Causes and Mechanisms of Cholestasis
The foundation of these syndromes is a mechanical obstruction that blocks bile outflow. If the obstruction is located at the level of the bile canaliculi, intrahepatic cholestasis occurs; if the bile ducts or gallbladder are affected, extrahepatic (posthepatic) cholestasis develops.
There are three main mechanisms of biliary tract obstruction:
- Intraluminal blockade: The lumen can be obstructed by gallstones, tumor masses, parasites (e.g., Ascaris lumbricoides), or granulomatous tissue proliferation in biliary cirrhosis.
- Extrinsic compression: Outflow is impaired due to tumors of the pancreatic head or the major duodenal papilla, as well as enlarged lymph nodes and scar tissue.
- Motility dysfunction: Decreased tone and contractility of the duct walls (dyskinesia).
Pathogenesis: Obstruction leads to a sharp increase in pressure within the bile canaliculi. They become over-distended, resulting in micro-ruptures. Wall permeability increases, and bile components begin to enter the bloodstream, initiating cholaemia. Concurrently, biliary hepatitis may develop, further damaging liver tissue.
Cholaemia Syndrome: Bile in the Blood
The clinical presentation of cholaemia is entirely driven by the toxic effects of bile acids and bilirubin on various organs and systems.
Laboratory tests reveal pronounced hypercholesterolemia and elevated levels of conjugated (direct) bilirubin. The accumulation of bile acids in the blood leads to their deposition in tissues, causing:
- Cutaneous symptoms: Intractable pruritus (itching) due to the irritation of sensory nerve endings.
- Neurological shifts: Patients become irritable and excessively excitable.
- Cardiovascular disorders: Bile acids affect the cardiac sinus node and the vagus nerve, provoking bradycardia and arterial hypotension.
Acholia Syndrome: Bile Deficiency in the Intestine
Acholia is a condition in which bile delivery to the duodenum is critically reduced or completely halted. As a result, the essential functions of bile—fat emulsification and bactericidal action—are lost.
Key manifestations of acholia:
- Stool changes: Stools become clay-colored (acholic) due to the complete absence of stercobilin. Steatorrhoea (fatty stools) occurs because unabsorbed lipids cannot be digested.
- Intestinal disorders: The lack of antibacterial control by bile leads to dysbiosis, autoinfection, and progressive intoxication.
- Metabolic disturbances: Polyhypovitaminosis develops. The body loses the ability to absorb fat-soluble vitamins (A, D, E, K).
- Haemorrhagic syndrome: Vitamin K deficiency impairs the synthesis of clotting factors, increasing the risk of bleeding.
- Bone pathology: A lack of vitamin D and calcium reduces bone mineral density, increasing fracture risk. Additionally, tissue antioxidant defense is impaired.
Role of Haemolysis and Excess Bilirubin
In addition to mechanical obstructions, jaundice can result from bilirubin hyperproduction, when the liver simply cannot keep up with its uptake and conjugation.
The primary source is erythrocyte haemolysis (intravascular or extravascular), as well as the breakdown of erythrocyte precursors in the bone marrow during ineffective erythropoiesis. Unconjugated bilirubin can also form massively outside the vascular bed, such as in organ infarcts (within necrotic zones) or large haematomas. There is also 'shunt bilirubin', synthesized from cytochromes and myoglobin.
During intense haemolysis, anaemia (leading to hemic hypoxia) comes to the fore. Blood levels of unconjugated (indirect) bilirubin rise, and urobilinogen appears. During intravascular cell destruction, free haemoglobin is found in the urine, while the stool becomes hypercholic (very dark) due to an excess of stercobilin.