Lecture 33: Digestive Glands And Liver Pancreas Flashcards Preview

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Flashcards in Lecture 33: Digestive Glands And Liver Pancreas Deck (14)
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Pancreas: Generalizations

* 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.


Main Pancreas Ducts

* 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


Acinus Structure

* 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.


Exocrine Secretions

* 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


Islets of Langerhans

* 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


Functions of Liver

* 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


Organization of Liver

* 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).


Hepatic Lobules

* 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



* 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


Hepatic Sinusoids

* 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


Bile Canaliculus

* 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


Structure of the gall bladder

* 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


3 Major Liver Ducts

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


Vascular Liver Supply

* 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