V. Microanatomy of the Accessory Glands for the GI System

Question 1

List three organs with accessory glands, and are they endocrine or exocrine glands.

Answer 1

Liver, Pancrease, and Gall Bladder All are exocrine glands Liver and pancrease also have endocrine functions

Question 2

Liver: Glandular Structure

Answer 2

1. Each lobe of the liver is covered by serosa (visceral peritoneum) over a thin connective tissue capsule. 2. Connective tissue of the capsule continues into the parenchyma of the liver as interlobular connective tissue and surrounds individual liver lobules and supports vasculature and bile duct.

Question 3

The parenchyma of the liver is composed of what?

Answer 3

Lobules of organized hepatocytes

Question 4

Structural definition of a liver lobule

Answer 4

Hepatic Lobule

Question 5

Distinction of hepatic lobules based on connective tissue

Answer 5

1. Hexagonal in shape (6 sided) 2. Organized around a central vein 3. Three of the six corners contain portal areas 4. Portal areas contain: portal vein/venule, hepatic artery/arteriole, bile duct, lymphatic vessel, unmyelinated nerve fibers

Question 6

What species have distinct hepatic lobules?

Answer 6

In most species, hepatic lobules are not distinct. An exception is porcine liver that has well developed interlobular connective tissue septa.

Question 7

What is the largest gland in the body?

Answer 7

Liver, at 2-5% of the body weight of an animal

Question 8

What kind of gland is the liver?

Answer 8

Compound tubular gland with both exocrine (bile) and endocrine functions.

Question 9

Where does the liver sit within the abdominal cavity?

Answer 9

Situated between the GI tract and the caudal vena cava

Question 10

Liver blood supply, where does it enter the liver

Answer 10

Dual blood supply: 1. Portal vein 2. Hepatic artery Enters liver parenchyma with connective tissue at a hilus on the visceral surface, the porta.

Question 11

Portal vein is enriched with_______. Hepatic artery is enriched with _____.

Answer 11

1. Portal vein is enriched with nutrients from small intestine. 2. Hepatic artery is enriched with oxygen.

Question 12

Arterial blood supply

Answer 12

Hepatic artery –> interlobular arterioles of the portal area –> capillaries –> sinosoids

Question 13

Which hepatocytes receive the most oxygen enriched blood, and which receive the least oxygen enriched blood.

Answer 13

1. Most oxygen enriched blood provided to hepatocytes closest to portal areas. 2. Hepatocytes around the central vein receive the lowest oxygen enriched blood. 3. This is because blood flows from the portal areas to the central vein.

Question 14

Venous blood supply

Answer 14

Portal vein –> interlobar veins –> interlobular portal veins –> distributing venules –> sinusoids (discontinuous capillaries, lined by porous endomthelium)

Question 15

Which hepatocytes receive the most nutrient enriched blood and which receive the least.

Answer 15

Hepatocytes closest to portal areas receive the most nutrient enriched blood compared to hepatocytes around the central vein.

Question 16

Venous drainage

Answer 16

1. Sinosoids –> 2. Central vein –> 3. Sublobular, or intercalated veins –> 4. Collective veins –> 5. Hepatic vein –> 6. Caudal vena cava

Question 17

Can there be cross sections of the hepatic vein within the portal areas?

Answer 17

No, based on the flow of the venous drainage, there cannot be cross sections of the hepatic vein within the portal areas. Any veins/venules within the portal areas are portal veins/venules that provide nutrients to the liver.

Question 18

Functional or metabolic definition of the liver lobule

Answer 18

Liver Acinus

Question 19

Liver acinus

Answer 19

1. Centered around nutrient supply (distributing veins) 2. Diamond shaped 3. Central veins at two points, portal area at 2 points

Question 20

Liver Functions

Answer 20

1. Excretion: waste products 2. Secretion: bile 3. Storage: lipids, vitamins A and B, glycogen 4. Synthesis: clotting factors and porteins, plasma proteins, sugars, lipids, urea 5. Phagocytosis 6. Detoxification 7. Conjugation: toxic substances, steroid hormones 8. Esterification: free fatty acids to triglycerides 9. Metabolism: protein, carb, fats, hemoglobin 10. Hemopoiesis in neonatal animals with only potential in adult

Question 21

All functions of the liver are carried out by what two cell types?

