GI #32
Thur 02/27/03 2pm
Dr. Wordinger
R. Vayani
Proscribe Samera Kasim
Page 1 of 5
Histology: Accessory Organs
Liver, Gall Bladder and Exocrine Pancreas
--Liver-I. Functions of the liver
a. The liver has 2 main functions:
i. Exocrine
1. Includes synthesis and secretion of bile via the duct system
ii. Endocrine
1. Includes synth and secretion of plasma proteins,
cholesterol, lipoproteins and glucose to the bloodstream
b. Another function of the liver is detoxification of lipid soluble drugs,
breakdown of steroid hormones, glycogen storage and urea production.
i. Steroid hormones include estrogen, progesterone and testosterone
ii. Accomplished by the work of hepatocytes, the fundamental cell of
the liver
II. Lobules
a. Hepatocytes make up the bulk of the liver
b. Connective tissue (CT) is a minor component
c. When looking at a slide of the liver, there are 3 ways to analyze its
function. Different shapes can be drawn onto the slide, each emphasizing
a different function, namely its endocrine, exocrine and metabolic
functions
d. They are as follows:
e. Classic lobules (see “classic liver lobule” in the study guide handout)
i. Emphasizes the endocrine function of the liver because the central
v. is at the center of the lobule
ii. Shaped like hexagonal cylinders
iii. Hepatocytes are radially arranged in plates around small venules
(the central vein)
iv. The corners of the hexagon are portal triads
1. triads include a branch of:
a. hepatic a.
b. portal v. (interlobular v)
c. bile duct (interlobular bile duct)
v. because the liver is supplied by both the hepatic a. and the portal
v., it is said to have dual blood supply.
f. Portal lobules
i. Emphasizes the exocrine function of the liver because the
interlobular bile duct is at the center of each lobule.
ii. Bile flows: bile canaliculi  terminal ductules interlobular bile
duct  Right and Left hepatic ducts cystic duct  common bile
duct.
iii. Bile flows in the opposite direction of blood flow (which serves
the endocrine function of the liver)
GI #32
Thur 02/27/03 2pm
Dr. Wordinger
R. Vayani
Proscribe Samera Kasim
Page 2 of 5
iv. Bile canaliculi are formed by tight juctions between hepatocytes,
but are not lined by a specialized cell layer.
1. the tight junctions keep fluids from going into the sinusoids
g. liver acinus (Rappaport lobules)
i. diamond shaped
ii. the liver acinus emphasizes metabolic gradients and the
functional activity of the liver
iii. corners of the diamonds are formed by 2 central vv. and two portal
triads.
iv. Each acinus has 3 zones as determined by gradation of blood
supply:
1. Zone 1
a. Near center
b. Receives blood first from terminal distributing
vessels
c. Thus receives most of the glucose/nutrients
d. Higher glycogen storage
e. Last cells to die
f. First to regenerate
g. Higher oxygen levels
h. First to be overloaded by toxins that come through
the liver
i. Have the greatest mitotic activity after toxins
introduced to the kidney
2. Zone 2
a. Less active than Zone 1
b. Lipid and aging pigments found
3. Zone 3
a. Same as Zone 2
III. Sinusoids of the liver
a. The blood vessels between the cords of hepatocytes are lined by a
discontinuous, fenestrated layer composed of:
i. Typical intimal vascular cells
ii. Kupffer cells which phagocytose damaged RBC that are not
removed by the spleen (or in the event of an injured spleen)
1. derived from monocytes
2. may contribute to endothelial lining or just rest on the
lining in the lumen of the sinusoid
b. Space of Disse
i. An extracellular space between the sinusoids and the hepatic cells
ii. Site of traffic of materials between hepatocytes and the lumen of
the sinusoids
iii. Particles that are too large may be stopped from passing through
IV. Hepatocytes
a. The ONE cell of the liver
GI #32
Thur 02/27/03 2pm
Dr. Wordinger
R. Vayani
Proscribe Samera Kasim
Page 3 of 5
b. Diverse functions
c. Polyhedral cells with 3 surfaces
i. One exposed to space of Disse
ii. One exposed to canaliculus
iii. One adjacent hepatocytes
d. Products can be directed to the various borders
e. Have lots of organelles with many functions:
i. RER synthesizes plasma proteins and the protein portion of
lipoproteins
ii. GOGLI appareatus is always present at the pole of the cell that
form the bile canaliculus
iii. SER is used for:
1. drug detox
2. steroid hormone breakdown
3. conjugation of bilirubin before it’s excreted to bile
4. VLDL synth
5. cholesterol synth
6. enzymatic conversion of the inactive form of glycogen
synthase into the active form
--gallbladder-V. Gallbladder structure
a. A diverticulum of the common hepatic duct
b. 3 inches long, 1.5 inches wide
c. can undergo considerable distension
d. the wall only has 3 layers: there is NO SUBMUCOSA
i. mucosal layer:
1. has folds that are branched
2. simple columnar epithelium with apical microvilli and
basal nuclei
3. Sodium pump n the basal membranes to facilitate water
absorption from stored bile
ii. Muscularis externa
1. smooth mm under the lamina propria of the mucosal layer
2. (REMEMBER: there’s not a submucosa!!)
