Carbohydrates and Their Classification

Carbohydrates

• Primary source of energy for the brain, erythrocytes, and retinal cells.
• Major food source and energy supply of the body, primarily stored as liver and muscle glycogen.
• Provide structural integrity to the cell membrane.
• Composed of carbon, hydrogen, and oxygen.
• Contain carbonyl and hydroxyl functional groups.

Classification of Carbohydrates

• Classified based on properties:
  • Number of carbon atoms
  • Location of the carbonyl group
  • Stereoisomerism

Stereoisomers

• Molecules with the same order and type of bonds but different spatial arrangements.
• For each asymmetric carbon, 2^n possible isomers.

Monosaccharides

• Assigned to the D or L series based on the configuration of the highest-numbered asymmetric carbon.
• Hydroxyl group projects to the right: D-series.
• Hydroxyl group projects to the left: L-series.

Enantiomers

• Mirror images of each other that are not superimposable.
• Most sugars in humans are in the D-form.

Insulin

• Inhibits glucose production in insulin-sensitive tissues (liver, skeletal muscles, and adipose tissues).
• Peptide hormone with a mass of approximately 5,000 Daltons.
• Composed of 21 amino acids in the A chain and 30 amino acids in the B chain linked by disulfide bonds.

Proinsulin

• Seen in Type 2 diabetes with decreased beta-cell insulin secretion, pre-Type 1 diabetes, insulinomas, and familial hyperinsulinemia.
• Processed by cleavage to form C-peptide and insulin.
• Ratio of C-peptide to insulin in serum is 5:1 to 15:1.

C-peptide

• Marker for endogenous insulin production.
• Measured with insulin and blood glucose to identify the cause of hypoglycemia.
• Primarily degraded by the kidneys.

Insulin Secretion Stimulated by:

• Stress
• Severe infection
• Dehydration or pregnancy
• Pancreatectomy
• Hemochromatosis
• Insulin deficiency or abnormal insulin receptor.

Hypoglycemia

• Characterized by low or decreased plasma glucose level.
• Results from an imbalance between glucose utilization and production.
• Symptoms are related to the CNS.

Whipple's Triad

• Low blood glucose concentration.
• Typical symptoms of hypoglycemia.
• Relief of symptoms with glucose administration.

Diabetes Mellitus

• Three classic manifestations:
  • Polyuria (excessive urination).
  • Polydipsia (excessive thirst).
  • Polyphagia (excessive hunger).

### Type 1 Diabetes Mellitus (T1DM)

• Caused by an absolute deficiency of insulin due to autoimmune attack of the beta-cells of the pancreas.
• Causes hyperglycemia, ketoacidosis, and hypertriglyceridemia.

Causes of T1DM

• Viral infection and environmental factors.
• Genetic susceptibility (HLA DR3/DR4 on chromosome 6).

Type 2 Diabetes Mellitus (T2DM)

• Characterized by insulin resistance, where tissues fail to respond normally to insulin.

Types of Insulin Resistance

• Pre-receptor: Insulin is defective and has difficulty binding to receptors or insulin levels are low.
• Receptor: Patient fails to respond to insulin due to deficient or defective receptors.
• Post-receptor: Patient has normal insulin levels and receptors, but signal transduction is impaired or glucose transporters are unable to process glucose.

Effects of Insulin

• Increases glycogenesis, lipogenesis, and glycolysis.
• Decreases glycogenolysis.

Interferences in Measurement of Insulin, C-peptide, and Proinsulin

• Alimentary (reactive) hypoglycemia.
• Idiopathic (functional) postprandial hypoglycemia.

Symptoms of Hypoglycemia:

• Adrenergic (mediated by epinephrine): Anxiety, weakness, palpitations, tremor, and sweating.
• Neuroglycopenic: Headache, confusion, slurred speech, seizures, coma, and death.

Classification of Hypoglycemia

• Post-prandial (Reactive): More common; Exaggerated insulin release and microvascular complications.
• Non-traumatic amputation, adult blindness, diabetic neuropathy, atherosclerotic disease, heart attacks, and strokes.

Untreated Type 2 DM

• Results in nonketotic hyperosmolar coma due to overproduction of glucose (>300 mg/dL) with severe dehydration, electrolyte imbalance, and increased BUN and creatinine.

This quiz explores the fundamentals of carbohydrates, their classification based on structure and function, and key concepts like stereoisomerism and monosaccharides. Test your knowledge on the role of carbohydrates in energy supply and cellular integrity.