Answer 21

Hepatocytes and macrophages

Question 22

Characteristics of a hepatocyte

Answer 22

1. Polyhedral in shape 2. Zonula occludens functions 3. Polyploid 4. Extensive SER and RER 5. Well developed golgi complex 6. Membrane invaginations (bile canliculi) 7. Hepatocytes arranged in laminae (sheets) with sinusoids contacting at least two sides.

Question 23

Define sinusoids

Answer 23

Sinusoids are discontinuous capillaries lined by endothelium.

Question 24

Define bile canaliculi

Answer 24

Canaliculi are invaginations of hepatocyte plasma membrane. They DO NOT have an epithelial lining.

Question 25

Flow of Bile

Answer 25

Bile canaliculi → Bile Ductule → Bile Ducts of Portal area (arrows) → Hepatic Duct → Gall Bladder

Question 26

Functional, exocrine definition of a liver lobule

Answer 26

Portal Lobule

Question 27

Portal Lobule

Answer 27

1. Functional, exocrine definition and centered around bile ductule 2. Traingular in shape 3. Central veins at three corners 4. Bile from three hepatic lobules drains into bild duct of one protal area

Question 28

Three definitions of a liver lobule

Answer 28

1. Hepatic lobule 2. Liver acinus 3. Portal lobule

Question 29

Endothelial cells in the liver

Answer 29

Form sinuosoid wall, no basal lamina, rests on microvilli of hepatocyte

Question 30

Macrophages in Liver

Answer 30

Kupffer cells, stellate macrophages: In sinuosid wall, monocytic

Question 31

Spaces of Disse

Answer 31

Arrow shows perisinusoidal space of Disse. Endothelial cells sit on microvillar processes of hepatocytes. Space is filled with plasma. Processes of Kupffer Cells extend into Space of Disse

Question 32

Functions of Gallbladder

Answer 32

1. Stores bile made by the liver 2. Concentrates the bile 3. Releases bile when stimulated by cholecystokinin

Question 33

Which domestic species does not contain a gall bladder?

Answer 33

Equine

Question 34

Gallbladder: Structure

Answer 34

1. **Tunica mucosa:** many plicae or folds, simple columnar epithelium, striated (microvilli), tight junctions between cells 2. **Lamina propria-submucosa** (NO lamina muscularis): loose connective tissue, highly vascular, lymphatic tissue, simple tubuloalveolar gland in some species (ruminants) 3. **Tunica muscularis**: smooth muscle, thin and mostly circular 4. **Tunica adventitia** from side facing liver, **Tunica serosa** from side facing peritoneal cavity

Question 35

Pancreas

Answer 35

1. Lobulated gland with thin connective tissue capsule that forms septa to separate lobules 2. **Endocrine gland** produces hormones (insulin, glucagon, somatostatin) 3. **Exocrine gland** produces digestive enzymes (amylase, proteases, lipases, nucleases)

Question 36

Another name of pancreatic islets, and definition

Answer 36

Islets of langerhans: regions of the pancreas that contain endocrine cells

Question 37

Exocrine Pancrease

Answer 37

1. Compound tubuloacinar gland 2. Ruminants tend to have mostly tubular units 3. Acinar cells are serous (zymogen cells) 4. Between the acinar cells are secretory canaliculi 5. Centroacinar cells line the acinar lumen 6. No myoepithelial cells around acinar units

Question 38

Pancreatic Duct System

Answer 38

1. Lumen of acinus (small duct bounded by centraoacinar cells) --\> 2. Intercalated ducts (lining cells, low cuboidal) 3. Intralobular ducts 4. Interlobular ducts (low cuboidal eptiehlium WITH _goblet cells_) 5. Pancreatic duct and accessory pancreatic duct

Question 39

Answer 39

Centroacinar cell

Question 40

Answer 40

Intercalated duct of pancreas

Question 41

Key features in distinguishing the salivary glands from pancreas

Answer 41

Mixed/Parotid Salivary Gland: * Parotid - all serous, mixed - mucoserous * NO centroacinar cells * Intercalated ducts AND striated ducts * NO pancreatic islets Pancrease: * Serous secreting * Centroacinar cells are present * Inercalated and intralobular ducts but NO striated ducts * Pancreatic islets may be present