The kidney

The study of kidney diseases is facilitated by dividing them into four basic morphologic components: glomeruli, tubules, interstitium, and blood vessels.

Most glomerular diseases are immunologically mediated, whereas tubular and interstitial disorders are frequently caused by toxic or infectious agents.

Clinical Manifestations of Renal Diseases

Azotemia (biochemical abnormality): Elevation of the blood urea nitrogen (BUN) and creatinine levels, and is related largely to a decreased glomerular filtration rate (GFR).

Uremia: When azotemia becomes associated with a constellation of clinical signs and symptoms and biochemical abnormalities.

Nephritic syndrome is due to glomerular disease and is dominated by the acute onset of usually grossly visible hematuria (red blood cells in urine), mild to moderate proteinuria, and hypertension; it is the classic presentation of acute post-streptococcal glomerulonephritis.

Rapidly progressive glomerulonephritis is characterized as a nephritic syndrome with a rapid decline (hours to days) in GFR.

The nephrotic syndrome (due to glomerular disease): Heavy proteinuria (more than 3.5 gm/day), hypoalbuminemia, severe edema, hyperlipidemia, and lipiduria (lipid in the urine).

Asymptomatic hematuria or proteinuria, or a combination of these two, is usually a manifestation of subtle or mild glomerular abnormalities.

Acute renal failure: Oliguria or anuria (reduced or no urine flow), and recent onset of azotemia.

(It can result from glomerular, interstitial, or vascular injury or acute tubular injury).

Chronic renal failure: Prolonged symptoms and signs of uremia, is the end result of all chronic renal parenchymal diseases.

Renal tubular defects are dominated by polyuria (excessive urine formation), nocturia, and electrolyte disorders (e.g., metabolic acidosis). They are the result of diseases (e.g., medullary cystic disease, familial nephrogenic diabetes, cystinuria, renal tubular acidosis, lead nephropathy).

Urinary tract infection: characterized by bacteriuria and pyuria (bacteria and leukocytes in the urine). The infection may affect the kidney (pyelonephritis) or the bladder(cystitis).

Nephrolithiasis (renal stones): Manifested by severe spasms of pain (renal colic) and hematuria, often with recurrent stone formation.

Urinary tract obstruction and renal tumors have varied clinical manifestations based on the specific anatomic location and nature of the lesion.

Renal Failure

Acute renal failure implies a rapid and frequently reversible deterioration of renal function.

The evolution from normal renal function to symptomatic chronic renal failure broadly progresses through a series of four stages that merge into one another.

In diminished renal reserve, the GFR is about 50% of normal. Serum BUN and creatinine values are normal, and the patients are asymptomatic.
In renal insufficiency, the GFR is 20% to 50% of normal. Azotemia appears, usually associated with anemia and hypertension.
In chronic renal failure, the GFR is less than 20% to 25% of normal. The kidneys cannot regulate volume and solute composition, and patients develop edema, metabolic acidosis, and hyperkalemia. Overt uremia may ensue, with neurologic, gastrointestinal, and cardiovascular complications.
In end-stage renal disease, the GFR is less than 5% of normal; this is the terminal stage of uremia. Recent clinical classifications of chronic kidney disease, adopted in part to better stratify patients in clinical trials, adhere to this schema of progressive injury but divide patients into five classes based on levels of GFR.

Principal Systemic Manifestations of Chronic Kidney Disease and Uremia

FLUID AND ELECTROLYTES

Dehydration

Edema

Hyperkalemia

Metabolic acidosis

CALCIUM PHOSPHATE AND BONE

Hyperphosphatemia

Hypocalcemia

Secondary hyperparathyroidism

Renal osteodystrophy

Glomerular Diseases
Glomerular diseases constitute some of the major problems in nephrology; indeed, chronic glomerulonephritis is one of the most common causes of chronic kidney disease in humans.

Primary glomerulonephritis or, because some do not have a cellular inflammatory component, glomerulopathy.

Secondary glomerular diseases to differentiate them from disorders in which the kidney is the only or predominant organ involved.

PRIMARY GLOMERULOPATHIES

Acute proliferative glomerulonephritis
-Post-infectious

-Other

Rapidly progressive (crescentic) glomerulonephritis
Membranous glomerulopathy
Minimal-change disease
Focal segmental glomerulosclerosis
Membranoproliferative glomerulonephritis
IgA nephropathy
Chronic glomerulonephritis
SYSTEMIC DISEASES WITH GLOMERULAR INVOLVEMENT
Systemic lupus erythematosus

Diabetes mellitus

Amyloidosis

Goodpasture syndrome

Microscopic polyarteritis/polyangiitis

Wegener granulomatosis

Henoch-Schönlein purpura

Bacterial endocarditis

HEREDITARY DISORDERS

Alport syndrome

Thin basement membrane disease

Fabry disease

 

CLINICAL MANIFESTATIONS
The Glomerular Syndromes
Syndrome:

Nephritic syndrome
Rapidly progressive glomerulonephritis
Nephrotic syndrome
Chronic renal failure
Isolated urinary abnormalities

Manifestations:

1. Hematuria, azotemia, variable proteinuria, oliguria, edema, and hypertension

2. Acute nephritis, proteinuria, and acute renal failure

3. >3.5 gm/day proteinuria, hypoalbuminemia, hyperlipidemia, lipiduria

4. Azotemia ➙ uremia progressing for months to years

5. Glomerular hematuria and/or subnephrotic proteinuria

Renal system

The glomerulus consists of an anastomosing network of capillaries lined by fenestrated endothelium invested by two layers of epithelium . The visceral epithelium is incorporated into and becomes an intrinsic part of the capillary wall, separated from endothelial cells by a basement membrane. The parietal epithelium, situated on the Bowman capsule, lines the urinary space, the cavity in which plasma filtrate first collects.