Disorders of Renal Function

Glomerulonephritis and Nephrotic Syndrome

• Edema in patients with glomerulonephritis is caused by the loss of protein in the urine due to damage in the glomerulus, leading to low protein (albumin) levels in the bloodstream, decreased capillary oncotic pressure, and fluid leakage into the interstitium.
• Inflammation of the glomerulus is the leading cause of chronic renal failure in the US, accounting for half of the people with end-stage renal disease.
• PSGN (post-streptococcal glomerulonephritis) is the most common form of glomerulonephritis, typically occurring 7-12 days after an infection, due to antigen-antibody complex formation.
• PSGN has a favorable prognosis in children, with 95% recovering without further renal damage, but only 60% of adults recover favorably.

Nephrotic Syndrome

• Nephrotic syndrome is a constellation of clinical findings due to massive protein loss in the urine, regardless of the cause of kidney damage.
• Patients with nephrotic syndrome lose over 3.5 g of protein in their urine per day.
• Hyaline casts indicate possible damage to the glomerular capillary membrane, permitting protein leakage.
• RBC casts indicate glomerular injury, while WBC casts indicate infection, interstitial injury, or tubular damage.
• Granular casts represent partially decomposed cellular casts, and broad casts develop in atrophied and dilated nephrons, indicating nephron death.

Chronic Renal Failure

• Chronic renal failure represents a progressive and irreversible destruction of kidney structures.
• The most common etiologies include diabetes, hypertension, glomerulonephritis, and polycystic kidney disease.
• Stages of chronic renal failure include:
  • Stage 1-2: diminished renal reserve, with GFR dropping to 60% of normal, but BUN and CR remaining normal.
  • Stage 3-4: renal insufficiency, with GFR decreasing to 50-20% of normal, and azotemia, anemia, and hypertension developing.
  • Stage 4-5: renal failure, with GFR decreasing to 20-5% of normal, and kidneys unable to regulate volume and solute composition.
  • End-stage renal disease (ESRD), with GFR less than 5%, requiring dialysis or transplantation for survival.

Glomerular Filtration Rate (GFR)

• GFR is the rate at which fluid filters from the blood into the Bowman's capsule and is dependent on renal blood flow (RBF).
• A decrease in cardiac output can decrease RBF, ultimately decreasing GFR.
• The major determinant of glomerular filtration is the blood pressure within the glomerular capillary network, which is regulated by RBF.

Renal Physiology

• Blood flows into the glomerulus via the afferent arteriole, and vasoconstriction of the afferent arteriole can decrease GFR.
• The descending loop of Henle has more reabsorption of H2O, while the ascending loop has more reabsorption of Na+ and Cl-.
• The distal tubule has more reabsorption of Na+, and the hormone aldosterone acts on the distal tubule to further increase reabsorption of Na+.
• The collecting tubules have more reabsorption of water in the presence of ADH (vasopressin), resulting in a highly concentrated urine.

Hormonal Influences

• The renin-angiotensin-aldosterone system (RAAS) regulates the ECF volume by regulating sodium content.
• ADH has two effects: vasoconstriction, increasing blood pressure, and increasing the permeability of the distal tubule and collecting duct membrane to water, increasing reabsorption of water.
• Diabetes insipidus is a condition where insufficient ADH is produced, resulting in minimal to no reabsorption of water in the collecting tubule, increased urine production, and dilute urine.