Cirrhosis is a severe form of liver damage, and ascites refers to the abnormal accumulation of fluid within the abdomen. Ascites commonly develops as a serious complication in individuals with advanced cirrhosis. Understanding the connection involves exploring the physiological changes that occur when the liver is extensively scarred.
Cirrhosis: A Damaged Liver
Cirrhosis represents the irreversible scarring of the liver, where healthy liver tissue is progressively replaced by fibrous scar tissue and regenerative nodules. This extensive damage alters the liver’s normal architecture, making it rigid and distorted. The structural changes impede the liver’s ability to perform its many essential functions, including the critical task of processing blood flow that enters it from the digestive system.
Ascites: Fluid in the Abdomen
Ascites is the abnormal buildup of fluid in the peritoneal cavity, which is the space surrounding the abdominal organs. This fluid accumulation can lead to a swollen abdomen, discomfort, and sometimes rapid weight gain.
The Primary Driver: Portal Hypertension
A major mechanism by which cirrhosis leads to ascites is portal hypertension. Blood from the digestive organs, spleen, and pancreas normally flows into the liver through the portal vein system. However, scar tissue within a cirrhotic liver obstructs this blood flow, creating significant resistance. This obstruction causes pressure to build up within the portal vein and its tributaries, a condition known as portal hypertension.
The elevated pressure within these blood vessels forces fluid to leak out of the capillaries in the intestines and liver. This fluid then seeps into the peritoneal cavity. The increased hydrostatic pressure pushes fluid from the vascular system into the abdominal space, making portal hypertension the direct cause of ascites in cirrhosis.
Compounding Factors: Fluid Imbalance
Beyond portal hypertension, several interconnected physiological mechanisms contribute to the formation and persistence of ascites in cirrhosis.
Reduced Albumin Production
One factor is the liver’s reduced capacity to produce albumin. Albumin is a protein that helps maintain oncotic pressure, the force that keeps fluid within the blood vessels. A liver damaged by cirrhosis produces less albumin, leading to lower levels in the blood. This reduction allows more fluid to leak from the bloodstream and accumulate in the abdominal cavity.
Kidney Fluid Retention
The kidneys also play a role in exacerbating fluid retention. When fluid shifts from the blood vessels into the abdominal space, the body perceives a reduction in effective circulating blood volume, even if total body fluid is high. This triggers neurohormonal systems, including the renin-angiotensin-aldosterone system (RAAS), which signals the kidneys to retain sodium and water. The kidneys reabsorb more sodium and water, contributing to fluid overload and ascites.
Impaired Lymphatic Drainage
The liver possesses its own lymphatic system designed to drain excess fluid. In cirrhosis, increased pressure within the liver, stemming from portal hypertension, leads to increased production of liver lymph. When the volume of lymph exceeds the lymphatic system’s capacity to drain it, this excess fluid contributes to the accumulation of fluid in the peritoneal cavity.