Pancreas and Blood Glucose
கணையமும் இரத்த குளுக்கோஸும்
Glucagon raises blood sugar (hyperglycaemic); insulin lowers it (hypoglycaemic). Mixing up these two words in an option is the most common way students lose this question.
The idea
The pancreas is a composite gland which acts as both an exocrine and an endocrine gland. The endocrine pancreas consists of the 'Islets of Langerhans'; there are about 1 to 2 million islets in a normal human pancreas, representing only 1 to 2 per cent of the pancreatic tissue. The two main types of cells in the islets are the α-cells and β-cells; the α-cells secrete a hormone called glucagon, while the β-cells secrete insulin. 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 increased blood sugar (hyperglycaemia); in addition it stimulates the process of gluconeogenesis, which also contributes to hyperglycaemia. Glucagon reduces cellular glucose uptake and utilisation, so it is a hyperglycaemic hormone. Insulin is a peptide hormone which 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; as a result there is a rapid movement of glucose from blood to hepatocytes and adipocytes, resulting in decreased blood glucose levels (hypoglycaemia). Insulin also stimulates the conversion of glucose to glycogen (glycogenesis) in the target cells. The glucose homeostasis in blood is thus maintained jointly by the two hormones — insulin and glucagon. Prolonged hyperglycaemia 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.
Why it matters
Brain cells need a steady glucose supply, but eating is intermittent; two opposing hormones keep blood glucose within a narrow range between meals and after meals.
NEET lens
Key: islets = 1-2 million, 1-2% of pancreatic tissue; α-cells → glucagon (hyperglycaemic: glycogenolysis, gluconeogenesis, ↓ cellular glucose uptake; acts mainly on liver); β-cells → insulin (hypoglycaemic: ↑ glucose uptake by hepatocytes and adipocytes, glycogenesis). Diabetes mellitus: glucose in urine (glycosuria), ketone bodies (ketonuria). Insulin and glucagon are antagonistic; both are peptide hormones.
Clinical significance
India has one of the world's largest populations with diabetes mellitus. Type 1 diabetes needs lifelong insulin; type 2 is linked to lifestyle and is often managed first with diet, exercise and tablets.
Introduction
The pancreas is both exocrine and endocrine. Its endocrine part, the Islets of Langerhans, controls blood glucose with two opposing hormones.
Core concept
Islets of Langerhans: 1-2 million per pancreas, 1-2% of pancreatic tissue. α-cells → glucagon (peptide): acts mainly on hepatocytes; stimulates glycogenolysis and gluconeogenesis; ↓ cellular glucose uptake and utilisation → hyperglycaemic. β-cells → insulin (peptide): acts mainly on hepatocytes and adipocytes; ↑ cellular glucose uptake and utilisation → hypoglycaemic; stimulates glycogenesis. Glucose homeostasis = insulin + glucagon. Prolonged hyperglycaemia → diabetes mellitus: glucose lost in urine, harmful ketone bodies formed; treated with insulin therapy.
Go deeper
Insulin does not act on pancreatic α-cells to cause glycogenesis — it acts mainly on liver and fat cells; glucagon is associated with hyperglycaemia, not hypoglycaemia.
From Class 10
Class 10 told you insulin controls blood sugar and its lack causes diabetes. NEET adds glucagon, the cell types and target organs.