Lecture 28: Histology of the ParaAlimentary Tract

Question 1

What is the para-alimentary system?

Answer 1

That which lies alongside a system pertaining to food and digestion

Question 2

What are the components of the para-alimentary system?

Answer 2

1. Salivary glands
   
   • major
   • minor
2. Pancreas
3. Liver
4. Gallbladder/biliary tree

Question 3

How much fluid is secreted by the paraalimentary components?

Answer 3

4000ml/day
Pancreas = 2000
Salivary glands and liver/biliary system = 1000 each

Question 4

What is the function of the salivary glands?

Answer 4

1. Digestive enzymes
2. lipids and proteins impede demineralization of teeth (keeps teeth enamel health)
3. Lysozymes prevent bacterial growth (part of innate immunity)
4. secretion of IgA

Question 5

What are the two types of salivary glands?

Answer 5

1. Major

2. Minor

Question 6

What are the histological features of the parotid (major salivary) gland?

Answer 6

Cells are embedded in fat (like the Parathyroid)

Has acini that are the functional part of the gland

Question 7

What secretes the enzymes in the parotid gland?

Answer 7

Acini

Secretes shit into 1) striated duct, 2) intralobular and then interlobular ducts

Question 8

Why are acinar cells purple?

Answer 8

They secrete a lot of protein!
Indicative of SEROUS

Serous = protein = dark
Mucin = no protein = light

Question 9

What are the histological features of the minor salivary glands?

Answer 9

Purely mucinous cells so are very clear

Question 10

What are the characteristics of the major salivary glands?

Answer 10

1. Parotid = SEROUS

2. Sublingual = serous AND mucinous

Question 11

What are the characteristics of the minor salivary gland?

Answer 11

Mostly mucinous

Submucosa of the nose, paranasal sinuses, oral cavity, esophagus, etc.

Question 12

What is the function of the pancreas?

Answer 12

1. Exocrine secretions
   
   • bicarb
   • amylase, lipase, trypsinogen
2. endocrine functions (insulin, glucagon, somatostatin)

What is the structure of the pancreas?
Ductal system
i. lobules = visible unit composed of all functional cellular elements which drain into intralobular duct
ii. interlobular duct = drains several lobules via several intralobular ducts into main pancreatic cells

Question 13

What are the cells in the pancreas?

Answer 13

1. glandular/mucinous
2. acinar cells
3. islet cells

Question 14

What are the functions of the glandular/mucinous cells?

Answer 14

1. secrete bicarbonate and the hrmone secretin

Secretes high molecular weight glycoprotines

Question 15

What are the function of acinar cells?

Answer 15

1. secretes enzymes for digestion in small bowel
2. proteases, lipases, amylase
3. low pH in granules, protease nhibitors in granules and zymogen granules to protect from autodigestion

Question 16

What stimulates acinar cell secretion?

Answer 16

CCK

Question 17

What are the histological features of the pancreas?

Answer 17

1. acinar
2. islet
3. ducts

Question 18

What is the peritoneality of the pancreas?

Answer 18

Secondarily retroperitoneal except for its tail

Question 19

What is a pancreatic lobule?

Answer 19

Visible unit composed of all functional cellular elements which drain into intralobular duct

Question 20

What is the function of the pancreatic duct?

Answer 20

1. conduit for secretions of acinar cells to lumen of duodenum
2. secretes bicarb to duodenum
   Lined by CUBOIDAL cells

Question 21

Are the medulla and cortex of adrenal the same embryologically?

Answer 21

They are derived from different places embryologically

Question 22

Embryologically, where does pancreas derive from?

Answer 22

All the cells from pancreas come from the same place

Question 23

What is the structure of the acinar cell?

Answer 23

Pyramidal shape
Apex = acinar lumen, microvilli present
Eosinophilic cytoplasm = zymogen
Purple cytoplasm = RER…lots of protein made so the RER is dark

Question 24

What is the function of the liver?

