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Block D - Digestion and Metabolism > Histology Lecture 4 -- Liver and Pancreas > Flashcards

Histology Lecture 4 -- Liver and Pancreas Flashcards

1
Q

Anatomic location of the liver

A

Under the diaphragm in the upper right quadrant of the abdomen

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2
Q

What is the largset gland in the body?

A

Liver

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3
Q

What is the liver covered by?

A

A dense connective tissue capsule (Glisson’s capsule) lined by peritoneum

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4
Q

Lobes of the liver

A
  • Large right lobe
  • Smaller left lobe
  • 2 smaller lobes in between
    • Anterior = quadrate lobe
    • Posterior = caudate lobe
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5
Q

What lies between the quadrate and caudate lobes of the liver?

A

At the center of the liver = hilum-like indentation –> portal fissure / porta hepatis

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6
Q

3 structures of the porta hepatis / portal fissure

A
  • Hepatic artery
  • Portal vein
  • Bile duct
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7
Q

Define portal spaces

A

Spaces corresponding to the sites where branches of the hepatic artery, (hepatic) portal vein and bile duct are found, surrounded by connective tissue

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8
Q

How does the liver differ from other glands?

A

Connective tissue elements are sparse; most of the liver is made up of rather uniform parenchymal cells (hepatocytes)

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9
Q

What kind of gland is the liver?

A

Exocrine and endocrine

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10
Q

What functional cell of the liver performs its glandular functions?

A

Hepatocyte

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11
Q

4 exocrine secretion products of the liver

A
  • Bile
  • Bilirubin
  • (Also, phospholipids and cholesterol)
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12
Q

Contents of bile

A

Bile salts and conjugated bilirubin

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13
Q

Where are the endocrine products of the liver released into?

A

Blood

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14
Q

5 endocrine products of the liver

A
  • Albumin
  • Prothrombin
  • Fibrinogen
  • Lipoproteins
  • Transferrin
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15
Q

7 functions of the liver

A
  • Endocrine secretion
  • Exocrine secretion
  • Storage of carbohydrates as glycogen and triglycerides
  • Metabolic functions
  • Detoxification and conversion/ inactivation (i.e. of drugs)
  • Blood reservoir
  • Fetus = hemopoietic organ
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16
Q

2 metabolic functions of the liver

A
  • Gluconeogenesis
  • Transformation of ammonia into urea
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17
Q

3 structure forming the prominent features of liver histology

A
  • Portal spaces
  • Cords of liver cells and sinusoids
  • Central veins
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18
Q

Location of the portal spaces

A

At some corners of the hepatic lobule

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19
Q

How can hepatic (liver) lobules be distinguished?

A

By joining the portal spaces together

NOTE: In human liver, spaces are not actually joined together, but in pig liver, connective tissue of portal spaces delineate the outer perimater of the anatomical liver lobules (arrows)

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20
Q

5 contents of portal spaces

A
  • Lymphatic vessels
  • Nerves
  • Branches of the hepatic artery (usually seen as a small muscular artery/arteriole)
  • Branch of the portal vein (usually a small vein/venule)
  • Branch of the bile duct (interlobular bile duct)
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21
Q

Appearance of interlobular bile ducts

A

Regular ducts lined by a columnar or cuboidal epithelium

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22
Q

Describe the positions of cords (plates) of liver cells and sinusoids

A

From the perphery of the lobule, they radiate toward the middle of the lobule, where they converge on the central vein. Cords alternate with sinusoids.

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23
Q

Describe the blood supply of sinusoids

A
  • Branches of the hepatic artery deliver arterial blood into the sinusoid
  • Branches of the hepatic portal vein send venous blood rich in nutrients from the intestine into the same sinusoids
  • Both types of blood mix in the sinusoid
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24
Q

Describe the blood flow from the sinusoids

A
  • As blood flows towards the central vein, it gives up oxygen and nutrients to the liver cells and picks up metabolized and synthesized products made by liver cells (endocrine)
  • Blood empties into the central vein of the lobule
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25
Q

What forms hepatic veins and where do they go?

