PA1.1-3,PA2.1-8 | Cell Injury, Adaptation & Cell Death — Case Study

CLINICAL SCENARIO

A scaffolded case-study assignment in which you follow a 58-year-old man from the moment his left anterior descending artery occludes through the biochemical cascade of cell injury, the tipping point from reversible to irreversible damage, the morphology of coagulative necrosis, clinical biomarker release, and finally the reparative response. An optional integrative thread traces his prior decade of pressure overload and the adaptive hypertrophy that preceded the infarct.

Section 1 — The Ischaemic Insult and Immediate Biochemistry (PA1.1, PA1.2)

Within the first 20–30 minutes of LAD occlusion, a series of biochemical events unfolds inside the cardiomyocyte. Starting from the cessation of oxidative phosphorylation, trace the cascade that leads to cellular swelling and early membrane dysfunction. In your answer:
(a) Explain why anaerobic glycolysis fails to maintain ATP levels adequately.
(b) Describe how ATP depletion leads to failure of the Na⁺/K⁺-ATPase pump and the consequences for cell volume.
(c) Explain the role of intracellular Ca²⁺ accumulation at this stage and name two cellular targets that Ca²⁺ activates.

Guidance: Focus on the biochemical sequence (ischaemia → ↓O₂ → ↓oxidative phosphorylation → ↓ATP → pump failure → ionic imbalance → osmotic swelling). Mention lactic acid accumulation and intracellular pH fall. For Ca²⁺, consider phospholipases and proteases. Approximately 200–280 words.

Section 2 — Reversible vs. Irreversible Injury: The Point of No Return (PA1.3, PA1.4)

At what point does the reversible injury in Mr. Kumar's cardiomyocytes become irreversible? Discuss the structural and biochemical criteria that mark this transition, with reference to:
(a) The significance of membrane phospholipid loss and cytoskeletal disruption.
(b) The role of mitochondrial permeability transition pore (mPTP) opening.
(c) Given that Mr. Kumar received PPCI at 3.5 hours, briefly comment on whether significant irreversible injury is likely to have occurred in the core ischaemic zone and why.

Guidance: Distinguish early ultrastructural changes (cell swelling, ER dilation, myelin figures — reversible) from later changes (amorphous densities in mitochondria, membrane blebbing, nuclear chromatin clumping — irreversible). The 20–40 minute threshold for irreversible injury in cardiomyocytes is key. For part (c), apply the time-course knowledge clinically but avoid certainty — acknowledge the wavefront phenomenon. Approximately 200–280 words.

Section 3 — Reperfusion Injury (PA1.5, PA2.1)

PPCI restored flow to Mr. Kumar's LAD. Paradoxically, reperfusion itself can cause additional cell death. Explain the concept of reperfusion injury by addressing:
(a) Three mechanisms by which the sudden return of oxygenated blood damages already-compromised cells (reactive oxygen species, calcium overload, neutrophil activation — discuss at least two in detail).
(b) Why reperfusion injury does not negate the benefit of early revascularisation — what is the net therapeutic outcome?

Guidance: ROS burst from the electron transport chain and xanthine oxidase pathway should be central. The paradox of Ca²⁺ overload on reperfusion despite restoration of ionic gradients is worth exploring. Keep the answer balanced — acknowledge that early PPCI saves the peri-infarct 'at-risk' zone even though some reperfusion injury occurs. Approximately 180–240 words.

Section 4 — Morphology of Necrosis: Gross and Microscopic (PA2.2, PA2.3)

Using the autopsy description provided in the case vignette (72-hour infarct), answer the following:
(a) Name the type of necrosis seen in myocardial infarction and explain the pathological mechanism that produces 'ghost' cell outlines (coagulative necrosis).
(b) Describe the expected gross morphological progression of an MI over time: 0–6 hours, 6–24 hours, 1–3 days, 1–2 weeks, and >2 months.
(c) Why is coagulative necrosis the predominant pattern in solid organs subjected to ischaemia, whereas the brain undergoes liquefactive necrosis instead?

Guidance: For (a) — protein denaturation preserves structural outlines while destroying metabolic function. For (b) — use a clear timeline format; include pale infarct → hyperaemia → neutrophil infiltration → macrophage invasion → granulation tissue → scar. For (c) — the key difference is high lipid content of neural tissue and abundant lipases released from lysosomes. Approximately 220–300 words.

Section 5 — Biomarkers and Clinical Correlation (PA2.4)

Mr. Kumar's troponin-I rises from 0.05 ng/mL at presentation to 42 ng/mL at 12 hours, and CK-MB peaks at 8 hours.
(a) Explain the cellular basis for biomarker release — why do troponin and CK-MB appear in the blood during myocardial necrosis?
(b) Why does troponin peak later and remain elevated longer than CK-MB? (Consider molecular size and clearance mechanisms.)
(c) Correlate the biomarker pattern with the morphological stage of the infarct at 12 hours.

Guidance: Connect sarcolemmal disruption (irreversible injury) to cytosolic protein release. Troponin: structural protein released more slowly as contractile apparatus breaks down, cleared by kidneys over days. CK-MB: cytosolic enzyme, smaller, cleared faster. At 12 hours the infarct is morphologically in the 'early coagulative necrosis' phase — correlate this with the biomarker rise. Approximately 180–240 words.

Section 6 — Integrative Thread: Hypertrophy as Adaptation (PA1.6, PA2.5)

Mr. Kumar has a 12-year history of poorly controlled hypertension. On echocardiography performed on Day 2, the non-infarcted left ventricular wall thickness is 13 mm (normal ≤11 mm), consistent with concentric left ventricular hypertrophy (LVH).
(a) Classify LVH as a form of cellular adaptation using Robbins' framework (hypertrophy — define, and distinguish from hyperplasia).
(b) Explain the molecular stimulus for concentric LVH in hypertension: what mechanical signal triggers hypertrophy, and which growth factors and proto-oncogenes are involved?
(c) Critically analyse: did the pre-existing hypertrophy protect or predispose Mr. Kumar to more severe infarction? Give one argument for each side.

Guidance: Adaptation vs. injury spectrum — hypertrophy is an adaptive response to increased workload, up to the point of decompensation. For (b): mechanical stretch → AT-II, IGF-1 → c-fos, c-myc, β-MHC re-expression. For (c): hypertrophy increases oxygen demand per gram of myocardium (vulnerability) but also enlarges wall thickness, which may reduce wall stress (LaPlace — potential protection). Expect balanced, evidence-referenced reasoning. Approximately 200–280 words.

PEER REVIEW

You will be assigned two peers' submissions to review after the submission deadline. For each submission:

1. Read the full response before scoring any criterion.
2. Score each rubric criterion (Biochemical Cascade 0–8; Reversible vs. Irreversible 0–6; Morphology 0–6; Biomarkers 0–4; Integration 0–6) and enter the score on the peer-review form.
3. Write a comment for each criterion (minimum 2 sentences): identify one specific strength and one area for improvement. Be specific — quote or paraphrase the peer's text rather than giving generic feedback.
4. Overall comment (3–5 sentences): summarise the submission's key strength, the most important gap, and one concrete suggestion for how the peer could deepen their understanding of this topic.
5. Tone: constructive and collegial. The goal is to help your peer learn, not to find fault.
6. Academic integrity: your review must be your own. Do not share scores with your peer before faculty release grades.

Peer reviews that consist entirely of generic praise (e.g., 'Good work, well done') without specific feedback will be returned for revision and may attract a mark deduction for the reviewer.