Acute kidney injury refers to abrupt onset of renal dysfunction characterized by an acute increase in serum creatinine often associated with oliguria or anuria (decreased or no urine flow). It can result from glomerular injury (such as rapidly progressive GN), interstitial injury, vascular injury (such as thrombotic microangiopathy), or acute tubular epithelial cell injury.
Chronic kidney disease results from progressive scarring in the kidney of any cause. It is characterized by various metabolic and electrolyte abnormalities such as hyperphosphatemia, dyslipidemia, and metabolic acidosis. However, it is often asymptomatic until the most advanced stages, when symptoms of uremia develop.
End-stage renal disease (ESRD) is irreversible loss of renal function requiring dialysis or transplantation typically due to severe progressive scarring in the kidney from any cause.
Urinary tract infection (UTI) is characterized by bacteriuria and pyuria (bacteria and leukocytes in the urine). It may be symptomatic or asymptomatic, and may affect the kidney (pyelonephritis) or the bladder (cystitis) only.
Nephrolithiasis refers to formation of stones in the collecting system and is manifested by renal colic and hematuria (without red cell casts).
The glomerulus consists of an anastomosing network of capillaries invested by two layers of epithelium. The visceral epithelium (composed of podocytes) is part of the http://ebooksmedicine.net
Complex of signaling and cytoskeletal proteins capillary wall, whereas the parietal epithelium encircles Bowman space (urinary space), the cavity in which filtrate of plasma collects. The glomerular capillary is the filtration unit and consists of the following components (
Figs. 14.1 14.2
Fenestrated endothelial cells, with each fenestra being 70 to 100 nm in diameter.
The glomerular basement membrane (GBM), which has a thick, electron-dense central layer called the lamina densa, and two thinner, electron-lucent peripheral layers, the lamina rara interna and lamina rara externa. The GBM consists of collagen (mostly type IV), laminin, polyanionic proteoglycans, fibronectin, and several other glycoproteins.
Podocytes, cells that possess interdigitating foot processes that are embedded in and adherent to the lamina rara externa. Adjacent foot processes are separated by 20to 30-nm–wide filtration slits, which are bridged by a thin slit diaphragm composed mainly of the protein nephrin (see later).
Mesangial cells, which lie in a mesangial matrix between the capillaries that supports the glomerular tuft. These
Fig. 14.2 Low-powerelectronmicrographofratglomerulus.B, Basementmembrane;CL, capillarylumen;End, endothelium;Ep, visceralepithelialcells(podocytes)withfootprocesses;Mes, mesangium;US, urinaryspace.
cells, of mesenchymal origin, are contractile and are capable of proliferation, of laying down collagen and other matrix components, and of secreting a number of biologically active mediators in response to cytokines and other factors (described later).