15. Endocrine Functions of the Pancreas – Types of Hormones, Physiological Effects, and Control of Secretion. Disorders of Endocrine Pancreas Secretion

Endocrine Functions of the Pancreas

The islets of Langerhans consist of four major cell types, each producing a different hormone:

1. Alpha cells:

   • Secrete glucagon

   • Physiological effect: Increases blood glucose levels by promoting glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (production of glucose from non-carbohydrate sources).

2. Beta cells:

   • Secrete insulin

   • Physiological effect: Lowers blood glucose levels by promoting glycogenesis (conversion of glucose to glycogen) and facilitating glucose uptake into cells.

3. Delta cells:

   • Secrete somatostatin

   • Physiological effect: Acts as an inhibitory hormone, regulating and suppressing the secretion of insulin and glucagon, thereby maintaining hormonal balance.

4. F (PP) cells:

   • Secrete pancreatic polypeptide

   • Physiological effect: Plays a role in the self-regulation of pancreatic secretion (both endocrine and exocrine) and affects gastrointestinal motility and appetite.

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Control of Hormone Secretion

Hormonal secretion from pancreatic islet cells is tightly regulated by nutrient levels, nervous system inputs, and hormone interactions:

• High blood glucose → Stimulates beta cells → Increases insulin secretion.

• Low blood glucose → Stimulates alpha cells → Increases glucagon secretion.

• Somatostatin:

  • Inhibits both alpha and beta cells, suppressing insulin and glucagon release.

  • Is secreted when insulin or glucagon levels are excessively high.

  • Is itself inhibited by pancreatic polypeptide.

• Sympathetic nervous system → Stimulates alpha cells to secrete glucagon.

• Pancreatic polypeptide → Secretion is stimulated after a meal, modulates both exocrine and endocrine functions.

Disorders of Endocrine Pancreas Secretion

Normal blood glucose: 2.8–6.1 mmol/L

1. Hypoglycaemia

• Definition: Blood glucose < 2.8 mmol/L; hypoglycaemic coma < 2.3 mmol/L

• Causes:

  • Hormonal imbalances (e.g., insulin overproduction)

  • Certain medications

  • Skipping meals

• Symptoms: Sweating, confusion, palpitations, in severe cases – coma

2. Hyperglycaemia and Diabetes Mellitus

• Hyperglycaemia: Blood glucose > 6.1 mmol/L

• Glycosuria (glucose in urine): Blood glucose > 11 mmol/L

Types of Diabetes Mellitus:

• Type 1 Diabetes Mellitus (T1DM):

  • Cause: Autoimmune destruction of beta cells

  • Result: No insulin production → insulin-dependent

• Type 2 Diabetes Mellitus (T2DM):

  • Cause: Insulin resistance (target tissues are less responsive to insulin)

  • Risk factors: Obesity, sedentary lifestyle

  • Treatment: Lifestyle changes, oral hypoglycemics, sometimes insulin

Common Symptoms of Diabetes:

• Polyuria – Increased urination

• Polydipsia – Increased thirst

• Polyphagia – Increased hunger

• Fatigue

• Ketones in urine (especially in Type 1, due to fat breakdown)

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