The Endocrine System

• Definition: The endocrine system comprises glands that are widely separated, lacking physical interconnections; these are secretory cells surrounded by capillary networks for hormone diffusion.

• Ductless Glands: Hormones are secreted directly into the bloodstream.

• Hormones: Act as chemical messengers transported through the bloodstream to influence cell growth and metabolism in target tissues and organs.

• Homeostasis: Maintained by the autonomic nervous system (rapid response) and the endocrine system (slower, precise adjustments).

• Main Glands: Include the pituitary, hypothalamus, thyroid, parathyroid, adrenal glands, and pancreas; other organs like adipose tissue (produces leptin) and the heart (produces atrial natriuretic peptide) also have endocrine functions.

• Hypothalamus: Regulates the pituitary gland and influences other glands; it is crucial for maintaining hormonal balance.

• Reproductive Hormones: Ovaries and testes release hormones post-puberty, and the placenta has temporary endocrine functions during pregnancy.

Overview of Hormone Action

• Hormone-Receptor Binding: Hormones bind to specific receptors, acting as switches for metabolic reactions.

  • Peptide Hormones: Receptors located on cell membranes.

  • Lipid-Based Hormones: Receptor sites are inside cells.

• Regulation: Hormone levels are variable and self-regulate within a normal range.

• Feedback Mechanisms:

  • Negative Feedback: Hormone release in response to a stimulus, reversing or negating the stimulus (e.g., insulin/glucagon regulation via plasma glucose levels).

  • Positive Feedback: Amplification of the stimulus, continuing hormone release until a process is completed (e.g., oxytocin during labor).

Diabetes Mellitus

• Definition: The most common endocrine disorder characterized by hyperglycemia and disrupted carbohydrate and fat metabolism.

• Causes: Includes complete absence, relative deficiency, or resistance to insulin production.

• Types:

  • Primary DM: Includes Type 1 and Type 2 diabetes.

  • Secondary DM: Results from other health conditions; gestational diabetes occurs during pregnancy.

  • Epidemic Growth: Global prevalence increased from 4.7% in 1980 to 8.5% in 2014, with significant rise in affected individuals (from 108 million to 422 million).

Type 1 Diabetes Mellitus

• Description: Previously insulin-dependent; common in children/young adults with sudden onset.

• Cause: Severe deficiency of insulin due to destruction of pancreatic β-islet cells by autoantibodies.

• Treatment: Insulin administration is required.

Type 2 Diabetes Mellitus

• Description: Previously non-insulin dependent; most common form, accounting for about 90% of cases.

• Causes: Multifactorial; predisposing factors include:

  • Obesity

  • Sedentary lifestyle

  • Age, primarily affecting middle-aged and older adults

  • Genetic factors.

• Onset: Gradual, often goes undetected until complications arise; can have normal or high insulin levels with defective glucose uptake by cells.

• Treatment: Involves diet, drugs, or insulin depending on severity.

Pathophysiology of Diabetes Mellitus

• Hyperglycemia:

  • Increased plasma glucose after a carbohydrate-rich meal due to:

    • Inability of cells to utilize glucose

    • Reduced conversion to glycogen in liver/muscles

    • Gluconeogenesis due to intracellular glucose deficiency.

• Consequences: Long-term vascular and nerve damage.

Glycosuria and Polyuria

• Mechanism: Increased glucose in renal filtrate results in osmotic pressure causing reduced water reabsorption, leading to increased urine volume (polyuria), dehydration, and excessive thirst (polydipsia).

Weight Loss

• Reason: Cells cannot extract glucose; reliance on alternative energy pathways leads to:

  • Gluconeogenesis from proteins

  • Fat breakdown, ketone body production.

Ketosis and Ketoacidosis

• Ketoacidosis: Severe metabolic derangement due to insufficient insulin, leads to energy source shifts, ketone accumulation, acidosis, and potential coma.

  • Signs: Ketonuria, characteristic breath odor, and acidosis symptoms.

Acute Complications of Diabetes Mellitus

• Diabetic Ketoacidosis (DKA): Medical emergency due to severe insulin deficiency.

• Hypoglycaemic Coma: Resulting from excess insulin relative to food intake/expenditure, characterized by rapid onset and disturbed neurological function due to glucose deprivation.

Long-Term Complications of Diabetes Mellitus

• Cardiovascular Disturbances: Increased risk of cardiovascular disorders; macroangiopathy includes:

  • Ischemic heart disease

  • Stroke

  • Peripheral vascular disease.

• Microangiopathy: Affects small vessels, leading to consequences:

  • Diabetic retinopathy

  • Nephropathy

  • Neuropathy.

Infection Risk

• Predisposal: DM increases infection risk, notably from bacterial and fungal sources due to reduced phagocyte activity.

Renal Failure

• Consequences: Chronic kidney disease due to nephropathy is common.

Visual Impairment

• Risks: Diabetic retinopathy is the leading cause of blindness in adults aged 30-65 in developed countries.

• Cataracts: Increased risk of early cataract development.

Diabetic Foot

• Factors: Contributing factors include:

  • Vascular disease affecting blood supply

  • Neuropathy reducing sensation in the extremities.

• Consequences: Slow healing, potential for severe infection and gangrene, occasionally necessitating amputation.