V. Microanatomy of the Accessory Glands for the GI System Flashcards
List three organs with accessory glands, and are they endocrine or exocrine glands.
Liver, Pancrease, and Gall Bladder All are exocrine glands Liver and pancrease also have endocrine functions
Liver: Glandular Structure
- 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.
The parenchyma of the liver is composed of what?
Lobules of organized hepatocytes
Structural definition of a liver lobule
Hepatic Lobule
Distinction of hepatic lobules based on connective tissue
- 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
What species have distinct hepatic lobules?
In most species, hepatic lobules are not distinct. An exception is porcine liver that has well developed interlobular connective tissue septa.
What is the largest gland in the body?
Liver, at 2-5% of the body weight of an animal
What kind of gland is the liver?
Compound tubular gland with both exocrine (bile) and endocrine functions.
Where does the liver sit within the abdominal cavity?
Situated between the GI tract and the caudal vena cava
Liver blood supply, where does it enter the liver
Dual blood supply: 1. Portal vein 2. Hepatic artery Enters liver parenchyma with connective tissue at a hilus on the visceral surface, the porta.
Portal vein is enriched with_______. Hepatic artery is enriched with _____.
- Portal vein is enriched with nutrients from small intestine. 2. Hepatic artery is enriched with oxygen.
Arterial blood supply
Hepatic artery –> interlobular arterioles of the portal area –> capillaries –> sinosoids
Which hepatocytes receive the most oxygen enriched blood, and which receive the least oxygen enriched blood.
- 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.
Venous blood supply
Portal vein –> interlobar veins –> interlobular portal veins –> distributing venules –> sinusoids (discontinuous capillaries, lined by porous endomthelium)
Which hepatocytes receive the most nutrient enriched blood and which receive the least.
Hepatocytes closest to portal areas receive the most nutrient enriched blood compared to hepatocytes around the central vein.
Venous drainage
- Sinosoids –> 2. Central vein –> 3. Sublobular, or intercalated veins –> 4. Collective veins –> 5. Hepatic vein –> 6. Caudal vena cava
Can there be cross sections of the hepatic vein within the portal areas?
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.
Functional or metabolic definition of the liver lobule
Liver Acinus
Liver acinus
- Centered around nutrient supply (distributing veins) 2. Diamond shaped 3. Central veins at two points, portal area at 2 points
Liver Functions
- 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
All functions of the liver are carried out by what two cell types?
Hepatocytes and macrophages
Characteristics of a hepatocyte
- 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.
Define sinusoids
Sinusoids are discontinuous capillaries lined by endothelium.
Define bile canaliculi
Canaliculi are invaginations of hepatocyte plasma membrane. They DO NOT have an epithelial lining.
Flow of Bile
Bile canaliculi → Bile Ductule → Bile Ducts of Portal area (arrows) → Hepatic Duct → Gall Bladder
Functional, exocrine definition of a liver lobule
Portal Lobule
Portal Lobule
- Functional, exocrine definition and centered around bile ductule
- Traingular in shape
- Central veins at three corners
- Bile from three hepatic lobules drains into bild duct of one protal area
Three definitions of a liver lobule
- Hepatic lobule
- Liver acinus
- Portal lobule
Endothelial cells in the liver
Form sinuosoid wall, no basal lamina, rests on microvilli of hepatocyte
Macrophages in Liver
Kupffer cells, stellate macrophages:
In sinuosid wall, monocytic
Spaces of Disse
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
Functions of Gallbladder
- Stores bile made by the liver
- Concentrates the bile
- Releases bile when stimulated by cholecystokinin
Which domestic species does not contain a gall bladder?
Equine
Gallbladder: Structure
- Tunica mucosa: many plicae or folds, simple columnar epithelium, striated (microvilli), tight junctions between cells
- Lamina propria-submucosa (NO lamina muscularis): loose connective tissue, highly vascular, lymphatic tissue, simple tubuloalveolar gland in some species (ruminants)
- Tunica muscularis: smooth muscle, thin and mostly circular
- Tunica adventitia from side facing liver, Tunica serosa from side facing peritoneal cavity
Pancreas
- Lobulated gland with thin connective tissue capsule that forms septa to separate lobules
- Endocrine gland produces hormones (insulin, glucagon, somatostatin)
- Exocrine gland produces digestive enzymes (amylase, proteases, lipases, nucleases)
Another name of pancreatic islets, and definition
Islets of langerhans: regions of the pancreas that contain endocrine cells
Exocrine Pancrease
- Compound tubuloacinar gland
- Ruminants tend to have mostly tubular units
- Acinar cells are serous (zymogen cells)
- Between the acinar cells are secretory canaliculi
- Centroacinar cells line the acinar lumen
- No myoepithelial cells around acinar units
Pancreatic Duct System
- Lumen of acinus (small duct bounded by centraoacinar cells) –>
- Intercalated ducts (lining cells, low cuboidal)
- Intralobular ducts
- Interlobular ducts (low cuboidal eptiehlium WITH goblet cells)
- Pancreatic duct and accessory pancreatic duct
Centroacinar cell
Intercalated duct of pancreas
Key features in distinguishing the salivary glands from pancreas
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
