Glucose Importance and Regulation

Glucose Importance

• Glucose is a crucial simple sugar found in dietary carbohydrates.
• The body can also synthesize it from protein or triglycerides.
• Glucose is stored as glycogen in the liver.
• All tissues use glucose for energy, biosynthesis of amino acids, lipids, and nucleic acids.
• Skeletal muscle uses glycogen and blood glucose for energy during strenuous exercise.
• The brain and red blood cells almost entirely depend on glucose for energy; low blood glucose impairs brain function.
• Fasting blood glucose (FPG) for non-diabetics is between 3.9 – 5.6 mmol/L.
• When blood glucose exceeds the renal threshold (around 10 mmol/L), glucose spills into urine (glycosuria).
• The body metabolizes fat for energy when glucose is unavailable, leading to ketone production and ketoacidosis.

Regulation of Blood Glucose

• Insulin is produced by beta cells in the pancreas after meals.
  • Stimulates glucose uptake from blood into liver and muscle.
  • Decreases blood glucose levels.
  • Synthesizes glycogen in the liver and muscle for storage.
  • Inhibits glucagon release.
• Glucagon is produced by alpha cells in the pancreas and increases blood glucose levels during fasting.
  • Stimulates liver glycogenolysis (breakdown of liver glycogen to release glucose into the bloodstream).
  • Stimulates gluconeogenesis (formation of glucose from lactate, amino acids, and fat) to maintain blood glucose levels.
• Other hormones that increase blood glucose: growth hormone (GH), adrenaline, cortisol, adrenocorticotropichormone (ACTH), and thyroid hormones.

Hyperglycemia

• Hyperglycemia (increased blood glucose concentration) is a common carbohydrate metabolism disorder.
• Diabetes mellitus (DM): A metabolic disorder characterized by hyperglycemia due to problems making or using insulin.
• Endocrine disorders: Increased levels of growth hormone (GH), adrenaline, cortisol, thyroid hormones, and adrenocorticotropichormone (ACTH) can cause hyperglycemia.
• Medication: Glucocorticoids (corticosteroids) used for allergic, inflammatory, and autoimmune disorders can lead to hyperglycemia.
• Prolonged stress: Increased stress hormones (prolactin, cortisol, adrenaline) can cause hyperglycemia.

Diabetes Mellitus (DM)

• Type 1 DM (Insulin-dependent Diabetes Mellitus or Juvenile Onset DM):
  • 5% to 10% of DM cases.
  • Caused by an autoimmune disease that destroys beta cells, resulting in a complete lack of insulin.
  • Associated with histocompatibility leukocyte antigen (HLA) in 40-50% of familial type 1 DM.
  • Some individuals have increased islet cell antibodies and insulin antibodies.
  • Some cases may be triggered by an infectious agent (e.g., enteroviruses).
  • Requires lifelong treatment with insulin injections.
  • Characterized by an acute onset.
  • Mainly affects children and young adults.
  • Insulin-dependent.
  • Fat metabolism causes ketoacidosis, potentially leading to coma.
• Type 2 DM (Previously Non-Insulin Dependent Diabetes Mellitus):
  • 90% of DM cases.
  • Caused by progressive loss of beta cell insulin secretion and/or insulin resistance (body cells are unable to respond effectively to insulin).
  • Associated with sedentary lifestyles, obesity, diet, and polygenic factors.
  • Presents insidiously (gradual and subtle).
  • Primarily affects middle-aged and elderly individuals.
  • Management includes oral hypoglycemic drugs (metformin, sulfonylurea, insulin) and lifestyle modifications (exercise and diet control).
• Gestational Diabetes Mellitus (GDM):
  • Defined as any degree of glucose intolerance during pregnancy.
  • Affects both mother and baby.
  • Most patients return to normal glucose levels after delivery.
  • Frequency ranges from less than 1% to 28%.
  • 40% of GDM patients may develop Type 2 DM later in life.

Diagnostic Tests for Diabetes

• Fasting Blood Glucose:
  • Blood sample taken after a specific fasting period (e.g., 8 hours).
  • Convenient screening test.
• Oral Glucose Tolerance Test (OGTT):
  • Procedure: Patient fasts overnight (8 hours), then receives a glucose load (g anhydrous glucose dissolved in water). Blood is drawn for glucose measurement at 0, 1, and 2 hours.
  • Time-consuming.
• Laboratory Tests for Diabetic Monitoring and Management:
  • Glycated Hemoglobin (HbA1c): Reflects average glucose levels over the lifespan of red blood cells (2-12 weeks).
  • Urinary Albumin Excretion (Microalbumin): Early indicator of diabetic kidney damage (nephropathy).
  • Glycated Albumin: A less commonly used test that provides a shorter-term picture of glucose control.

Glycated Hemoglobin (HbA1c)

• Hemoglobin: Oxygen-carrying pigment giving blood its red color.
• HbA1c: A minor component of hemoglobin with bound glucose (glycated).
• HbA1c levels correlate with blood glucose concentration. Higher glucose levels lead to higher HbA1c levels.
• HbA1c is not influenced by daily blood glucose fluctuations and reflects average glucose levels over the lifespan of red blood cells (2-12 weeks).
• HbA1c serves as a useful indicator of long-term blood glucose levels in the recent past (2-12 weeks) and is used to monitor the effectiveness of diet, exercise, and drug treatment.
• In non-diabetics, HbA1c levels are typically lower.

Correlation Between HbA1c and Fasting Blood Glucose

• HbA1c levels correlate with fasting blood glucose levels, particularly in Type 2 DM patients.
• HbA1c provides a longer-term perspective on glucose control compared to single-point fasting blood glucose tests.

References

• American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care S81–90.

This quiz explores the critical role of glucose in the human body, including its sources, storage, and metabolic functions. You'll also learn about the regulation of blood glucose levels and the impact of insulin. Test your knowledge on glucose's importance in energy production and overall health.