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Histology and Embryology > Liver and Pancreas > Flashcards

Liver and Pancreas Flashcards

1
Q
A
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2
Q

What develops from the dorsal and ventral endodermal buds of the caudal end of the foregut?

A

Both the exocrine acini and the endocrine islets of Langerhans.

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3
Q

The pancreas has both ___________ and _____________ components; diseases of both are primarily seen in ________________.

A

Exocrine, endocrine, dogs and cats.

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4
Q

Describe the structure of the pancreas of dogs and cats.

A

Two lobes (limbs) that diverge near the pylorus; left lobe lies against the stomach and right lobe lies along the duodenum.

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5
Q

How do pancreatic secretions drain?

A

Into the duodenum through 1 or 2 main pancreatic ducts.

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6
Q

Describe the pancreatic ducts of dogs.

A

Most have 2; main accessory duct entering the minor duodenum papilla and a smaller duct enters with the common bile duct at the major duodenal papilla.

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7
Q

Describe the pancreatic ducts of the cat.

A

80% have a single duct that fuses with the common bile duct before entering the duodenum at the major duodenal papilla.

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8
Q

What is the main component of the endocrine pancreas?

A

Islets of Langerhans which are small clusters of endocrine cells that are scattered throughout the exocrine acinar pancreas.

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9
Q

How many cell types are in the islets of Langerhans?

A

4.

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10
Q

What are the 4 main cell types of the islets of Langerhans?

A
  • Alpha cells (20%)
  • Beta cells (60-70%)
  • Delta cells (5%)
  • F or PP cells (10%).
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11
Q

What do the alpha cells of the islets of Langerhans secrete?

A

Glucagon.

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12
Q

What do the beta cells of the islets of Langerhans secrete?

A

Insulin.

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13
Q

What does glucagon cause?

A

An increase in the concentration of glucose in the ECF by target cell catabolism (especially glycogenolysis and gluconeogenesis in the liver and some lipolysis in adipose tissue).

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14
Q

What does insulin cause?

A

Decreases glucose concentration in the ECF by target cell anabolism/storage with direct effects on CHO, protein, and fat metabolism; also decreases glucose concentration by increasing membrane transport of glucose, especially in adipose and skeletal/cardiac muscle tissues.

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15
Q

How do insulin and glucagon act in concert?

A

Maintain glucose concentration in the ECF within relatively narrow limits.

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16
Q

What do the delta cells of the islets of Langerhans produce?

A

Produce somatostatin which inhibits release of insulin, glucagon, and GI peptides.

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17
Q

What do the F/PP cells of the islets of Langerhans produce?

A

Make pancreatic polypeptide which inhibits intestinal motility and stimulates secretion of gastric/intestinal enzymes.

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18
Q

Describe the components of the exocrine pancreas.

A
  • CT septa extend from the outer capsule to divide the pancreas into numerous lobules.
  • Blood vessels and interlobular ducts run through these septa and connect to smaller branches within the lobules.
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19
Q

How are acini formed?

A

By acinar cells which are pyramid-shaped serous cells which have a basophilic base and numerous acidophilic secretory granules in the apical cytoplasm which contain a variety of digestive enzymes.

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20
Q

What are the acidophilic secretory granules of the acini of the exocrine pancreas called?

A

Zymogen granules.

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21
Q

What is the basophilic base of the acini?

A

Abundant rough ER.

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22
Q

How do the acini of the exocrine pancreas drain?

A

Within lobules, they drain into intercalated ducts which are lined by cuboidal epithelium.

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23
Q

What are the 2 sources of blood circulation to the acinar tissue of the exocrine pancreas?

A
  1. Insuloacinar portal system: venules that emerge from the islet capillary network supply adjacent acini.
  2. Acinar vascular system: independent arterial system.
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24
Q

What does the insuloacinar portal system allow for?

A

Allows hormones from the islets to exert trophic or inhibitory effects on acinar cells.

