Carbohydrate Metabolism and Diabetes - Review

A comprehensive set of Q&A flashcards covering carbohydrate metabolism, hormonal regulation, diabetes types and criteria, HbA1c, and essential lab concepts from the lecture notes.

What are the principal functions of carbohydrates in the human body?

Provide energy through oxidation; store energy as glycogen; supply carbon for the synthesis of proteins, lipids, and nucleic acids; form part of DNA/RNA; components of cell membranes; participate in cell–cell and cell–molecule recognition.

How are carbohydrates classified?

By (a) location of the CO functional group (aldehyde vs ketone), (b) number of sugar units (monosaccharides, disaccharides, oligosaccharides, polysaccharides), (c) number of carbons (triose to octose), and (d) Haworth structure (pyranose vs furanose) and stereochemistry.

What are monosaccharides, disaccharides, oligosaccharides, and polysaccharides?

Monosaccharides: one sugar unit; disaccharides: two; oligosaccharides: three to ten; polysaccharides: ten or more.

What is glucose commonly called, and what is its typical blood level?

Also known as grape sugar or dextrose; normal fasting blood glucose is about 70–100 mg/dL.

Describe glycogen and its structure.

Storage polysaccharide in humans/animals; contains only glucose units; highly branched with (1→4) glycosidic bonds in straight chains and (1→6) bonds at branches; up to about 1,000,000 glucose units; more highly branched than amylopectin.

Outline the major steps of dietary carbohydrate digestion.

Mouth: salivary amylase begins hydrolysis; stomach: gastric juice has little effect; small intestine: pancreatic enzymes partially digest polysaccharides; brush-border enzymes (maltase, sucrase, lactase) hydrolyze disaccharides to monosaccharides; monosaccharides (glucose, fructose, galactose) are absorbed into mucosal cells and enter the bloodstream.

Name the four major glucose metabolic pathways.

Glycolysis, gluconeogenesis, glycogenesis, glycogenolysis.

Which enzymes are key control points in glycolysis?

Hexokinase (glucokinase in liver), phosphofructokinase, and pyruvate kinase.

What is the role of glycogenesis?

Synthesis of glycogen from glucose for storage (primarily in liver and muscle).

What is glycogenolysis?

Breakdown of glycogen to glucose to supply energy during fasting or exercise.

What is gluconeogenesis?

Formation of glucose from non-carbohydrate sources such as lactate, glycerol, and certain amino acids.

What is lipogenesis in carbohydrate metabolism?

Synthesis of fatty acids from acetyl-CoA during excess glucose, leading to triglyceride formation.

What is the primary action of insulin?

Increases uptake of glucose into cells; promotes glycogenesis, lipogenesis, and glycolysis; decreases glycogenolysis.

What is the primary action of glucagon?

Stimulates glycogenolysis and gluconeogenesis to raise plasma glucose.

How does epinephrine influence glucose metabolism?

Raises plasma glucose by inhibiting insulin and promoting glycogenolysis and lipolysis.

What is the effect of cortisol (glucocorticoids) on glucose metabolism?

Increases plasma glucose by promoting gluconeogenesis, liver glycogen storage, and lipolysis; may reduce intestinal glucose entry.

What is the effect of growth hormone on glucose metabolism?

Increases plasma glucose by decreasing cellular uptake of glucose and by modulating glycolysis; secretion is stimulated by low glucose and inhibited by high glucose.

What is ACTH and how does it affect glucose metabolism?

Stimulates the adrenal cortex to release cortisol, which increases plasma glucose via glycogenolysis and gluconeogenesis.

What is the effect of thyroxine on carbohydrate metabolism?

Increases glycogenolysis, gluconeogenesis, and intestinal absorption of glucose.

What does somatostatin do in carbohydrate metabolism?

Inhibits insulin, glucagon, growth hormone, and other endocrine hormones.

How is hyperglycemia identified in laboratory findings?

Decreased or absent insulin; increased glucose in plasma and possibly urine; increased urine osmolality; ketones in serum/urine; decreased blood/urine pH; electrolyte imbalance.