A
  • Central veins converge –> hepatic veins
  • Do not run in the portal spaces
  • Join to leave the posterior aspect of the liver and enter the IVC
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26
Q

Describe the general morphology of liver cells

A
  • Polyhedral shape
  • 2 distinct surfaces
    • Those facing other liver cells to make up the cord (or wall of cells)
    • Those facing toward the sinusoids (usually the cord is 1 cell thick, so there are 2 sinusoid-facing sides)
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27
Q

Describe the histology of the sinusoid-facing sides of liver cells

A
  • Microvilli
  • Face an extracellular space (perisinusoidal space; space of Disse)
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28
Q

Describe the histology of the hepatocyte-facing side of liver cells

A
  • Hemispherical depressions on surface –> Match similar depressions on the adjacent liver cell
  • Two halves form a “bile canaliculus” between liver cells
  • Golgi region faces this –> bile secretion into small intercellular duct
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29
Q

Describe the direction of bile flow

A

Toward the portal space (opposite to the direction that blood flows in the sinusoids)

30
Q

Where do the bile canaliculi drain into?

A

Form a chicken wire network –> drain into cholangioles (canals of Hering)

31
Q

Describe the histology of cholangioles

A
  • At first lined in part by hepatocytes and by low cuboidal cells
  • Then become entirely lined by low cuboidal cells
32
Q

Where do the cholangioles empty into?

A

Interlobular ducts in the portal space

33
Q

What is the portal lobule centered on?

A

Portal space

34
Q

What is the anatomical liver lobule centered on?

A

Central vein

35
Q

Define the hepatic acinus

A
  • Tissue supplied by a terminal branch of the portal vein and hepatic artery and drained by a terminal branch of the bile duct
  • No anatomical landmark limit
36
Q

What does each acinus comprise?

A

Parenchyme from two adjacent lobules

37
Q

Describe the 3 regions of the acinus of the liver

A

3 poorly defined concentric regions of hepatic tissue:

  • Zone 1 = richest oxygen supply
  • Zone 3 = poorest
38
Q

Describe the histology of sinusoids

A
  • Lined by fenestrated endothelial cells
  • Large macrophages (Kupffer cells)
  • Some reticular fibers under the endothelium
  • Fat-storing Ito cell associated to sinusoid, but located in the space of Disse (which communicates directly to the pores of the sinusoidal endothelium)
39
Q

Describe the histology of the central vein

A
  • No more than endothelium
  • A little connective tissue lining the ends of the liver cords as they come towards the lobule centre
  • Vein receives numeroud openings of the sinusoids
40
Q

Describe the histology of the wall of the gall bladde

A
  • Mucosa = simple columnar epithelium with a few microvilli and a lamina propria
  • Tunica muscularis of non-oriented smooth muscle
  • Thick connective tissue coat covered by a serosa
  • NOTE: No muscularis mucosa at the borderline of the mucosa and submucosa
41
Q

Describe the anatomic location of the pancreas

A
  • Large encapsulated gland located retroperitoneally at the level of L1 - L3
  • Enclosed on the right by the duodenal loop
  • Head against the 2nd part of the duodenum
  • Body and tail extending to the spleen on the left side
42
Q

What kind of gland is the pancreas?

A

Mixed gland:

  • Large compound acinar exocrine portion
  • Small spheres of endocrine portion scattered among the exocrine portions appearing as circular islands = Islets of Langerhans
  • Exclusively serous
43
Q

Describe the histology of serous pancreatic acini

A
  • Pyramidal cells with round basal nuclei
  • Basophilic cytoplasm at the base
  • Eosinophilic zymogen granules
  • Small lumen
  • Duct cells enter the luminal space and line part of the lumen with thin flattened cells (centroacinar cells)
44
Q

Describe the nuclei of the centroacinar cells

A

Prominent and appear in the center of the acinus of the pancreas

45
Q

How must one identify the pancreas to differentiate it histologically from the parotid gland?

A

Confirming the nuclei of centroacinar cells lining the lumen since their nuclei are characteristic of the pancreas

46
Q

Type of duct that arises from the centroacinar cells of the pancreas

A

Intercalated ducts

47
Q

Describe the histology of the duct system of the pancreas

A
  • Beginning = centroacinar cells
  • Intercalated ducts lined by cells similar to centroacinar cells –> join with intralobular collecting ducts, but are not striated
  • Rest of duct system is as describe the salivary glands (see that lecture)
48
Q

What stimulate the hormones produce by enteroendocrine cells in the duodenal mucosa?

