Histology of the GI Glands

Question 1

In general, what are the digestive glands good for?

Answer 1

lubricating, protecting, digestive, absorptive stuff mediated by their secretory products

Question 2

what are the three main digestive glands?

Answer 2

major salivary glands –> associated with the oral cavity through independent excretory ducts (parotid, submandibular, sublingual)

exocrine pancreas –> secretes alkaline aqueous and enzymatic product to the duodenum

liver - endocrine and exocrine gland with extensive access to blood circulation

Question 3

Exocrine glands have two parts, what are they and what do they do?

what’s the umbrella term that combines both of these together?

Answer 3

an acinus and a duct

acinus = circular organized sac of secretory cells that synthesize and release product (mucous or serous based, or even mixed)

Duct - conducting passageway for product to be released.

Salivon –> which also include the intercalated duct + Striated Duct + excretory duct

Question 4

Salivary glands, what are they controlled by and what do they produce?

how are these salivary glands divided and what is important about these besides simply dividing?

what goes in between these lobules through the connective tissue septa?

Answer 4

ANS to produce saliva

the gland as a whole is surrounded by a connective tissue capsule.

the capsule extends into the gland dividing into lobes by Septa (interloper septa) and even smaller lobules (interlobular septa)

they are a route for neurovasculature

Question 5

Saliva functions? (4)

Answer 5

lubricates oral mucosa for speech and digestive purposes

has enzymes that assist with antimicrobial function.

mineralize the teeth after tooth eruption.

also aids in digestion of food via enzymes.

Question 6

What are the different types of acinus glands in the oral cavity?

Answer 6

Mucous Acini –> very pale pink to white staining

Serous Acini –> exact opposite, intensely hot pink/dark pink/red

Mucoserous Acini (mixed) –> components where you see mucous acini surrounded by a serous demilune (yellow) (hat or bonnet of serous cells that sit on the boundary)

Question 7

myoepithelial cells?

Answer 7

located between epithelial cells and basal lamina; assist in moving secretory products towards the excretory duct

Question 8

pathway of saliva flow? include the cell type of each.

what is most commonly seen in the excretory duct?

Answer 8

Acinus –> Intercalated duct –> Striated duct –> Excretory Duct

goes from Acinus –> low simple cuboidal epithelium –> simple cuboidal to columnar epithelium –> simple cuboidal to pseudo stratified columnar or stratified cuboidal

Excretory duct is most commonly stratified cuboidal but other options are seen

Question 9

Which cell has the largest length of excretory duct?

largest length of striated duct?

largest intercalated duct?

Answer 9

Sublingual

Submandibular

Parotid

Question 10

What are the parotid glands?

3 hallmarks?

Answer 10

largest salivary gland, that are serous only! (HM)

You’ll see a variable amount of adipose tissue! (HM)

CN VII (facial nerve) passes through! (HM) –> damage this and you’ll have facial paralysis.

intensely pink to reddish because of serous acini present.

Question 11

What kind of cell shapes are in the parotid glands?

what is seen at their basal region?

Answer 11

they have pyramidal cells with a basally located nucleus

super prominent RER at their basal region.

Question 12

What is the sublingual gland?

Answer 12

predominantly mucous, but mixed! so you’ll see a large majority of mucous. (HM)

they are separate from the serous acini.. they’re not mixed like the mucoserous.. so won’t see demilunes!

here in the sublingual gland, you won’t see a good capsule but still see the CT dividing it into lobes and lobules.

Question 13

Submandibular gland?

what specific cell type do you also see in this section?

Answer 13

SEROUS cells are predominant (HM) but mucous also present

also you have serous demilunes (bonnet) (HM)! Its a centralized core with a little hat of the serous demilune sitting on top.

myoepithelial cells to control serous secretions to squeeze and mix stuff.

Question 14

The pancreas?

what exocrine function does it have?

Which do we care about?

what divides it and surrounds it?

