Which of the following mechanisms is primarily responsible for the development of portal hypertension in cirrhosis?

Explanation

## Pathophysiology of Portal Hypertension in Cirrhosis **Key Point:** Portal hypertension in cirrhosis results primarily from **increased intrahepatic vascular resistance**, not from increased portal blood inflow. The architectural distortion and fibrous septa create a mechanical obstruction to blood flow through the liver. ### Mechanism of Increased Intrahepatic Resistance 1. **Fibrous septa** replace normal hepatic parenchyma and disrupt the normal vascular architecture. 2. **Loss of sinusoidal compliance** — cirrhotic sinusoids become rigid and cannot accommodate normal blood flow. 3. **Capillarization of sinusoids** — loss of the fenestrated endothelium increases resistance. 4. **Hepatic stellate cell activation** produces collagen and further increases stiffness. 5. Result: Portal pressure rises above the normal 5–10 mmHg threshold (>12 mmHg = clinically significant portal hypertension). ### Why Intrahepatic Resistance, Not Inflow? ```mermaid flowchart TD A[Cirrhotic liver]:::outcome --> B[Fibrous septa + loss of architecture]:::outcome B --> C[Increased intrahepatic vascular resistance]:::outcome C --> D[Portal pressure rises]:::outcome D --> E[Portal hypertension develops]:::outcome E --> F[Varices, ascites, splenomegaly]:::outcome ``` **High-Yield:** The primary defect in cirrhosis is **resistance to flow WITHIN the liver**, not increased inflow. This is why portal hypertension in cirrhosis is classified as "post-sinusoidal" (the obstruction is at and beyond the sinusoid level). ### Comparison: Types of Portal Hypertension | Type | Location of Block | Cause | Example | |------|-------------------|-------|----------| | **Prehepatic** | Before liver | Portal vein thrombosis | PVT | | **Intrahepatic** | Within liver | Cirrhosis, schistosomiasis | Cirrhosis (post-sinusoidal) | | **Posthepatic** | After liver | Budd-Chiari, IVC obstruction | Budd-Chiari | **Clinical Pearl:** In cirrhosis, splenic blood flow actually increases *secondary* to portal hypertension (causing splenomegaly), but this is a consequence, not the primary cause. The primary driver is the mechanical resistance within the cirrhotic liver itself.