The pancreas is a soft, elongated gland located in the abdominal cavity behind the stomach. The pancreas is a mixed (composite) gland, as it performs two major functions. Its exocrine part secretes digestive enzymes that help in the breakdown of food, while its endocrine part (Islets of Langerhans) secretes hormones like insulin and glucagon, which regulate blood glucose levels.
Characteristics of the Pancreas
- The pancreas is a composite gland that acts as both an exocrine and an endocrine gland.
- It is about 6 inches long and is an important part of both the digestive and endocrine systems.
- The endocrine pancreas consists of ‘Islets of Langerhans’.
- There are about 1 to 2 million Islets of Langerhans in a normal human pancreas, representing only 1 to 2 per cent of the pancreatic tissue.
- The two main types of cells in the Islet of Langerhans are called α-cells and β-cells.
- The α-cells secrete a hormone called glucagon, while the β-cells secrete insulin.
Structure of the Pancreas
The pancreas is located in the abdominal cavity, behind the stomach. It is a soft, elongated gland divided into three parts:
- Head (broad part)
- Body (middle part)
- Tail (narrow end)
Structurally, the pancreas contains two types of tissues:
- Exocrine part (acini)
- Endocrine part (Islets of Langerhans)
Hormones of the Pancreas
Glucagon
- Glucagon is a peptide hormone and plays an important role in maintaining normal blood glucose levels.
- Glucagon acts mainly on the liver cells (hepatocytes) and stimulates glycogenolysis, resulting in an increased blood sugar (hyperglycemia).
- It also stimulates the process of gluconeogenesis, which also contributes to hyperglycemia.
- Glucagon reduces the cellular glucose uptake and utilisation. Thus, glucagon is a hyperglycemic hormone.
Insulin
- Insulin is a peptide hormone that plays a major role in the regulation of glucose homeostasis.
- Insulin acts mainly on hepatocytes and adipocytes (cells of adipose tissue), and enhances cellular glucose uptake and utilisation.
- Normal insulin action lowers blood glucose to normal, not necessarily hypoglycemia.
- It also stimulates the conversion of glucose to glycogen (glycogenesis) in the target cells.
Functions of the Pancreas
Exocrine Function
- The pancreas contains exocrine glands that produce digestive enzymes.
- Trypsin and chymotrypsin are enzymes that digest proteins; amylase is an enzyme that digests carbohydrates, and lipase is an enzyme that breaks down fats.
- Pancreatic juice is released into the duodenum, mainly regulated by hormones like secretin and CCK.
- The pancreatic duct joins the common bile duct to form the ampulla of Vater, which is located in the duodenum, the first portion of the small intestine.
- The common bile duct carries bile produced by the liver and stored in the gallbladder. The pancreatic juices and bile released into the duodenum aid in the digestion of fats, carbohydrates, and proteins.
Endocrine Function
- The pancreatic endocrine component consists of islet cells (islets of Langerhans) that produce and release significant hormones directly into the bloodstream.
- Insulin (which lowers blood sugar) and glucagon (which raises blood sugar) are two of the most essential pancreatic hormones.
- Maintaining proper blood sugar levels is critical for the proper functioning of critical organs such as the brain, liver, and kidneys.
Disorders of the Pancreas
The glucose homeostasis in blood is thus maintained jointly by the two – insulin and glucagon. Prolonged hyperglycemia leads to a complex disorder called diabetes mellitus, which is associated with loss of glucose through urine and formation of harmful compounds known as ketone bodies. Diabetic patients are successfully treated with insulin therapy.
- Diabetes Mellitus: It is caused by insufficient insulin secretion and leads to high blood sugar (hyperglycemia). Glucose may appear in urine.
- Hypoglycemia: It is caused by excess insulin and results in low blood sugar levels.
- Pancreatitis: Inflammation of the pancreas, which occurs when digestive enzymes act within the pancreas.