The correct option is 2 and 3 only.
Explanation
The pancreas is a composite gland that functions as both an exocrine and an endocrine organ. The endocrine portion consists of clusters of cells known as the Islets of Langerhans, which play a critical role in glucose homeostasis.
Statement 1 is Incorrect:
In a normal human pancreas, there are approximately 1 to 2 million Islets of Langerhans, not 10 to 20 million. The figure provided in the statement is significantly exaggerated.
Statement 2 is Correct:
Despite the large number of islets (1 to 2 million), they constitute only about 1 to 2 % of the total pancreatic tissue. The vast majority of the pancreas is composed of exocrine tissue (acini) which secretes digestive enzymes.
Statement 3 is Correct:
The Islets of Langerhans primarily contain two types of cells:
- $\alpha$-cells (Alpha cells): These secrete glucagon, a peptide hormone that increases blood glucose levels (hyperglycemic).
- $\beta$-cells (Beta cells): These secrete insulin, a peptide hormone that decreases blood glucose levels (hypoglycemic).
Key Takeaway:
The endocrine pancreas makes up a very small fraction (1-2%) of the organ but contains 1-2 million Islets of Langerhans. $\alpha$-cells secrete glucagon, while $\beta$-cells secrete insulin.