6.2.4 Pancreas

The pancreas is a complex glandular organ that performs both endocrine and exocrine functions. As an endocrine gland, it contains patches of tissue called the Islets of Langerhans, which secrete the hormones insulin and glucagon. These hormones regulate blood glucose levels.

Definition

Pancreas: Pancreas is composed of two types of tissues. Exocrine tissue produces and secretes digestive juice. Endocrine tissues are distributed in the form of patches in the pancreas and these patches are called Islets of Langerhans.

Islets of Langerhans: Islets of Langerhans are patches of endocrine tissue in the pancreas that secrete the hormones insulin and glucagon.

Main Idea

• Pancreas is composed of two types of tissues:
• Islets of Langerhans secrete two hormones:
• These cells respond directly to the level of blood glucose.
• Insulin is secreted when blood sugar rises.
• Glucagon is released when blood glucose level is low.
• Insulin and glucagon act antagonistically.

Core Concept

• Pancreas = both exocrine and endocrine gland
• Exocrine tissue = produces digestive juice
• Endocrine tissue = Islets of Langerhans
• Beta (β) cells = secrete insulin; larger in number
• Alpha (α) cells = secrete glucagon; lesser in number
• Insulin = lowers blood glucose
• Glucagon = raises blood glucose
• Insulin and glucagon = antagonistic hormones
• Diabetes mellitus = under secretion of insulin
• Hypoglycemia = excess insulin

Detailed Explanation

Pancreas

• Pancreas is composed of two types of tissues.
• Exocrine tissue produces and secretes digestive juice.
• Endocrine tissues are distributed in the form of patches in the pancreas and these patches are called Islets of Langerhans.
• Islets of Langerhans secrete two hormones insulin and glucagon.

Insulin

• Insulin is secreted by the Beta (β) cells which are larger in number.
• These cells respond directly to the level of blood glucose.
• Insulin is secreted when the level of blood sugar rises, such as right after a meal.
• Its overall effect is to reduce blood glucose level to the normal level by increasing the rate of glucose uptake by most body cells especially skeletal muscles and fat cells.
• It promotes glycogenesis (conversion of glucose to glycogen).
• It increases the use of glucose in cellular respiration.
• It promotes the conversion of excess glucose to fats.
• It inhibits gluconeogenesis (glucose synthesis).

Glucagon

• Glucagon is secreted by alpha (α) cells which are lesser in number.
• Glucagon is released by α cells when blood glucose level is low.
• Sympathetic nervous system also stimulates its secretion.
• High blood glucose levels, insulin and somatostatin suppress its secretion.
• Its role is to increase the blood glucose level.
• It acts antagonistically to the insulin and thus reverses the activities performed by insulin.

Science Titbits

• Pancreatic acinar cells are functional units of the exocrine pancreas.
• They synthesize, store, and secrete inactive digestive enzymes into the lumen of the acinus.

Summary Table of Pancreatic Hormones

Effects of Insulin

Effects of Glucagon

Disorders of Pancreas

Intermediate Level

Pancreatic Hormones

Effects of Insulin

Effects of Glucagon

Regulation of Insulin and Glucagon Secretion

Disorders of Pancreas

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Pancreas has two types of tissues.
• 2. Exocrine tissue produces digestive juice.
• 3. Endocrine tissue forms Islets of Langerhans.
• 4. Islets of Langerhans secrete insulin and glucagon.
• 5. Insulin is secreted by beta cells.
• 6. Beta cells are larger in number.
• 7. Insulin is secreted when blood sugar rises.
• 8. Insulin reduces blood glucose level.
• 9. Insulin promotes glycogenesis.
• 10. Insulin increases glucose use in cellular respiration.
• 11. Insulin promotes conversion of excess glucose to fats.
• 12. Insulin inhibits gluconeogenesis.
• 13. Glucagon is secreted by alpha cells.
• 14. Alpha cells are lesser in number.
• 15. Glucagon is released when blood glucose level is low.
• 16. Sympathetic nervous system stimulates glucagon secretion.
• 17. High blood glucose, insulin, and somatostatin suppress glucagon secretion.
• 18. Glucagon increases blood glucose level.
• 19. Glucagon acts antagonistically to insulin.
• 20. Under secretion of insulin causes diabetes mellitus.

