Diabetes Mellitus: Types, Insulin Function, and Complications

Posted on Nov 5, 2025 in Medicine

Diabetes Mellitus: Definition and Classification

Diabetes Mellitus (DM) is a chronic disease associated with poor or non-functional production of insulin in the pancreas. This syndrome is characterized by hyperglycemia, altered metabolism of carbohydrates, lipids, and proteins, and an increased risk of vascular complications.

Clinical Classification of Diabetes

DM is clinically classified as:

  • Type 1 Diabetes (IDDM): Insulin-Dependent Diabetes Mellitus.
  • Type 2 Diabetes (NIDDM): Non-Insulin-Dependent Diabetes Mellitus (approximately 90% of cases).

The Pancreas and Glucose Regulation

The pancreas is a gland that functions as both an endocrine and exocrine organ, producing digestive enzymes and secreting hormones.

Key Pancreatic Hormones

  • Insulin and Glucagon: Regulate blood glucose levels.
  • Somatostatin: Modulates the absorption of nutrients by the gastrointestinal tract (GI).

Insulin Secretion Regulation

Insulin secretion is tightly regulated to maintain stable concentrations of glucose in the blood. The regulation is achieved by:

  • Gastrointestinal Hormones
  • Pancreatic Hormones
  • Neurotransmitters of the Autonomic Nervous System (ANS)

Factors Facilitating Insulin Secretion

  • Glucose
  • Amino acids
  • Fatty acids
  • Ketones

Insulin Action: Anabolism and Catabolism Control

Insulin is a powerful hormone that promotes intracellular use and storage of energy substrates. Its actions are categorized into anabolic promotion and catabolic inhibition.

Metabolic Roles of Insulin

  • Anabolism Power: Promotes intracellular use and storage of Glucose, Amino acids, and Fatty acids.
  • Blocking Catabolism: Inhibits the hydrolysis of glycogen, fat, and protein.

Specific Effects of Insulin

  • Promotes glucose entry into muscle and fat cells.
  • Stimulates glycogen synthesis in the liver and muscle.
  • Increases fatty acid synthesis.
  • Stimulates protein synthesis.

Hypoglycemic Action of Insulin

Action in the Liver

  • Inhibits hepatic glucose production by decreasing gluconeogenesis and glycogenolysis.
  • Stimulates hepatic glucose uptake.
  • Inhibits the flow of gluconeogenesis precursors (alanine, lactate, pyruvate) to the liver.

Action in Adipose Tissue and Muscle

  • Stimulates muscle glucose uptake.
  • Stimulates glucose uptake in adipose tissue (similar to muscle).
  • Reduces the flow of energy substrates required for hepatic gluconeogenesis.

Glucagon Function

Glucagon is secreted in response to:

  • Low blood glucose levels.
  • Increased amino acids.
  • Stimulation by growth hormone.

Its primary function is to increase circulating glucose levels by converting stored glucose (in the liver) into circulating glucose. It also promotes the formation of glucose from fat and protein when the liver’s stored supply is insufficient.

Type 1 Diabetes Mellitus (IDDM)

Also known as insulin-dependent diabetes, Type 1 DM typically:

  • Onset: Often starts between 10 to 13 years of age.
  • Diagnosis: Usually confirmed before age 20.
  • Symptoms: Florid and alarming symptoms, often involving ketosis.
  • Pathology: Characterized by the absence of insulin and Proinsulin C-peptide, and a marked reduction or absence of Beta (B) cells from the islets of Langerhans.

Associated Complications of Type 1 DM

  • Microvascular: Nephropathy, retinopathy, peripheral neuropathy, and cataracts.
  • Macrovascular: Coronary heart disease, stroke, and peripheral vascular disease.

Type 2 Diabetes Mellitus (NIDDM)

Also known as non-insulin-dependent diabetes, Type 2 DM results from the body’s inability to respond properly to insulin signals, leading to insulin resistance in target cells (muscle, adipocytes, and hepatocytes).

Characteristics and Risk Factors

  • Onset: Typically occurs after 35–40 years of age.
  • Predisposition: Strong genetic predisposition.
  • Metabolic Factors: Frequent hyperinsulinemia, obesity, and physical inactivity.
  • Associated Risks: Hypertension, hypertriglyceridemia, hypercholesterolemia, and low HDL.

These factors contribute significantly to atherosclerosis and cardiovascular disease.

Metabolic Syndrome

Metabolic Syndrome is a cluster of conditions that occur together, increasing the risk of heart disease, stroke, and Type 2 Diabetes Mellitus (T2DM). Key components include:

  • Obesity
  • Dyslipidemia (Elevated LDL, low HDL cholesterol, and raised triglycerides)
  • Resistance to insulin action (often leading to T2DM)
  • Hypertension
  • Hyperuricemia
  • Elevated fibrinogen levels