hepatic arteries combine before heading to the hepatic vein
hepatic veins
hepatic sinusoids -> central veins -> inferior vena cava
hepatic lobules
blood comes in through portal triad at 6 points around central vein, flows in through sinusoids towards central vein
* sinusoids are not straight
zone 1 hepatocytes
periportal, high nutr + O2
- gluconeogenesis
- urea synthesis
zone 2 hepatocytes
pericentral, zone 3
- insulin/glucagon ratio
- glycolysis
- phase I drug metabolism
hepatocyte - sinusoidal domain
empties into sub-sinusoidal space of disse
- endocrine products: plasma proteins + lipoproteins
space of disse
space between hepatocyte basal membrane and sinusoidal lining cell
hepatocyte - biliary domain
empties into bile canaliculi, closed by hepatocyte tight junctions
- drains to bile ducts
- Exocrine products: water soluble bilirubin, bile salts, cholesterol
kupffer cells
macrophages patrolling hepatic sinusoids and space of disse
liver stellate cells
in space of disse, make collagen, not large.
In liver injury: proliferate + make collagen, decr permeability at space of disse, backing up blood
liver cirrhosis
inflammation: incr collagen and decr hepatocytes
- decr blood flow through sinusoids -> portal vein hypertension
- backs up veins that drain GI tract, can lead to venous swelling in anal canal (hemorrhaging)
gall bladder - epi
simple columnar
- highly absorptive
- concentrates bile
gall bladder - LP
highly vascular
- loose CT
gall bladder - mucosa
highly folder
- no organization of villi/crypts
gall bladder - muscularis
prominent smooth muscle beneath LP
- overlapping fibers
- peristalsis in response to CCK
gall bladder - adventitia
dense CT
gall stones
precipitation of bile (esp salts + cholesterol) => gall stones
- trapped in draining cystic duct
