Histology of the Accessory Organs of the GI Tract Flashcards
Functions of Digestive Glands:
- Lubrication
- Protection
- Digestion
- Absorption
3 Main Digestive Glands:
(1) Major Salivary Glands
(2) Exocrine Pancreas
(3) Liver
Digestive Gland: Major Salivary Glands
Associated with the oral cavity through independent excretory ducts
Digestive Gland: Exocrine Pancreas
Secretes its alkaline aqueous and enzymatic product into the duodenum
Digestive Gland: Liver
Endocrine and exocrine gland with extensive access to the blood circulation
Salivary Glands
- Connective tissue capsule with septa, dividing the gland into lobes and smaller lobules – provides route for neurovasculature
- Contains secretory cells and myoepithelial cells
Salivary Glands: Secretory Cells
- Organized in an acinus
- Produce salvia via ANS control
Salivary Glands: Myoepithelial Cells
Aid in release of secretions
Pathway of Saliva Flow:
(1) Acinus
(2) Intercalated Duct (low cuboidal epithelium)
(3) Striated Duct (simple cuboidal to columnar epithelium)
(4) Excretory Duct (simple cuboidal –> pseudostratified columnar or stratified cuboidal)
What is the largest salivary gland?
Parotid Gland
Parotid (Serous) Gland
- Salivary gland
- Acini consist of serous secretory cells
- Pyramidal cells with a basally located nucleus
- Prominent RER in basal region
- Secretory granules visible in apical region
Parotid Gland: Duct Lengths
Equal lengths of excretory, striated, and intercalated ducts
Sublingual Gland
- Branched tubule-alveolar gland
- Acini consists of both serous and mucous cells, but is predominantly mucous
- Lacks defined capsule but is divided by connective tissue into small lobes
- Intercalated and striated ducts are poorly developed
Sublingual Gland: Duct Lengths
Ducts vary in length; Excretory Duct is longest and Striated Duct is shortest
Submandibular Gland
- Acini consists of both serous and mucous cells, but predominantly serous cells
- Mucous cell-containing acini are capped by serous demilunes
- Intercalated ducts are shorter and striated ducts are longer than those in parotid gland
Submandibular Gland: Duct Lengths
Ducts vary in length; Excretory Duct is longest and Intercalated Duct is shortest
Pancreas
- Large gland with endocrine and exocrine functions, but bulk of gland is exocrine
- Thin layer of connective tissue forms capsule
Pancreas: Capsule
- Thin layer of loose connective tissue
- Divides gland into ill-defined lobules
- Provides pathway for neurovasculature and ducts
Pancreas: Exocrine Component
Synthesizes and secretes enzymes that are essential for digestion in the intestine
Pancreas: Endocrine Component
Synthesizes and secretes hormones (insulin and glucagon) into the blood – regulate glucose, lipid and protein metabolism
Exocrine Pancreas: Serous Acinus
- Functional unit of exocrine pancreas
- Contains Pancreatic Acinar Cells (produce digestive enzymes)
In the exocrine pancreas, the intercalated duct begins as:
Centroacinar cells within the acinus
Centroacinar Cells
- Duct cells located in the center of the pancreatic acinus
- Continuous with the low cuboidal epithelium of intercalated duct
Centroacinar Cells secrete:
HCO3-, Na+, H2O
Histological Hallmarks of Exocrine Pancreas:
- Acinar cells stain intensely
- Centroacinar cells stain lightly
- Islets are pink
Pancreatic Acinar Cell is Characterized by:
- Well-developed RER
- Prominent Golgi apparatus
- Apical domain of zymogen granules
Zymogen Granules in the Pancreatic Acinar Cell
Contain about 20 different pancreatic proenzymes including trypsinogen, chymotrypsinogen, amylolytic enzymes (alpha amylase), lipases, deoxyribonuclease, and ribonuclease
Role of Trypsinogen and Chymotrypsinogen:
Digest proteins
Role of Amylolytic Enzymes (alpha amylase):
Digest carbohydrates
Role of Lipases:
Digest lipids
Role of Deoxyribonuclease and Ribonuclease:
Digest nucleic acids
Pancreatic Acinar Cells increase synthesis of Proteases with a ___-___ diet
Protein-rich
Pancreatic Acinar Cells increases synthesis of Amylases and decrease synthesis of proteases with ____-___ diet
Carbohydrate-rich
Pancreatic endocrine cells are organized into clusters called:
Pancreatic Islets (Islets of Langerhans)