GI II: Small Intestine, Large Intestine, Salivary Glands, Pancreas, Liver
Small Intestine
Anatomic
Three parts:
1) duodenum
2) jejunum
3) ileum
Cross section: Ross p.441
(See below)
Mucosa
Submucosa
Components:
1) epithelium: simple
columnar
2) lamina propria
a) inflammatory
cells: macrophages
and mast cells –
stain pink on PAS
b) lacteals:
lymphatic capillaries
used in fat
absorption
3) muscularis
mucosae: two thin
layers of smooth
muscle cells
Crypts of Lieberkuhn =
intestinal gland: simple
tubular structures which
extend from m. mucosae to
base of villi (empty into
lumen) Ross p.485 Fig. 1
Dense CT (many cells),
arteries, veins, lymphatics,
Meissner’s plexus
Functional
Surface area maximized for
digestion and absorption:
1) plicae circularis: luminal
folds with submucosal
core
2) villi: mucosal projections
with lamina propria core
3) microvilli: cellular
appendages of actin
filaments
Cell types:
1) Enterocytes: absorptive
function and secretion of
digestive enzymes
2) Goblet cells: secrete
mucus; white on H&E
3) Paneth cells: found at
base of crypts of Lieb.;
contain apical acidophilic
granules and secrete
lysozyme and other antibacterial products
4) Enteroendocrine cells:
also in the crypts; secrete
CCK, GIP, secretin; stain
with Bodian silver (look
granular)
5) M cells: found over
Peyer’s patches;
phagocytose
macromolecules and
unload them into the
lymphatic nodules below
In duodenum submucosa contains
Brunner’s glands:
1) alkaline secretions to
protect duodenum from
gastric acid
2) good way to distinguish
stomach from duodenum
at the junction
Muscularis externa
Serosa
Large Intestine
Recto-Anal
Junction
1) Inner circular
smooth muscle layer:
segmental
contractions
2) Outer longitudinal
layer: propulsion of
contents forward
(peristalsis)
A layer of simple squamous
epithelium (mesothelium)
and some underlying dense
irregular CT
1) Smooth mucosal
surface: NO plicae or
villi
2) Teniae coli: 3 bands
formed by
longitudinal layer of
muscularis externa
3) Many goblet cells,
increasing number as
you progress distally
4) Crypts with goblet
cells and regenerative
cells
Simple columnar → stratified
columnar → stratified
squamous keratinized
1) Internal anal
sphincter: circular
smooth muscle
2) External anal
sphincter: striated
muscle of perineum
Auerbach’s plexus: part of the
enteric nervous system; found in
between the two muscularis
externa layers
It’s equivalent to visceral
peritoneum
GALT (gut-associated lymphatic
tissue) well developed for
handling microorganisms and
noxious metabolic and other
products
Plexus of veins in submucosa of
rectum can become hemorrhoidal
with portal hypertension
Anatomic
Salivary Glands
Parotid gland
Sublingual gland
Functional
Acinus:
May contain serous, mucus or
basic secretory unit of the
both types of cells:
salivary gland; looks like a
1) serous cells: RER and
bunch of grapes
ribosomes basally
(blue), secretory
Ducts:
granules apically
1) Intercalated ducts:
(pink)
cuboidal epithelium;
2) mucus cells: granules
absorb Cl- secrete HCO3
lost in H&E preps
2) Striated ducts
3) mixed acini: serous
(intralobular ducts): more
demilunes – mucus
columnar; absorb Na+
cell with a serous cap
secrete K+; render
primary secretion
hypotonic; nucleus found
in central position
3) Excretory ducts
(interlobar ducts): Parotid
and Submandibular
ducts; located within
large CT septa; no
modification of
secretions
1) Purely serous
2) Striated ducts and
adipose tissue helps to
distinguish it from
pancreas
1) Mixed gland
2) More heterogenous than
the parotid
Pancreas
Liver
1) Exocrine component:
serous gland; secretes
inactive enzymes into
duodenum necessary for
digestion (ex:
trypsinogen)
2) Endocrine component:
secretes into blood
insulin and glucagon
(Islets of Langerhans –
useful landmark to
distinguish pancreas)
-- The duct system of the
pancreas begins with the oval,
pale, centroacinar cell unique to
pancreas
“Classic lobule” organization
(Ross p. 498 diagram)
1) Hexagon with central
vein in the center
2) Each corner has a portal
triad:
a) hepatic artery
(thick wall)
b) portal vein (thin
wall, irreg. shape)
c) bile duct
(lymph also drains
from liver around
portal “triad” area)
3) Each lobule is filled with
hepatocytes and
sinusoids (sinusoids
perfuse cells with mixed
portal and arterial blood)
Bile canaliculi are formed by
apposition of two hepatocytes
Canaliculi → canals of Hering
→ bile ducts (interlobular)
Bile ducts are lined by simple
cuboidal epithelium that
gradually becomes columnar
-- Zymogens (inactive
enzymes) are located in
acidophilic secretory vesicles
in apical part of cell.
-- Basal parts of cell:
basophilic due to RER,
ribosomes
-- CCK secreted by
enteroendocrine cells induces
zymogen release
-- Intercalated ducts secrete
bicarbonate and respond to
secretin
“Liver acinus” organization
emphasizes function – Three
zones:
-- hepatocytes of Zone 1,
closest to periphery of classic
lobule, get most oxygenated
blood
-- in Zone 3, closest to central
vein, hepatocytes get least
oxygenated blood → has
significance for liver
pathology (ex: in
hypoperfusion of the liver
Zone 3 affected first)
Space of Disse: lies b/w the
basal surface of hepatocytes
and endothelial and Kupffer
cells that line sinusoids –
exchange of materials b/w
blood and liver cells
Kupffer cells: macrophages
found in sinusoidal space;
participate in destroying
senescent RBCs