Answer 14

large glands with endocrine and exocrine functions, but bulk of glands is exocrine.

exocrine –> secrete zymogens that are needed to aide digestion

there’s a thin layer of loose CT that forms the capsule, and it divides gland into lobules, and just like the septa, neurovasculature travels within it too.

Question 15

What is the functional unit of the exocrine pancreas?

What does this make up?

what is the other cell type of the pancreas to know?

Answer 15

serous acinus –> contains PANCREATIC ACINAR CELLS (which secrete zymogens) –> stain intensely

the serous acinus cells surround the acinus, and then you have the intercalated duct that projects out into the duodenum, but there are cells that extend down into the core of the acinus which is unique… these are called centroacinar cells

centroacinar are the boundary from the true acinus to the intercalated duct.

centroacinar cells are responsible for secreting HCO3, Na+, H20 to neutralize secretions

Question 16

What do Pancreatic Acinar Cells do?

fact about dietary intake?

Answer 16

package up zymogen granules needed to digest the four macromolecules.

if you eat a high protein diet, your amount of synthesis of proteases goes up compared to someone who has high carb diet.

if you transition your diet, the enzymes transition accordingly

Question 17

Trypsinogen?
Amylolytic enzymes (a-amylase)?
Lipases?
Deoxyribonuclease?

Answer 17

digest proteins
digests carbs
digests lipids
digests nucleic acids

Question 18

Hallmark for a pancreas histo slide?

Answer 18

pancreas as a whole is usually very hot pink. and you see these little pockets where the islands are less staining and faintly staining (which are endocrine). that’s how you identify the pancreas

Question 19

How do you distinguish parotid glands with pancreas?

Answer 19

Islets are the way to distinguish. parotids DO NOT have any islets.. instead you’ll find adipose tissue in parotid glands

Question 20

The liver classic organization?

what is the major cell type?

what are 3 functions of these?

Answer 20

the liver is organized into octaganal shaped lobules structures. the cell types that comprise the liver are hepatocytes.

the hepatocytes are organized into cellular “cords”.. so you will NOT see an acinar structure, it’ll be In cords.

they function in metabolism, storage, and bile production (exocrine)

Question 21

What is the blood supply to the liver?

which is oxygenated, which isn’t?

Answer 21

portal vein (80%) –> transports deoxygenated blood from GI tract, spleen, and pancreas

Hepatic artery (20%) –> oxygenated from systemic circulation.

Question 22

how does the classic definition of the liver work with blood supply? (octagonal structure)

Answer 22

there’s a central large structure (central vein) and on the outer periphery we have the delivery of the portal system via the branch of the hepatic portal vein and a branch of the hepatic artery.

these both mix and drain into sinusoids, which is exposed to the lining of the hepatocytes and drains back out the central vein –> sublobular veins –> IVC

so goes from outer to the inner.

Question 23

what’s good to know about hepatocytes and bile?

Answer 23

hepatocytes in these cords have exocrine function which is to produce bile. this bile goes in the opposite direction that the blood does.

they drain away from the central vein (in a tube called the bile canaliculus) to go to right and left hepatic bile duct –> hepatic duct –> common bile duct –> gallbladder

Question 24

hepatocytes.. what do they look like?

Answer 24

large, polygonal cells. Many are binucleate and some even tetraploid (have a lot of DNA then).

hallmark = have a ton of organelles dedicated to metabolism and breaking down of toxins (peroxisomes, lysosomes, extensive sER, large Golgi)

Secrete bile (which is a mix of water and bile salts). bile drains into a tube called the bile canaliculus

Question 25

What should you know about the bile canaliculus?

what happens if you have less bile?

functions of bile?

Answer 25

it’s lined with cholangiocytes.

these join up to contribute to to the biliary tree

loose stools because more fat is in there not able to be absorbed

emulsification of fats, fat absorption, excretion of cholesterol, bilirubin, iron, copper

Question 26

What is the general orientation the octagonal structure?

this is called the “classic lobule bounded by the portal triad”

Answer 26

we have hepatocytes arranged in cords (1 cell thick)… interspersed between are sinusoids.

blood comes in from the branches of hepatic portal vein and hepatic artery come in, it mixes, and when it flows through the sinusoids it’s exposed to the hepatocytes so they can absorb nutrients and toxins (from the diet) .

they metabolize it to break it down but also making lipoproteins, albumins, etc and bile and that bile is collected in the canaliculus (draining tube), and it drains into the bile duct.

