Pancreas Flashcards
Describe the functional anatomy of the exocrine pancreas.
- Groups of acini
- Simple cuboidal epithelium surrounding an excretory duct
- Several excretory ducts combine with increasing dimension to terminate as pancreatic duct
Describe the principle function of the exocrine pancreas.
- Digestion
- Pancreatic juice: HCO3- to neutralise stomach acid (optimum pH for enzymes) and enzymes to digest food material
What enzymes does the pancreas secrete?
Proteases, amylase and lipases
How is bicarbonate released into the lumen of the small intestine?
- Bicarbonate is generated within ductal cells.
- Bicarbonate is transported into the ductal lumen via a chloride-bicarbonate exchanger on the apical membrane of the ductal cells.
- Sodium ions (Na⁺) and water follow bicarbonate into the ducts via passive transport and osmosis, forming a bicarbonate-rich fluid.
- The bicarbonate-rich pancreatic fluid is delivered to the duodenum through the pancreatic duct.
How is trypsinogen activated in the duodenum?
- Duodenal epithelial surface contains enteropeptidase
Trypsinogen –> Trypsin - Trypsin auto-catalyses itself as well as activating other proteases
- As a precaution pancreatic cells produce “trypsin inhibitor” to prevent auto-digestion
What mediates the cephalic/gastric phase of digestion?
Vagus/gastrin
What mediates the intestinal digestion phase (pancreatic juice secretion)?
Secretin/CCK
Describe secretin release.
- Released from duodenum in response to H+.
- Increases bicarbonate secretion.
- Negative feedback stimulus.
Describe CCK release.
- Released from duodenum in response to fat / protein metabolites.
- Increases enzyme secretion
- Also causes gall bladder to contract.
- Positive feedback mechanism
What is the function of the endocrine pancreas?
Regulation of metabolism
Describe the functional anatomy of the endocrine pancreas.
- Clusters of cells scattered throughout the pancreatic tissue = islets of Langerhans
- 3 major types of cell: beta, alpha and delta
What do the cells in the pancreatic tissue secrete and where does it go?
Insulin - beta
Glucagon - alpha
Somatostatin - delta
Secreted in blood stream and passes to liver via hepatic portal vein prior to circulating to other tissues.
Describe insulin regulation.
- Stimulated by increase in plasma glucose/amino acids.
- Bi-phasic secretion: initial immediate secretion of stored insulin, followed by more prolonged secretion of newly synthesised insulin.
- Also stimulated by GI hormones released when food enters duodenum.
- Parasympathetic activity via vagus increases insulin secretion
Describe insulin action.
- Binds to receptors on target cells.
- Stimulates cell uptake of nutrients during absorptive phase.
- Most important anabolic mediator.
- Glucose uptake enhanced by mobilisation of glucose transporter (GLUT4) to cell membrane.
- Nearly all tissues (especially skeletal muscle / adipose tissue).
- Also increases triglyceride, glycogen and protein synthesis.
Define glucosuria.
Glucose in urine as capacity for kidneys to re-absorb glucose exceeded.
