The correct option is Islets of Langerhans.
Explanation
The pancreas is a composite (heterocrine) gland, meaning it functions as both an exocrine and an endocrine organ. Its tissue is differentiated based on these two distinct functions.
- Islets of Langerhans: These are the cell clusters that constitute the endocrine portion of the pancreas. There are approximately 1 to 2 million Islets of Langerhans in a normal human pancreas, representing only 1% to 2% of the pancreatic tissue. They contain different types of cells, primarily α-cells (secreting glucagon) and β-cells (secreting insulin), which regulate blood glucose levels.
- Acini: These form the exocrine portion of the pancreas. They secrete pancreatic juice containing digestive enzymes into the pancreatic ducts.
- Ducts: These are tubular structures that transport the exocrine secretions (enzymes) to the duodenum.
- Lobules: The pancreas is structurally divided into lobules, which contain the secretory units (acini), but the term itself refers to the macroscopic structural division rather than the specific endocrine cell clusters.
Key Takeaway: The Islets of Langerhans are the specific endocrine units of the pancreas responsible for hormone secretion, whereas the acini are the exocrine units responsible for enzyme secretion.