Answer 24

1. Synthetic
   
   • synthesizes LDL/VLDL
   • synthesizes bile (bile salts derived from cholesterol + bilirubin from hemoglobin)
2. Clearing
   e. g. excretes copper through biliary secretion
3. Detox
4. Secretion
5. Delivery
6. Hormone converter (OH vit D and T4 to T3)
7. Storage

Question 25

What does the liver detox/clear?

Answer 25

1. bilirubin 2. endogenous/exogenous toxins 3. ammonia 4. copper

Question 26

What does the liver store?

Answer 26

1. lipid 2. vitamin A 3. glucose (glycogen)

Question 27

What does the liver synthesize?

Answer 27

1. albumin | 2. Vit K dependent factors, 2, 7, 9 and 10

Question 28

Where does the urea cycle take place?

Answer 28

Liver So liver makes urea Ammonium go to glutamine

Question 29

What is the function of the gallbladder/biliary tree?

Answer 29

Serves as conduit for bile | Stores bile

Question 30

What are the functions of the bile?

Answer 30

1. remove bilirubin from blood 2. enhance lipid absorption in small bowel 3. rid the body of wastes/toxins

Question 31

What are the key characteristics of liver histology?

Answer 31

Repeating units of i. hepatocytes ii. portal tract iii. sinusoids

Question 32

What is the terminal venule?

Answer 32

Where all the blood from the sinusoids Ultimately drain to (green stuff = hepatocytes Fenestrated epithelium is UNIQUE to the liver and kidney to allow for exchange

Question 33

How many hepatic veins are there?

Answer 33

3 hepatic veins (left, right and middle)

Question 34

What separates the blood and the hepatocytes?

Answer 34

Fenestrated endothelium

Question 35

How do hepatocytes regenerate?

Answer 35

Every hepatocyte has the ability to re-enter the cell cycle

Question 36

What are the types of collagen? Significance?

Answer 36

1. fibrillar 2. network 3. FACIT 4. Tran membrane Holds together the portal tract, liver cords and central vein Collagen also is involved in SIGNALING

Question 37

What is the space of Disse?

Answer 37

The space between the fenestrated endothelium and hepatocyte | Blood  endothelial cell  space of Disse  hepatocyte

Question 38

What is the purpose of collagen signaling?

Answer 38

Helps with cell polarity | Also can signal regeneration of hepatocytes

Question 39

What is the mechanism of collagen signaling?

Answer 39

Matrix (fibronectin) binds to the integrin on cell surface | Integrin is bound to linker proteins and is attached to the F-actin

Question 40

How do you form bile salts?

Answer 40

Cholesterol is converted into bile salts

Question 41

Can you usually see bile canaliculi in a H&E stain?

Answer 41

No | Only can see it if the bile is blocked or backed up

Question 42

What is the canaliculus?

Answer 42

The space through which bile is transported

Question 43

What are the zones of the liver? Significance?

Answer 43

Zone 1: those heaptocytes exposed to the blood right after entry from the portal tract Zone 2: in between 1 and 3 Zone 3: those hepatocytes that se the blood right before exit into the terminal venule Enzymes are ZONALLY distributed P450 rich in zone 3

Question 44

Which zone is most sensitive to ischemia?

Answer 44

Zone 3 (because farthest from hepatic artery0 Oxygen is LOWEST in zone 3 Oxygen is HIGHEST in zone 1

Question 45

What stimulates the gall bladder to contract and release its stores?

Answer 45

Cholecystokinin (CCK)

Question 46

How does the structure of the gallbladder differ from luminal gut?

Answer 46

``` Gall bladder can and does alter luminal fluid above 290 osm Has the following components i. epithelium ii. lamina propria iii. muscularis propria NO submucosa ```

Question 47

How does the pancreas prevent autodigestion?

Answer 47

1. low pH in granules 2. protease inhibitors in granules 3. zymogen granules to protect from autodigestion