A
  • Food in the gastric antrum
  • Passage of the acidic stomach chyme into the duodenum
49
Q

2 hormones produced by enteroendocrine cells in the duodenal mucosa in response to a meal

A
  • Secretin
  • Cholecystokinin
50
Q

Define secretin and its role in the pancreas

A
  • 27 amino acid polypeptide
  • Stimulates the centroacinar duct cells to secrete a bicarbonate-rich fluid that forms part of the exocrine secretion and neutralizes the chyme
51
Q

Define cholecystokinin and its role in the pancreas/duodenum

A
  • 33 amino acid polypeptide
  • Cause secretion of the enzymes by the acinar cells
  • Stimulates contraction of the smooth muscle in the gall bladder
52
Q

Contents of pancreatic juice

A
  • Bicarbonate fluid of the ducts
  • Many enzymes that were present in the inactive zymogen form in the zymogen granules
    • Pancreatic lipase
    • Pancreatic amylase
    • Trypsin
    • Chymotrypsin
    • Carboxypeptidase
    • Ribonuclease
    • Deoxyribonuclease
  • Trypsin inhibitor
53
Q

Purpose of pancreatic lipase

A

Hydrolysis of glycerol and fatty acids

54
Q

Purpose of pancreatic amylase

A

For starch and glycogen breakdown

55
Q

Purpose of trypsin inhibitor

A

Prevent premature activation of trypsin (otherwise it would digest the digestive system)

56
Q

During stimulation of acinar secretion in the pancreas, what happens to the granules?

A

Granules serially fuse and are exocytosed together

57
Q

Describe the histology of the islets of Langerhans

A
  • Scattered between the acini of the exocrine pancreas
  • Paler-stained circular bodies of various sizes
  • Not dileneated by noticeable amounts of connective tissue
  • Reticular fibers are present
  • Made of pale stained cords of cells that contain spherical nucleu
  • Network of fenestrated capillaries between the cords
58
Q

Purpose of fenestrated capillaries between the cords in the islets of langerhans

A

Receive the endocrine secretions of the cord cells

59
Q

Describe the 5 cell types present in the cords of the endocrine pancreas

A
  • Cannot be distinguished without immunocytochemical staining
  • A (alpha) cells = 20% of islet, located at periphery
  • B (beta) = 70% of islet, central
  • D (delta) = 5% of islet, variable position
  • G cells = 1%
  • PP (or F) cells = 1%
60
Q

What do A (alpha) cells secrete in the pancreas?

A

Glucagon

61
Q

What do B (beta) cels secrete in the pancreas?

A

Insulin

62
Q

What do D (delta) cells secrete in the pancreas?

A

Somatostatin

63
Q

What do G cells produce?

A

Gastrin

64
Q

What do PP (or F) cells produce?

A

Pancreatic polypeptide (unknown function)

65
Q

Describe the nuclei of the flattened epithelial cells lining the branches of the small intralobular duct leading to the pancreatic acini

A

Fusiform

66
Q

Describe the histologic appearance of pancreatic B cells

A
  • Abundant
  • Pale, vaguely granulated cytoplasm
67
Q

Describe the histologic apperance of pancreatic A cells

A
  • Less abundant than B cells
  • Cytoplasm contains fine acidophilic granules
68
Q

Describe the inactivation/elimination functions of the liver

A
  • Glucuronyl transferase conjugates glucuronic acid to bilirubin AND other drugs
  • Endocytosis of hormones and cholesterol (LDL particles)
69
Q

4 kinds of drugs that glucuronyl transferase can conjugate glucuronic acid into

A
  • Barbiturates
  • Antihistaminics
  • Anticonvulsants
  • Insecticides
70
Q

Give an example of substance conversion in the liver

A

Tetra-iodothyronine (T4; thyroxine) –> Tri-iodothyronine (T3)

71
Q

The central vein of the liver lobule drains into what?

A

Sub-lobular vein

72
Q

The sub-lobular vein drains into what?

A

Hepatic vein

Block D - Digestion and Metabolism (29 decks)

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