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25
What are Pacinian corpuscles?
Mechanoreceptors commonly found within the CT of the pancreas of many species which detect pressure and vibration when compressed.
26
What are the functions of the pancreas?
- Exocrine pancreas includes electrolytes for pH control, and a variety of digestive enzymes for dietary lipids, proteins, and carbs.
27
What are the digestive enzymes for lipids stored in the pancreas?
Lipase and phospholipase.
28
What are the digestive enzymes for proteins stored in the pancreas?
Trypsin, chymotrypsin, and elastase.
29
What is the digestive enzyme for CHO stored in the pancreas?
Amylase.
30
How are digestive enzymes of the pancreas stored and released?
Stored and released as proenzymes which require activation before they are functional.
31
What happens if a pancreatic proenzyme is activated prematurely?
They can cause serious damage.
32
How is pancreatic secretion controlled?
Mainly by 2 hormones, secretin and cholecystokinin, produced by neuroendocrine cells in the duodenal mucosa.
33
What originates from an endodermal bud on the ventral region of the duodenum?
Liver and extrahepatic biliary tract.
34
What are hepatocytes and cholangiocytes derived from?
Hepatoblasts.
35
What are other liver cells such as sinusoidal endothelial cells, hepatic stellate cells, and hematopoietic cells/Kupffer cells derived from?
Mesoderm.
36
What is the largest visceral organ of the body?
Liver.
37
What % of BW does the liver makeup in carnivores, omnivores, and herbivores?
Carnivores: 3-4% Omnivores: 2% Herbivores: 1-2%.
38
Describe the structure of the liver.
Distinct lobes, the number of which varies among species.
39
How does the liver receive cardiac output?
About 25% of cardiac output through the portal vein (2/3) and hepatic artery (1/3); therefore oxygen and nutrients are carried to the liver by both these vessels.
40
Blood from what locations drains into the liver from the portal vein?
Stomach, intestines, spleen, and pancreas.
41
What is the function of the liver?
Central organ for the metabolism of CHO, proteins, lipids, vitamins, and hormones as well as for detoxification, excretion, storage, and digestion.
42
_________ and ___________ of the liver expose it to a myriad of injurious agents.
Size, location.
43
How does the liver counteract its susceptibility to injurious agents?
Has a remarkable functional reserve and regenerative capacity via remaining hepatocytes that can enter the cell cycle and/or proliferation of hepatic stem cells.
44
What is the Glisson capsule?
CT capsule that surrounds the liver and is covered by a mesothelium.
45
Hepatic parenchyma is divided into what?
Classic hepatic lobules.
46
How are the hepatic lobules generally separated?
By a scant CT, except for in pigs who have a significant CT in portal tracts.
47
Describe the structure of the lobules of the liver.
Roughly hexagonally-shaped and about 1-2 mm wide; have a central vein at the center and portal triads at the periphery.
48
What are the components of the portal triads of the liver?
- Bile ducts - Hepatic arterioles - Portal venule - Lymphatic vessels - Nerves - The limiting plate.
49
What is the function of bile ducts?
Drain bile from hepatocytes.
50
What is the function of the hepatic arterioles?
Supplies oxygen-rich blood to the sinusoids.
51
What is the function of the portal venule?
Supplies nutrient-rich blood from the GIT to sinusoids.
52
What is the limiting plate?
First row of hepatocytes adjacent to the portal tract CT.
53
What is the functional unit of the liver?
Acinus.
54
Describe the acinus of the liver.
- Centered around the portal tracts (vessels extend between triads) with the central vein at the periphery. - Blood from portal tracts mixes in the adjacent sinusoids then flows in the direction of and into the central vein.
55
What are the 3 zones of the hepatic acinus?
1. Zone 1/periportal (centroacinar) zone surrounding the portal triads. 2. Zone 2/midzone is the midlobular area. 3. Zone 3/centrilobular (periacinar) zone surrounds the central vein.
56
What cells of the liver receive the highest concentrations of oxygen, nutrients, and hormones?
Hepatocytes located near portal triads.
57
Which cells of the liver receive the least oxygen, nutrients, and hormones and are prone to hypoxia?
Those in zone 3.
58
Describe the flow of bile.
Flows in the opposite direction; from the canaliculi into the bile ductules (cholangioles), then into the bile ducts.
59
How are hepatocytes arranged?
In radiating plates (cords) separated by sinusoids and supported by reticular fibers.
60
What are sinusoids of the liver lined by?
Sinusoidal/discontinuous endothelial cells with Kupffer cells attached along the luminal surface of the endothelium.
61
What are Kupffer cells?
Sinusoidal macrophages of the liver.
62
What is the perisinusoidal space (space of Disse)?
Separates hepatocytes from the sinusoids and contains a delicate extracellular matrix and scattered hepatic stellate cells (Ito cells).
63
Where does exchange occur between hepatocytes and blood plasma?
Perisinusoidal space (space of Disse).
64
What is the primary role of Kupffer cells?
Phagocytosis and clearance of immune complexes.
65
Describe Kupffer cells.
Derived from macrophage progenitors in the yolk sac/fetal liver during early embryonic development and are long lived/self-renewing.
66
In times of need, how are Kupffer cells replenished?
By blood monocytes.
67
What are Ito cells?
Hepatic stellate cells that are located in the space of Disse and have lipid droplets for storage of vitamin A and other fat-soluble vitamins.
68
What are the functions of the Ito cells?
- Maintain and remodel the delicate sinusoidal extracellular matrix. - Following liver injury, they contribute strongly to hepatic fibrosis.
69
How do Ito cells contribute to fibrosis?
Able to alter their morphology into a myofibroblast conformation and secrete ECM components such as collagen, proteoglycans, and laminin.
70
Describe the flow of the biliary tract (biliary tree).
Hepatocytes secrete water and bile components into bile canaliculi that are present between adjacent hepatocytes in the hepatic plates. Bile flows from canaliculi to bile ductules and then into bile ducts in the portal triads. Bile ducts merge to form larger hepatic ducts that carry bile from the separate liver lobules to unite with the cystic duct and be taken to the gallbladder for storage and concentration. Gallbladder empties into the duodenum via common bile duct.
71
What is contraction of the common bile duct stimulated by?
CCK released when digesta is in the duodenum.
72
All hepatic ducts after the canaliculi are lined by what?
Simple cuboidal or columnar cells called cholangiocytes.
73
In what species is the gallbladder absent?
Some mammals (horses, rats, laminoids) and some birds.
74
What is the function of the gallbladder?
Storage and concentration of bile.
75
Epithelial cells can pump __________ and ___________ from the bile.
Water, ions.
76
Describe the mucosa of the gallbladder.
Has many surface folds when contracted and is lined by columnar epithelium; some animals have mucosal glands which can be mucous or serous.
77
Describe the lamina propria of the gallbladder.
Well-vascularized.
78
Describe the muscularis of the gallbladder.
Arranged in a circular to oblique direction.
79
How is bile emptied from the gallbladder into the duodenum?
Food in the duodenum triggers cholecystokinin (CCK) release from enteroendocrine cells which causes contraction of the gallbladder muscularis.
80
What are the functions of bile?
- Bile acids necessary for digestion of dietary fats. - Excretory route for various metabolites and drugs. - Acts as a buffer to neutralize acid pH from the stomach.

Histology and Embryology (20 decks)

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