Ketogenesis and Diabetic Ketoacidosis (DKA): Study Notes

1. Fed State (High Blood Glucose)

• After a meal, glucose enters the bloodstream.

• Pancreas senses high blood glucose:

  • Beta cells → release insulin

  • Insulin inhibits alpha cells, reducing glucagon secretion.

• Insulin actions:

  1. Promotes glucose uptake in muscle and adipose tissue via glucose transporters.

  2. Stimulates glycolysis (glucose → pyruvate) in liver.

  3. Promotes pyruvate entry into mitochondria, forming acetyl-CoA → enters Krebs cycle → produces NADH and FADH₂ → feed electron transport chain → ATP production.

• Result: High glucose → high ATP.

2. Fasting / Low Blood Glucose

• Low blood glucose stimulates alpha cells → glucagon release.

• Glucagon inhibits glycolysis and Krebs cycle → conserves glucose for homeostasis.

• Mechanisms to increase blood glucose:

  1. Glycogenolysis: Glycogen → glucose

  2. Gluconeogenesis: Non-carbohydrate sources → glucose

     • Substrates:

       • Glycerol (from triglycerides via lipolysis)

       • Amino acids

       • Oxaloacetate (from pyruvate)

       • Lactate

• Fatty acids cannot form glucose directly → converted to acetyl-CoA.

  • Low oxaloacetate (used for gluconeogenesis) → acetyl-CoA accumulates → ketogenesis.

3. Ketogenesis

• Excess acetyl-CoA → forms ketone bodies:

  1. Acetoacetate

  2. Beta-hydroxybutyrate

  3. Acetone (exhaled, sweet/fruity smell)

• Ketones as energy:

  • Can cross blood-brain barrier → converted to acetyl-CoA in brain → Krebs cycle → ATP.

  • Occurs primarily in liver; brain uses ketones as backup energy.

4. Diabetes Mellitus and DKA

Type 1 Diabetes

• Autoimmune destruction of beta cells → no insulin.

• Consequences:

  • Low insulin, high glucagon

  • Glycolysis/Krebs cycle inhibited

  • High blood glucose persists

  • Glucagon stimulates gluconeogenesis + lipolysis → ketone accumulation → acidosis

Type 2 Diabetes

• Insulin produced but ineffective (insulin resistance).

5. Diabetic Ketoacidosis (DKA)

Diagnostic criteria:

1. Hyperglycemia (high blood glucose)

2. Ketosis (high blood/urine ketones)

3. Metabolic acidosis (high anion gap)

• Mechanism of high anion gap:

  • Ketone bodies release H⁺ ions → bind bicarbonate → bicarbonate drops → anion gap rises.

  • Normal anion gap ≈ 12 mEq/L; DKA → >16 mEq/L

• Consequences:

  • Acidosis: stimulates chemoreceptors → vomiting, fluid loss

  • Hyperventilation (Kussmaul breathing) to expel CO₂

  • Hypokalemia: H⁺ exchanged for K⁺ → K⁺ lost in urine

  • Glucosuria & polyuria: high glucose → osmotic diuresis → dehydration

6. Treatment of DKA

1. Insulin → suppresses glucagon, restores glucose utilization

2. Fluid replacement → correct dehydration

3. Electrolyte replacement → especially potassium

7. Key Concepts

• Fed state: insulin dominates → glucose uptake + ATP production

• Fasting: glucagon dominates → glycogenolysis, gluconeogenesis, ketogenesis

• Ketone bodies: acetoacetate, beta-hydroxybutyrate, acetone

• Type 1 diabetes: insulin deficiency → uncontrolled ketogenesis → DKA

• DKA complications: acidosis, dehydration, hypokalemia, fruity breath, Kussmaul breathing.