CDE Pathophysiology 4 — Questions and Answers
Question 1: Advanced glycation end products (AGEs) contribute to diabetic complications primarily by:
- Blocking insulin receptor binding on target tissues
- Cross-linking proteins and activating RAGE receptors to cause inflammation (Correct answer)
- Directly inhibiting aldose reductase in the polyol pathway
- Increasing nitric oxide production causing vasodilation
Correct answer: Cross-linking proteins and activating RAGE receptors to cause inflammation
AGEs accumulate on long-lived proteins causing cross-linking that stiffens vessels and tissues, and activate RAGE receptors triggering inflammatory cascades that damage endothelium and other structures.
Question 2: The polyol pathway contributes to diabetic complications through which primary mechanism?
- Sorbitol accumulation and osmotic stress combined with NADPH depletion (Correct answer)
- Direct glycation of hemoglobin reducing oxygen delivery
- Excess glucose entering the hexosamine pathway only
- Activation of protein kinase C causing vasoconstriction
Correct answer: Sorbitol accumulation and osmotic stress combined with NADPH depletion
Excess glucose is converted to sorbitol by aldose reductase (consuming NADPH), then to fructose (generating NADH), causing osmotic damage and depleting antioxidant capacity via reduced glutathione regeneration.
Question 3: Diabetic nephropathy progresses from microalbuminuria to overt proteinuria primarily because of:
- Glomerular basement membrane thinning allowing protein filtration
- Intraglomerular hypertension causing progressive podocyte injury and loss (Correct answer)
- Tubular reabsorption of albumin becoming saturated at high glucose levels
- Renal artery stenosis reducing filtration pressure over time
Correct answer: Intraglomerular hypertension causing progressive podocyte injury and loss
Intraglomerular hypertension driven by efferent arteriolar constriction causes mechanical stress on podocytes, leading to their detachment and foot process effacement, allowing increasing protein filtration.
Question 4: In diabetic peripheral neuropathy, which nerve fiber type is typically affected earliest?
- Large myelinated A-alpha motor fibers
- Small unmyelinated C fibers and thinly myelinated A-delta fibers (Correct answer)
- Large myelinated A-beta sensory fibers for vibration
- Motor neurons of the anterior horn of the spinal cord
Correct answer: Small unmyelinated C fibers and thinly myelinated A-delta fibers
Small unmyelinated C fibers (pain, temperature) and A-delta fibers are most vulnerable to the metabolic insults of hyperglycemia, explaining why burning pain and temperature loss typically precede vibration loss.
Question 5: Nonproliferative diabetic retinopathy progresses to the proliferative stage primarily driven by:
- Increased retinal blood flow causing microaneurysm rupture
- Retinal ischemia triggering VEGF-mediated neovascularization (Correct answer)
- Leukocyte adhesion blocking venules and causing retinal detachment
- Sorbitol accumulation in lens fibers diffracting light onto retina
Correct answer: Retinal ischemia triggering VEGF-mediated neovascularization
Pericyte loss and capillary occlusion cause retinal ischemia, which upregulates VEGF secretion; this drives growth of fragile new blood vessels that can bleed and cause traction retinal detachment.
Question 6: Charcot neuroarthropathy (Charcot foot) in diabetes develops through which pathophysiologic sequence?
- Peripheral vascular disease → ischemia → bone infarction → collapse
- Peripheral neuropathy → repetitive unperceived trauma → hyperemic bone resorption → fracture and deformity (Correct answer)
- Osteomyelitis → septic arthritis → periarticular bone destruction → instability
- Autonomic neuropathy alone causing complete joint denervation and rapid bone loss
Correct answer: Peripheral neuropathy → repetitive unperceived trauma → hyperemic bone resorption → fracture and deformity
Loss of protective sensation allows repetitive microtrauma; neurogenic inflammation and autonomic vasodilation then cause hyperemia and osteoclast-mediated bone resorption, leading to fracture and progressive joint destruction.
Question 7: Protein kinase C (PKC) activation in diabetic vasculopathy results primarily from:
- Excessive sorbitol inhibiting PKC phosphatases in endothelial cells
- Increased diacylglycerol synthesis from elevated intracellular glucose (Correct answer)
- AGE-RAGE interaction downregulating PKC inhibitory pathways
- Hyperinsulinemia directly stimulating PKC beta isoform expression
Correct answer: Increased diacylglycerol synthesis from elevated intracellular glucose
High intracellular glucose increases de novo diacylglycerol (DAG) synthesis, which activates PKC (especially beta isoform), impairing NO production, increasing VEGF, and promoting vascular dysfunction.
CDE Pathophysiology 4
Advanced glycation end products (AGEs) contribute to diabetic complications primarily by: