Lecture 33: Digestive Glands And Liver Pancreas

Question 1

Pancreas: Generalizations

Answer 1

• Lobulated, compound, tubulo-alveolar gland with both an exocrine and an endocrine secretory function. (Refer to Figure 17-6)
• Connective tissue support:
• No organized capsule
• Thin layer of loose CT from which septa pass internally dividing the gland into many small lobules
• The delicate CT contains blood vessels, lymphatics, nerves, and excretory ducts.

Question 2

Main Pancreas Ducts

Answer 2

• Duct of Wirsungis the main excretory duct.
• Duct of Santorini is the smaller accessory duct.
• Interlobular ducts:
• Lined with simple columnar epithelium and goblet cells.
• Intercalated ducts:
• Lined with low cuboidal cells:
• Cells with receptors for secretin
• Cells secrete water and bicarbonate ion
• See Slide 6-7

Question 3

Acinus Structure

Answer 3

• Acini are serous.
• Acinar cells are pyramidal serous cells:
• Basal zone is basophilic and contains nucleus and RER
• Apical zone with zymogen granules
• • Precursors of the enzymes in pancreatic juice
• • Trypsin, chymotrypsin, amylase, and lipase.
• • Specific receptors for cholecystokinin
• Centroacinar cells:
• Form a truncated cuboidal epithelium within the lumen of acini
• Continuous with the epithelium of the intercalated duct.
• Unique to pancreas
• No striated ducts
• No myoepithelial cells
• Release of digestive enzymes from serous acinar cells is stimulated by CCK.
• Bicarbonate-rich, alkaline fluid is released by ductal epithelial cells in response to secretin.

Question 4

Exocrine Secretions

Answer 4

• Digestive enzymes:
• Concentrated and stored in vesicles by Golgi:
• • Referred to as zymogen granules.
• • Refer to Figures 17-6 and 17-7.
• Synthesis and secretion is controlled by peptides secreted by duodenal enteroendocrine cells
• Synthesized as inactive proenzymes on RER of acinar cells.
• Bicarbonate ions:
• Secretion is regulated by secretin:
• • Secreted by duodenal enteroendocrine cells when stimulated by food entering small intestine
• Synthesis of bicarbonate ions (Refer to Figure 17-9):
• • Carbon dioxide diffuses into intercalated ducts from blood.
• • CO2+ H2O) → H2CO3(requires carbonic anhydrase)
• • H2CO3→ HCO3─+ H+
• • HCO3─ is actively transported to lumen of intercalated duct.
• • Na+and H+are exchanged with Na+ flowing into duct lumen and H+ flowing into blood.
• See Slides 10-13

Question 5

Islets of Langerhans

Answer 5

• These are endodermal-derived cell aggregations which are interspersed irregularly among the acini.
• Cell types include:
• A-cells (alpha cells):
• • Have fine cytoplasmic granules and are presumed to form glucagon.
• B-cells (beta cells):
• • Have coarse cytoplasmic granules; they are more numerous than alpha cells and produce insulin.
• D-cells (delta cells):
• • Secrete somatostatin, which helps to control levels of insulin and glucagon
• See Slides 16-18

Question 6

Functions of Liver

Answer 6

• Removal of bile pigments from the blood and secretion of these pigments into the bile.
• Storing of glycogen
• Converting fats and perhaps proteins to carbohydrates (gluconeogenesis)
• Maintaining constancy of blood glucose level
• Chief site of amino acid deamination with urea as a by-product
• Metabolizing fat and storing in liver
• Synthesizing plasma proteins such as fibrinogen, prothrombin, and albumin
• Storing of essential vitamins: A, D, B2, B3, B4, B12, and K
• Serving as an embryonic hematopoietic organ
• Ethanol metabolism
• Detoxification of drugs, steroids, vitamins A and D, fatty acids, and carcinogens

Question 7

Organization of Liver

Answer 7

• Epithelial parenchyma is composed of hepatic cells irregularly arranged as plates seen on edge as cell cords and radially arranged around the central vein.
• Space of Disse:
• Separates hepatic cells from endothelial cells
• Active in transfer between blood and parenchyma
• Space of Mall continuous with space of Disse:
• Drains into lymphatics
• Glisson’s thin capsule of FECT covers the surface except at the diaphragmatic attachment
• CT septa extend from the capsule to form lobes and lobules (hepatic lobules).

Question 8

Hepatic Lobules

Answer 8

• Classic:
• Central venule is in the center of the lobule.
• Portal triads are at the angles.
• Portal:
• Three central venules of adjacent lobules form a triangle.
• Portions of the bile canaliculi of the three lobules drain into the same bile duct.
• Liver acinus:
• Includes three zones defined by hepatic tissue receiving blood from a branch of the hepatic artery conducting blood to opposite central veins.
• Metabolic gradient extends from hepatic triad to central vein.
• See slide 22-24

Question 9

Hepatocytes

Answer 9

• Polyhedral in form
• Central nucleus with one or more nucleoli
• Cytoplasm may contain glycogen, fat droplets, and pigment granules.
• Basolateral domain:
• Microvilli
• Faces space of Disse
• Involved in:
• • Absorption of blood-borne substances
• • Secretion of plasma proteins
• Apical domain:
• Borders bile canaliculus

Question 10

Hepatic Sinusoids

Answer 10

• Lining:
• Fenestrated endothelial cells
• Discontinuous basal lamina
• Perisinusoidal cells:
• Located in space of Disse
• Store vitamin A
• Produce collagen fibers and extracellular matrix components
• During cirrhosis:
• • Transform into myofibroblasts
• • Become the main collagen type I producing cells
• • Stimulated by cytokines from hepatocytes, Kupffer cells and lymphocytes.
• Subendothelial space of Disse:
• Space between basal lamina and hepatocytes
• Contains microvilli of basolateral domain of hepatocytes
• Contains types I, III, IV collagens
• Contains interstitial fluid that drains into the space of Mall that drains into lymphatics
• Kupffer cells:
• Phagocytic cell
• Derived from monocytes
• Lines hepatic sinusoids
• See Slide 27

Question 11

Bile Canaliculus

Answer 11

• Extracellular canal located between two rows of hepatocytes
• Receives bile from hepatocytes
• Canal of Hering (cholangiole):
• Receives bile from canaliculus
• Carries bile to bile ductule
• See Slide 30-32

Question 12

Structure of the gall bladder

Answer 12

• Fundus
• Body
• Neck
• Mucosal folds form the spiral valve of Heister.
• Wall:
• Mucosa:
• • Epithelium is tall columnar with a striated border.
• • Lamina propriaof CT has extensive vascular plexuses and may contain a few smooth muscle cells.
• • Rokitansky-Aschoff sinuses are small diverticula of the mucosa which extend into the muscular and perimuscular layers and may indicate pathological change.
• Muscularisexterna:
• • Layers of smooth muscle separated by layers of CT
• Serosa:
• • Has a broad perimuscular CT coat, rich in blood and lymphatic vessels and elastic fibers.
• See Slide 35

Question 13

3 Major Liver Ducts

Answer 13

• Major ducts:
• Cystic duct
• Hepatic duct
• Common bile duct
• Mucosa:
• Ducts are lined with columnar epithelium with goblet cells.
• Muscularis externa:
• No definite pattern.

Question 14

Vascular Liver Supply

Answer 14

• Afferent blood vessels (give off interlobular branches):
• Portal vein
• Hepatic artery
• Branches from the portal vein enter the lobule and empty into the hepatic sinusoids
• Converge toward the center to empty into the:
• Central vein, an efferent vessel.
• Central veins unite to form a sublobular vein –tributary of the hepatic vein.
• Hepatic artery follows the branching of the portal vein through the interlobular CT; interlobular arterioles empty into the hepatic sinusoids, which drain to the central vein.
• See Slide 39