Biology · Chemical Coordination and Integration · NEET
Insulin is a peptide hormone made by the beta-cells (β-cells) of the Islets of Langerhans in the pancreas. It acts mainly on hepatocytes (liver cells) and adipocytes (fat cells), where it increases cellular glucose uptake and utilisation, so glucose moves quickly from blood into cells and blood glucose falls (hypoglycemia). Memory hook: Insulin puts glucose "in" the cells, so it is the sugar-lowering (hypoglycemic) hormone; glucagon does the opposite.
Insulin from pancreatic β-cells acts on hepatocytes, adipocytes and muscle cells: it raises glucose uptake (via GLUT-4) and drives glycogenesis, so blood glucose falls.
Your doubts, answered
Does insulin increase or decrease blood glucose?
Insulin DECREASES blood glucose. It is a hypoglycemic hormone. When blood glucose is high, β-cells release insulin, which speeds up the movement of glucose from blood into hepatocytes and adipocytes and turns extra glucose into glycogen. So blood sugar comes down. Do not confuse it with glucagon, which raises blood glucose (hyperglycemic).
Which cells does insulin act on — liver cells or pancreatic cells?
Insulin acts mainly on hepatocytes (liver cells) and adipocytes (fat cells). A common NEET trap says insulin 'acts on pancreatic cells' — this is WRONG. Insulin is MADE in the pancreas (by β-cells) but it does its job on liver and fat cells, plus muscle cells.
Which glucose transporter is insulin-dependent?
GLUT IV (GLUT4) is the insulin-dependent transporter. Insulin makes GLUT4 move to the cell membrane of muscle and fat cells so glucose can enter. GLUT I, II and III work without insulin (insulin-independent). NEET 2019 asked this directly, so remember: insulin-dependent = GLUT IV.
What is glycogenesis and how is it linked to insulin?
Glycogenesis is the conversion of glucose into glycogen (the stored form). Insulin stimulates glycogenesis in target cells, so extra blood glucose is stored, not left in the blood. Do not mix this with glycogenolysis (breaking glycogen back to glucose), which glucagon stimulates.
Do α-cells or β-cells secrete insulin?
β-cells (beta-cells) of the Islets of Langerhans secrete insulin. α-cells secrete glucagon. A frequent NEET error is 'α-cells secrete insulin' — that statement is incorrect. Remember: Beta = Blood-sugar-lowering (insulin); Alpha = raises sugar (glucagon).
⚠️ The NEET trap ✗ Insulin acts on pancreatic cells and raises blood glucose. ✓ Insulin acts on hepatocytes and adipocytes (and muscle cells) and LOWERS blood glucose (hypoglycemic). It is only MADE in the pancreas; it does not act on pancreatic cells. 🧠 Insulin is 'born' in the pancreas but 'works' in the liver and fat — and it pushes sugar IN, so sugar goes DOWN.
Real NEET questions
NEET 2016
Name a peptide hormone which acts mainly on hepatocytes, adipocytes and enhances cellular glucose uptake and utilization.
A · Insulin ✓
B · Glucagon
C · Secretin
D · Gastrin
Solution: Insulin is a peptide hormone secreted by the β-cells of the Islets of Langerhans. It acts mainly on hepatocytes and adipocytes and enhances cellular glucose uptake and utilisation, lowering blood glucose. Glucagon does the opposite (reduces uptake); secretin and gastrin are GI hormones.
NEET 2019
Which of the following glucose transporters is insulin-dependent?
A · GLUT I
B · GLUT II
C · GLUT III
D · GLUT IV ✓
Solution: Insulin enhances glucose uptake in target cells such as adipocytes and muscle cells by promoting translocation of the GLUT IV transporter to the cell membrane; hence GLUT IV is insulin-dependent. GLUT I, II and III are insulin-independent.
NEET 2018
Which one of the following statements is incorrect?
A · α-cells of pancreas secrete glucagon
B · α-cells of pancreas secrete insulin ✓
C · Glucagon stimulates glycogenolysis
D · β-cells of pancreas secrete insulin
Solution: In the Islets of Langerhans, α-cells secrete glucagon and β-cells secrete insulin. Glucagon stimulates glycogenolysis (raises blood glucose). The incorrect statement is that α-cells secrete insulin — they secrete glucagon.
Solved Chemical Coordination and Integration NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Insulin is produced by the β-cells (beta-cells) of the Islets of Langerhans, the endocrine part of the pancreas.
What is the main function of insulin?
Insulin lowers blood glucose. It increases glucose uptake and utilisation by hepatocytes and adipocytes and stimulates glycogenesis (glucose to glycogen), so blood sugar falls.
Why is insulin called a hypoglycemic hormone?
Because it reduces blood glucose (hypo = low, glycemia = blood sugar). It moves glucose from blood into cells and stores it as glycogen, lowering blood sugar.
What happens if insulin is deficient?
Prolonged high blood glucose (hyperglycemia) leads to diabetes mellitus, with loss of glucose in urine (glycosuria) and formation of ketone bodies. Diabetic patients are treated with insulin therapy.
How do insulin and glucagon work together?
They are antagonistic. Insulin lowers blood glucose while glucagon raises it. Together they maintain glucose homeostasis in the blood.