Question 27

What is the periportal space (space of Mall)?

Answer 27

space located at the edges of the canals between stromal CT and hepatocytes

so there’s an enwrapping of the portal triad and between the space of the hepatocyte and that connective tissue wrapping is the space of mall. that’s where LYMPH is collected, pulled into lymphatic vessels and drained out of the liver!

Question 28

What is the perisinusoidal space of disse?

Answer 28

sinusoids have an endothelial lining and in this case it’s discontinuous.. but the hepatocytes still have a cell boundary and there’s a gap between there.

so its the site of exchange of material between blood and liver.

this is the site of the material exchange from stuff coming in to feed into the hepatocytes and releasing lipoproteins into the blood supply too.

it looks like there’s a whole lot of nothing in it, a bunch of junk.

Question 29

What are hepatic sinusoids?

what cell type would you see here that is kind of a hallmark?

Answer 29

thin discontinuous epithelium with discontinuous basal lamina.

super large fenestra to allow exchange to occur

Kupffer cell = macrophage based cell and it functions like a macrophage but its specific. it monitors the age and composition of red blood cells.

they’re the hallmark to hepatic sinusoids

Question 30

How do we categorize the functional liver (favoring exocrine)

Answer 30

through the portal lobule –> draw imaginary lines between 3 central veins and that’s it. it’s like a triangle.

Outlines bile drainage pathway from adjacent lobules into the same bile duct. the bile duct will be in the core. the hepatocytes within this triangle drain to that bile duct.

this is best if you only care about exocrine function

Question 31

Clinically, which is the best acinus? (functional liver again, but best for the clinic)

Answer 31

Liver acinus –> draw a diamond from one central vein to another.

in the center of that diamond perpendicular to the central veins are 2 sets of the portal triads. (making the sides of the diamond)

as they move away from the portal triad is zone 1, 2, 3.

cells in zone 1 will be exposed to the highest amount of nutrients and oxygen, but also the highest amount of toxins.

zone 3 has the least toxins + least oxygen.

Question 32

if someone cut off blood supply to the liver, which zone of the liver acinus would be most impaired first?

what if most sensitive to toxins?

Answer 32

3! because the blood supply is already super low and deoxygenated, so cutting off blood supply would be awful. (3 is most sensitive to ischemic events)

1! because the highest toxins is exposed to cells in zone 1.

Question 33

Classic Hepatic vs. Portal vs. Hepatic Acinus, which one is for which?

Answer 33

Classic = structural

Portal = Exocrine function

Acinus = clinical (blood)

Question 34

Gallbladder

what does it look like under the microscope?

what kind of epithelium?

does it have muscle?

does it have adventitia or serosa?

Answer 34

Sac like structure that concentrates bile

SUPER highly folded mucosa because it needs to expand when its full. (looks like villi)

lined with simple columnar epithelium.

lined with muscular to maintain tension and release components that have been stored.

gallbladder has BOTH AN ADVENTITIA AND SEROSA depending on where its exposed

adventitia is found where the gallbladder is against the liver. serosa where it’s exposed to the peritoneal cavity

Question 35

What are Rokitansky-Aschoff Sinuses?

Answer 35

deep diverticula of mucosa that extend into the muscular external layer.

what happens if they increase your risk for chronic inflammation so increased risk for developing gallstones.

Question 36

Acinar cells vs centroacinar cells, what kind of staining would you see?

Answer 36

acinar = intense staining
centroacinar = stain lightly

Question 37

Of the portal triad, histologically which is biggest and which is smallest

Answer 37

Portal vein –> Hepatic Artery –> Bile Duct

from largest to smallest