Topic: Endocrine system
Question: Why pancreas is called a dual gland? What is the mechanism of hyperphagia in insulin deficiency?
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The pancreas is called a dual gland because it has two distinct functions:
1. Exocrine function: Produces pancreatic digestive enzymes (amylase, lipase, proteases) that are secreted into the duodenum to help digest nutrients. This constitutes about 98% of the pancreatic tissue.
2. Endocrine function: Produces hormones (insulin, glucagon, somatostatin) that are secreted into the bloodstream to regulate blood glucose levels and other functions. This makes up only about 2% of pancreatic tissue.
Despite the small amount of endocrine tissue, pancreatic hormones play an essential role in metabolism and maintaining homeostasis. Hence, the pancreas has a dual exocrine and endocrine function.
Mechanism of hyperphagia in insulin deficiency:
1. Low insulin levels lead to decreased glucose uptake and utilization by cells. This causes the body to perceive a state of starvation even after eating.
2. The satiety center in the brain, located in the ventromedial hypothalamus, is sensitive to glucose levels. Low glucose signals to the brain that more food is needed, increasing appetite and hunger. This drives excess eating (hyperphagia).
3. Insulin also has central effects in the brain, and low insulin levels may directly stimulate the feeding and reward centers, increasing the drive to eat.
4. Fat breakdown is increased due to low insulin, releasing fatty acids that can accumulate in the liver and blood. This further stimulates appetite and feeding behavior.
5. Other hormones like ghrelin, leptin and neuropeptide Y levels become imbalanced, promoting appetite stimulation and decreasing satiety.
6. Gastrointestinal function and nutrient absorption are impaired without insulin, triggering increased appetite to compensate. However, more eating further worsens hyperglycemia since glucose cannot be utilized properly.
In summary, insulin deficiency leads to a perceived state of starvation, imbalances of hormones and neurotransmitters that regulate feeding behavior, impaired nutrient absorption and changes in metabolic pathways that stimulate appetite – all of which drive excessive hunger, eating and hyperphagia. Controlling insulin levels either through medication, diet or weight loss is necessary to break this cycle and regulate appetite and food intake.
