A 35-year-old woman undergoes partial hepatectomy for benign tumor removal. The remaining liver tissue undergoes rapid regeneration to restore original mass. Which of the following best describes the type of cellular adaptation occurring in the hepatocytes?

Explanation

## Hepatic Regeneration: Hyperplasia Model **Key Point:** Liver regeneration after partial hepatectomy is a classic example of **hyperplasia** — an increase in cell number, not cell size. The process is driven by specific growth factors and cytokines, particularly hepatocyte growth factor (HGF) and interleukin-6 (IL-6). ### Mechanism of Hepatic Regeneration 1. **Immediate response (minutes to hours):** Removal of hepatic mass triggers loss of growth inhibition and release of growth factors 2. **HGF signaling:** HGF binds to c-Met receptor on hepatocytes, activating MAPK and PI3K/Akt pathways → promotes cell cycle entry and DNA synthesis 3. **IL-6 signaling:** IL-6 (produced by Kupffer cells and hepatocytes) activates STAT3 → promotes hepatocyte proliferation and survival 4. **Result:** Hepatocytes re-enter the cell cycle (G0 → G1 → S → G2 → M) and divide 5. **Timeline:** Liver mass is restored to ~90% of original within 7–10 days in rodents; slower in humans (2–4 weeks) ### Hyperplasia vs. Hypertrophy in Liver Context | Aspect | Hyperplasia (Regeneration) | Hypertrophy | |--------|---------------------------|------------| | **Cell number** | ↑↑ (increases) | Unchanged | | **Cell size** | Normal | ↑ (increases) | | **DNA synthesis** | ↑↑ (S phase active) | Minimal | | **Cell cycle** | Active (G1, S, G2, M phases) | Quiescent (G0) | | **Growth factors** | HGF, IL-6, TNF-α | Mechanical stretch, hormones | | **Reversibility** | Reversible; stops when mass restored | Reversible if stimulus removed | | **Example** | Liver after partial hepatectomy | Hepatomegaly in fatty liver disease | **High-Yield:** The liver is unique among solid organs in its capacity for **true regeneration** — it can restore lost mass and function. This is why partial hepatectomy is tolerated clinically and why the liver can recover from significant injury. **Mnemonic:** **HGF-IL6** = **H**epatocyte **G**rowth **F**actor and **I**nterleukin-**6** — the two key cytokines driving hepatic hyperplasia. **Clinical Pearl:** Impaired hepatic regeneration (seen in cirrhosis, advanced fibrosis, or sepsis) is associated with poor outcomes after partial hepatectomy. Patients with Child-Pugh C cirrhosis have significantly prolonged regeneration and higher perioperative mortality. [cite:Robbins 10e Ch 1]