Essence and Clinical Significance of Atherosclerosis
Atherosclerosis is a systemic pathological condition based on a profound disturbance of lipid metabolism. The essence of this vascular pathology is that cholesterol (CH) and its esters begin to deposit abnormally in the inner layer of blood vessels, known as the intima. As a result of this chronic process, specific structures—atherosclerotic plaques—are formed.
The localization of lesions in atherosclerosis follows distinct patterns. The pathological process predominantly affects large- and medium-sized arteries. The primary vascular beds most frequently affected are the aorta, coronary arteries, and cerebral vessels. Somewhat less frequently, atherosclerotic changes are observed in the lower extremity arteries.
Hemodynamic and pathophysiological consequences of plaque formation lead to a significant deterioration of regional blood flow. The narrowing of the arterial lumen results in tissue hypoperfusion. In clinical practice, these changes inevitably lead to ischemic heart disease (IHD), severe cerebrovascular accidents (including strokes), and other serious cardiovascular complications.
Physiological Role of Key Lipids
A deep understanding of the pathogenesis of atherosclerosis requires a detailed review of the physiological roles of key lipids. Lipid metabolism involves three primary classes, each performing strictly specific functions in the human body:
- Phospholipids (PL): Perform a crucial structural function, serving as the fundamental basis for the construction of all cell membranes.
- Triglycerides (TG): Serve as the main energy substrate. The body uses them as a primary source of energy, and excess triglycerides are stored in specialized adipose tissue cells—adipocytes.
- Cholesterol (CH): Performs several critically important functions simultaneously. First, it has a structural function, actively participating in cell membrane synthesis. Second, it executes a metabolic (hormonal) function as the basic precursor for steroid hormone synthesis. Third, cholesterol plays a digestive role: it is the precursor for bile acids, which are absolutely essential for the adequate emulsification and subsequent absorption of fats from the intestinal lumen.
Role of the Liver in Regulating Cholesterol Metabolism
The central organ regulating cholesterol metabolism and maintaining its strict homeostasis is the liver. Liver cells—hepatocytes—act as the primary storage depot. Cholesterol reserves in this depot are constantly replenished from four main sources:
- Endogenous Synthesis: The formation of cholesterol molecules de novo directly within hepatocytes. This is the largest pathway for replenishing reserves, accounting for up to 75% of the total cholesterol pool in the body.
- Dietary Pathway: Intake of exogenous cholesterol via food and its subsequent absorption from the intestine.
- Enterohepatic Circulation: The physiological process of the reabsorption of bile acids from the intestine, allowing the body to reuse these compounds.
- Receptor-Mediated Uptake (Plasma Transport): The uptake of cholesterol from blood plasma. Here, hepatocytes use specialized receptors to capture circulating lipoproteins containing cholesterol.