3. muscle fibers respond to CCK
iii. Adventitia/Serosal layer
1. has BOTH
2. adventitia covers the part attached to the liver
3. serosa covers its free surface
VI. function
a. Absorb water
b. Store bile produced in the liver
c. Concentrate the bile
GI #32
Thur 02/27/03 2pm
Dr. Wordinger
R. Vayani
Proscribe Samera Kasim
Page 4 of 5
d. As mentioned above, CCK is a hormone that stimulates contraction of
smooth mm of the gallbladder. Remember that CCK is produced by
enteroendocrine cells of the small intestines in response to ingested fats.
--exocrine pancreas-VII. Structure
a. Overall the pancreas is a Lobulated, compound tubuloalveolar gland that
has both endocrine and exocrine function.
i. The endocrine functions are carried out by the islet of langerhan
b. The acini or alveoli of the pancreas are tubular shaped and surrounded by
a basal lamina
c. They are composed of 5-8 pyramidal cells arranged around a central
lumen
d. The lumen may have centroacinar cells
i. These are the cells of the duct system
ii. In the absence of islet cells, these are the only way that you would
be able to determine pancreatic exocrine cells apart from parotid
gland cells. They look very similar.
VIII. The duct system
a. The pancreas does not have striated ducts
i. This is the other way that you may be able to distinguish the
pancreas from the parotid gland.
b. There are intercalated ducts
i. Lined by low cuboidal epithelium
ii. Extend into the lumen of the alveolus as centroacinar cells
c. Merge into the main excretory duct
IX. Secretions
a. Acini make serous secretions that are released into the intercalated ducts
b. Stimulated to secrete products by CCK
c. Cells of the intercalated ducts are stimulated to secrete their products by
secretin (from the small intestine)
Notes:
-Lipid Absorption material will be covered by Gwirtz.
-the histo slides that were used during lecture were mainly from the study guide. Below
are additional comments made about each slide or items that you should be able to notice:
Liver:
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Liver-low mag
o Delineations of the lobules are by connective tissue
o The “matrix” is composed of hepatocytes and blood vessels
Liver lobule – Central Vein
o Blood flows from the periphery through the sinusoids to the central
vein
Liver sinusoids
GI #32
Thur 02/27/03 2pm
Dr. Wordinger
R. Vayani
Proscribe Samera Kasim
Page 5 of 5
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Gallbladder
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o Each of the nuclei on the slide is a hepatocyte
o Notice that they are surrounded by vascular supply
Portal triads
o Know the content of the triad
o They’re at the periphery of the classic lobule
o The bile duct (BD) has simple columnar/cuboidal) epithelium
 Thus you can distinguish it from a vascular vessel which
would have simple squamous epith.
Classic liver lobule
o Endocrine function
o Hexagon
Portal liver lobule
o Exocrine function
o Bile duct in the center
Acinar liver lobule
o Metabolic function: Glycogen breakdown and glucose production
o Corner consist of portal triads on the Right and Left and central
veins at the top and bottom the diamond
o Zone 1 is near the center.
o Blood flow occurs in the direction along the line depicted from the
portal triad to the central vein
Liver sinusoids – phagocytosis (2nd to last slide)
o This demonstrates an experiment done with a cat.
o Ink particles were injected to the cat
o They are being phagocytozed by Kupffer cells
Liver sinusoids – phagocytosis (last slide)
o Notice that the nuclei of the Kupffer cells are flattened
o They nuclei of the hepatocytes are more rounded.
First 2 slides:
o The projections that protrude into the lumen are NOT villi, but are
folds
Surface epithelium
o Simple columnar
Pancreas
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Pancreas – endocrine and exocrine
o The exocrine pancreas surrounds the endocrine (the islet cells
grouped together in the center)
Exocrine Pancreas
o Notice there are no islet cells present
o This closely resembles the parotid salivary gland
Last 2 slides:
o Notice the centroacinar cells: the distinguishing feature compared
to the parotid gland