🩸 DM Pathophysiology

PI: 10Γ— | 2006–2021 | Ominous octet 2Γ— (2016,2019) | GDM 3Γ— | Sep 2025: Diabetic nephropathy (staging excluded, patho wide open)
Predicted framing
"Discuss pathophysiology of Type 2 DM" (direct) Β· "Ominous octet in diabetes" (asked 2Γ—) Β· Clinical vignette: obese patient found diabetic, discuss pathophysiology + diagnostic criteria + management approach (asked 2020, 2021 as long essay)
1. Ominous Octet 3 marks β€” name all 8
DeFronzo's 8 pathogenic mechanisms in T2DM. PROPER-NOUN GATE β€” naming all 8 is a zero-or-ten differentiator.
1Decreased insulin secretion β€” Ξ²-cell failure (progressive, starts before diagnosis, ~50% function lost at diagnosis)
2Increased glucagon secretion β€” Ξ±-cell dysfunction, non-suppressed glucagon β†’ hepatic glucose output
3Increased hepatic glucose production β€” gluconeogenesis + glycogenolysis, driven by insulin resistance + excess glucagon
4Decreased muscle glucose uptake β€” skeletal muscle insulin resistance (GLUT4 downregulation), largest glucose disposal site
5Increased lipolysis β€” adipocyte insulin resistance β†’ ↑FFA β†’ lipotoxicity β†’ worsens hepatic & muscle IR
6Decreased incretin effect β€” GLP-1 and GIP impaired β†’ basis for GLP-1 RA and DPP-4 inhibitor therapy
7Increased renal glucose reabsorption β€” SGLT2 upregulated in proximal tubule β†’ basis for SGLT2 inhibitors
8Neurotransmitter dysfunction β€” hypothalamic appetite dysregulation, dopamine pathway β†’ basis for bromocriptine use
πŸ“ Each of the 8 maps to a drug class. The examiner loves: "Name the octet and the drug targeting each." This is a 3-mark question answered in a table.
2. Insulin Resistance Mechanism 1.5 marks
Normal: Insulin binds Ξ±-subunit of insulin receptor (tyrosine kinase) β†’ autophosphorylation of Ξ²-subunit β†’ IRS-1 phosphorylation β†’ PI3K β†’ GLUT4 translocation to membrane β†’ glucose uptake.

In T2DM: Post-receptor defect β€” serine phosphorylation of IRS-1 (instead of tyrosine) β†’ blocks PI3K pathway β†’ GLUT4 stays intracellular. Driven by: FFA (lipotoxicity), inflammatory cytokines (TNF-Ξ±, IL-6 from visceral adipose), ER stress.

Insulin receptor was asked directly in 2007. Key: it's a heterotetrameric receptor (2Ξ± + 2Ξ² subunits) with intrinsic tyrosine kinase activity on the Ξ²-subunit.
πŸ“ One sentence answer: "Post-receptor defect with serine (not tyrosine) phosphorylation of IRS-1 blocking GLUT4 translocation." This single sentence scores the mechanism mark.
3. Ξ²-Cell Failure 1 mark
Progressive. ~50% Ξ²-cell function lost at diagnosis. Mechanisms: glucotoxicity (chronic hyperglycemia β†’ oxidative stress β†’ Ξ²-cell apoptosis), lipotoxicity (FFA β†’ ceramide β†’ apoptosis), amyloid deposition (IAPP/amylin aggregates in islets), genetic susceptibility (TCF7L2 strongest T2DM gene).
πŸ“ "50% function lost at diagnosis" + "glucotoxicity + lipotoxicity + amyloid" = complete answer. TCF7L2 is the proper-noun gate if genetics is asked.
4. Diagnostic Criteria 1 mark
ADA criteria (any one, confirmed on repeat): FPG β‰₯126 mg/dL Β· 2h OGTT β‰₯200 mg/dL Β· HbA1c β‰₯6.5% Β· Random glucose β‰₯200 + symptoms

Prediabetes: FPG 100-125 (IFG) Β· 2h OGTT 140-199 (IGT) Β· HbA1c 5.7-6.4%

GDM screening (asked 3Γ— in PI): IADPSG/WHO one-step 75g OGTT at 24-28 weeks. Thresholds: FPG β‰₯92, 1h β‰₯180, 2h β‰₯153. One abnormal value = diagnosis.
πŸ“ GDM numbers (92/180/153) are proper-noun gates β€” asked 3 times. Must memorize exactly.
5. Octet β†’ Drug Map 1.5 marks (if management asked)
1Ξ²-cell failure β†’ Sulfonylureas, Meglitinides (insulin secretagogues)
2Ξ±-cell glucagon β†’ GLP-1 RA, DPP-4i (suppress glucagon)
3Hepatic glucose β†’ Metformin (↓hepatic gluconeogenesis via AMPK)
4Muscle IR β†’ Thiazolidinediones (PPARΞ³ β†’ ↑insulin sensitivity)
5Lipolysis β†’ TZDs (also adipocyte)
6Incretin defect β†’ GLP-1 RA (exenatide, liraglutide, semaglutide), DPP-4i (sitagliptin)
7Renal reabsorption β†’ SGLT2i (empagliflozin, dapagliflozin)
8Brain dysfunction β†’ Bromocriptine (D2 agonist)
πŸ“ This table IS the answer to "Discuss ominous octet with therapeutic implications." Draw it as a two-column table in the exam = maximum marks.
Proper-noun gates for 7-8/10 (12 total)
1. DeFronzo's ominous octet (all 8 named) Β· 2. Insulin receptor: heterotetrameric, 2Ξ±+2Ξ², tyrosine kinase Β· 3. IRS-1 serine vs tyrosine phosphorylation Β· 4. GLUT4 transporter Β· 5. 50% Ξ²-cell function lost at diagnosis Β· 6. Amylin/IAPP amyloid deposition Β· 7. TCF7L2 (strongest T2DM gene) Β· 8. FPG 126 / OGTT 200 / HbA1c 6.5% Β· 9. GDM: 92/180/153 Β· 10. Glucotoxicity + lipotoxicity Β· 11. GLP-1 and GIP (incretins) Β· 12. SGLT2 in proximal tubule