Pathogenesis of renal edema

What mechanisms underlie the pathogenesis of nephrotic edema?

The pathogenesis of nephrotic edema is based on oncotic, hydrostatic, and lymphogenic factors, as well as secondary aldosteronism. The leading mechanism is hypo-oncotic fluid retention. The reaction cascade includes:

• Oncotic factor — massive proteinuria causes hypoproteinemia and a drop in plasma oncotic pressure, leading to fluid leaking into the interstitium.
• RAAS activation — fluid loss causes hypovolemia, decreased cardiac output, and renal hypoperfusion, triggering secondary aldosteronism.
• Hydrostatic and lymphogenic factors — join in dynamically.
• Decreased sensitivity to ANP — the kidneys lose responsiveness to atrial natriuretic peptide, worsening water-sodium metabolism disorders.

What is the main cause of nephritic edema development?

Nephritic edema, according to sources, is associated with the early stage of acute diffuse glomerulonephritis. Its pathogenesis is realized through several main mechanisms:

• Membranogenic factor — generalized damage to capillaries leads to increased microvessel wall permeability.
• RAAS activation — reduced renal blood flow activates the renin-angiotensin-aldosterone system, leading to Na+ and H2O retention.
• Hypervolemia — decreased glomerular filtration reduces urine output and increases circulating blood volume (CBV); this is associated with elevated hydrostatic pressure in the vascular bed.
• Oncotic factor — hypervolemia causes plasma protein dilution, while moderate proteinuria and protein leakage into tissues due to increased permeability lead to progressive blood hypo-oncia.

How is the RAAS activated in renal edema?

Activation of the RAAS in renal edema occurs as a result of renal hypoperfusion or a primary reduction in renal blood flow. The mechanism depends on the pathology:

• In nephrotic syndrome, the decrease in oncotic pressure leads to fluid movement into the interstitium. This causes a reduction in circulating plasma volume (hypovolemia) and decreased cardiac output, leading to renal hypoperfusion and activation of the system.
• In nephritic syndrome, the triggering factor is a primary reduction in renal blood flow against the background of glomerular damage.

In response to ischemia or hypoperfusion, renin secretion is activated, triggering angiotensin II production and secondary hyperaldosteronism, which leads to sodium and water retention.

How do nephritic and nephrotic edema differ pathogenetically?

The pathogenetic differences between nephritic and nephrotic edema lie in the triggering factors, blood volume status, and level of proteinuria.

What factors cause increased glomerular capillary permeability in renal pathology?

Increased glomerular capillary permeability in renal pathology is caused by immune or inflammatory damage to the filtration barrier. The main factors are:

• Immune mechanisms — autoaggressive immune damage to the glomerular basement membrane and epithelium, as well as the deposition of circulating immune complexes on the membrane, which triggers autoimmune inflammation.
• Inflammatory and allergic mediators — histamine, kinins, hydrolytic enzymes, and other biologically active substances.

The impact of these factors leads to loosening of the basement membrane, impairment of barrier function, and increased protein filtration, which triggers the protein cascade and the development of edema.