How does the ADA classify diabetes mellitus?

Type 1: autoimmune destruction of pancreatic beta cells with absolute insulin deficiency; Type 2: insulin resistance with relative insulin deficiency; Gestational diabetes; Other specific types; (also latent autoimmune diabetes of adulthood as a subset).

What autoantibodies are associated with Type 1 diabetes?

Islet cell autoantibodies, insulin autoantibodies, glutamic acid decarboxylase (GAD) autoantibodies, and IA-2/IA-2B autoantibodies.

What are the classic signs and symptoms of Type 1 diabetes?

Polydipsia, polyphagia, polyuria; rapid weight loss; may have hyperventilation, mental confusion, and progression to coma in severe cases.

What microvascular complications are associated with diabetes?

Nephropathy, neuropathy, and retinopathy; increased risk of cardiovascular disease.

What characterizes Type 2 diabetes mellitus?

Hyperglycemia due to insulin resistance with an insulin secretory defect; may progress to reduced insulin production.

What are impaired fasting glucose and impaired glucose tolerance definitions?

IFG: fasting glucose 100–125 mg/dL; IGT: 2-hour OGTT 140–199 mg/dL.

What are the diagnostic criteria for gestational diabetes mellitus (GDM)?

One-step: 75-g OGTT with fasting ≥92 mg/dL, 1-h ≥180 mg/dL, 2-h ≥153 mg/dL. Two-step: fasting ≥95 mg/dL, 1-h ≥180 mg/dL, 2-h ≥155 mg/dL (and sometimes a 3-h 140 mg/dL threshold).

What are the four diagnostic criteria for diabetes mellitus (per Table 9.5)?

HbA1c ≥6.5% (NGSP); fasting plasma glucose ≥126 mg/dL; 2-h plasma glucose ≥200 mg/dL after OGTT; random plasma glucose ≥200 mg/dL with diabetes symptoms. Two abnormal results are generally required unless hyperglycemia is unequivocal.

What is HbA1c and why is it used in diabetes management?

A measure of long-term glycemic control reflecting average blood glucose over the past 2–3 months due to the 120-day lifespan of red blood cells.

How is HbA1c translated into an estimated average glucose (eAG)?

HbA1c percentages correspond to eAG values (NGSP); e.g., 5% ≈ 97 mg/dL, 6% ≈ 126 mg/dL, 7% ≈ 154 mg/dL, 8% ≈ 183 mg/dL, 9% ≈ 212 mg/dL, 10% ≈ 240 mg/dL, etc.

What are common methods for measuring HbA1c?

Immunoassays; boronate affinity chromatography; ion-exchange chromatography; electrophoresis; high-performance liquid chromatography (HPLC). Each method has specific advantages and potential interferences (e.g., Hb variants, HbF).

What specimen handling considerations are important for glucose measurement?

Glucose concentration is about 11% lower in whole blood than in plasma; serum/plasma should be separated from cells promptly; fluoride-containing tubes inhibit glycolysis to preserve glucose levels.

What are the two main methods for ketone measurement in the lab?

Nitroprusside method (measures acetoacetate) and enzymatic method (measures 3-hydroxybutyrate with NAD+.

What is albuminuria and its significance in diabetes?

An early sign of diabetic kidney disease (nephropathy); indicates renal involvement and progression risk.

What is Whipple’s triad in hypoglycemia?

Low blood glucose concentration, typical hypoglycemic symptoms, and relief of symptoms after glucose administration.

What are the levels in the hypoglycemia glycemic criteria (Level 1, 2, 3)?

Level 1: <70 mg/dL (glucose alert value); Level 2: <54 mg/dL (clinically significant); Level 3: severe hypoglycemia with no specific threshold, requiring treatment/external assistance.

What are the two main ketone measurement methods and what do they detect specifically?

Nitroprusside method detects acetoacetate (and acetone to a lesser extent); enzymatic method measures beta-hydroxybutyrate (via NAD+ system).