Microanatomy of the pancreas

Question 1

Overview of pancreas

Answer 1

• Composed of both endocrine cells (secrete products basolaterally) and exocrine cells (products secreted apically)
• The endocrine cells are clustered together in islets of langerhans, which are small light-staining patches within the sea of exocrine cells
• Each islet is provided w/ a large number of fenestrated capillaries

Question 2

Principal cell types of islets

Answer 2

• Alpha cells: 15-20% of the islet cells are A-cells, they are located on the periphery of the islets and they secrete glucagon
• Beta cells: 70% of the islet cells are B-cells, they are located centrally and secrete insulin
• Delta cells: 5-10% of the islet cells are D-cells, they are located on the periphery and secrete somatostatin (inhibits both glucagon and insulin release)
• Since A and D cells are on the periphery they are exposed to blood first
• Thus, A and D cells will release glucagon/somatostatin (if conditions indicate the release) before B cells release insulin

Question 3

Regulation of islet cell activity

Answer 3

• Blood glc levels >70 stimulate B cells to secrete insulin, glc levels <70 stimulate A cells to secrete glucagon
• GLP1 stimulates insulin, it is released from GI mucosa
• Glucagon stimulates insulin release ?
• Autonomic innervation + gap junctions cause release of the hormones: SNS stimulates glucagon release, PsNS stimulates both insulin and glucagon release

Question 4

Signaling satiation

Answer 4

• Multiple sites of the GI tract release peptides in response to food and contribute to satiation (mostly from intestines- GLP1)
• Gastric distension is the main contributor to satiation arising from the stomach
• The secretions of satiating peptides seems to be in part due to taste receptors that reside in the GI mucosa lining
• Also there is intracellular metabolism of glc that contributes to release of satiating peptides from the GI tract