Remember

• - Pancreas = both exocrine and endocrine gland
• - Exocrine tissue = produces digestive juice
• - Endocrine tissue = Islets of Langerhans
• - Beta (β) cells = secrete insulin; larger in number
• - Alpha (α) cells = secrete glucagon; lesser in number
• - Insulin = lowers blood glucose
• - Glucagon = raises blood glucose
• - Insulin and glucagon = antagonistic hormones
• - Diabetes mellitus = under secretion of insulin
• - Hypoglycemia = excess insulin

Common Mistakes

• 1. Confusing insulin and glucagon — Insulin lowers blood sugar; glucagon raises it.
• 2. Mixing up the cells — Beta cells = insulin; alpha cells = glucagon.
• 3. Forgetting the role of the pancreas — It is both exocrine and endocrine.
• 4. Thinking insulin raises blood sugar — Insulin lowers blood sugar.
• 5. Believing glucagon lowers blood sugar — Glucagon raises blood sugar.
• 6. Mixing up the effects — Insulin promotes glycogenesis; glucagon promotes glycogenolysis.
• 7. Forgetting the role of the sympathetic nervous system — It stimulates glucagon secretion.
• 8. Confusing diabetes mellitus and diabetes insipidus — Mellitus = insulin; insipidus = ADH.
• 9. Thinking hypoglycemia is caused by too little insulin — Hypoglycemia is caused by excess insulin.
• 10. Believing insulin and glucagon work together — They work antagonistically.

Quick Revision

Pancreas is composed of two types of tissues. Exocrine tissue produces and secretes digestive juice. Endocrine tissues are distributed in the form of patches in the pancreas and these patches are called Islets of Langerhans. Islets of Langerhans secrete two hormones insulin and glucagon. Insulin is secreted by the Beta (β) cells which are larger in number and glucagon is secreted by alpha (α) cells which are lesser in number. These cells respond directly to the level of blood glucose. Insulin is secreted when the level of blood sugar rises, such as right after a meal. Its overall effect is to reduce blood glucose level to the normal level by increasing the rate of glucose uptake by most body cells especially skeletal muscles and fat cells. It promotes glycogenesis (conversion of glucose to glycogen), increases the use of glucose in cellular respiration, promotes the conversion of excess glucose to fats and inhibits gluconeogenesis (glucose synthesis). Glucagon is released by α cells when blood glucose level is low. Sympathetic nervous system also stimulates its secretion. High blood glucose levels, insulin and somatostatin suppress its secretion. Its role is to increase the blood glucose level. It acts antagonistically to the insulin and thus reverses the activities performed by insulin. The under secretion of insulin leads to the metabolic disease known as diabetes mellitus which is characterized by high glucose level in the blood and urine. If excess of insulin is produced the utilization of glucose is too great and its level falls in the blood which upsets nerve and muscles functioning.

60-Second Revision

• Pancreas = both exocrine and endocrine gland
• Exocrine tissue = produces digestive juice
• Endocrine tissue = Islets of Langerhans
• Beta (β) cells = secrete insulin; larger in number
• Alpha (α) cells = secrete glucagon; lesser in number
• Insulin = lowers blood glucose
• Glucagon = raises blood glucose
• Insulin and glucagon = antagonistic hormones
• Diabetes mellitus = under secretion of insulin
• Hypoglycemia = excess insulin
• Warning: Insulin lowers blood sugar; glucagon raises it

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• Chapter:
• 6. Endocrine System of Man

• Topic:
• 6.2.5 ADRENAL GLANDS

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